ANESTHESIA Hadzic's Peripheral Nerve Blocks Hadzic parte 04
Thrombin Inhibitors
Recombinant hirudin derivatives, such as desirudin (Revasc), lepirudin (Refludan), and bivalirudin
(Angiomax), inhibit both free and clot-bound thrombin.4
Argatroban, although an L-arginine
derivative, is also a thrombin inhibitor. These drugs are used in the treatment of heparin-induced
thrombocytopenia and as an adjunct when angioplasty is performed.33 Their anticoagulant effect is
present for 1 to 3 hours after intravenous administration and is monitored by the aPTT. There is no
pharmacologic reversal to the effect of these drugs. Desirudin is used as thromboprophylaxis after
total hip replacement.34 There are no published reports of spinal hematoma related to neuraxial
anesthesia in patients who have received a thrombin inhibitor, probably because of the hesitancy of
clinicians to perform neuraxial injections in patients taking the drugs, which is probably related to
their unfamiliarity with the drugs. The most recent ASRA guidelines recommend against the
performance of neuraxial techniques in patients who received thrombin inhibitors.
Newer Anticoagulants
Dabigatran Etexilate
Dabigatran is an oral direct thrombin inhibitor. Its bioavailability is only 5%, peak plasma levels
occur at 2 hours, and its half-life is 8 hours after a single dose but up to 17 hours after multiple doses.
The drug is approved for clinical use in Europe. Studies showed dabigatran (150 or 220 mg daily) to
be less effective than enoxaparin (30 mg twice daily) when used for thromboprophylaxis after total
joint surgery.35,36A 48-hour interval is recommended before a neuraxial injection.
Rivaroxaban
Rivaroxaban is an oral factor Xa inhibitor approved for use in Europe and Canada. It is awaiting
approval by the Food and Drug Administration (FDA) in the United States. It has an 80%
bioavailability; its peak effect occurs after 1 hour; the duration of effect is 12 hours; and it has a halflife of 9 to 13 hours. Clinical studies comparing rivaroxaban, at doses of 5 to 40 mg, to enoxaparin
showed similar or superior efficacy.37–40 There were no reports of spinal hematoma in these studies.
Apparently, a 24-hour interval (2 × half-life) was observed between the rivaroxaban dose and
epidural catheter placement or removal; subsequent dosing of the drug was 6 hours after removal of
the catheter (personal communication with the company). The drug offers several salutary
characteristics including efficacy and simplicity with once-daily oral dosing.
Prasugrel
Prasugrel is an oral anticoagulant approved for use by the FDA in July 2009. Its mechanism of action
is similar to clopidogrel; that is, it acts as a noncompetitive antagonist of P2Y12, inhibiting the ability
of platelet ADP to induce aggregation for the life of the platelet.41 Prasugrel and clopidogrel are
prodrugs; however, prasugrel has a quicker onset of action, a longer duration (the effect of 60 mg is
1–1.5 hours compared with 6 hours with 300 mg clopidogrel); it is 10 times more potent; and less
prone to drug–drug interactions and variability in patient response than clopidogrel.41,42 A 7–10 day
interval is recommended before a neuraxial injection. Other novel antiplatelet drugs are in
development, including ticagrelor and cangrelor, which are under study for use in patients with acute
coronary syndromes.43
Anticoagulation and Peripheral Nerve Blocks
Spontaneous hematomas have been reported in patients who took anticoagulants. Abdominal wall
hematomas, intracranial hemorrhage, psoas hematoma, and intrahepatic hemorrhage have occurred
after LMWH.44–47 Major hemorrhagic complications occur in 1.9 to 6.5% of patients on enoxaparin.48
The increased bleeding that occurs after vascular or cardiac procedures and regional nerve blocks in
these patients can result in an expanding hematoma with resultant ischemia of the nerve.
TABLE 8-1 Summary of Guidelines on Anticoagulants and Neuraxial Blocks*
There has been no prospective study on peripheral nerve blocks in the presence of anticoagulants.
However, there have been several case reports of hematomas when peripheral blocks are performed
in patients who are on these drugs. The hematomas occurred in patients with abnormal and normal
coagulation status, and in patients who were given LMWH, ticlopidine and clopidogrel, warfarin,
heparin, or a combination of the drugs.49–55 In most cases, however, recovery of neurologic deficits
occurred within a year.
The diagnosis of bleeding after peripheral nerve block in patients on anticoagulants include pain
(flank, paravertebral, or in the groin with psoas bleeding), tenderness in the area, fall in
hemoglobin/hematocrit, fall in blood pressure, and sensory and motor deficits. Although definite
diagnosis is made by computed tomography, ultrasound can be a diagnostic aid, and its increasing use
will make this modality a useful tool for the diagnosis and subsequent monitoring of peripheral
hematomas. Treatment of peripheral hematomas usually includes surgical consult, blood transfusion
as necessary, and watchful waiting versus surgical drainage.
The most recent ASRA guidelines recommended that the same guidelines on neuraxial injections
apply to deep plexus or peripheral nerve blocks. Some clinicians may find this to be too restrictive
and apply the same guidelines only to deep plexus and noncompressible blocks (e.g., lumbar plexus
block, deep cervical plexus blocks) or to blocks near vascular areas, such as celiac plexus blocks or
superior hypogastric plexus blocks. If peripheral nerve blocks are performed in the presence of
anticoagulants, the anesthesiologist must discuss the risks and benefits of the block with the patient
and the surgeon, and follow the patient very closely after the block.
Guidelines of Various Societies
Guidelines on use of regional anesthesia in the presence of anticoagulants have been published by a
number of societies throughout the world to better fit them to the realm of the local practices. By
necessity, there are similarities and differences among them. A good example is the new ASRA
guidelines56 and the Belgian and German guidelines.57,58 The guidelines of the three organizations are
similar with regard to antiplatelet medications, unfractionated heparin, and thrombolytic agents. With
regard to LMWH, the ASRA guidelines are more conservative, partly due to the differences in the
dosing of the drug. For fondaparinux, the German guidelines allow an indwelling epidural catheter,
whereas the ASRA and the Belgian guidelines recommend against it. The Belgian and German
guidelines allow neuraxial injections in patients on direct thrombin inhibitors; the ASRA guidelines
do not. Finally, some of the newer anticoagulants have been approved for use in Europe and are
awaiting approval in the United States so the guidelines for these drugs are forthcoming.
Summary
Adherence to the discussed guidelines should lead to a lesser risk of hemorrhagic complications after
regional anesthesia, including spinal hematomas. Likewise, implementation of the guidelines leads to
improved vigilance and better care of patients on anticoagulants in whom nerve blocks are performed
or entertained. Consensus guidelines, however, should be viewed only as recommendations; specific
decisions on nerve blocks in patients on anticoagulants should be individualized. Adequate
monitoring, follow-up, and timely treatment should be implemented in patients on anticoagulants who
are receiving neuraxial or peripheral nerve blocks (see algorithms on the following pages).
DECISION MAKING ALGORITHM IN THE SELECTION OFNEURAXIAL OR PERIPHERAL
NERVE BLOCKADE
FOLLOW-UP OF PATIENTS WHO ARE AT RISK FOR SPINAL OR PERIPHERAL HEMATOMA
ANTICOAGULANTS: MECHANISM OF ACTION AND RECOMMENDED GUIDELINES FOR
PRACTICE OF NEURAXIAL ANESTHESIA
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0. Wu CL, Perkins FM. Oral anticoagulant prophylaxis and epidural catheter removal. Reg Anesth.
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The safety and efficacy of extended thromboprophylaxis with fondaparinux after major orthopedic
surgery of the lower limb with or without a neuraxial or deep peripheral nerve catheter: the EXPERT
Study. Anesth Analg. 2007;105:1540-1547.
2. Rosencher N, Bonnet MP, Sessler DI. Selected new antithrombotic agents and neuraxial anesthesia
for major orthopedic surgery: management strategies. Anaesthesia. 2007;62:1154-1160.
3. Greinacher A, Lubenow N. Recombinant hirudin in clinical practice: focus on lepirudin.
Circulation. 2001;103:1479-1484.
4. Ericksson BI, Wille-Jorgensen P, Kalebo P, et al. A comparison of recombinant hirudin with a lowmolecular-weight heparin to prevent thromboembolic complications after total hip replacement. N
Engl J Med. 1997;337:1329-1335.
5. Ericksson BI, Dahl OE, Rosencher N, et al. RE-MODEL Study Group: Oral dabigatran etexilate vs.
subcutaneous enoxaparin for the prevention of venous thromboembolism after total knee replacement:
the RE-MODEL randomized trial. J Thromb Haemost. 2007;5:2178-2185.
6. The RE-MOBILIZE Writing Committee. Oral thrombin inhibitor dabigatran etexilate versus North
American enoxaparin regimen for prevention of venous thromboembolism after knee arthroplasty
surgery. J Arthroplasty. 2009;24:1-9.
7. Ericksson BI, Borris LC, Dahl OE, et al; ODIXa-HIP Study Investigators. A once-daily, oral, direct
factor Xa inhibitor, rivaroxaban (BAY 59-7939), for thromboprophylaxis after total hip replacement.
Circulation. 2006;114:2374-2381.
8. Eriksson BI, Borris LC, Friedman RJ, et al; RECORD1 Study group. Rivaroxaban versus
enoxaparin for thromboprophylaxis after hip arthroplasty. N Engl J Med. 2008;358:2765-2775.
9. Lassen MR, Ageno W, Borris LC, et al; RECORD3 Investigators. Rivaroxaban versus enoxaparin
for thromboprophylaxis after total knee arthroplasty. N Eng J Med. 2008;358:2776-2786.
0. Kakkar AK, Brenner B, Dahl O, et al. RECORD2 Investigators. Extended duration rivaroxaban
versus short-term enoxaparin for the prevention of venous thromboembolism after total hip
arthroplasty: a double-blind, randomized controlled trial. Lancet. 2008;372:31-39.
1. Reinhart KM, White CM, Baker WL. Pharmacotherapy. 2009;29:1441-1451.
2. Bhatt DL. Prasugrel in clinical practice. N Engl J Med. 2009;361:940-942.
3. Shalito I, Kopyleva O, Serebruany V. Novel antiplatelet agents in development: prasugrel,
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report of two cases. Am Surgeon. 2000;66:797-800.
5. Dickinson LD, Miller L, Patel CP, Gupta SK. Enoxaparin increases the incidence of postoperative
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6. Ho KJ, Gawley SD, Young MR. Psoas hematoma and femoral neuropathy associated with
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8. Noble S, Spencer CM. Enoxaparin: a review of its clinical potential in the management of coronary
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9. Klein SM, D’Ercole F, Greengrass RA, Warner DS. Enoxaparin associated with psoas hematoma
and lumbar plexopathy after lumbar plexus block. Anesthesiology. 1997;87:1576-1579.
0. Weller RS, Gerancher JC, Crews JC, Wade KL. Extensive retroperitoneal hematoma without
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1. Maier C, Gleim M, Weiss T, et al. Severe bleeding following lumbar sympathetic blockade in two
patients under medication with irreversible platelet aggregation inhibitors. Anesthesiology.
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Anesthesiology. 1989;71:162-164.
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55. Maier C, Gleim M, Weiss T, Stachetzki U, Nicolas V, Zenz M. Severe bleeding following lumbar
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Anesthesiology. 2002;97:740-743.
56. Horlocker TT, Wedel DJ, Rowlingson JC, et al. Regional anesthesia in the patient receiving
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9
Toxicity of Local Anesthetics
Steven Dewaele, and Alan C. Santos
Introduction
Systemic toxicity of local anesthetics can occur after administration of an excessive dose, with rapid
absorption, or because of an accidental intravenous injection. The management of local anesthetic
toxicity can be challenging, and in the case of cardiac toxicity, prolonged resuscitation efforts may be
necessary.1,2 Therefore, understanding the circumstances that can lead to systemic toxicity of local
anesthetics and being prepared for treatment is essential to optimize the patient outcome.
Systemic toxicity is typically manifested as central nervous system (CNS) toxicity (tinnitus,
disorientation, and ultimately, seizures) or cardiovascular toxicity (hypotension, dysrhythmias, and
cardiac arrest).3
The dose capable of causing CNS symptoms is typically lower than the dose and
concentration result in cardiovascular toxicity. This is because the CNS is more susceptible to local
anesthetic toxicity than the cardiovascular system. However, bupivacaine toxicity may not adhere to
this sequence, and cardiac toxicity may precede the neurologic symptoms.4
Although less common,
cardiovascular toxicity is more serious and more difficult to treat than CNS toxicity.
Other reported, but much less common, adverse effects of certain local anesthetics include allergic
reactions,5
methemoglobinemia,6
and bronchospasm.7
Direct neural8
and local tissue toxicity9
have
been reported also; however, discussion about these topics is beyond the scope of this chapter.
Signs and Symptoms of Systemic Local Anesthetic Toxicity
The earliest signs of systemic toxicity are usually caused by blockade of inhibitory pathways in the
cerebral cortex.10 This allows for disinhibition of facilitator neurons resulting in excitatory cell
preponderance and unopposed (generally enhanced) excitatory nerve activity. As a result, initial
subjective symptoms of CNS toxicity include signs of excitation, such as lightheadedness and
dizziness, difficulty focusing, tinnitus, confusion, and circumoral numbnesss.11,12 Likewise, the
objective signs of local anesthetic toxicity are excitatory, for example, shivering, myoclonia, tremors,
and sudden muscular contractions.13 As the local anesthetic level rises, tonic-clonic convulsions
occur. Symptoms of CNS excitation typically are followed by signs of CNS depression: Seizure
activity ceases rapidly and ultimately is succeeded by respiratory depression and respiratory arrest.
In the concomitant presence of other CNS depressant drugs (e.g., premedication), CNS depression
can develop without the preceding excitatory phase.
The CNS toxicity is directly correlated with local anesthetic potency.14–17 However, there is an
inverse relationship between the toxicity of local anesthetics and the rate at which the agents are
injected: Increasing speed of injection will decrease the blood-level threshold for symptoms to
appear.
All local anesthetics can induce cardiac dysrhythmias,18,19 and all, except cocaine, are
myocardium depressants.20–25 Local anesthetic–induced arrhythmias can manifest as conduction
delays (from prolonged PR interval to complete heart block, sinus arrest, and asystole) to ventricular
dysrhythmias (from simple ventricular ectopy to torsades de pointes and fibrillation). The negative
inotropic action of local anesthetics is exerted in a dose-dependent fashion and consists of depressed
myocardial contractility and a decrease in cardiac output. Dysrhythmias due to local anesthetic
overdose may be recalcitrant to traditional therapies; the reduced myocardial contractility and low
output state further complicate the treatment.
The sequence of cardiovascular events is ordinarily as follows: Low blood levels of local
anesthetic usually generate a small increase in cardiac output, blood pressure, and heart rate, which is
most likely due to a boost in sympathetic activity and direct vasoconstriction. As the blood level of
local anesthetic rises, hypotension ensues as a result of peripheral vasodilation due to relaxation of
the vascular smooth muscles. Further rise of local anesthetic blood levels leads to severe
hypotension, resulting from the combination of reduced peripheral vascular resistance, reduced
cardiac output, and/or malignant arrhythmias. Eventually, extreme hemodynamic instability may lead
to cardiac arrest.
Acid–base status plays an important role in the setting of local anesthetic toxicity.26 Acidosis and
hypercarbia amplify the CNS effects of local anesthetic overdose and exacerbate cardiotoxicity.
Hypercarbia enhances cerebral blood flow; consequently, more local anesthetic is made accessible to
the cerebral circulation. Diffusion of carbon dioxide across the nerve membrane can cause
intracellular acidosis, and as such, it is promoting the conversion of the local anesthetic into the
cationic, or active, form. Because it is impossible for the cationic form to travel across the nerve
membrane, ionic trapping occurs, worsening the CNS toxicity of the local anesthetic. Hypercarbia
and/or acidosis also reduce the binding of local anesthetics by plasma proteins,27 and as a result, the
fraction of free drug readily available for diffusion expands.
Prevention
Prevention of toxicity is key to safer practice, and it starts with making sure that the work environment
is optimized for performing regional anesthesia.28 The logistics for treating an emergency, including
equipment for airway management and treating cardiac arrest, must be readily available and
functioning.
A judicious selection of the type, dose, and concentration of the local anesthetic, and the regional
anesthesia technique, is important. As a rule, the optimal dose and concentration is the lowest one that
achieves the aimed for effect. The effects of pretreatment with a benzodiazepine is often debated but
almost routinely used in our practice. Benzodiazepines lower the probability of seizures29–32 but can
mask early signs of toxicity.33 A sedated patient is theoretically less able to keep the physician
updated on the subjective symptoms of light toxicity, and severe toxicity can establish itself without a
recognizable toxic prodrome. This concern remains only theoretical; many symptoms of limited, mild
CNS toxicity can be prevented by routine premedication with benzodiazepines in addition to making
the PNB procedure more pleasant to patients.
Therefore, the presence of premedication or general anesthesia is not perceived to increase the
risk of local anesthetic toxicity. Considerable research has been invested into the subject of the ideal
test for detecting intravenous injection and to what constitutes the ideal test dose. Epinephrine (5–15
μg) is still widely in use as a marker of intravascular injection. End points with an acceptable
sensitivity are defined by an increase in heart rate >10 bpm, increase in systolic blood pressure by
>15 mm Hg,34 or a 25% decrease in lead II T-wave amplitude.35 However, elderly patients are less
responsive to beta stimulation36 as are those on beta-blocking agents. Low cardiac output can prolong
drug circulation and delay the clinical effect of the beta mimetic, and therefore, the sensitivity of the
test. Accordingly, the interpretation of the test result is not always as straightforward as one would
wish. The significant proportion of false negative test results warrants a reevaluation of the routine
use of this test as a sole determinant to detect inadvertent intravenous injection.
Regardless of whether epinephrine is used as a marker of an intravascular injection, it is of utmost
importance to use slow, incremental injections of local anesthetic, with frequent aspirations (every 3–
5 mL) between injections while monitoring the patient for signs of toxicity.37 A slow rate of injection
of divided doses at distinct intervals can decrease the possibility of summating intravascular
injections. With a rapid injection the seizures may occur at higher blood level because there is no
time for distribution of the drug as compared to a slow infusion where the seizure occurs at a lower
drug level because of the distribution. It is prudent to decrease the local anesthetic dosage in elderly
or debilitated patients and in any patient with diminished cardiac output. However, there are no firm
recommendations on the degree of dose reduction.
Treatment
Early recognition of the toxicity and early discontinuation of the administration is of crucial
importance.38 The administration of local anesthetics should be stopped immediately. The airway
should be maintained at all times, and supplemental oxygen is provided while ensuring that the
monitoring equipment is functional and properly applied. Neurologic parameters and cardiovascular
status should be assessed until the patient is completely asymptomatic and stable.39
Administration of a benzodiazepine to offset or ameliorate excitatory neurological symptoms or a
potential tonic-clonic seizure is indicated.40 Early treatment of convulsions is particularly meaningful
because convulsions can result in metabolic acidosis, thus aggravating the toxicity. Seizures should be
controlled at all times. Based on the recent data in animal studies,41–43 as well as mounting case
reports,44–53 starting an infusion of lipid emulsion (intralipid), especially in those cases where
symptoms of cardiac toxicity are present, should be contemplated early.54 Importantly, there is a
mounting consensus that infusion of intralipids may be initiated early, to also prevent, rather then treat
cardiac arrest. If available, arrangements for transfer to an operating room where cardiopulmonary
bypass can be instituted should also be contemplated in situations where the response to early
treatment is not favorable.55–58
Malignant arrhythmias and asystole are managed using standard cardiopulmonary resuscitation
protocols,59,60 acknowledging that a prolonged effort may be needed to increase the chance of
resuscitation. The rationale of this approach is to maintain the circulation until the local anesthetic is
redistributed or metabolized below the level associated with cardiovascular toxicity, at which time
spontaneous circulation should resume. Because the contractile depression is a core factor underlying
severe cardiotoxicity, it would be intuitive to believe that the use of sympathomimetics should be
helpful. Nonetheless, epinephrine can induce dysrhythmia or it can exacerbate the ongoing arrhythmia
associated with local anesthetic overdose.61,62 Consequently, in the setting of local anesthetic toxicity,
vasopressin may be more appropriate to maintain the blood pressure, support coronary perfusion, and
facilitate local anesthetic metabolism.63 The appropriateness of phosphodiesterase inhibitors
administration is not corroborated by published research results. Although these inhibitors can
promote hemodynamics, there is no evidence of a better outcome. As potent vasodilators,
phosphodiesterase inhibitors do no support blood pressure,64 and they have been associated with
ventricular arrhythmias.65
The current advanced cardiac life support algorithm emphasizes amiodarone as the mainstay drug
for treatment of arrhythmias.66,67 Also, for ventricular arrhythmias prompted by local anesthetic
overdose, current data favor amiodarone. Published studies of using lidocaine to treat arrhythmias
reveal conflicting results, but it is logical to think that treating local anesthetic–induced arrhythmias
with just another local anesthetic antiarrhythmic is likely to add to the cardiotoxicity. The use of
bretylium is no longer endorsed. Occurrence of Torsades des Pointes with bupivacaine toxicity may
require overdrive pacing if that rhythm predominates.
Calcium channel blockers and phenytoin are contraindicated because their coadministration with
local anesthetics may increase the risk of mortality.68,69 Recovery from local anesthetic–induced
cardiac arrest can take enduring resuscitation efforts for more than an hour. Propofol is not an
adequate alternative for treatment with intralipid, although judicious administration to control
seizures when used in small divided doses is appropriate.70,71 Administration of the lipid emulsion
has become an important addition to the treatment of severe local anesthetic toxicity.72 Because it is
still an innovative therapy, future laboratory and clinical experiences are needed for a better
understanding of the mechanisms and further refinement of the treatment protocols.73
Allergic Reactions
The amino-esters, such as chloroprocaine, are all derivatives of the allergen paraaminobenzoic acid
(PABA). Accordingly, the local anesthetics belonging to the ester group may cause positive skin
reactions, ranging from toxic eruptions in situ to generalized rash or urticaria.74 Previous study results
indicate an incidence of 30%, but no subject developed anaphylaxis. However, true allergic reactions
to the local anesthetics of the amino-amide group are extremely rare. By and large, preparations of
amide anesthetics do not cause allergic reactions, unless they contain the preservative methylparaben,
which is in its chemical structure virtually the same as PABA.75 For patients who reported an allergy
to amino-amides, one can safely use a preservative-free amide anesthetic unless a well-documented
allergology reports point to an unambiguous allergy. Anaphylaxis due to local anesthetics remains a
rare event, even within the ester group. It should be considered if the patient starts wheezing or
develops respiratory distress instantly following injection. However, many symptoms can be
explained by a variety of other causes including anxiety, hyperventilation, toxic effects of the drug,
vasovagal reactions, reactions to epinephrine, or contamination with latex.
Management of local anesthetic triggered allergic reactions does not differ from the treatment
algorithms for other more common allergic reactions. Intravenous lidocaine can result in paradoxical
airway narrowing and bronchospasm in patients with asthma. The mechanism of this reaction is not
well understood. Apparently, it is not explained by an exacerbation of the asthmatic condition itself or
by some anaphylactoid cascade activated by lidocaine or its preservatives.
A unique side effect of some local anesthetics is methemoglobinemia.76,77 It has been associated
with the topical, epidural, and intravenous administration of prilocaine. Hepatic metabolism of
prilocaine produces orthotoluidine, which converts hemoglobin into methemoglobin. The doses
needed to effectuate diminished oxygen saturation levels that are clinically significant, however, are
typically above what is used in the clinical practice of regional anesthesia. Regardless, because of
this theoretical possibility, in some countries, the use of prilocaine in regional anesthesia is banned.
The condition of methemoglobinemia caused by prilocaine is spontaneously self-limiting and
reversible. Reversal can be accelerated with the administration of methylene blue intravenously (1
mg/kg).
Summary
Prevention
Always maintain a high degree of suspicion.
Monitor electrocardiogram, blood pressure, and arterial oxygen saturation.
When feasible, communicate with the patient.
Be conservative with local anesthetic (LA) dose in patients with advanced age, poor cardiac function,
conduction abnormalities, or abnormally low plasma protein concentration.
Gently aspirate every 3–5 mL.
Inject slowly (<20 mL/min), and avoid forceful high-pressure injections.
Use a pharmacologic marker (e.g., epinephrine 5 μg/mL of LA) with high-volume blocks.
Monitor the patient after high-dose blocks for 30 minutes.
Be prepared: A plan for managing systemic local anesthetic toxicity should be established in facilities
where local anesthetics are used.
Current recommendations are to have 20% lipid emulsion stocked close to sites where local
anesthetics are used.
Consider infusing lipid emulsion early to help prevent cardiac toxicity.
Detection of Systemic LA Toxicity
Maintain a high degree of suspicion.
The single most important step in treating local anesthetic toxicity is to consider its diagnosis.
CNS symptoms are often subtle or absent.
Cardiovascular signs (e.g., hypertension, hypotension, tachycardia, or bradycardia) may be the first
signs of local anesthetic toxicity.
CNS excitation (agitation, confusion, twitching, seizure), depression (drowsiness, obtundation, coma,
or apnea), or nonspecific neurologic symptoms (metallic taste, circumoral paresthesias, diplopia,
tinnitus, dizziness) are typical of LA toxicity.
Ventricular ectopy, multiform ventricular tachycardia, and ventricular fibrillation are hallmarks of
cardiac toxicity of LA.
Progressive hypotension and bradycardia, leading to asystole, are the hallmark of severe
cardiovascular toxicity.
Treatment of Systemic LA Toxicity
Get help and call for 20% lipid emulsion.
Perform airway management. Hyperventilate with 100% oxygen.
Abolish the seizures.
Perform cardiopulmonary resuscitation
Epinephrine–controversial; may have to use higher doses then recommended in ACLS.
Consider using vasopressin to support circulation
Alert the nearest facility having cardiopulmonary bypass capability.
Perform lipid emulsion treatment (for a 70-kg adult patient):
Bolus 1.5 mL/kg intravenously over 1 minute (about 100 mL)
Continuous infusion 0.25 mL/kg per minute (about 500 mL over 30 minutes)
Repeat bolus every 5 minutes for persistent cardiovascular collapse.
Double the infusion rate if blood pressure returns but remains low.
Continue infusion for a minimum of 30 minutes.
DIAGNOSIS AND TREATMENT OF LOCAL ANESTHETIC TOXICITY
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10
Neurologic Complications of Peripheral Nerve Blocks
Jeff Gadsden
Nerve injury following peripheral nerve blockade (PNB) is a potentially devastating complication
that can result in permanent disability.1
Data from a recent review of published studies suggest that
the incidence of neurologic symptoms following PNB varies depending on the anatomic location,
ranging from 0.03% for supraclavicular blocks to 0.3% for femoral blocks to up to 3% for
interscalene blocks.2
Fortunately, the vast majority of these neuropathies appear to be temporary
rather than permanent neuropathy and resolve over weeks to months.
The exact etiology of neurologic injury related to PNB remains unclear in many instances.
Suggested etiologies include mechanical trauma from the needle, nerve edema and/or hematoma,
pressure effects of the local anesthetic injectate, and neurotoxicity of the injected solutions (both local
anesthetics and adjuvants, e.g., epinephrine).3
Confounding factors that may play a role in nerve injury
include preexisting neuropathies (e.g., diabetes mellitus), surgical manipulation, prolonged tourniquet
pressure, or compression from postoperative casting.4
It is well-established that direct injection into peripheral nerves (i.e., accidentally during
intramuscular administration) can result in nerve injury.5
This is one of the reasons why intraneural
injections are avoided during peripheral nerve blockade. More recent data however, suggest that
intraneural injections are not always associated with nerve injury. This chapter summarizes the
clinically relevant considerations regarding the etiology of nerve injury during peripheral nerve
blockade.
Histology and Histopathology of Peripheral Nerves
Knowledge of the functional histology of nerves is essential to understanding the consequences of
intraneural injection. Nerves are made up of fascicles supported and enveloped by perineurium and a
loose collection of collagen fibers termed the epineurium. The epineurium is easy permeable and
carries the nutritive vessels of larger nerves. Each fascicle is made up of bundles of nerve fibers
(axons) and their associated Schwann cells held together by a tough squamous epithelial sheath called
the perineurium, which acts as a semipermeable barrier to local anesthetics. The nerve fibers are
supported within the perineurium by a delicate connective tissue matrix called the endoneurium,
which contains capillaries that arise from the larger epineurial vessels. Figure 10-1 features normal
anatomy of a mixed peripheral nerve and relationship of the epineurium and perineurium.
FIGURE 10-1. Anatomy of the peripheral nerve as seen on an electron microscopy image. 1-
Epineurium, 2-Fascicle, 3-Fascicular bundles (several fascicles bound together), Arrowsperineurium.
Peripheral nerve lesions can be classified in terms of their degree of functional disruption.6
Neurapraxia refers to a mild insult in which the axons and connective tissue structures supporting
them remain intact. This type of injury is often associated with focal demyelination and generally
reversible over the course of weeks to several months. Axonal interruption with conservation of the
neural connective tissues is termed axonotmesis. Regeneration at a rate of 1 to 2 mm/day occurs, and
recovery is generally favorable although not always complete. Neurotmesis represents complete
fascicular interruption, including the axons and the connective tissue supporting tissues. Because the
nerve is severed, recovery depends on surgical reapproximation of the two stumps. Even with prompt
surgical intervention, recovery is often poor. It is important to note that most nerve injuries are mixed,
with different fascicles exhibiting characteristics of these three different injury types.
The Problem, or Is It?
Selander et al provided evidence of the deleterious effects of intraneural injection over 30 years ago7
Indeed, the objective during peripheral nerve blockade has been to deposit local anesthetic in the
vicinity, but not within, the substance of the nerve. This tacit convention has been challenged in recent
years with the publication of a series of reports suggesting that intraneural needle placement, and
indeed injection of local anesthetic, may not necessarily result in detectable clinical injury. In 2004
Sala-Blanch et al described two cases of placement of a catheter within the epineurium of the sciatic
nerve, confirmed by computerized tomographic imaging.8
Both patients demonstrated clinically
efficacious blocks without postoperative neurologic deficit. The advent of ultrasound guidance for
nerve blocks has likely led to an increase in the recognition of inadvertent intraneural injections.
Accidental femoral9
and musculocutaneous10 intraneural injections have been described, as
evidenced by nerve swelling on the ultrasound image, both without lasting neurologic effect.
In 2006, Bigeleisen published a series of axillary brachial plexus blocks performed on 22 patients
undergoing thumb surgery.11 Using ultrasound guidance, the authors deliberately placed the needle
intraneurally and injected 2 to 3 mL of local anesthetic, which resulted in 72 intraneural injections as
evidenced by nerve swelling. Despite the common occurrence of paresthesia or dysesthesia (66
times), none of the patients developed an overt neurologic deficit up to 6 months postoperatively.
Similarly, Robards et al studied 24 patients receiving sciatic nerve blocks in the popliteal fossa
using both nerve stimulation and ultrasound guidance.12 The end point for needle advancement was a
motor response using a current intensity of 0.2 to 0.5 mA, or an apparent intraneural needle tip
location, whichever came first. These investigators found that the motor response could only be
obtained upon entry of the needle into the nerve in 83.3% of patients; in the remaining 16.7%, a motor
response with a stimulating current of 1.5 mA could not be obtained, even when the needle tip was
intraneural. There was no postoperative neurologic dysfunction.
Taken together, these studies suggest that an intraneural needle placement with resultant injection
of the local anesthetic within internal epineurium does not lead to an imminent neurologic injury. The
data by Robards et al, suggest that many nerve blocks without the benefit of ultrasound visualization,
have likely resulted in intraneural (intra-epineural) injections. The reason why nerve injury is
infrequent is that the vast majority of these injections do not occur within fascicles.
Extrafascicular versus Intrafascicular Injections
A needle placed within a peripheral nerve can be in one of two locations: within the loose epineurial
matrix that surrounds the fascicles or inside a fascicle itself. It is well-established that injection of
even very small amounts of local anesthetic within the fascicle can lead to widespread axonal
degeneration and permanent neural damage in animals, whereas extrafascicular injection does not
disrupt the normal nerve architecture.7,13 Part of this can be explained mechanically because the
perineurium, a tough multilayer epithelial sheath, is not easily distensible to compensate to an
increase in intrafascicular pressure. Intrafascicular pressure rises on injection and can remain higher
than the capillary perfusion pressure longer than the duration of the injection itself, predisposing to
neural ischemia and inflammation.14 Furthermore, pressure curves derived from intrafascicular versus
extrafascicular injections in canine sciatic nerves show that a pattern of very high initial injection
pressures followed by a sharp drop to baseline is associated with poor outcome and severe neural
histologic damage, and may suggest fascicular rupture.15 In contrast, injections into the compliant
epineurial space appear to be associated with a minimal rise in pressure, which can be explained by
its loose and accommodating stromal architecture.
The risk of an intrafascicular injection differs from site to site in the peripheral nervous system,
and it correlates with the cross-sectional fascicle-epineurium ratio. For example, the sciatic nerve at
the popliteal fossa contains more nonneural tissue than fascicles in its cross-sectional area, which
corresponds with its low incidence of post-PNB neuropathy.16 By contrast, the brachial plexus at the
level of the trunks contains much more neural than connective tissue; a needle entering the nerve here
is more likely to encounter a fascicle on its trajectory that may contribute to the disproportionately
higher rate of postoperative neuropathy following PNB with interscalene blocks.17 As peripheral
nerves move away from the neuraxis, the ratio of connective tissue to neural tissue within the nerve
tends to increase. The brachial plexus elements below the clavicle have a ratio of connective tissue to
neural tissue of approximately 2:1, whereas the more proximal trunks and divisions have a ratio of
1:1.18
Mechanisms of Nerve Injury Following Intraneural Injection
Once the perineurium is breached, the spectrum of subsequent injury is wide and multifactorial.
Needle Trauma
The mechanical disruption of the perineurial sheath may result in injury to the axons and/or the
leakage/herniation of endoneural contents.19 However, the composition of the injectate may play a
larger role in the outcome of intrafascicular injection. For example, normal saline injected into
fascicles did not cause any damage in one study, suggesting that mere puncture of the perineurium
does not necessarily result in clinically overt injury.13 In contrast, nerve puncture with intravenous
cannulae or electroneurography needles has been shown to result in lasting neurologic deficit.20–22 A
variety of cellular changes accompany needle trauma, including alterations in membrane channel
expression, activation of signal transduction, neuropeptide production, and an overall increase in
excitability at the dorsal horn.23,24 The effect of the needle size on the likelihood and severity of the
injury is controversial, however, smaller needles (24 gauge) may lead to less nerve injury than larger
needles (19 gauge).25
Despite the concern over fascicular puncture, due to their compact nature, fascicles are more likely
to escape the advancing needle, rather than be penetrated under normal PNB conditions. Early work
by Selander et al in rabbits demonstrated that needle tip characteristics influenced the likelihood of
fascicular penetration.26 This study demonstrated that long-bevel (12–15°) needles were more likely
to puncture the fascicle than short-bevel (45°) needles, and resulted in the author advocating for their
use during PNB. A more recent study compared blunt (30°) versus sharp (15°) needles by passing
these needles through a cadaveric sciatic nerve and examining the nerve microscopically afterward
for signs of fascicular damage.27 Although a total of 134 fascicles were identified as being in contact
with the needle tracks, only 4 fascicles were damaged, all of which belonged to the sharp-tip group.
These data suggest that a needle passing through a fascicle is more likely only to encounter
epineurium and may in fact displace the tough fascicles away from the needle path. Although blunt
needles are less likely to enter the fascicle, once penetrated, blunt needles appear to cause a greater
degree of injury compared with sharp needles, especially if the sharp needles are oriented with the
bevel in the same direction as the nerve fibers (i.e., not cutting transversely across the fibers).28
Regardless of which needle type or size enters the nerve, a needle insertion into nerve and consequent
injection invariably leads to inflammation and cellular infiltration regardless of whether a clinical
injury occurs.
Toxicity of Local Anesthetics and Additives
Although all local anesthetics are potentially neurotoxic,29 the mechanism remains unclear. Proposed
mechanisms include increases in intracellular calcium concentration, disturbance in mitochondrial
function, interference with membrane phospholipids, and cell apoptosis.30–33 The perineurium and
blood vessel endothelium serve as a barrier to entry into the fascicle. However, even local
anesthetics placed within the epineurium have been shown to cause altered perineural permeability
and fascicular edema, leading to compression of the fascicle and reduced neural blood flow.13,34 This
effect appears to be dose dependent.
Intraneural administration of local anesthetics exposes the axons to higher concentrations of drug
than extraneural application. One study comparing the extraneural, extrafascicular, and intrafascicular
administration of ropivacaine 0.75% showed that histologic damage was least severe extraneurally
and most severe intrafascicularly.35 However, even when injected inside the epineurium, others have
shown ropivacaine 0.75% to have no adverse effect on functional recovery.36 Ester local anesthetics
such as tetracaine and chloroprocaine were shown in some studies to cause a greater degree of injury
than those of the amide group, but recent data have challenged those conclusions.34,37 What is well
known is that the injection of local anesthetics into the fascicle results in widespread and immediate
axonal injury.14
Local anesthetics alone are also capable of decreasing neural blood flow. Lidocaine 2% reduces
neural blood flow in rat sciatic nerves by 20–40%, and this difference persists after washout of the
local anesthetic solution.38,39 Increasing concentrations of lidocaine appear to reduce neural blood
flow further; the reverse is true for bupivacaine. Altering the concentration of tetracaine appears to
have no effect on neural blood flow. Various concentrations of levobupivacaine and ropivacaine have
been found to reduce rat sciatic nerve blood flow significantly.40
Epinephrine is a common adjuvant used to prolong the duration of blockade and to warn of
intravascular injection/absorption. At concentrations of 5 μg/mL and 10 μg/mL, epinephrine reduces
neural blood flow by 20% and 35%, respectively.39 In contrast, at lower concentrations (2.5 μg/mL),
neural blood flow increases by 20% transiently before returning to baseline, suggesting that at lower
concentrations the β-adrenergic effects predominate. The effects of combining lidocaine and
epinephrine are additive: A solution of 2% lidocaine plus 5 μg/mL of epinephrine reduced neural
blood flow by 80%.38
The clinical significance of the effects of various local anesthetics and additives is unknown. The
experimental data must be weighed within the context of clinical practice; countless of nerve blocks
of blocks are performed in daily practice using a combination of local anesthetic and epinephrine
with no neurologic consequences. This reinforces the hypothesis that nerve injury is multifactorial,
and one theoretical aspect may be insufficient to cause injury consistently.
Prevention of Peripheral Nerve Injury
Several techniques have been advocated to enhance safety during the performance of PNBs. The
merits of each technique in preventing nerve injury are addressed individually.
Pain on Injection
Pain on injection has traditionally been taught as a reliable and effective means to guard against
intraneural injection because intraneural injections are thought to be exquisitely painful. However,
there are multiple problems with this logic. First, pain is notoriously difficult to evaluate in terms of
intensity and quality. Consequently, differentiating between a benign, commonly present discomfort
during injection of local anesthetic (pressure paresthesia) and that of intrafascicular injection can be
elusive. Second, various patient conditions (e.g., diabetes mellitus, peripheral neuropathy) and
premedication may interfere with pain perception. Third, there appears to be little evidence that pain
on injection is either sensitive or specific. Fanelli et al conducted a prospective study of nearly 4000
patients receiving multiple-injection PNBs and found that the overall rate of neurologic complications
was 1.7%, independent of whether the patient reported a paresthesia or not.41 In other words, it does
not appear to matter whether the patient reports a paresthesia or not—they have an equal likelihood of
postoperative neuropathy. Bigeleisen’s report of 72 intraneural injections was associated with 66
reports of paresthesia or dysesthesia, yet none of the patients had neurologic complications,
suggesting the symptom itself has a low specificity for complications.11 Fourth, the nature of nerve
injury might preclude its use as a useful monitor: By the time a patient registers pain, communicates it
to the anesthesiologist, and the injection is halted, the damage is likely to have been done. Because a
fraction of a milliliter is sufficient to cause irreversible fascicular damage, the patient’s subjective
symptom may be too late.7,15 Finally, there are situations in which performing PNBs in an
asleep/heavily sedated/blocked patient might be the safest approach, for example, pediatric cases,
mentally incompetent patients, the traumatically injured, patients needing rescue or repeat blocks, and
so on. The use of more objective monitors, as listed here, may provide increased confidence that an
intrafascicular injection can be avoided when compared with a subjective patient symptom.
Electrical Nerve Stimulation
Electrical stimulation is a means to locate nerves but also may be used to rule out an intraneural
(intrafascicular) location of the needle. Voelckel et al demonstrated that sciatic blocks in pigs
performed with a motor response at <0.2 mA resulted in inflammatory nerve changes in 50% of the
specimens, compared with none when the motor response was achieved at 0.3 to 0.5 mA.42 Others
have investigated the relationship between current intensity and needle-nerve distance in pigs and
found that, although the relationship is unpredictable outside the epineurium, a motor response at a
current intensity of <0.3 mA occurs only with intraneural needle placement.43,44 These findings have
been substantiated in a clinical study of patients undergoing ultrasound-guided supraclavicular block,
in which minimal threshold currents were recorded at “extraneural” and “intraneural” positions.45
The investigators found that no motor response could be elicited at a current of ≤0.2 mA unless the
needle tip was intraneural.
These studies suggest that, although neurostimulation techniques may not be a highly sensitive
method of detecting intraneural needle tip position (i.e., high current intensities may still be required
to elicit motor responses even with intra-epineural needle placement), neurostimulation has a high
specificity for identifying intraneural needle tip placement (i.e., motor response at ≤0.2 mA obtained
only with intraneural needle tip location) Based on the cumulative experimental and clinical data,
using no motor response at <0.2–0.3 mA as a cutoff for safe practice before injecting local anesthetic
makes clinical sense as a routine monitoring method for most nerve blocks.
Ultrasonography
Ultrasound guidance is theoretically an attractive means of preventing intraneural injection due to
real-time imaging of the needle and nerve. Indeed, nerve swelling visualized on the sonographic
image appears to represent true histologic intraneural injection as evaluated by the presence of India
ink staining within the epineurium.44,46 However, the clinical implications of this are also unclear
because nerve swelling and even histologic changes associated with nerve injury appear not to result
in detectable neurologic deficit in pigs, although there may be subtle changes that cannot be assessed
by the evaluators.47
Ultrasound guidance may not be a substantially effective means of preventing nerve injury. The
reliability of ultrasound to keep the needle tip extraneural depends largely on the skill of the operator
and the imaging characteristics of the needle and tissue. Several case reports of accidental nerve (and
vascular) puncture despite the use of ultrasound guidance highlight the fact that ultrasound monitoring
is not a fail-proof method of avoiding neurologic (and other mechanical) complications.9,10,48
Furthermore, at the present time the resolution of the sonographic image is such that it would be
impossible to tell if the needle tip was intrafascicular or extrafascicular, which is the critical
anatomic differentiation to make to avoid nerve injury. Finally, as is the case with paresthesia, by the
time the nerve is seen swelling on the image, the damage may have already been done if the injection
is made with the needle tip inside the fascicle.
Injection Pressure Monitoring
The crux of the intraneural injection problem thus far appears to lie in the avoidance of penetrating the
perineurium and entering the fascicle. The presence of a high opening injection pressure (>20 psi) in
a canine model is a very sensitive (if not highly specific) sign of intrafascicular needle tip placement,
whereas extrafascicular needle tip placement is associated with low (<10 psi) pressures.15 Another
dog study showed that some, but not all, intraneural injections resulted in high (>20 psi) pressures,
whereas high pressures were absent during extraneural injection.49 More importantly, high pressure
injection was associated with neurologic deficits and severe axonal damage after the block, in
contrast to normal neurologic and histologic findings following any low-pressure injection (extra or
intraneural). Indeed, PNBs associated with high injection pressure, despite a lack of paresthesia, have
been reported to result in permanent neurologic injury.50 Although objective injection pressure
monitoring and documentation has not yet been universally adopted, assessment of resistance to
injection is a standard clinical practice. Unfortunately, clinical data on the role of injection pressure
monitoring may never become available as it would be unethical to randomize patients to receive a
high versus low pressure nerve block injection. However, the available clinical and experimental
evidence points that injection pressure is useful in detecting needle-nerve contact (Table 10-1).
TABLE 10-1
Given this, safe practice should include the objective assessment of the resistance to injection with
most single injection peripheral nerve blocks. An assessment of injection resistance is often assessed
using a “syringe-hand-feel” technique. However, it has been well documented (in at least two
models) that practitioners are unable to gauge injection pressure by using a syringe-hand-feel
subjective technique.51,52 Therefore, if monitoring of resistance to injection is to have clinical merit,
objective monitoring of injection pressure should be used to standardize the injection force. This may
be achieved by use of commercially available inline devices or with the use of a “compressed air
injection technique.”53 One shortcoming of injection pressure monitoring is that injection pressure is
highly sensitive but lacks specificity. In other words, absence of high injection pressure appears to
effectively rule out an intrafascicular injection. However, high injection pressure also can be caused
by PNB needle obstruction, attempted injection into a tendon, or tissue compression caused by the
ultrasound transducer.
Future Directions
The regional anesthesia community is witnessing the beginning of a paradigm shift in the thinking
surrounding intraneural injection during PNB. Clearly they can be performed safely in certain
patients. The question is: Should they? Even intranueral extrafascicular injection of local anesthetic
often results in histologic evidence of inflammation in animal experiments. However, intraneural
extrafascicular injection in patients often does not result in symptoms. The risk may be different in
patients who have preexisting or subclinical neuropathy. It is important to note that the studies
demonstrating safe intraneural injections in humans deliberately excluded patients with preexisting
neuropathy.
Deliberate injection of local anesthetic into peripheral nerves and plexuses is controversial with
regards to its safety and clinical advantages. Such injections in distal nerves may be more forgiving,
owing to their increased ratio of nonneural tissue to neural tissue. In particular, injuries to the sciatic
nerve at the popliteal fossa appear to be uncommon following intraneural injection or intraneural
catheter placement.54,55 In fact, it has been noted that intraneural injection of local anesthetic in the
popliteal sciatic nerve leads to a rapid onset of sensory and motor blockade, without complications.55
Some practitioners now routinely attempt to place the needle tip within the epineurium at this
location, in an attempt to hasten onset, improve block success, and decrease the total amount of local
anesthetic required. However, this practice should be done only with a combination of objective
monitoring because the need to remain extrafascicular is paramount.
One of the challenges is to elucidate the precise factors that provide for a safe intraneural
injection, whether anatomic (popliteal sciatic versus subgluteal), technological (injection pressure
monitoring, improved resolution of ultrasound imaging), educational (improved training), or
otherwise. More clinical research is needed to clarify the safety of intraneural injection in various
nerves such as the femoral nerve, and distal nerves of the upper and lower limbs. This should be
undertaken with care and with proper safeguards to prevent penetration of the perineurium. Lastly,
intraneural injection may allow for reduction in the volume and/or concentration of local anesthetic
required for effective nerve block.54 This is a worthwhile avenue to explore, both in terms of the
implications for nerve injury and for reducing the potential for systemic local anesthetic toxicity. A
combination of monitoring to decrease the risk of an intrafascicular injection during peripheral nerve
blocks is demonstrated in Figure 10-2 as well as in Chapter 5.
MONITORING DURING NERVE BLOCKS: COMBINING ULTRASOUND (US), NERVE
STIMULATION (NS) AND INJECTION PRESSURE MONITORING
FIGURE 10-2.
Practical Management of Postoperative Neuropathy
Despite the best precautions, a postoperative sensory or motor deficit that outlasts the expected
duration of the PNB may occur. It is important to note that the vast majority of neuropathies resolve
spontaneously, and patient reassurance is vital.36 Processes that are either evolving (i.e. compartment
syndrome) or are reparable (i.e. surgical transection of a nerve) should be ruled out. Here are a few
principles to bear in mind when managing a postoperative neuropathy:
. Good communication is essential, both from a patient care and medicolegal standpoint.
. Approximately 95% of postoperative sensory changes will resolve within 4–6 weeks, and most of
these will occur during the first week. 99% of sensory changes will resolve within the first year.
. Early diagnosis of postoperative peripheral nerve injury can be challenging due to:
residual sedation and/or PNB
• pain that limits the examination
• casts, dressings, splints, slings
• movement restrictions
• patient expectations regarding block—"I didn’t know how long it was supposed to last"
. Neuropathies can also be caused by prolonged tourniquets, casting, excessive intraoperative traction,
or a misplaced surgical clip. Early involvement of the surgical team is prudent.
. In general, the presence of motor deficits is an ominous sign, and a referral to a neurologist and/or
neurosurgeon is indicated.
. Neuropathies that are evolving, and those that are severe/complete should be seen immediately by a
neurologist and/or neurosurgeon.
Referral for electrophysiologic testing may be indicated when the symptoms are not purely
sensory, or when the neuropathy is severe and/or long-lasting. Studies performed usually consist of
the following:
. Electromyography. This is undertaken to determine which muscle units are affected by a denervation
lesion. Small needle electrodes are placed in various muscles and the pattern of electrical activity
both at rest and with contraction is analyzed. The results can help to localize a lesion, and, depending
on the pattern, suggest a time frame for the injury.
. Nerve conduction studies. In these tests, a device similar to the peripheral nerve stimulator used by
anesthesiologists to monitor the degree of neuromuscular blockade is attached over various nerves in
the affected area. A characteristic waveform is generated following stimulation of the nerve, which
may allow the neurologist to pinpoint a conduction block.
The optimal timing of these tests depends on the indication. An exam within 2–3 days of the onset
of injury may give information regarding the completeness of the lesion (and therefore prognosis), as
well as clues about the duration of the lesion, which often has medicolegal ramifications, particularly
if the lesion is deemed to predate the nerve block or surgical procedure. As such, this can be seen as
a “baseline” exam. More information is obtained at approximately 4 weeks post-injury, when the
electrophysiologic changes have had an opportunity to evolve more fully.
A practical algorithm for the management of postoperative neuropathy is shown in Figure 10-3.
PRACTICAL APPROACH TO MANAGEMENT OF A PATIENT WITH NEUROLOGIC DEFICIT
AFTER PERIPHERAL NERVE BLOCK
FIGURE 10-3.
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SECTION 2
Nerve Stimulator and Surface-Based Nerve Block Techniques
Chapter 11 Cervical Plexus Block
Chapter 12 Interscalene Brachial Plexus Block
Chapter 13 Supraclavicular Brachial Plexus Block
Chapter 14 Infraclavicular Brachial Plexus Block
Chapter 15 Axillary Brachial Plexus Block
Chapter 16 Wrist Block
Chapter 17 Cutaneous Nerve Blocks of the Upper Extremity
Chapter 18 Lumbar Plexus Block
Chapter 19 Sciatic Block
Part 1. Transgluteal Approach
Part 2. Anterior Approach
Chapter 20 Popliteal Sciatic Block
Part 1. Intertendious Approach
Part 2. Lateral Approach
Chapter 21 Femoral Nerve Block
Chapter 22 Ankle Block
Chapter 23 Thoracic Paravertebral Block
Chapter 24 Intercostal Block
11
Cervical Plexus Block
FIGURE 11-1. Needle insertion for superficial cervical plexus block. The needle is inserted behind
the posterior border of the sternocleidomastoid muscle.
General Considerations
Cervical plexus block can be performed using two different methods. One is a deep cervical plexus
block, which is essentially a paravertebral block of the C2-4 spinal nerves (roots) as they emerge
from the foramina of their respective vertebrae. The other method is a superficial cervical plexus
block, which is a subcutaneous blockade of the distinct nerves of the anterolateral neck. The most
common clinical uses for this block are carotid endarterectomy and excision of cervical lymph nodes.
The cervical plexus is anesthetized also when a large volume of local anesthetic is used for an
interscalene brachial plexus block. This is because local anesthetic invariably escapes the
interscalane groove and layers out underneath the deep cervical fascia where the branches of the
cervical plexus are located.
The sensory distribution for the deep and superficial blocks is similar for neck surgery, so there is
a trend toward favoring the superficial approach. This is because of the potentially greater risk for
complications associated with the deep block, such as vertebral artery puncture, systemic toxicity,
nerve root injury, and neuraxial spread of local anesthetic.
Functional Anatomy
The cervical plexus is formed by the anterior rami of the four upper cervical nerves. The plexus lies
just lateral to the tips of the transverse processes in the plane just behind the sternocleidomastoid
muscle, giving off both cutaneous and muscular branches. There are four cutaneous branches, all of
which are innervated by roots C2-4. These emerge from the posterior border of the
sternocleidomastoid muscle at approximately its midpoint, and they supply the skin of the
anterolateral neck (Figures 11-2 and 11-3). The second, third, and fourth cervical nerves typically
send a branch each to the spinal accessory nerve or directly into the deep surface of the trapezius to
supply sensory fibers to this muscle. In addition, the fourth cervical nerve may send a branch
downward to join the fifth cervical nerve and participates in formation of the brachial plexus. The
motor component of the cervical plexus consists of the looped ansa cervicalis (C1-C3), from which
the nerves to the anterior neck muscles originate, and various branches from individual roots to
posterolateral neck musculature (Figure 11-4). The C1 spinal nerve (the suboccipital nerve) is
strictly a motor nerve, and is not blocked with either technique. One other significant muscle
innervated by roots of the cervical plexus includes the diaphragm (phrenic nerve, C3,4,5) (Table 11-
1).
FIGURE 11-2. The superficial cervical plexus and its terminal nerves. Anatomy of the superficial
cervical plexus and its branches are shown emerging behind the posterior border of the
sternocleidomastoid muscle.
FIGURE 11-3. Anatomy of the superficial cervical plexus. Sternocleidomastoid muscle
mastoid process clavicle external jugular vein.
FIGURE 11-4. The roots origin of the cervical plexus.
TABLE 11-1 Cervical Plexus
Distribution of Blockade
Cutaneous innervation of both the deep and the superficial cervical plexus blocks includes the skin of
the anterolateral neck and the ante- and retroauricular areas (Figure 11-5). In addition, the deep
cervical block anesthetizes three of the four strap muscles of the neck, geniohyoid, the prevertebral
muscles, sternocleidomastoid, levator scapulae, the scalenes, trapezius, and the diaphragm (via
blockade of the phrenic nerve).
FIGURE 11-5. Sensory innervation of the lateral aspect of the head and neck and contribution of the
superficial cervical plexus.
Superficial Cervical Plexus Block
Equipment
A standard regional anesthesia tray is prepared with the following equipment:
Sterile towels and gauze packs
A 20-mL syringe with local anesthetic, attached to a 1½-in, 25-gauge needle, typically via a flexible
tubing
Sterile gloves, marking pen
Landmarks and Patient Positioning
The patient is in a supine or semi-sitting position with the head facing away from the side to be
blocked. These are the primary landmarks (Figure 11-6) for performing this block:
FIGURE 11-6. Surface landmarks for superficial cervical plexus block. White dot: insertion of the
clavicular head of the sternocleidomastoid muscle. Blue dot: Mastoid process. Uncolored circle:
Transverse process of C6 vertebrate. Red dot: Needle insertion site at the midpoint between C6 and
mastoid process behind the posterior border of the sternocleidomastoid muscle.
. Mastoid process
. Clavicular head of the sternocleidomastoid
. The midpoint of the posterior border of the sternocleidomastoid (this is aided by identifying the first
two landmarks)
Maneuvers to Facilitate Landmark Identification
The sternocleidomastoid muscle can be better differentiated from the deeper neck structures by asking
the patient to raise their head off the table.
TIP
The proportions of the shoulder girdle, size of the neck, prominence of the muscles, and other areas
vary among patients. When in doubt, always perform a “reality check” and estimate the two bony
landmarks, the clavicle and the mastoid process.
Technique
After cleaning the skin with an antiseptic solution, the needle is inserted along the posterior border of
the sternocleidomastoid, and three injections of 5 mL of local anesthetic are injected behind the
posterior border of the sternocleidomastoid muscle subcutaneously, perpendicularly, cephalad, and
caudad in a “fan” fashion (Figure 11-7).
FIGURE 11-7. Injection of local anesthetic for superficial cervical plexus. The injection is made
fan-wise behind the posterior border of the sternocleidomastoid muscle at a depth of approximately 1
cm in average-size patients.
GOAL
The goal of the injection is to infiltrate the local anesthetic subcutaneously but deep to the
cervical fascia and behind the sternocleidomastoid muscle. Deep needle insertion (i.e., >1–2 cm)
should be avoided to minimize the risk of subarachnoid or vertebral artery injection.
Block Dynamics and Perioperative Management
A superficial cervical plexus block is associated with minor patient discomfort. Small doses of
midazolam 1 to 2 mg for sedation and alfentanil 250 to 500 μg for analgesia just before needle
insertion should result in a comfortable, cooperative patient during block injection. The onset time for
this block is 10 to 15 minutes. Excessive sedation should be avoided before and during head and neck
procedures because airway management, when necessary, can prove difficult because access to the
head and neck is shared with the surgeon. Due to the complex arrangement of the sensory innervation
of the neck and the cross-coverage from the contralateral side, the anesthesia achieved with a cervical
plexus block is rarely complete. Although this should not discourage the use of the cervical block, the
surgeon must be willing to supplement the block with a local anesthetic if necessary.
TIPS
A subcutaneous midline injection of local anesthetic extending from the thyroid cartilage distally to the
suprasternal notch will block the branches crossing from the opposite side. This injection can be
considered a “field” block. It is useful for preventing pain from surgical skin retractors on the medial
aspect of the neck.
Carotid surgery requires blockade of the glossopharyngeal nerve branches. The surgeon can
accomplish this intraoperatively by injecting local anesthetic inside the carotid artery sheath.
Deep Cervical Plexus Block
Equipment
A standard regional anesthesia tray is prepared with the following equipment:
Sterile towels and gauze packs
A 20-mL syringe with local anesthetic, attached via tubing to 1½ to 2 in, 22-gauge short bevel needle
A 3-mL syringe plus 25-gauge needle with local anesthetic for skin infiltration
Sterile gloves, marking pen, ruler
Landmarks and Patient Positioning
The patient is in the same position as for the superficial cervical plexus block. The three landmarks
for a deep cervical plexus block are similar to those for the superficial cervical plexus block:
. Mastoid process
. Chassaignac tubercle (transverse process of C6) (Figure 11-8)
FIGURE 11-8. Palpation technique to determine location of the transverse process of C6. The head
is rotated away from the palpated side while the palpated fingers explore for the most lateral bony
prominence, often in the vicinity of the external jugular vein.
. Posterior border of the sternocleidomastoid muscle (Figure 11-9)
FIGURE 11-9. Palpation technique to determine the posterior border of the sternocleidomastoid
muscle. With the head of the patient rotated away from the palpation side, the patient is asked to lift
his or her head off of the bed to accentuate the sternocleidomastoid muscle.
To estimate the line of needle insertion overlying the transverse processes, the mastoid process
and the transverse process of C6 are identified and marked. The latter is easily palpated behind the
clavicular head of the sternocleidomastoid muscle just below the level of the cricoid cartilage.
Next, a line is drawn connecting the mastoid process to the C6 transverse process. The palpating
hand is best positioned just behind the posterior border of the sternocleidomastoid muscle. Once this
line is drawn, the insertion sites over C2 through C4 are labeled as follows: C2: 2 cm caudad to the
mastoid process, C3: 4 cm caudad to the mastoid process, and C4: 6 cm caudad to the mastoid
process (Figure 11-10).
FIGURE 11-10. The landmarks for the deep cervical plexus block. White circle indicates the
transverse process of C6 The pen is outlining the transverse process of C4.
Maneuvers to Facilitate Landmark Identification
The sternocleidomastoid muscle can be accentuated by asking the patient to raise his or her head off
of the table.
Technique
After cleaning the skin with an antiseptic solution, local anesthetic is infiltrated subcutaneously along
the line estimating the position of the transverse processes. The local anesthetic is infiltrated over the
entire length of the line, rather than at the projected insertion sites. This allows reinsertion of the
needle slightly caudally or cranially when the transverse process is not contacted, without the need to
infiltrate the skin at a new insertion site.
A needle is connected via flexible tubing to a syringe containing local anesthetic. The needle is
inserted between the palpating fingers and advanced at an angle perpendicular to the skin plane
(Figure 11-11). The needle should never be oriented cephalad. A slightly caudal orientation of the
needle is important to prevent inadvertent insertion of the needle toward the cervical spinal cord. The
needle is advanced slowly until the transverse process is contacted. At this point, the needle is
withdrawn 1 to 2 mm and firmly stabilized, and 4 to 5 mL of local anesthetic is injected after a
negative aspiration test for blood. The needle is removed, and the entire procedure is repeated at
consecutive levels.
FIGURE 11-11. Needle insertion for the deep cervical plexus block. The needle is inserted between
fingers palpating individual transverse processes.
TIPS
The transverse processes are typically contacted at a depth of 1–2 cm in most patients. This distance
can be further shortened by exerting pressure on the skin during needle advancement.
The needle should never be advanced beyond 2.5 cm to avoid the risk of cervical cord injury or
carotid or vertebral artery puncture.
GOAL
• Contact with the posterior tubercle of the transverse process.
• Slightly withdraw the needle after the contact and before making an injection.
Troubleshooting Deep Cervical Plexus Blocks
When insertion of the needle does not result in contact with the transverse process within 2 cm, the
following maneuvers are used:
. While avoiding skin movement, keep the palpating hand in the same position and the skin between the
fingers stretched.
. Withdraw the needle to the skin, redirect it 15° inferiorly, and repeat the procedure.
. Withdraw the needle to the skin, reinsert it 1 cm caudal, and repeat the procedure.
TIPS
When these maneuvers fail to result in contact with the transverse process, the needle should be
withdrawn and the landmarks reassessed.
Redirecting the needle cephalad in an attempt to contact the transverse process should be avoided
because it carries a risk of cervical cord injury when the needle is advanced too deeply.
Block Dynamics and Perioperative Management
Premedication is useful for patient comfort; however, excessive sedation should be avoided. During
neck surgery, airway management can be difficult because the anesthesiologist must share access to
the head and neck with the surgeon. Surgeries like carotid endarterectomy require the patient to be
fully conscious, oriented, and cooperative during the entire procedure. In addition, excessive sedation
and the consequent lack of patient cooperation can result in restlessness and create difficulty for the
surgeon. The onset time for this block is 10 to 20 minutes. The first sign is decreased sensation in the
area of distribution of the respective components of the cervical plexus. Complications of cervical
plexus blocks and strategies to avoid them are listed in Table 11-2.
TABLE 11-2 Complications and How to Avoid Them
DEEP CERVICAL PLEXUS BLOCK
SUGGESTED READING
Superficial Cervical Plexus Block
Aunac S, Carlier M, Singelyn F, De Kock M. The analgesic efficacy of bilateral combined superficial
and deep cervical plexus block administered before thyroid surgery under general anesthesia. Anesth
Analg. 2002;95:746-750.
Brogly N, Wattier JM, Andrieu G, et al. Gabapentin attenuates late but not early postoperative pain after
thyroidectomy with superficial cervical plexus block. Anesth Analg. 2008;107:1720-1725.
Choi DS, Atchabahian A, Brown AR. Cervical plexus block provides postoperative analgesia after
clavicle surgery. Anesth Analg. 2005;100:1542-1543.
e Sousa AA, Filho MA, Faglione W Jr, Carvalho GT. Superficial vs combined cervical plexus block
for carotid endarterectomy: a prospective, randomized study. Surg Neurol. 2005;63 Suppl 1:S22-25.
D’Honneur G, Motamed C, Tual L, Combes X. Respiratory distress after a deep cervical plexus block.
Anesthesiology. 2005;102:1070.
Dieudonne N, Gomola A, Bonnichon P, Ozier YM. Prevention of postoperative pain after thyroid
surgery: a double-blind randomized study of bilateral superficial cervical plexus blocks. Anesth
Analg. 2001;92:1538-1542.
Eti Z, Irmak P, Gulluoglu BM, Manukyan MN, Gogus FY. Does bilateral superficial cervical plexus
block decrease analgesic requirement after thyroid surgery? Anesth Analg. 2006;102:1174-1176.
Guay J. Regional anesthesia for carotid surgery. Curr Opin Anaesthesiol. 2008;21:638-644.
Herbland A, Cantini O, Reynier P, et al. The bilateral superficial cervical plexus block with 0.75%
ropivacaine administered before or after surgery does not prevent postoperative pain after total
thyroidectomy. Reg Anesth Pain Med. 2006;31:34-39.
Heyer EJ, Gold MI, Kirby EW, et al. A study of cognitive dysfunction in patients having carotid
endarterectomy performed with regional anesthesia. Anesth Analg. 2008;107:636-642.
ankovic D, Wells C, eds. Regional Nerve Blocks. 2nd ed. Berlin, Germany: Blackwell Scientific
Publications; 2001.
unca A, Marret E, Goursot G, Mazoit X, Bonnet F. A comparison of ropivacaine and bupivacaine for
cervical plexus block. Anesth Analg. 2001;92:720-724.
Kim YK, Hwang GS, Huh IY, et al. Altered autonomic cardiovascular regulation after combined deep
and superficial cervical plexus blockade for carotid endarterectomy. Anesth Analg. 2006;103:533-
539.
Kwok AO, Silbert BS, Allen KJ, Bray PJ, Vidovich J. Bilateral vocal cord palsy during carotid
endarterectomy under cervical plexus block. Anesth Analg. 2006;102:376-377.
Luchetti M, Canella M, Zoppi M, Massei R. Comparison of regional anesthesia versus combined
regional and general anesthesia for elective carotid endarterectomy: a small exploratory study. Reg
Anesth Pain Med. 2008;33:340-345.
Masters RD, Castresana EJ, Castresana MR. Superficial and deep cervical plexus block: technical
considerations. AANA J. 1995;63:235-243.
Mulroy M. Regional Anesthesia: An Illustrated Procedural Guide. 3rd ed. Philadelphia, PA:
Lippincott, Williams & Wilkins; 2002.
Murphy T. Somatic blockade of head and neck. In: Cousins MJ, Bridenbaugh PO, eds. Neuronal
Blockade in Clinical Anesthesia and Management of Pain. Philadelphia, PA: Lippincott-Raven;
1988:489-514.
Nash L, Nicholson HD, Zhang M. Does the investing layer of the deep cervical fascia exist?
Anesthesiology. 2005;103:962-968.
andit JJ, Bree S, Dillon P, Elcock D, McLaren ID, Crider B. A comparison of superficial versus
combined (superficial and deep) cervical plexus block for carotid endarterectomy: a prospective,
randomized study. Anesth Analg. 2000;91:781-786.
intaric TS, Hocevar M, Jereb S, Casati A, Jankovic VN. A prospective, randomized comparison
between combined (deep and superficial) and superficial cervical plexus block with levobupivacaine
for minimally invasive parathyroidectomy. Anesth Analg. 2007;105:1160-1163.
chneemilch CE, Bachmann H, Ulrich A, Elwert R, Halloul Z, Hachenberg T. Clonidine decreases
stress response in patients undergoing carotid endarterectomy under regional anesthesia: a
prospective, randomized, double-blinded, placebo-controlled study. Anesth Analg. 2006;103:297-
302.
toneham MD, Doyle AR, Knighton JD, Dorje P, Stanley JC. Prospective, randomized comparison of
deep or superficial cervical plexus block for carotid endarterectomy surgery. Anesthesiology.
1998;89:907-912.
uresh S, Templeton L. Superficial cervical plexus block for vocal cord surgery in an awake pediatric
patient. Anesth Analg. 2004;98:1656-1657.
Umbrain VJ, van Gorp VL, Schmedding E, et al. Ropivacaine 3.75 mg/ml, 5 mg/ml, or 7.5 mg/ml for
cervical plexus block during carotid endarterectomy. Reg Anesth Pain Med. 2004;29:312-316.
Winnie AP, Ramamurthy S, Durrani Z, Radonjic R. Interscalene cervical plexus block: a singleinjection technic. Anesth Analg. 1975;54:370-375.
Deep Cervical Plexus Block
Benzon HT, Raja SN, Borsook D, Molloy RE, Strichartz G. Essentials of Pain Medicine and Regional
Anesthesia. Philadelphia, PA: Churchill Livingstone; 1999.
Brown D. Atlas of Regional Anesthesia. Philadelphia, PA: Saunders; 1992.
Carling A, Simmonds M. Complications from regional anaesthesia for carotid endarterectomy. Br J
Anaesth. 2000;84:797-800.
Davies MJ, Silbert BS, Scott DA, Cook RJ, Mooney PH, Blyth C. Superficial and deep cervical plexus
block for carotid artery surgery: a prospective study of 1000 blocks. Reg Anesth. 1997;22:442-446.
Emery G, Handley G, Davies MJ, Mooney PH. Incidence of phrenic nerve block and hypercapnia in
patients undergoing carotid endarterectomy under cervical plexus block. Anaesth Intensive Care.
1998;26:377-381.
ohnson TR. Transient ischaemic attack during deep cervical plexus block. Br J Anaesth. 1999;83:965-
967.
Kulkarni RS, Braverman LE, Patwardhan NA. Bilateral cervical plexus block for thyroidectomy and
parathyroidectomy in healthy and high risk patients. J Endocrinol Invest. 1996;19:714-718.
Lo Gerfo P, Ditkoff BA, Chabot J, Feind C. Thyroid surgery using monitored anesthesia care: an
alternative to general anesthesia. Thyroid. 1994;4:437-439.
Stoneham MD, Wakefield TW. Acute respiratory distress after deep cervical plexus block. J
Cardiothorac Vasc Anesth. 1998;12:197-198.
Weiss A, Isselhorst C, Gahlen J, et al. Acute respiratory failure after deep cervical plexus block for
carotid endarterectomy as a result of bilateral recurrent laryngeal nerve paralysis. Acta Anaesthesiol
Scand. 2005;49:715-719.
12
Interscalene Brachial Plexus Block
FIGURE 12-1. Needle insertion for interscalene brachial plexus block. The needle is inserted
between palpating fingers that are positioned in the scalene groove (between anterior and middle
scalene muscles). 1 = sternal head of the sternocleidomastoid muscle. 2 = clavicular head of the
sternocleidomastoid muscle.
General Considerations
An interscalene block relies on the spread of a relatively large volume of local anesthetic within the
interscalene groove to accomplish blockade of the brachial plexus. In our practice, we almost always
use a low interscalene block technique, which consists of inserting the needle more caudally than in
the commonly described procedure performed at the level of the cricoid cartilage. Our reasoning is
that at the lower neck, the interscalene groove is more shallow and easier to identify, and the
distribution of anesthesia is also adequate for elbow and forearm surgery. In addition, the needle
insertion is more lateral, which makes puncture of the carotid artery less likely and performance of
the block easier to master by trainees. Low approach to interscalene block is used in shoulder, arm,
and forearm surgery. In our practice, the most common indications for this procedure are shoulder and
humerus surgery and the insertion of an arteriovenous graft for hemodialysis.
Functional Anatomy
The brachial plexus supplies innervation to the upper limb and consists of a branching network of
nerves derived from the anterior rami of the lower four cervical and the first thoracic spinal nerves.
Starting from their origin and descending distally, the components of the plexus are named roots,
trunks, divisions, cords, and, finally, terminal branches. The five roots of the cervical and the first
thoracic spinal nerves (anterior rami) give rise to three trunks (superior, middle, and inferior) that
emerge between the medial and anterior scalene muscles to lie on the floor of the posterior triangle of
the neck (Figure 12-2). The roots of the plexus lie deep to the prevertebral fascia, whereas the trunks
are covered by its lateral extension, the axillary sheath. Each trunk divides into an anterior and a
posterior division behind the clavicle, at the apex of the axilla (Figure 12-3). The divisions combine
to produce the three cords, which are named lateral, median, and posterior according to their
relationship to the axillary artery. From this point on, individual nerves are formed as these neuronal
elements descend distally (Figure 12-3 and Table 12-1).
FIGURE 12-2. Anatomy of the brachial plexus. The sternocleidomastoid muscle is removed and the
brachial plexus is seen emerging between the scalene muscles. internal jugular vein. carotid
artery. subclavian artery. Retracted pectoralis muscle. medial and lateral pectoral nerves.
The number “1” also indicates the approximate level at which the block is performed where the roots
of the muscles are emerging between the scalene muscles.
FIGURE 12-3. Functional organization of the brachial plexus and formation of the terminal nerves.
TABLE 12-1 Distribution of the Brachial Plexus
Distribution of Blockade
The interscalene approach to brachial plexus blockade results in anesthesia of the shoulder, arm, and
elbow (Figure 12-4). Note that the skin over and medial to the acromion is supplied by the
supraclavicular nerve, which is a branch of the cervical plexus. Supraclavicular nerves are usually
blocked with the brachial plexus when an interscalene block is performed. This is because the local
anesthetic invariably spills over from the interscalene space into the prevertebral fascia and blocks
the branches of the cervical plexus. The classic interscalene block is not recommended for hand
surgery due to potential sparing of the inferior trunk and the lack of blockade of the C8 and T1 roots.
FIGURE 12-4. Sensory distribution of the brachial plexus. The innervation is shown for didactic
purposes; the exact extent of anesthesia with interscalane block varies considerably and often spares
the hand.
Single-Injection Interscalene Block
Equipment
A standard regional anesthesia tray is prepared with the following equipment:
Sterile towels and gauze packs
2 × 20-mL syringes containing local anesthetic
A 3-mL syringe and 25-gauge needle with local anesthetic for skin infiltration
A 3.5-cm, 22-gauge, short-bevel insulated stimulating needle
Peripheral nerve stimulator
Sterile gloves; marking pen
Landmarks and Patient Positioning
The patient is in a supine or semi-sitting position with the head facing away from the side to be
blocked (Figure 12-5). The arm should rest comfortably on the bed, abdomen, or arm-board to allow
detection of responses to nerve stimulation. Removal of a cast (when present) can help to detect
motor response, although removal is not essential because the responses to nerve stimulation are
usually mixed (stimulation of trunks and divisions rather than specific nerves) and proximal motor
response is adequate (e.g., deltoid, pectoralis).
FIGURE 12-5. Landmarks for the interscalene brachial plexus. White arrows: clavicle. Red arrows:
posterior border of the sternocleidomastoid muscle. Blue arrow: external jugular vein. The palpating
fingers are positioned lateral and posterior to the clavicular head of the sternocleidomastoid muscle
in the space between anterior and middle scalene muscles. The scalene groove is often palpated just
in front or behind the external jugular vein.
These are the primary landmarks for performing this block:
. The clavicle
. Posterior border of the clavicular head of the sternocleidomastoid muscle
. External jugular vein (usually crosses the interscalene groove at the level of the trunks)
Maneuvers to Facilitate Landmark Identification
Identification of the interscalene groove can be made easier by performing the following steps:
Ask the patient to reach for the ipsilateral knee with the limb to be blocked or passively pull the
patient’s wrist inferiorly. This maneuver flattens the skin of the neck and helps identify both the
scalene muscles and the external jugular vein.
The sternocleidomastoid muscle can be accentuated by asking the patient to raise the head off the table
(Figure 12-6).
FIGURE 12-6. Maneuver to extenuate the posterior border of the sternocleidomastoid muscle and
external jugular vein by asking the patient to lift her head off of the table while looking away from the
side to be blocked.
The external jugular vein can be accentuated by asking the patient to perform a brief Valsalva
maneuver.
While palpating the interscalene groove, ask the patient to sniff forcefully. Sniffing tenses the scalene
muscles, and the fingers of the palpating hand often fall into the interscalene groove.
The described landmarks should routinely be marked on the patient’s skin prior to performing the
block.
TIP
The proportions of the shoulder girdle, size of the neck, prominence of the muscles, and other
anatomic features vary among patients. When in doubt, always perform a “reality check” and estimate
three bony landmarks: the sternal notch, clavicle, and mastoid process. This helps identify the
sternocleidomastoid muscle and its relations.
Technique
After cleaning the skin with an antiseptic solution, 1 to 3 mL of local anesthetic is infiltrated
subcutaneously at the determined needle insertion site.
TIP
During skin infiltration, care should be taken to infiltrate local anesthetic into the subcutaneous tissue
plane only because the brachial plexus is very shallow at this location. A deeper needle insertion can
result in deposition of local anesthetic into the plexus; this can result in nerve injury and/or make
attempts at obtaining a motor response unsuccessful.
The fingers of the palpating hand should be gently but firmly pressed between the anterior and
middle scalene muscles to shorten the skin-brachial plexus distance. The skin over the neck can be
very mobile, and care should be taken to stabilize the fingers as well as to stretch the skin gently
between the two fingers to ensure accuracy in needle advancement and redirection. The palpating
hand should not be allowed to move during the entire block procedure to allow for precise
redirection of the needle when necessary.
GOAL
The goal is stimulation of the brachial plexus with a current intensity of 0.2–0.5 mA (0.1 ms). The
following motor responses result in a similar success rate:
• Pectoralis muscle
• Deltoid muscle
• Triceps muscles
• Biceps muscle
• Any twitch of the hand or forearm
The needle is inserted 3–4 cm (approximately 2 fingerbreadths) above the clavicle and advanced
at an angle almost perpendicular to the skin plane (Figure 12-7). The needle must never be oriented
cephalad; a slight caudal orientation reduces a chance for an inadvertent insertion of the needle into
the cervical spinal cord. The nerve stimulator should be initially set to deliver 0.8 to 1.0 mA (2 Hz,
0.1 ms). The needle is advanced slowly until stimulation of the brachial plexus is obtained. This
typically occurs at a depth of 1 to 2 cm in most all patients. Once appropriate twitches of the brachial
plexus are elicited, 25 to 35 mL of local anesthetic are injected slowly with intermittent aspiration to
rule out intravascular injection.
FIGURE 12-7. Needle insertion for interscalene brachial plexus block. The needle is inserted
between fingers positioned in the interscalene groove with a slight caudad orientation to decrease the
chance of entrance in the cervical spinal cord. White arrow: insertion of the sternal head of the
sternocleidomastoid muscle. Red arrows: posterior border of the sternocleidomastoid muscle. Blue
arrow: external jugular vein. The insertion point for the block is often immediately posterior to the
external jugular vein.
This “low-interscalene” approach differs from the classic description of the interscalene block,
which uses the cricoid cartilage as a landmark. The principal advantage to the low approach is that
the brachial plexus is more compact at the lower levels, and reliable coverage of the upper, middle,
and lower trunks can be achieved with a single injection (Figure 12-8). In contrast, the classic
approach may spare the lower trunk, which limits its use for forearm and elbow surgery.
FIGURE 12-8. Distribution of the mixture of local anesthetic and a radiopaque contrast after an
interscalene brachial plexus injection. The arrows and the circle indicate “negative” contrast image
of the roots of the brachial plexus.
When insertion of the needle does not result in upper extremity muscle stimulation, the following
maneuvers can be used (Figure 12-9):
FIGURE 12-9. Maneuvers to obtain a motor response of the brachial plexus during electric nerve
localization. When the motor response is not obtained on the initial needle pass, the needle is
redirected anteriorly or posteriorly to the original insertion plane as shown in the figure.
. Keep the palpating hand in the same position and the skin between the fingers stretched.
. Withdraw the needle to the skin level, redirect it 15° posteriorly, and repeat the needle advancement.
. Withdraw the needle to the skin level, redirect it 15° anteriorly, and repeat the needle insertion.
TIPS
The needle should never be advanced beyond 2.5 cm to avoid the risk of mechanical complications
(cervical cord injury, pneumothorax, vascular puncture).
Never inject when resistance (high pressure) on injection of local anesthetic is met. High resistance to
injection (>15 psi) may indicate an intrafascicular needle placement. Instead, withdraw and/or rotate
the needle slightly and reattempt the injection to assure absence of resistance.
Stimulation of the brachial plexus with a higher stimulating current (e.g., >1.0 mA) results in an
exaggerated response and unnecessary discomfort for the patient. In addition, an unpredictably strong
response often causes dislodgment of the needle and a withdrawal reaction by the patient.
Local anesthetic should not be injected when a motor response is obtained at a current intensity <0.2
mA because this is associated with intraneural needle placement.
Intraneural injection of the trunks can lead not only to nerve injury but also retrograde backflow of
local anesthetic toward neuraxial space, resulting in total spinal anesthesia.
Care should always be taken to avoid attributing diaphragmatic and trapezius twitches to stimulation
of the brachial plexus. Misinterpretation of these twitches is one of the most common causes of block
failure.
When in doubt, palpate the muscle that appears to be twitching to ensure the proper response.
Troubleshooting
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