Lumbar Puncture

Pilar G uerrero, MD

Key Points

• Knowledge of anatomical landma rks and proper steri le

techn ique are important when performing a lumbar

puncture (LP).

• Absolute contraindications to LP are skin infection over

puncture site and a brain mass causing increased intracranial pressure.

INDICATIONS

Lumbar puncture (LP) is performed in the emergency

department (ED) primarily to diagnose central nervous

system (CNS) infections (ie, meningitis) and subarachnoid

hemorrhage (SAH). It may also be performed to relieve

cerebrospinal fluid (CSF) pressure and to confirm the

diagnosis of idiopathic intracranial hypertension (pseudo ­

tumor cerebri). Other indications include the diagnosis of

demyelinating or inflammatory CNS processes and carcinomatous/metastatic disease.

CONTRAINDICATIONS

Absolute contraindications for performing a LP include

infected skin over the puncture site, increased intracranial

pressure (ICP) from any space-occupying lesion (mass,

abscess), and trauma or mass to lumbar vertebrae. A noncontrast head computed tomography ( CT) scan should be

performed to rule out an intracranial mass before performing an LP in the following clinical situations: altered

mental status, focal neurologic deficits, signs of increased

ICP (papilledema), immunocompromise, age >60 years,

or recent seizure. Relative contraindications include

patients who have bleeding diathesis or coagulopathy

(Table 5-1).

16

• Herniation is the most serious compl ication of a LP,

whereas post-LP headache is most common.

Table S-1. Contraind ications to lumbar pu ncture.

Skin infection near the site of lumbar puncture

Central nervous system lesion causing increased intracranial pressure

or spinal mass

Platelet count <20,000 mm3 is an absolute contraindication; platelet

counts >50,000 mm3 are safe for lumbar puncture*

International normal ized ratio 2:1 .5*

Administration of unfiltered heparin or low-molecular-weight heparin

in past 24 hours*

Hemophil ia, von Willebrand disease, other coagulopathies''

Trauma to lumbar vertebrae

···correct clotting factor and/or platelet levels before lumbar puncture.

Reprinted with permission from Ladde JG. Chapter 1 69. Central Nervous

System Procedures and Devices. In: Tintinalli JE, Stapczynski JS, Cline OM,

Ma OJ, Cydulka RK, Meckler GO, eds. Tintinalli's Emergency Medicine:

A Comprehensive Study Guide. 7th ed. New York: McGraw-Hill, 201 1.

EQUIPMENT

Most EDs have a commercially available LP kit, which contains a 20-gauge spinal needle, 22- and 25-gauge needles

for lidocaine administration, 4 collection tubes, stopcock

LUMBAR PUNCTURE

.A. Figure 5-1. Lumbar puncture kit.

and manometer with extension tubing, sterile drapes, skincleansing sponges, and lidocaine (Figure 5- 1). Smaller

spinal needles may be used ( 22, 25 gauge) and may

decrease the incidence of post-LP headache; however, a

22 or larger gauge needle must be used to determine an

accurate opening pressure. Other required supplies include

additional 1% lidocaine without epinephrine, povidoneiodine (Betadine), and sterile gloves.

PROCEDURE

Lumbar puncture is an invasive procedure. Always perform

a neurologic examination before LP. Explain the proce ­

dure, risks and benefits, and potential complications and

obtain written consent.

Level of i l iac crests

Assemble all equipment and have it within easy reach.

Position the patient in a lateral decubitus position with

hips and knees flexed and the upper back arched. This

will allow better opening of the interlaminar spaces.

Make sure the patient's shoulders, back, and hips are perpendicular to the stretcher. Alternatively, the patient may

be in a sitting position, leaning forward and resting their

arms on a tray stand. The latter may work well for

patients who are obese, have degenerative joint disease, or

have problems breathing. However, an accurate opening

pressures can only be obtained with the patient in the

lateral decubitus position.

Next, identify your landmarks by palpating the top of

the posterior superior iliac crests, moving your fingers

medially, as if drawing an imaginary line toward the spine.

This should be at the L4 interspace level. Palpate the spinous processes and identify the 13-14 and the 14-15

interspace. Either of these spaces can be used for the procedure (Figure 5-2).

Open the sterile tray and pour Betadine into the

empty receptacle in the kit. Put on the sterile gloves .

Draw up your lidocaine and place the collection tubes in

sequential order (numbers are written on the tubes,

#1-4). Connect the manometer to the stopcock. Clean the

area with Betadine-soaked handheld sponges in a circular

motion, from the site of planned puncture outward.

Include a spinal level above and below 14. Allow the area

to completely dry. Place the unfenestrated drape on the

patient's bed and the fenestrated drape (with the opening)

over the procedure site. Palpate landmarks again. Using

the 25-gauge needle, raise a skin wheal of lidocaine over

the interspace. Then, use a 20- or 22-gauge needle to

anesthetize the deeper subcutaneous tissue along the

approximate line that the spinal needle will pass. Aspirate

before injecting to make sure you are avoiding intravascular administration.

Identify your landmarks again by palpating the interspinous space with your nondominant hand. With the

.A. Figure 5-2. Decubitus position for lumbar puncture. (Reproduced with permission from Krupp MA, et al. Physician's

Handbook. 21st ed. Lange, 1 985.)

CHAPTER 5

Cauda equina

.A Figure 5-3. Anatomy of the lumbar spinal

interspaces for LP. (Reprinted with permission from

Ladde JG. Chapter 1 69. Central Nervous System

Procedures and Devices. In: Tintina lli JE, Stapczynski JS,

Cline OM, Ma OJ, Cyd ulka RK, Meckler G O, eds.

Tintinolli's Emergency Medicine: A Comprehensive

Study Guide. 7th ed. New York: McGraw-Hi ll, 201 1 .)

needle parallel to the stretcher, slowly insert in the mid ­

line aiming 10 degrees cephalad. T he needle will cross

3 ligaments (supraspinous, interspinous, and the strong

elastic ligamentum flavum) before entering the dura and

subarachnoid space (Figure 5-3). You may feel a "pop" as

you transverse the ligamentum flavum. T he bevel of the

needle should be pointed to the patient's side (left or

right) to prevent it from cutting the longitudinally oriented fibers of the dura. T heoretically, this will r educe the

risk of persistent CSF leak and subsequent post-LP headache. After inserting the needle 4-5 em or after feeling a

"pop;' remove the stylet and look for the efflux of CSF at

the base of your needle. If no fluid returns, replace the

stylet and advance or withdraw the needle and recheck.

You may have to withdraw the needle to the subcutaneous tissue and redirect it more cephalad. T he depth of

insertion before getting into the subarachnoid space

depends on the size of the patient. Never advance or

remove the needle without the stylet in place to avoid it

from becoming obstructed.

When the subarachnoid space is entered and CSF

begins to flow, assess the opening pressure. Attach the

manometer to the needle and direct the lever of the 3 -way

stopcock away from the needle to create a communication between the needle and glass column. At the point

when fluid stops flowing into the manometer, the pressure is recorded. Normal opening pressure is between

7-18 cmHp. Deposit the CSF from the manometer into

tube #1 and disconnect the manometer. In adults, proceed to collect 1 -2 mL of CSF per tube. More tubes may

be needed for additional tests or special situations

(VDRL, viral titer, Cryptococcus antigen, etc). When the

fluid has been collected in all 4 tubes, the needle is

removed with the stylet in place. T his too has been shown

to reduce the incidence of post-LP headache. T he theoretical explanation for this effect is that the stylet pushes

back any pia mater that may be sticking out from the hole

made in the dura. Any tissue in the dura puncture can act

to keep the hole from closing and result in a persistent

CSF leak.

Tubes #1 and 4 should be sent for cell counts with differential. Tube #2 is sent for protein and glucose. Tube #3

should be sent for culture and Gram stain. Patients with an

obese body habitus or with degenerative joints may present

a challenge when performing an LP. Fluoroscopy (per ­

formed by a radiologist) or the use of ultrasound may aid

in identifying the anatomical landmarks, making it possible to perform the procedure.

COMPLICATIONS

A "traumatic" LP (from injury to the dura or arachnoid

vessels) is a common occurrence, with more than 50o/o of

all LP procedures having from 1 to 50 red blood cells

(RBCs) in the CSF. T he incidence of traumatic LP may be

minimized by proper patient and needle positioning. T he

best method to differentiate a traumatic LP from an SAH

is noting that the number of RBCs significantly decrease

from tube #1 to tube #4 in a traumatic LP. Tube #4 should

have close to zero RBCs. T he presence of xanthochromia

indicates a SAH.

Spinal hematomas (epidural, subdural, and subarach ­

noid) are rare complications of LP, which are more likely to

occur in patients with coagulation disorders. Correcting

coagulation disorders (eg, Factor for a hemophiliac) is

required before LP is performed.

Herniation can occur when CSF is removed from a

patient with increased ICP from a mass, emphasizing the

importance of performing a head CT if a mass lesion is

suspected.

Post-LP headaches are the most common complication of LP and are thought to be from continued CSF

leakage through the dura at the puncture site. A post-LP

headache is observed in 20-?0o/o of patients and is more

common in young adults. Post-LP headaches are usually

fronto-occipital and may have associated nausea, vomiting, and tinnitus. In most cases, the headache begins

within 24-48 hours of the LP and is usually postural

(worse in the upright position or with valsalva maneuvers). Post-LP headaches usually last 1-2 days, but occasionally can persist up to 14 days. Treatment consists of

IV fluids, caffeine (IV or oral), antiemetics, analgesics,

barbiturates, diphenhydramine, and ergots. Headaches

lasting >24 hours may be alleviated by an epidural blood

patch performed by an anesthesiologist. If the headache

does not have a postural component, lasts more than 1

week, or recurs after initially resolving, consider the

LUMBAR PUNCTURE

possibility of a subdural hematoma. Subdural hemato ­

mas are due to tearing of bridging veins from decreased

CSF volume.

Patients may also complain of mild backache after an

LP. This is common from trauma of the spinal needle and

is usually self-limited, resolving in a few days. Other potential complications include iatrogenic infection caused by

improper sterile technique, a contaminated field, or contaminated needle. Infectious complications include cellulitis, skin abscess, epidural or spinal abscess, discitis, or

osteomyelitis.

SUGGESTED READING

Fong B, VanBendegom J. Lumbar puncture. In: Reichman EF,

Simon RR. Emergency Medicine Procedures. 1st ed. New York,

NY: McGraw-Hill, 2004.

Ladde JG. Central nervous system procedures and devices. In:

Tintinalli JE, Stapczynski JS, Ma OJ, Cline DM, Cydulka RK,

Meckler GD. Tintinalli's Emergency Medicine: A Comprehensive

Study Guide. 7th ed. New York, NY: McGraw-Hill, 2011:1178-1180.

Miles S. Ellenby, et al. Lumbar puncture. N Engl J Med. 2006;335:12.

Wright BL, Lai JT, Sinclair AJ. Cerebrospinal fluid and lumbar

puncture: a practical review. ] Neural. 2012;259:1 530-1545.