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 rather than the CTZ. Diphenhydramine, which blocks Ach receptors in the vestibular apparatus as well as histamine receptors that

activate the CTZ, would also be an appropriate choice for rescue

for J.E. Because excessive sedation could delay J.E.’s discharge

from the ambulatory surgery center, doses should not exceed

25 mg IV for diphenhydramine. In addition, it is important to

assess J.E. for postoperative factors that could increase the likelihood of PONV. If postural hypotension is present, IV fluids and

ephedrine would be appropriate therapy.

Anesthetic Agents With a Low Incidence

of Postoperative Nausea and Vomiting

CASE 8-13, QUESTION 4: How could J.E.’s anesthetic regimen have been modified to reduce the likelihood of PONV?

Several changes could be made in the anesthetic regimen to

reduce the likelihood of PONV. When propofol is used for both

induction and maintenance of anesthesia, it reduces the risk of

PONV similar to the administration of a single antiemetic.94

Because perioperative administration of opioids is associated

with PONV, the use of NSAIDs (oral agents preoperatively and

postoperatively, parenteral acetaminophen or ketorolac intraoperatively and postoperatively), when appropriate, can reduce the

need for postoperative opioids. In addition, surgical wound infiltration with a long-acting local anesthetic, such as bupivacaine,

should also be used, as needed, to reduce postoperative incisional

pain.

ANALGESIC AGENTS AND

POSTOPERATIVE PAIN

MANAGEMENT

Acute Pain

Surgery causes injury to the body, resulting in acute pain. Specifically, the tissue damage from surgery releases substances that

directly stimulate or sensitize nociceptors (free nerve endings in

167Perioperative Care Chapter 8

the skin, muscle, bone, and connective tissue that detect damaging or unpleasant stimuli). These substances (e.g., bradykinin,

serotonin, prostaglandins, and cytokines) mediate pain impulses,

which then travel from the periphery (surgical incision) to the

dorsal horn of the spinal cord. Glutamate and substance P

are released in the dorsal horn to cause the pain impulses to

ascend to higher centers in the brain. Nerves originating in

the brainstem descend to the spinal cord and release substances

(norepinephrine, serotonin, endogenous opioids) that modulate

(inhibit) pain transmission. The final integration of all these processes is perception—this is when the patient “feels” the pain.

Because cortical and limbic systems are involved, the same

surgery can result in significant individual differences in pain

perception.101,102

Most patients will have pain at rest after surgery, with the magnitude of the pain generally correlating to the invasiveness of the

surgery. More intense pain would be expected after major abdominal surgery than after laparoscopic hernia repair, for example.

In addition, certain types of movement after major surgery (e.g.,

coughing after major upper abdominal surgery or knee flexion

after total knee replacement) can evoke pain that is more intense,

less responsive to opioids, and longer lasting than pain at rest.103

Nerve injury or peripheral or central nerve sensitization can

occur, leading to pain hypersensitivity, pain in response to a stimulus that is not usually painful (allodynia), pain that is difficult to

manage, or chronic pain after surgery. Immobility and body positioning after surgery, for example, can lead to musculoskeletal

pain.103–105 Patients vary in their response to pain (and interventions) and in their personal preferences toward pain management. Acute pain usually resolves when the injury heals (hours

to days). Unrelieved acute postoperative pain has detrimental

physiological and psychological effects, including impaired pulmonary function (leading to pulmonary complications); thromboembolism; tachycardia; hypertension and increased cardiac

work; impairment of the immune system; nausea, vomiting, and

ileus; chronic pain; and anxiety, fatigue, and fear.105

Adequate pain assessment and management are essential

components of perioperative care. Education of patients and families about their roles, as well as the limitations and side effects of

pain treatments, is critical to managing postoperative pain. Pain

management must be planned for and integrated into the perioperative care of patients. Proactive planning includes obtaining

a pain history based on the patient’s own experiences with pain

and a frank discussion of a realistic comfort–function goal for

the patient (e.g., complete pain relief after major surgery is not

a realistic goal). The intensity and quality of pain, as well as the

patient’s response to treatment and the degree to which pain

interferes with normal activities, should be monitored. Ideally,

pain should be prevented by treating it adequately because once

established, severe pain can be difficult to control.

Management Options

Effective postoperative pain management should provide subjective pain relief while minimizing analgesic-related adverse effects,

allow early return to normal daily activities, and minimize the

detrimental effects from unrelieved pain. The following techniques can be used to manage postoperative pain: (a) systemic

administration of opioids, NSAIDs, and acetaminophen; (b) ondemand administration of IV opioids, also known as patientcontrolled analgesia (PCA); (c) epidural analgesia (continuous and

on-demand, usually with an opioid–local anesthetic mixture); (d)

local nerve blockade, such as local infiltration or peripheral nerve

block; and (e) application of heat or cold, guided imagery, music,

relaxation, or other nonpharmacologic intervention. Local anesthetics, opioids, acetaminophen, and NSAIDs can be used alone

or in combination to create the optimal analgesic regimen for

each patient based on factors such as efficacy of the agent to

reduce pain to an acceptable level, type of surgery, underlying

disease, adverse effects, and cost of therapy. For patients experiencing mild to moderate postoperative pain, local anesthetic

wound infiltration, peripheral nerve blockade, or administration

of a nonopioid analgesic such as an NSAID or acetaminophen

are appropriate approaches to analgesia. For moderate or severe

postoperative pain, an opioid is required. The choice of agent,

dose, and route of administration depends on the clinical situation. For example, a patient who cannot take anything by mouth

may receive an IV opioid in a dose appropriate for the severity of the pain and the presence or absence of risk factors for

opioid-induced respiratory depression. A patient who is tolerating crackers and a soft drink before discharge from the surgery

center should receive the first dose of the analgesic that will

be prescribed for the patient at home. This will ensure that the

analgesic (commonly, acetaminophen plus hydrocodone) will

be effective and tolerated by the patient. For moderate to severe

pain after more-invasive surgery, an IV opioid (e.g., morphine,

hydromorphone), an epidural containing a local anesthetic and

opioid, or a peripheral nerve block with local anesthetic is necessary. (For more information about general pain management, see

Chapter 7, Pain and Its Management.) Analgesia for acute pain in

the perioperative setting is best achieved by using a multimodal

(balanced) approach with a combination of two or more analgesic medications or modalities that have different mechanisms

of action to provide additive or synergistic analgesia with fewer

adverse effects when compared with a single analgesic medication or modality.105 Examples of multimodal analgesic regimens used in the perioperative setting include (a) local anesthetic

wound infiltration, acetaminophen, NSAIDs, and if necessary, a

weaker opioid analgesic (e.g., hydrocodone plus acetaminophen)

after laparoscopic cholecystectomy, (b) continuous epidural analgesia (with opioid plus local anesthetic) with IV acetaminophen

and, if necessary, a potent IV opioid for rescue analgesia in an

area not covered by the epidural catheter, and (c) continuous

peripheral nerve blockade, with acetaminophen, NSAIDs, and,

if necessary, an opioid for rescue analgesia in an area not covered

by the nerve block.106

PATIENT-CONTROLLED ANALGESIA

ADVANTAGES

CASE 8-14

QUESTION 1: J.A., a 50-year-old, 5-foot 4-inch, 50-kg

woman, is immediately postoperative from a total abdominal hysterectomy for a neoplasm. Her laboratory values are

remarkable for a serum creatinine of 1.3 mg/dL. She is allergic to penicillin. She will be admitted to the postsurgical

floor for a planned stay of 2 to 3 days. What mode of pain

management should be chosen for J.A.?

PCA is a popular method of administering analgesics and

has been shown to provide an overall improvement in analgesia

and greater patient satisfaction when compared with traditional

intermittent IV opioid injections.107 Patients treated with traditional intermittent IV dosing of opioids “as needed” can experience severe pain because the serum opioid concentration is

allowed to fall to less than the minimum effective analgesic concentration (the concentration that provides approximately 90%

pain relief ). In addition, high peak plasma opioid concentrations

can be seen with this administration method, often resulting in

excessive nausea, vomiting, or sedation, as well as respiratory

depression. Small, frequent opioid doses on demand, as seen in

168 Section 1 General Care

PCA, minimize the peaks and valleys in serum concentrations

seen with relatively larger intermittent IV doses and allow the

patient control over his or her pain management. This is helpful

in minimizing adverse effects associated with high peak serum

concentrations and inadequate pain relief caused by subtherapeutic serum concentrations. Small, frequent, patient-controlled

dosing of opioids is efficacious because opioids have a steep sigmoidal dose–response curve for analgesia, resulting in the ability

of a small opioid dose to move the plasma concentration from

being subtherapeutic to above the minimum effective plasma

concentration that will provide effective pain relief. However,

one must remember that these small, frequent on-demand doses

are intended tomaintain analgesia. The patient should be reasonably comfortable (e.g., from a loading dose) before the initiation

of PCA.108,109 In terms of safety, sedation generally precedes respiratory depression.110 Therefore, if a patient becomes sedated,

self-administration of additional patient-controlled bolus doses

will stop, allowing the serum opioid concentration to fall to a

safe level.

Therapy can be individualized by using small doses of opioids

at preset intervals (e.g., 1 mg of morphine every 10 minutes),

with the patient in control of his or her analgesic administration.

An infusion pump with a programmed on-demand dose (the dose

the patient can self-administer), number of minutes between

allowable doses (lock-out interval), and maximum number of

boluses per hour is equipped with a button that the patient presses

to receive a dose. An IV bolus is the most common PCA route,

with opioids being the drugs of choice to provide analgesia.

If the patient is educated to use PCA properly, it can be used

to alleviate anticipated pain before movement or physical therapy in a pre-emptive fashion. J.A. has undergone a procedure for

which moderate to severe pain is expected in the immediate postoperative period. J.A.’s pain requirement in the immediate

postoperative period could be met with PCA opioid administration after first administering a loading dose of an IV opioid, which is titrated to achieve the appropriate level of analgesia. Analgesia can then be maintained with patient-controlled

bolus doses. When her opioid requirements decline or when

she can tolerate oral intake, she can then be switched to oral

analgesics.

PATIENT SELECTION

CASE 8-14, QUESTION 2: J.A.’s surgeon decides to prescribe PCA for postoperative pain management. How

should J.A. be evaluated for her ability to appropriately participate in her analgesic administration?

Patients receiving PCA therapy must be able to understand

the concept behind PCA and to operate the drug administration button. J.A. must be alert, oriented, and willing to assume

control of her own pain management. She must be able to comprehend the relationships between a stimulus (pain), a response

(pushing the button), and a delayed result (pain relief ). She must

understand verbal or written instructions about the function

and safety features of the infusion pump and how to titrate the

drug as needed for satisfactory analgesia. The anticipated intensity of the patient’s pain after surgery should be such that an

IV opioid would be required for pain management. PCA has

been used successfully in children, generally after ages 8 or 9

(adjusting doses appropriately), and in elderly patients. It is not

indicated in patients who are expected to require parenteral opioids for analgesia for less than 24 hours because these patients

will generally be able to tolerate oral analgesics shortly after

surgery.