Postoperative Pain in Adults

Jane C. Ballantyne

Elizabeth Ryder

Rich the treasure, Sweet the pleasure

Sweet is pleasure after pain

For all the happiness man can gain

Is not in pleasure, but in rest from pain.

—John Dryden, 1631–1700

Thirty years ago, patients were encouraged to rest for days, even weeks, after surgery. Postoperative hospital stay was longer, feeding was delayed, patients were not expected to get out of bed, and analgesia was needed only for pain at rest. Since then, the concept of accelerated recovery, whereby normal physiologic function is restored as rapidly as possible, has replaced the idea that rest is best. Patients are encouraged to mobilize, take oral fluids, eat, and return home as rapidly as possible. Multiple trials confirm that accelerated recovery is associated with improved surgical outcome. Optimal pain control is an integral component of accelerated recovery; and paradoxically, although opioids are the most effective analgesics available, postoperative pain management is now based on multimodal analgesia and opioid sparing. Opioid side effects that delay recovery, particularly sedation and decreased bowel mobility, are therefore minimized. Multimodal analgesia also makes sense because acute pain is an integrated process mediated by a range of transmitters and neural pathways, so it seems rational to target analgesics to a number of different processes. Present-day postoperative pain management involves using a number of different approaches, embracing
modern technology (e.g., microprocessor-controlled pumps, refined catheters, other infusion technologies) and, most important, optimizing pain relief by listening to patients’ complaints of pain.

I. PRINCIPLES OF POSTOPERATIVE PAIN MANAGEMENT

1. Psychologic Preparation

Patients who are carefully prepared for the experience of surgery and postoperative pain are markedly less anxious and easier to treat postoperatively. Patients need reassurance. If they have never had surgery before, they should be told what to expect. They should be aware that some degree of postoperative pain is inevitable, and that their doctors and nurses will work with them to treat it. Patients should also be familiar with the chosen pain assessment method and the need to assess pain on a regular basis. They should be told about the choices for postoperative pain management, and these options should be discussed during their preoperative visit.

2. Assessing Pain

A policy of regular assessment is important because it draws attention to the existence of pain and prompts improved treatment. Assessments of pain severity, analgesic side effects, and markers of recovery are the tools by which analgesic regimens can be tailored to need. The method used does not need to be elaborate; in fact, it is preferable to use rudimentary scales such as the 0 to 10 verbal analog scale (VSA). It is standard practice at Massachusetts General Hospital (MGH) to record pain scales on the vital signs chart (the so-called fifth vital sign) as well as in the patient’s medical record. Regular pain assessment has become part of standard care in hospitals and other health care facilities throughout the United States, and the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) has developed new standards for both pain assessment and pain management (see Appendix II for Web address).

3. Preemptive Analgesia

The concept of preemptive analgesia was born from the observation in animals that changes occur in the central nervous system (CNS) secondary to peripheral injury and inflammation. The term central sensitization embraces a number of different and complex neurobiologic changes that arise after peripheral injury and ultimately increase pain sensitivity. It seemed rational, then, that an analgesic intervention that reduced pain transmission to the CNS might prevent central sensitization, thereby reducing postinjury or postoperative pain. In animal models of injury, preemptive analgesic interventions such as neural blockade and high-dose opioid treatment convincingly reduce postinjury pain sensitivity. Yet in human studies, preemptive analgesia has not been consistently effective, and to date, preemptive analgesia does not seem to have much clinical utility.

More recently, it was established that the N-methyl-d-aspartate (NMDA) receptor plays an important role in the development of central sensitization. Clinical preemptive analgesia studies now
focus on using NMDA receptor antagonists to reduce central sensitization, and real benefits have been demonstrated. Unfortunately, none of the currently available NMDA antagonists (ketamine, dextromethorphan, and amantadine) are ideal and their use is limited by either side effects or poor efficacy. Studies are now focused on dose finding to optimize current drugs, and on a search for better NMDA antagonists.

A different but related phenomenon is that of central sensitization that is already present at the time of surgery, as it occurs in chronic pain syndromes. The question here is whether the treatment of central sensitization before surgery, notably before an amputation, can reduce postamputation pain, particularly phantom pain. In 1988, when Bach et al. demonstrated a statistically significant difference in the occurrence of phantom limb pain between patients treated for 72 hours preamputation with epidural blockade and those who did not receive preoperative epidural therapy, his findings were hailed as strong validation of the concept of preemptive analgesia. Yet what these investigators really did, if anything, was eliminate any central sensitization that existed before the surgery, rather than prevent the onset of central sensitization after the incision. Bach’s results have never been reproduced, despite attempts to replicate his findings. Therefore, one must be cautious about recommending preamputation epidurals at present. However, the idea of being able to reduce phantom pain by means of perioperative neuromodulation remains attractive, and further research is needed, particularly into methods of reducing phantom pain with NMDA antagonists.

II. SPECIAL POPULATIONS

1. The Elderly

Older individuals often appear stoical, and it is not clear whether they have a different threshold for pain, whether past experience has altered their attitude toward pain or whether they truly do not feel pain to the same extent as younger adults. It is tempting to undertreat pain in older individuals because they do not always communicate pain clearly. Moreover, they may not metabolize drugs efficiently, which is an additional concern, especially when using opioids. Older individuals are more likely to become sedated and confused when given opioids, and are at increased risk of sedation and confusion when sleep deprived and outside their normal environment. Often the best approach is the simplest. For severe pain, small, intermittent doses of IV morphine (2 to 6 mg every 4 hours) or the equivalent should be used. Epidural therapy can be helpful and circumvents the use of systemic opioids, although even epidural fentanyl can cause confusion in older patients.

2. The Mentally and Physically Disabled

These patients present a challenge because they may be unable to communicate the status of their pain clearly. As with the very young, effective pain management with the very old may require time and patience to be spent learning what patients are experiencing and how best to help them. Vital signs, behavioral
cues, positioning, muscle guarding, and grimacing may be the only guiding factors at first. The cooperation of those who normally care for these patients is indispensable. Although drugs are metabolized normally in most of these patients, individuals with baseline breathing difficulties may be more sensitive to the respiratory depressant effects of opioids.

3. Substance Abusers and Drug Addicts

Patients with a history of past or present substance abuse may be difficult to manage during an acute pain episode. The behavioral factors that make inpatient management difficult are compounded because opioids do not work well in patients who have become opioid-tolerant. It is often difficult to determine whether opioid-seeking behavior is due to inadequate pain control or to addictive behavior. The medical staff may become exasperated, thereby compromising patient care. These patients should be given the benefit of optimal control of acute pain, while detoxification should be postponed until the acute pain has resolved. It is helpful to work closely with addiction specialists, including psychiatrists and social workers, to prepare the patients for discharge and possible rehabilitation.

It is important to obtain a history of “recreational drug use,” both past and present. The information may be unreliable but should at least be sought. It should be ascertained whether the patient is in withdrawal, and if so, the withdrawal should be treated. Large doses of opioids may be needed to avoid withdrawal and treat pain. Even patients who abuse substances such as alcohol, cocaine, and marijuana may exhibit some degree of cross-tolerance with opioids, thus requiring higher than normal opioid doses. Patients on methadone maintenance should continue their preadmission dose, or this should be converted to an alternative opioid or mode of delivery, and additional opioid prescribed as needed. Patient-controlled analgesia (PCA) is an effective modality for drug abusers, because it provides an element of control and lessens the anxiety associated with trying to obtain additional medication.

Opioid analgesia can usefully be supplemented with nonopioid treatments such as nonsteroidal antiinflammatory drugs (NSAIDs), epidurals, local nerve blocks and anxiolytics. Alpha-agonists such as clonidine may be useful because they provide analgesia and reverse symptoms of withdrawal. Other treatments for withdrawal include benzodiazepines and neuroleptics, in addition to supportive measures.

4. Intensive Care Patients

Patients admitted to intensive care form a special population because, in many cases, they are unable to communicate, either because of severe illness or because they are ventilated, sedated, and sometimes even paralyzed. It is important to treat pain in these patients in order to reduce the anxiety associated with pain and inability to communicate pain. When it is impossible to assess pain, as in heavily sedated or unconscious patients, it is reasonable to assess analgesic requirements on the basis of the amount of surgical or other trauma the patient has undergone. Patients on a ventilator can be treated with higher than normal
doses of opioids (if desired) because there is no risk of respiratory depression. Continuous infusion is the most frequently chosen mode of delivery. Fentanyl or hydromorphone may be preferred to morphine in patients with renal insufficiency who tend to accumulate the active morphine metabolite morphine-6-glucuronide. Methadone may also be useful for prolonged intensive care unit (ICU) stays because there is less risk of developing tolerance than with other opioids. It has recently been found beneficial to use the α2 agonist dexmedetomidine for ICU sedation, not only because of its hypnotic effects but also because of its analgesic synergy with opioids (opioid sparing). It may also help minimize withdrawal symptoms during weaning from opioids.

Alert or ICU patients who are breathing on their own can be treated for pain like patients in other units, with the proviso that severely ill patients may handle drugs inefficiently. Epidurals are useful even in patients on a ventilator, and they ease weaning from ventilation.

III. TREATMENT OPTIONS

1. Nonsteroidal Antiinflammatory Drugs

NSAIDs are useful as sole analgesics for mild to moderate pain, and useful alternatives or adjuncts to opioid therapy and regional analgesia. Because they act by a unique mechanism, mostly in the periphery (not in the CNS), their action complements that of other analgesic therapies. Their analgesic effect is secondary to their antiinflammatory effect, which in turn is due to prostaglandin inhibition. Prostaglandin inhibition is also responsible for their chief side effects—gastritis, platelet dysfunction, and renal damage. NSAIDs are contraindicated in patients with a history of peptic ulcer disease, gastritis, or NSAID intolerance, with renal dysfunction (creatinine >1.5), and with bleeding diatheses. Many surgeons prefer not to use NSAIDs in the immediate postoperative period for patients who have undergone renal or liver surgery, grafts, muscle flap procedures, or bone fusions, since they may increase bleeding or impede healing. The newer coxibs seem to be relatively free of gastrointestinal (GI) effects and are platelet sparing, but the incidence of other side effects is similar to that of the standard NSAIDs. The exact role of coxibs in the management of acute pain is still being evaluated.

Ketorolac is a potent NSAID (equipotent with morphine), with a chief indication for acute pain. It is the only NSAID analgesic available for parenteral use in the United States. It is expensive (approximately 20 times more costly than morphine), and because its potency extends to its side effects, its use is restricted to 5 days (manufacturers’ recommendation). Ketorolac can also be used to supplement epidural analgesia, particularly when the epidural does not cover the whole surgical area, for example, after thoracotomy.

The NSAIDs are described in more detail in Chapter 8.

2. Systemic Opioids

Systemic opioid therapy has long been the conventional treatment approach for postoperative pain, and is the standard by which other treatments are measured. This does not make it
inferior to other pain treatments. In fact, systemic opioid therapy (either oral or parenteral) remains the primary treatment used for patients experiencing moderate to severe acute pain. No new treatment has entirely replaced the opioids, yet newer accelerated recovery protocols demand an alternative to opioids as the sole analgesic because opioid side effects (nausea, sedation, reduced bowel mobility) interfere with the goal of rapid resumption of normal physiologic functions (eating, drinking, urinating, defecating, walking, coughing). Today’s standard is to use multimodal analgesia, opioids being an important component, whereas the regime also aims to minimize opioid use.

Routes of opioid administration and their indications are summarized in Table 1. The oral route is the simplest and used for patients who are prescribed nothing by mouth (NPO). The rectal route is not popular in the United States. The intramuscular and subcutaneous routes are rarely chosen because it is considered unnecessary to subject patients to painful injections. Judiciously administered intravenous opioids (i.e., given as small boluses while monitoring pain level, respiratory effort, and alertness) are safe and preferable. The intravenous route is also ideal for PCA, which is discussed in the subsequent text. Most postoperative patients receive bolus administration of opioids, which allows for ready titration of dose according to need. Continuous intravenous or subcutaneous therapy is sometimes useful—for example, in patients on ventilators. Oral administration is resumed as soon as oral intake is reestablished. The short-term use of long-acting opioids is sometimes helpful.

Commonly used opioids and their doses are summarized in Table 2. Morphine is the opioid of choice at the MGH. Dose ranges are usually prescribed so that nurses can select specific doses that best meet the patients’ needs. Morphine is a simple agonist at μ, κ, and δ receptors, and its actions are not complicated by partial agonism or mixed agonism/antagonism. Its effects and side effects are well known and understood. Morphine may be contraindicated in patients with biliary spasm because it is believed that it can worsen the spasm, but this issue is still under debate. Other opioids are used when patients express a preference for another drug, when they are either “allergic” to or report significant side effects from morphine, or when morphine does not appear to be effective. Hydromorphone is a useful alternative to morphine, and may be associated with less dizziness, nausea, and light-headedness in some patients. For many years, meperidine was popular for treating acute pain, but it is no longer used as first-line treatment because of its known toxicity (excitatory effects in the CNS due to the metabolite normeperidine).

The side effects of opioid drugs limit their use. Respiratory depression is a true risk, and patients receiving opioids should be closely watched, especially at the start of treatment. Monitoring for adequacy of ventilation includes observing the patients’ state of arousal, respiratory rate, including depth and pattern of breathing, as well as color (skin and mucous membranes). Pulse oximeters and respiratory monitors can be helpful, especially

during periods of high risk, for example, during early recovery. Severe respiratory depression should be treated with small intravenous boluses of naloxone (Narcan). If naloxone is given too quickly, severe agitation, and in extreme cases, flash pulmonary edema secondary to aggressive respiratory effort, may result. The ampule of naloxone (0.4 mg) can be diluted in saline in a 10 mL syringe and then 2 to 3 mL can be given every minute as needed. After naloxone reversal, patients should continue to be closely monitored because naloxone’s duration of action is only approximately 20 minutes, and the effects of the agonist may outlast this. Naloxone will reverse opioid effects quite rapidly; so if the patient does not respond, one should consider alternative causes of the respiratory compromise.

Table 1. Methods for achieving pain control

Intervention	Comments
NSAIDs
Oral (alone)	Effective for mild to moderate pain. Begin preop. Relatively contraindicated in patients with history of pepticulcer or renal disease and risk of or actual coagulopathy. May mask fever.
Oral (adjunct to opioid)	Potentiating effect resulting in opioid sparing. Cautions as mentioned in preceding text.
Parenteral (ketorolac)	Effective for moderate to severe pain. Expensive. Useful where opioids contraindicated, especially to avoid respiratory depression and sedation. Cautions as in preceding text.
OPIOIDS
Oral	As effective as parenteral in appropriate doses. Use as soon as oral medication is tolerated.
IM	Has been the standard parenteral route, but injections painful and absorption unreliable. Hence, avoid this route when possible.
SQ	Preferable to IM for low-volume continuous infusion. Injections painful and absorption unreliable. Avoid this route for long-term repeated dosing.
IV	Parenteral route of choice after major surgery. Suitable for titrated bolus or continuous administration (including PCA), but requires monitoring. Significant risk of respiratory depression with inappropriate dosing.
PCA	IV or SQ routes recommended. Good, steady level of analgesia. Popular with patients but requires special infusion pumps and staff education. Cautions as for IV opioids (preceding text).
Epidural and intrathecal	When suitable, provides good analgesia. Expensive if infusion pumps employed. Significant risk of respiratory depression, sometimes delayed in onset. Requires careful monitoring.
LOCAL ANESTHETICS
Epidural and intrathecal	Limited indications. Expensive if infusion pumps employed. Effective regional analgesia. Opioid sparing. Addition of opioid to local anesthetic may improve analgesia. Risk of hypotension, weakness, numbness.
Peripheral block	Limited indications. Limited duration unless catheters employed. Effective regional analgesia. Opioid sparing.
TENS	Effective in reducing pain and improving physical function. Requires skilled personnel and special equipment. Useful as an adjunct to drug therapy.
EDUCATION/INSTRUCTION	Effective for reduction of pain. Should include procedural information and instruction aimed at reducing activity-related pain Requires staff time.

Other opioid-related side effects are not dangerous but they can interfere with treatment success. Some side effects can be effectively treated without adjusting the opioid dose—nausea with antiemetics, pruritus with antihistamines, and constipation with laxatives (postoperative ileus should not be treated with laxatives) (Table 2). Sometimes it is necessary to decrease the dose, change the opioid, or even stop it. Other causes of side effects should always be considered, for example, nausea could be caused by anesthetics, antibiotics, or by the surgery itself.

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