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21 Postoperative Pain in Adults

21 Postoperative Pain in Adults
The Massachusetts General Hospital Handbook of Pain Management

21
Postoperative Pain in Adults

Elizabeth Ryder and Jane Ballantyne

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)

I. Rationale for active treatment

1. Conventional versus active treatment

2. Ethical and humanitarian issues

3. Barriers to effective pain management

4. Patient comfort and satisfaction

5. Decreased morbidity and recovery time
II. Principles of postoperative pain management

1. Psychologic preparation

2. Assessing pain

3. Preemptive analgesia
III. Special populations

1. The elderly

2. Patients with mental or physical handicaps

3. Substance abusers and drug addicts

4. Intensive care patients
IV. Treatment options

1. Nonsteroidal anti-inflammatory drugs

2. Systemic opioids

3. Patient controlled analgesia

4. Epidural analgesia

5. Single-shot neuraxial morphine

6. Intraoperative neural blockade

7. Prolonged neural blockade: use of catheters

8. Transcutaneous electrical nerve stimulation

9. Behavioral therapy
V. Conclusion
Selected Reading

Few Americans will go through life without having surgery. Those who undergo surgery will experience varying degrees of pain, and in many cases this postoperative pain will be the worst pain of their lives. Postoperative pain is one of the most feared and is probably the most prevalent of all pain conditions, yet in many cases it continues to be inadequately controlled. Physicians, nurses, and patients alike fear opioids, even though they remain the mainstay of acute pain treatment. Furthermore, because of the acute and finite nature of postoperative pain, a degree of complacency in treating it sometimes prevails. Patients who have received exemplary pain management rate their surgical and hospital experience highly, and it may be important to optimize postoperative pain treatment for that reason alone. Research findings over the last several years have shown that the sequelae of undertreated pain are far reaching and often have a deleterious effect on patients, which provides a greater impetus to improve pain treatment in postoperative patients. This chapter outlines the principles of postoperative pain management and briefly describes the treatments used at the Massachusetts General Hospital (MGH).
I. RATIONALE FOR ACTIVE TREATMENT
1. Conventional versus active treatment
Conventionally, postoperative pain has been managed with intramuscular opioids given intermittently, as needed. “Active” pain management implies a greater effort to optimize pain control, and it entails preoperative preparation, patient choice of treatment, regular pain assessments, and the use of newer treatment modalities such as patient-controlled analgesia (PCA), epidural anesthesia and analgesia, and continuous nerve blocks. It will become clear later in this chapter that active pain management offers better pain relief than conventional treatment. First, we explore other reasons to support the use of active pain management.
2. Ethical and humanitarian issues
No one would argue against the ethical and humanitarian need to treat postoperative pain. But can the ethical and humanitarian argument be used to support active pain management? Do conventional methods satisfy the ethical need to treat pain, or should we improve on conventional methods? Perhaps the answer to these questions lies with the individual physicians, who weigh the risks and benefits of each treatment and, rightly or wrongly, use personal experience as well as scientific evidence to decide whether to use a specific treatment. But in weighing the risks and benefits, physicians should also assume the ethical responsibility of relieving pain and suffering. When treating pain, ethical and humanitarian issues are particularly important, since relief of suffering is the chief and the only undisputed benefit of pain treatment.
3. Barriers to effective pain management
There are, unfortunately, some barriers to effective pain management, usually in the form of prejudice on the part of caregivers, or even on the part of patients themselves. Perhaps most prominent is the fear of opioids. Addiction is a well-known and disastrous side effect of chronic opioid treatment, and its association with opioids places a stigma on the use of these drugs. In the case of acute pain, the fear of addiction is unfounded, and addiction does not seem to occur when the drugs are used short term. Nevertheless, many caregivers and patients are afraid of addiction and need to be reassured that opioid treatment is entirely appropriate in the acute pain setting. Other prejudices include fears of delayed recovery because of overuse of analgesics, and religious and cultural prejudices against removing the “natural phenomenon” of pain.
4. Patient comfort and satisfaction
Nothing satisfies operative patients more than having sailed through surgery with a minimum of pain and discomfort. Producing such a state of satisfaction is not, however, simply a matter of providing adequate doses of pain medication. Patients are more satisfied if their therapy is properly tailored to their needs, with side effects titrated against efficacy. They are also more likely to be satisfied if they have been adequately prepared for the experience of postoperative pain, if they understand that they will need to tolerate a certain degree of pain at times but that over the days the pain will abate, if they have been offered choices of methods of achieving pain relief, and if they know that their doctors and nurses are working with them to achieve the greatest possible relief.
5. Decreased morbidity and recovery time
Although some trials have demonstrated reduced recovery times and a shorter length of hospital stay associated with the use of the more aggressive pain treatments (such as epidural therapy and IV PCA), other trials have not shown significant improvement. There is no true consensus on whether aggressive pain treatment can speed recovery after surgery, although careful analysis of the evidence leads to the conclusion that there are advantages to aggressive pain management in certain patients and certain surgical groups.
For example, pulmonary function is undoubtedly improved by epidural therapy after thoracotomy and laparotomy; early results of a big multicenter trial confirm this and point to an increased magnitude of this effect in patients with preexisting lung disease. Bowel mobility recovers more rapidly in patients treated with epidural analgesia after bowel surgery, allowing an early return home. Cardiac ischemia occurs less frequently in the postoperative period when pain is adequately controlled, especially in patients with preexisting ischemic heart disease. After joint surgery, regional anesthesia/analgesia (via epidural catheters, femoral sheath catheters, and brachial plexus catheters) allows aggressive mobilization during the early recovery phase and can hasten postoperative rehabilitation, even months after surgery. On the other hand, inappropriate use or overuse of opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) can be deleterious, resulting in respiratory depression, slowing of the bowel, oversedation, gastric ulceration, bleeding, and so on. Clearly, the key is to choose the right treatment for each clinical situation, and to use it appropriately.
There may also be harmful sequelae of undertreated pain. The fact that pain treatment can alter physiologic stress responses to surgery and trauma is well established. Whether these changes are desirable is less clear. Pain treatment can modulate immune responsiveness, thus lessening immune suppression (presumably a desirable effect); on the other hand, high-dose opioid therapy can suppress immune responses (presumably an undesirable effect). At the level of the spinal cord, genetic alterations in neurons in response to unmodulated sensory stimuli have been observed, which may account for long-term problems such as trauma-related chronic pain syndromes and phantom limb pain. Of particular interest was one study’s finding that preoperative lumbar epidural blockade before lower limb amputation can lessen phantom limb pain.
II. PRINCIPLES OF POSTOPERATIVE PAIN MANAGEMENT
1. Psychological preparation
Patients who are well prepared psychologically for the experience of surgery and postoperative pain are markedly less anxious and easier to treat during their perioperative period than unprepared patients. Patients need reassurance from their surgeon, anesthesiologist, nurses, and others. If they have never had surgery before, they should be told about the operative process and about postoperative pain. 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 concept of pain assessment and the need to assess pain on a regular basis in order to modify treatments. They should be told about the choices for postoperative pain management, and they should discuss these options with their surgeon and anesthesiologist during their preoperative visit.
2. Assessing pain
Regular pain assessment is fundamental to good pain management; it is also essential to act on the assessments when necessary. Assessments of pain severity, analgesic side effects, and markers of recovery are the tools by which analgesic regimens can be tailored to meet patients’ needs. The method chosen does not need to be elaborate; in fact, it is inappropriate to use complicated analog scales in the setting of acute or postoperative pain. Simple questions such as “How bad is your pain?” “Do you have any nausea?” and “Do you feel like getting out of bed?” will provide important clues to the patient’s comfort.
It is also necessary, however, to have some means of quantifying pain, since physicians and nurses change shifts and are not always able to communicate with each other. For this reason, rudimentary pain scales are used, such as a 0 to 10 verbal analog scale (VAS). It is now standard practice at MGH to record pain scales on the vital signs chart (the so-called fifth vital sign) as well as in the patient’s chart. A policy of regular assessment is important because it draws attention to the existence of pain and forces improved treatment.
The assessment of pain has become a part of standard care in hospitals and other healthcare facilities throughout the United States. In fact, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) has developed new standards for both pain assessment and pain management (see web address, Appendix III). These standards apply to any organization involved in the direct provision of patient care wishing to receive accreditation from this organization.
3. Preemptive analgesia
It is well known that established pain is more difficult to treat than new pain. People with recurring pain, such as headache, know that if they treat their pain early, it is easier to abolish than if they allow it to mount. The same is true of postoperative pain. Patients who wake from anesthesia in pain appear to be more resistant to pain medication than those who are comfortable on awakening. Recently, a scientific basis for the “preemptive” effect of analgesia has been established. Using animal models of pain, researchers have convincingly demonstrated that changes occur in the spinal cord and brain in response to painful stimulation that result in enhanced pain transmission, and ultimately enhanced pain perception. These changes can be modified or abolished by opioid analgesics or by neural blockade. The importance of the phenomena of “wind-up” and “central sensitization,” both occurring in the spinal cord and both resulting in pain enhancement, is well established. Clinically, these changes may result in a worsening of postoperative pain, or even in establishment of a chronic pain syndrome.
The concept of preemptive analgesia grew from these observations. It was once surmised that if a good level of analgesia were established before a surgical incision, this would minimize postoperative pain. Unfortunately, treating the pain of an incision is only part of the story, and it is now clear that although the concept still applies, it applies to the preemption of spinal cord changes, not the preemption of a surgical incision per se. Trials of “preemptive analgesia” treating only incisional pain were remarkably unsuccessful. However, analgesia maintained throughout the surgical and postoperative phases of surgery, including pre-incision, is effective. This is illustrated in an important paper published in 1998 by Gottschalk and colleagues, who demonstrated clearly that good perioperative analgesia when compared to no intraoperative analgesia resulted in improved pain and mobility for up to 9.5 weeks after surgery.
The concept of preemptive analgesia was further confused by the publication in 1988 of a paper by Bach and colleagues who demonstrated that epidural analgesia maintained for 72 hours before limb amputation effectively prevented postamputation phantom limb pain. This was hailed as a convincing demonstration of preemptive analgesia, at a time when preemptive analgesia concepts were being developed. However, it now seems that the benefit Bach and colleagues achieved was not so much a preemptive analgesic effect but rather a manipulation of a preexisting pain memory. It is becoming clear that central mapping in the cerebral cortex is a key factor in the establishment of phantom limb pain, and that merely “preempting” the surgical incision is not sufficient to alter the postamputation pain experience.
III. SPECIAL POPULATIONS
1. The elderly
The elderly often appear to be 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 the elderly because these patients do not always communicate pain very clearly. Moreover, the elderly may not metabolize drugs efficiently, so this is an additional concern, especially when using opioids. The elderly are more likely to become sedated and confused when given opioids, and they are at increased risk of sedation and confusion when sleep deprived and taken out of their normal environment. The best approach is to offer structured treatment. For severe pain, small, intermittent doses of morphine (2 to 6 mg every 4 hours), or other opioids, are suitable. Epidural therapy can be helpful and circumvents the use of systemic opioids, although even epidural fentanyl can cause confusion in these patients.
2. Patients with mental or physical handicaps
Patients with mental or physical handicaps present a challenge because they may be unable to communicate pain in a normal way. As with the very young and the very old, effective pain management may involve time and patience in an effort to learn what patients are experiencing and how best to help them. Vital signs, behavioral cues, positioning, muscle guarding, and facial grimacing may be the only guiding factors. 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 who have actively abused drugs and other substances before surgery (or injury) are often difficult to manage in the postoperative or post-trauma phase. At the MGH, we believe this population, like all others, should be given the benefit of optimal pain control, and that treating their addiction should be postponed until the acute pain phase subsides. During patients’ hospitalization, we work closely with addiction specialists in preparing patients for discharge and possible rehabilitation.
Several factors should be considered when treating addicts. Always obtain a history of recreational substances used in both the past and the present; although this information may be unreliable, it should at least be sought. Ascertain if the patient is in a withdrawal state, and if so, treat the withdrawal. In cases of narcotic abuse, opioid drugs are a good choice for treating pain, but withdrawal symptoms may still be manifest if the patient has been consuming large quantities for recreation. PCA is an effective modality for drug abusers, since it provides an element of control and lessens the anxiety associated with trying to obtain additional medication. Adding a clonidine patch may be useful in this situation. Never use an opioid antagonist (naloxone) in narcotic addicts, as this could result in an immediate and extreme withdrawal response with a sympathetic outpouring, cardiac dysrhythmias, or even cardiac arrest and death.
It may be advantageous to minimize opioid requirements by supplementing treatment with opioid-sparing therapies (NSAIDs, epidurals, local nerve blocks, or anxiolytics). On the other hand, total reliance on these therapies and total withdrawal of opioids from a narcotic abuser are ill advised, partly because they will result in an unnecessarily severe withdrawal syndrome, and partly because pain will be very difficult to control without opioids.
Patients in methadone programs should continue with their preadmission doses, and additional medication should be prescribed to treat nociceptive pain as needed. Patients who have been abusing other substances such as alcohol, cocaine, and marijuana may exhibit some degree of cross-tolerance with the opioid, thus requiring higher than normal doses. At the same time, they may present with a withdrawal syndrome requiring treatment with neuroleptics, or various supportive measures. Medications should be titrated to effect (be it analgesia or side effects).
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 to reduce the extreme anxiety associated with pain and inability to communicate it, and to attenuate stress responses. 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.
Ventilated patients can be treated with higher than normal doses of opioids (if desired) because there is no risk of respiratory depression. Continuous infusions of opioids can be used in the intensive care unit (ICU) to sedate ventilated patients, independent of their use as analgesics. Morphine is the drug of choice for opioid infusions at the MGH, starting at 0.1 mg/kg per hour. Fentanyl at a starting dose of 1 µ g/kg per hour is a useful alternative in patients with renal insufficiency who have impaired excretion of the active morphine metabolite morphine-6-glucuronide. In normal patients, fentanyl has a greater tendency to accumulate than morphine because of its long elimination half-life. Alert or unventilated ICU patients can be treated as normal patients, with the proviso that sick patients may handle drugs inefficiently. Epidurals are useful even in ventilated patients and may actually aid weaning from ventilation.
IV. TREATMENT OPTIONS
1. Nonsteroidal anti-inflammatory drugs
NSAIDs are useful as sole analgesics for mild to moderate pain, and they are useful alternatives or adjuncts to opioid therapy and regional analgesia. Since they act by a unique mechanism, mostly in the periphery [i.e., not in the central nervous system (CNS)], their action complements that of other analgesic therapies. Their analgesic effect is secondary to their anti-inflammatory effect, which in turn is the result of prostaglandin inhibition. Prostaglandin inhibition is also responsible for their chief side effects—namely gastritis, platelet dysfunction, and renal damage. NSAIDs are contraindicated in patients with a history of peptic ulcer disease, gastritis, or NSAID intolerance, and in those with renal dysfunction (creatinine >1.5) or bleeding diatheses. Many of our surgeons prefer not to use NSAIDs in the immediate postoperative period for patients who have undergone renal or liver surgery, grafts, muscle flaps, or bone fusions, as the drugs may either increase bleeding or decrease healing time.
Only one NSAID, ketorolac, is available in a parenteral form. This medication is extremely potent (equipotent with morphine) and has become a popular alternative to opioid therapy in postoperative patients. There are a few drawbacks to its use, however. Ketorolac is expensive (about 20 times more costly than morphine) and, because of its potency, applying equally to side effects and efficacy, it may be safely used for only up to 5 days (manufacturer’s recommendation). The newer selective prostaglandin antagonists [cyclooxygenase (COX)-2 inhibitors], celecoxib and rofecoxib, are associated with fewer side effects (notably a lower incidence of gastrointestinal symptoms) but are only available in an oral formulation. (See Chapter 8 and Appendix VIII for full descriptions of these drugs.)
2. Systemic opioids
Systemic opioid therapy has long been the conventional treatment for postoperative pain, and it is the standard by which other treatments are measured. This does not, in any way, make it inferior to other pain treatments. In fact, systemic opioid therapy (either oral or parenteral) remains the primary treatment for patients experiencing moderate to severe acute pain.
When administering systemic opioids, the treatment goal is to maintain plasma levels within the therapeutic window. This ranges between the level at which satisfactory analgesia is reached and the level at which toxic effects are noted. The most challenging patients are those who have a narrow therapeutic window—that is, a limited dose range—in which useful analgesia without side effects is provided. The best principle of successful opioid therapy is to first administer enough drug to reach the patient’s threshold for analgesia and to then maintain a constant plasma level by administering low doses on a regular schedule.
Routes of opioid administration and their indications are summarized in Table 1. Conventionally, the intramuscular route was chosen for use in postoperative patients because the intravenous route was believed to be unsafe (because of the risk of respiratory depression), the subcutaneous route less reliable, and the per rectum route undesirable. The oral route is, of course, unusable in nil per os patients, and the sublingual route is limited by lack of availability of sublingual preparations. It is unnecessary to subject patients to painful intramuscular injections, as judiciously administered intravenous opioids (i.e., given as small boluses while monitoring pain level, respiratory effort, and alertness) are just as safe and preferable.

Table 1. Methods for achieving pain control

The intravenous route is also ideal for PCA, which is discussed later. Most postoperative patients receive bolus administration of opioids, which allows ready titration of dose according to need. Continuous intravenous or subcutaneous therapy may sometimes be useful—for example, in ventilated patients in whom there is no danger of respiratory depression. The oral route should be used as soon as patients are able to tolerate tablets. 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 naturally occurring opioid and is the oldest, best tried, and least expensive of all the opioid drugs. It is a simple agonist at mu, kappa, and delta 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.

Table 2. Analgesics and related drugs: Dosage examples for adults

Other opioids are used when patients express a preference for another drug, when they are either “allergic to” or report significant side effects to morphine, or when morphine does not appear to be effective. For many years, meperidine was popular for treating acute pain. We discourage the use of this drug as a first-line treatment because of its known toxicity (excitatory effects in the CNS due to the metabolite normeperidine), which may be especially marked in patients with renal dysfunction. Meperidine has traditionally been used in woefully deficient doses. A 50-mg bolus is inadequate for severe pain in most adults, and 100 to 150 mg should be considered the standard adult dose. Bolus administration should be given every 2 to 3 hours, not every 4 hours, to avoid reemergence of pain, as meperidine is a relatively short-acting drug. Hydromorphone is a useful alternative to morphine, and some patients who express an intolerance for morphine, particularly when this is a sense of dizziness, nausea, and light-headedness, do better on hydromorphone.
The side effects of opioid drugs occasionally limit their use. Respiratory depression is a true risk of opioid treatment, and patients receiving opioids should always be closely watched. Monitoring for adequacy of ventilation includes observing the patient’s state of arousal, respiratory rate, including depth and pattern of breathing, and color (skin and mucous membranes). Monitors such as the pulse oximeter are useful in the immediate postoperative period and in patients with known risk (e.g., baseline ventilatory compromise), but they are not necessary or even useful later in the postoperative phase.
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. We recommend diluting an ampule of naloxone (0.4 mg) into a 10-mL syringe of normal saline and administering 2 to 3 mL every minute or so. After naloxone reversal, patients should continue to be closely monitored, as naloxone’s duration of action is only approximately 20 minutes, and the effects of the agonist may outlast this. Naloxone reverses opioid effects quite rapidly, so if the patient does not respond, one should think about alternative causes of the respiratory compromise.
Other opioid-related side effects are more of a nuisance than a barrier to treatment and can most often be treated—nausea with antiemetics, pruritus with antihistamines, constipation with laxatives (see Table 2). Decreasing the opioid dose, changing the opioid, or even stopping opioid treatment may also decrease side effects. Other causes of side effects should always be considered— for example, nausea could be caused by anesthetics, antibiotics, or the surgery itself. The opioids are also described in Chapter 9 and Appendix VIII.
3. Patient-controlled analgesia
In many institutions, including MGH, PCA is the standard therapy for postoperative pain management. PCA is defined as the self-administration of analgesics (usually via the IV route) by patients instructed in the use of a device specifically designed for that purpose. The goal of PCA is to provide doses of analgesic immediately on the demand of the patient. The use of portable microcomputer-controlled infusion pumps allows this dosing to be achieved quickly and easily (literally at the touch of a button), so that small, frequent, and easily titratable doses can be given. This avoids the extreme swings in plasma levels and efficacy, and the side effects associated with the larger, less frequent doses associated with conventional analgesia (see earlier discussion). Other advantages of PCA are its inherent safety because of the small doses used and the fact that obtunded patients do not press for additional doses, and patients’ preference for the technique associated with the sense of control it offers.
An exception to the general safety of PCA is its use by elderly and confused individuals, who, despite confusion and early obtundation (or maybe because of it), sometimes overdose themselves. Studies show that patients vary widely in their physical need for opioids, and PCA accommodates a wide range of analgesic needs; with standard PCA orders, patients can receive anywhere between 0 and 10 mg of IV morphine each hour.
Carefully monitored, nurse-controlled boluses may be needed at the start of treatment, as patients may be too sedated by residual anesthesia to use PCA properly in the early postoperative period. It is tempting to think that once patients are connected to PCA pumps, they do not need further pain assessment or treatment, but if pain is neglected in the early postoperative period, it may be more difficult to treat later. Individualizing the PCA settings and frequently assessing patients’ analgesia levels are critical during the first 24 hours following surgery. The MGH PCA orders are shown in Figure 1. They include an alternative treatment should the intravenous route fail, as well as general guidelines for dosing and monitoring. Morphine continues to be the drug of choice for PCA, with hydromorphone used when morphine has failed or is contraindicated. Meperidine can also be used, but, as discussed previously, it has limited indications.

Figure 1. PCA order sheet.

The success of PCA depends first on patient selection. Patients who are too old, too confused, too young, or unable to control the button, and those who do not want the treatment, are not suitable candidates. Ideally, patients should be educated before surgery about PCA and the concept of self-dosing. Teaching points include expectations for pain relief, informing patients of their active role in pain management (both in pain reports and medication management), and elimination of fears and misconceptions about opioids, including fear of addiction and fear of overmedication.
4. Epidural analgesia
For certain well-chosen indications, a functioning epidural catheter produces superior pain relief, and is known to improve surgical outcome (Table 3). However, a considerable degree of technical expertise is needed to place epidural catheters and, even in the best hands, the treatment can fail. Thus, a promise of superb pain relief is not always fulfilled. Since it involves carefully and blindly locating the epidural space (Fig. 2), epidural placement and management is time consuming and labor intensive. Nevertheless, both surgeons and anesthesiologists at MGH are sufficiently convinced of the positive benefits of epidural analgesia to offer the treatment to all our patients in whom it is indicated, being careful to explain both its risks and its benefits. A description of the technique of epidural catheter placement can be found in Chapter 12 (II, 2, iii).

Table 3. Known benefits of postoperative epidural analgesia

Figure 2. Anatomy of the epidural space.

(i) Indications
We recommend epidurals for postoperative pain, primarily in the following situations (a discussion of when to use intraoperative epidurals is beyond the scope of this chapter):

Patients having thoracic or abdominal surgery

Patients having lower limb surgery, in whom early mobilization is important (early active or passive mobilization)

Patients having lower body vascular procedures, in whom a sympathetic block is desirable

Patients who are not anticoagulated, or for whom anticoagulation is not planned in the immediate postoperative period

Especially patients with compromised cardiac or pulmonary function
(ii) Contraindications
Contraindications to epidural placement are the following:

Patient refusal

Coagulopathy

Concurrent or planned treatment with low-molecular-weight heparin (LMWH)

Bacteremia

Local infection at epidural insertion site

Spine pathology (a relative contraindication)
(iii) Management principles
The management of epidural catheters should always be under the direct supervision of anesthesiologists. Patients should be seen daily to ensure that catheters and medications are working effectively. Pain reports should be satisfactory, and side effects such as pruritus, sedation, and changes in sensation or motor function should be carefully evaluated. Catheters and their insertion sites should be inspected for migration, integrity of the dressings, and inflammation or back tenderness. Anesthesia personnel should make prescription changes to the analgesic therapy and administer specific medications as necessary. At the end of treatment, the anesthesia team should be responsible for pulling the catheter and ensuring that it is removed intact.
Nurses should be properly educated before they care for patients with epidural catheters. Important teaching points include typical medication doses and concentrations, assessment parameters, the normal appearance of the catheter and catheter site, operation of the infusion pumps, common medication side effects that can be treated by them, and side effects requiring a call to the physician in charge.
(iv) Drug choices
The standard infusion for postoperative epidural therapy at the MGH is a mixture of 0.1% bupivacaine with 20 µ g/mL of hydromorphone. A synergistic effect occurs when local anesthetic is combined with opioid, rendering this mixture optimally effective. However, there may be reasons to remove one or the other component (e.g., a local anesthetic causing hypotension, or an opioid causing pruritus), in which case, dose adjustments need to be made to the remaining drug. In the case of sole local anesthetic treatment, it may be necessary to add a systemic analgesic (opioid or NSAID).
Continuous epidural infusions vary between 4 and 8 mL/hr depending on the catheter location, with possible infusion rates of up to 20 mL/hr. Fentanyl is the second choice of epidural opioid, reserved for patients who might be particularly sensitive to opioid effects (e.g., the very young and the very old). Because it is lipophilic, fentanyl tends to bind locally to spinal cord receptors rather than spread with cerebrospinal fluid (CSF) movement. The result is an analgesic effect localized around the level of insertion of the epidural catheter, in contrast to hydromorphone and particularly morphine (the least lipophilic of the opioids), which produce a better spread of analgesia but a greater risk of delayed respiratory depression resulting from the spread of drug to higher centers in the CNS. Standard epidural orders include infusion dose ranges for nurses to titrate based on the patient’s report, orders for alternative treatments should the epidural fail, and orders for the treatment of adverse side effects.
(v) Management of inadequate analgesia
The best way to ensure that an epidural catheter is well positioned to provide analgesia is to establish an anesthetic level using local anesthetic. Optimally, if a patient undergoes surgery under combined epidural or general anesthesia, catheter function should be tested preoperatively. Testing catheter function by establishing a level can be achieved at any stage, but (a) this is less specific in a patient who is in the early stages of recovery after anesthesia, and (b) it will be necessary to monitor for possible hypotension and to be prepared to treat hypotension. Another, less time-consuming and surprisingly helpful test is to inject 5 to 7 mL of the analgesic infusion (i.e., a low dose of local anesthetic). If the catheter is well positioned, analgesia should be noticeably improved by the injection, and this injection is unlikely to produce hypotension.
Once good catheter function is established, several approaches to improve analgesia can be taken. A bolus injection can be given (as described) if it has not already been given. The infusion rate can be titrated upward, as tolerated. Systemic analgesics can be given. NSAIDs are useful adjuncts to epidural analgesia, especially when the epidural level does not cover the area of surgical pain, as when the incision is high, or when pain is referred outside the epidural area (as in shoulder pain associated with chest tubes and diaphragmatic irritation). Systemic opioids (including PCA) can also be added, but in this case, the opioid should be removed from the epidural mix to avoid possible overdose.
(vi) Patient-controlled epidural analgesia
Patient-controlled epidural analgesia (PCEA) has become a standard of care in many institutions around the country. Although the MGH has not begun this modality yet, plans are underway to start this in the near future. Allowing patients to gain control over their own pain medication (as stated before) is one great advantage to PCEA.
When demand doses and lockout intervals are prescribed, several aspects of the opioid must be considered: how lipophilic it is, its onset of action, and the duration of pain relief that can be expected. The PCEA dosing for the standard MGH epidural mix (0.1% bupivacaine with 20 µ g/mL hydromorphone) is a 2-mL bolus every 20 minutes (lockout), with a basal infusion of 4 to 6 mL/hr.
(viii) Side effects
Most side effects (Table 4) are alleviated by either lowering the infusion rate or changing the drug or dose. Pruritus is a common side effect of neuraxial opioid that usually responds well to antihistamine treatment. The mixed agonist/antagonist nalbuphine (Nubaine) (5 to 10 mg IV, 4 to 6 times per hour) also works well, as does a low-dose naloxone infusion. Contrary to popular belief, nausea rarely occurs with epidural opioids, as doses used are extremely small. Gut mobility is in fact improved by epidural therapy, not the contrary.

Table 4. Common side effects of epidural analgesia

Urinary retention may be a problem, especially when lumbar catheters are used, so indwelling Foley catheters are kept in patients receiving epidural analgesia. Unilateral lower extremity numbness with occasional weakness or motor block is a side effect of the local anesthetic. This usually occurs when the epidural catheter tip has migrated along a nerve root, and pulling the catheter back or lowering the infusion rate tends to rectify the problem. However, one should always maintain vigilance and continue to watch for possible complications.
(ix) Complications
Although most complications are rare, when they do occur they can be devastating; an integral part of epidural management is the avoidance of serious complications (Table 5). Postdural puncture headache (PDPH) is a recognized and relatively common complication that is thought to be the result of a small CSF leak secondary to accidental dural puncture. Typically, there is a delay in onset of the headache (approximately 24 hours), so that the complication tends to manifest on the first postoperative day. Because PDPH tends to worsen on sitting up, and particularly on walking, and to improve on lying down, it may not appear until the patient gets out of bed for the first time after surgery. Other characteristics of the headache are that it tends to occur at the back of the head (occiput) and neck, and it produces a tight, pulling, and throbbing sensation. Conservative management consists of bed rest (up to bathroom only), plenty of fluids (IV or oral), and headache medication (NSAIDs, acetaminophen, caffeine, and theophylline all work well).

Table 5. Epidural complications arising postoperatively

If there is no resolution, or if conservative measures are contraindicated, a blood patch is recommended. This consists of an epidural injection of 20 mL of the patient’s own blood (drawn under sterile conditions), which is thought to close the dural puncture. The exact mechanism by which an epidural blood patch works is uncertain, but it is probably either a pressure effect or a laying down of clot or fibrosis onto the puncture site.
Much more serious are complications caused by the development of space-occupying lesions within the spinal canal—hematomas and abscesses—the former being the more common. If there is any reason for concern, the first response should be to discontinue the epidural infusion, and possibly to remove the epidural catheter, the latter especially if there is evidence of infection at the skin. (If there are coagulation issues, it may be better to leave the catheter until they are resolved—see below). As long as these lesions are recognized, they can be surgically decompressed without consequent permanent neurologic damage. Failing this, spinal cord compression, and later paraplegia, may develop.
Cardinal signs of impending spinal cord compression are sensory and motor changes in the lower extremity (often bilateral) and pain in the back. Although minimal sensory changes are common and may be benign, prolonged motor changes that do not resolve with discontinuation of the epidural infusion are always worrisome, as is back pain. In the case of lesions in the sacral canal, cardinal signs are changes in bladder and bowel function, and pain may be absent. If there is any concern, magnetic resonance imaging should be ordered and the involvement of neurology is always helpful. Early intervention is key to preventing disastrous complications. Other serious complications such as anterior spinal artery syndrome, transverse myelitis, and meningitis have been reported but are extremely rare.
(x) Anticoagulation and epidurals
Some patients are placed on anticoagulants while receiving epidural analgesia. Because there is a small but real risk of starting an epidural bleed when removing an epidural catheter in an anticoagulated patient (best estimate, between 0.01% and 0.1%), it is prudent to develop a protocol for catheter removal in these patients. The policy for removing epidural catheters at the MGH is based on a consensus statement from the American Society of Regional Anesthesia, entitled Neuraxial Anesthesia and Anticoagulation (available on the web from address listed in Appendix III).
If a patient is receiving a high-dose heparin infusion and the epidural catheter must be removed, the primary service is notified to coordinate an appropriate plan of care. Heparin is stopped for 2 to 3 hours before removing the epidural catheter and then resumed without a bolus dose approximately 2 hours after epidural catheter removal. Low-dose heparin (prophylaxis) is not a contraindication to catheter removal.
Patients on Coumadin should have the catheter removed within 48 hours of the first dose of Coumadin. Any time thereafter, prothrombin times (PTs) should be obtained to ensure that the range is appropriate. The acceptable range for PT is below 17, for International Normalized Ratio (INR) is below 1.9, and for partial thromboplastin time (PTT) is below 35.
LMWH should be held for at least 12 hours prior to catheter removal. It can be started or restarted 8–12 hours (or later) after the epidural catheter is pulled. There is no practical test for LMWH activity (the anti-Xa level is not a reliable predictor of the risk of bleeding, and the test is available on only a limited basis); PT, INR, and PTT values do not reflect LMWH activity. Administering fresh frozen plasma to restore coagulation factors is rarely indicated and entails many risks (fluid overload, cardiac failure, transfusion reaction, immunological changes, transmission of infection), some more common than others and some unpredictable and/or irreversible. Patients with a known risk of coagulopathy who have a catheter removed should be monitored for at least 24 hours to rule out hematoma development.
5. Single-shot neuraxial morphine
Neuraxial morphine can be safely used provided that large bolus doses and repeat bolus doses are avoided, and that patients are appropriately monitored. In general, infusions are safer than bolus doses; however, epidural morphine infusions are not used routinely at the MGH. A single shot of morphine into the epidural or intrathecal space can provide prolonged analgesia (up to 24 hours), but it carries a risk of delayed respiratory depression. As discussed, morphine is poorly lipophilic, tends to stay in CSF once there, and is subject to CSF flow with passage to higher centers including the respiratory center.
At the same time, the fact that morphine tends to remain in CSF is the reason that it produces excellent selective spinal analgesia (i.e., good spread to spinal cord receptors). Thus single-shot neuraxial morphine is an excellent means of providing analgesia when single-shot spinal (intrathecal injection) or epidural (epidural injection) anesthesia is used for surgery, provided the risk of delayed respiratory depression is recognized. At the MGH, we monitor patients who have been given neuraxial morphine in exactly the same way we monitor those with epidural opioid infusions, which we feel is an adequate level of monitoring for these patients (Fig. 3). We provide supplementary analgesia with PCA opioid, but for safety we rely solely on demand doses and do not use continuous opioid infusions.

Figure 3. Epidural order sheet.

6. Intraoperative neural blockade
Nerve blocks performed before or during surgery provide excellent pain control during the early postoperative period. Infiltration of wounds with local anesthetics by surgeons can also contribute significantly to the control of early postoperative pain. Intraoperative neural blockade can reduce postoperative analgesic requirements and, in some cases, negate the need for postoperative analgesia. Intraoperative nerve blocks are particularly useful in children, who tolerate analgesics poorly and in whom pain is particularly distressing.
7. Prolonged neural blockade: use of catheters
Neural blockade can be prolonged beyond the life of the chosen local anesthetic only by using continuous infusions of local anesthetic via catheters. Neural cryotherapy and direct severance of nerves used to be performed for prolonged nerve blockade, but these practices are no longer recommended as they are known to result in an unacceptably high incidence of chronic pain. Continuous infusions of local anesthetics can be administered at various sites. For example, local anesthetic infusion into the pleural space via an intrapleural catheter provides effective pain relief following thoracotomy and upper abdominal procedures, but this has yet to prove its worth in comparison to thoracic epidural therapy.
Local anesthetic infusion into the brachial plexus is useful after shoulder or hand surgery, especially when physical therapy is needed. Bupivacaine 0.1% at 10 to 15 mL/hr is used while the patient is hospitalized (approximately 2 days). If that is not effective, the concentration can be increased to 0.25% or a bolus of 20 mL of 0.25 to 0.375% bupivacaine can be added to the catheter prior to physical therapy. Patients may also take oral analgesics as needed.
8. Transcutaneous electrical nerve stimulation
Transcutaneous electrical nerve stimulation (TENS) is useful for postoperative pain in selected patients. The device consists of a series of electrodes that are placed on the site of the pain (either side of the surgical incision in the case of postoperative pain), through which a low-voltage electrical stimulus is passed. The treatment is based on the gate-control theory of pain by Melzack and Wall. Randomized, controlled trials have confirmed its efficacy in postoperative pain compared with controls (no TENS), but they have not shown it to be better than sham TENS (electrodes with no current); likewise, sham TENS is also better than no TENS. It is likely, therefore, to have predominant a placebo effect. It does not stand up against drug therapies as a sole treatment for anything other than mild postoperative pain, but it may be useful in reducing analgesic requirements and possibly improving pulmonary function in selected patients. At the MGH, TENS is not offered routinely for postoperative pain, but a few patients do request it and can obtain it through our physical therapy department.
9. Behavioral therapy
The goal of behavioral therapy is to provide patients with a sense of control over their pain. All patients benefit from being well prepared psychologically for the experience of surgery and postoperative pain. Simple relaxation strategies and imagery techniques can help those patients who find such interventions appealing. Relaxation strategies and imagery techniques do not need to be complex to be effective. Simple strategies, such as brief jaw relaxation, music-assisted relaxation, and recall of peaceful images, have been found to be effective in reducing anxiety and analgesic requirements. They take only a few minutes to teach, although they may require continual practice and reinforcement at times. Patients who wish to learn simple relaxation exercises can be given information and recommended techniques.
Therapeutic touch is becoming another popular mode of therapy and is particularly helpful when postoperative pain is refractory to other modalities. Elaborate behavioral therapy techniques (i.e., biofeedback or counseling) have no place in the treatment of acute postoperative pain, unless the pain is likely to be prolonged or to recur.
V. CONCLUSION
Effective postoperative pain management involves adherence to certain basic principles. First, pain must be assessed on an ongoing and systematic basis, with data documented in the medical records, so that pain treatment can be modified according to the patient’s needs and communicated throughout the healthcare disciplines. Pain that is treated preemptively or controlled early is easier to manage than established or severe pain, so treatment during the intraoperative and early postoperative period is essential. Patients should be involved with their treatment and be educated about their surgery and the options available for treating postoperative pain. The actual choice of treatment is of secondary importance, as long as the principles of postoperative pain management are adhered to.
Postoperative pain has often been inadequately treated in the past, partly because of complacency, and partly because of fear of analgesic side effects. But today’s patients expect better pain control and are better educated in their healthcare needs. The provision of exemplary pain management goes a long way toward improving patient satisfaction with hospital care. For this reason, and because good pain control is humane and reduces morbidity, we should endeavor to treat postoperative pain to the best of our ability.
SELECTED READING

1.
Bach S, Noreng MF, Tjellden NU. Phantom limb pain in amputees during the first 12 months following limb amputation, after preoperative lumbar epidural blockade. Pain 1988;33:297–301.

2.
Ballantyne JC. Does regional anesthesia improve outcome after surgery? Curr Opin Anesthesiol 1999;12:545–549.

3.
Ballantyne JC, Carr DB, DeFerranti S, et al. The comparative effects of postoperative analgesic therapies on pulmonary outcome: Cumulative meta-analyses of randomized, controlled trials. Anesth Analg 1998;86:598–612.

4.
Carr DB. Acute pain management: Operative or medical procedures and trauma. In: Clinical practice guideline. AHCPR pub no 92-0032. Rockville, MD: Agency for Health Care Policy and Research, Public Health Service, US Department of Health and Human Services, 1992.

5.
Cousins M, Power I. Acute and postoperative pain. In: Wall PD, Melzak R, eds. Textbook of pain, 4th ed. Philadelphia: Churchill Livingstone, 1999:447–491.

6.
de Leon-Casasola OA, Parker B, Lema MJ, et al. Postoperative epidural bupivacaine-morphine therapy: Experience with 4,227 surgical cancer patients. Anesthesiology 1994;81:368–375.

7.
Gottschalk A, Smith DS, Jobes DR, et al. Preemptive epidural analgesia and recovery from radical prostatectomy: A randomized controlled trial. JAMA 1998;279:1076–1082.

8.
Horlocker TT, Wedel DJ. Spinal and epidural blockade and perioperative low molecular weight heparin: Smooth sailing on the Titanic. Anesth Analg 1998;86:1153–1156.

9.
Liu S, Carpenter R, Neal JM. Epidural anesthesia and analgesia: Their role in postoperative outcome. Anesthesiology 1995;82: 1474–1506.

10.
Ready LB, Loper KA, Nessly M, Wild L. Postoperative epidural morphine is safe in the surgical ward. Anesthesiology 1991;75: 452–456.

11.
Melzack R, Wall PD. Pain mechanisms: a new theory. Science 1965;150:971–979.

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