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Postoperative Pain Management: An Anesthesiologists'Opportunity and Challenge

1991; King Faisal Specialist Hospital and Research Centre; Volume: 11; Issue: 6 Linguagem: Inglês

10.5144/0256-4947.1991.688

0975-4466

Khalid A. Sami,

Pain Management and Opioid Use

Special CommunicationPostoperative Pain Management: An Anesthesiologists'Opportunity and Challenge Khalid A. SamiMD, MS, FACA Khalid A. Sami Address reprint requests and correspondence to Dr. Sami: Department of Anesthesiology (MBC 22), King Faisal Specialist Hospital and Research Centre, P.O. Box 3354, Riyadh 11211, Saudi Arabia. From the Department of Anesthesiology and Pain Clinic, King Faisal Specialist Hospital and Research Centre, Riyadh. Search for more papers by this author Published Online::1 Nov 1991https://doi.org/10.5144/0256-4947.1991.688SectionsPDF ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail AboutIntroductionIn Paradise Lost, Milton described pain as “perfect miserie, the worst of all evils, an excessive which overturns all patience.” this elegant statement describes the plight of patients suffering the discomfort that inevitably follows surgical operation. Prolonged pain not only diminishes the quality of life but also fosters complications as a consequence of disturbed physiological functions. Other secondary effects such as impaired sleep and persistent anxiety result in fatigue which impede recovery and occasionally may even make the difference between life and death.MAGNITUDE OF THE POSTOPERATIVE PAIN PROBLEMAlthough the intensity and duration of postoperative pain cannot easily be quantified, there is ample evidence that, in general, postoperative pain is underestimated by surgical personnel and is often improperly or inadequately managed [1–6]. The study of Marks and Sacher [7] of medical inpatients at New York's Montefiore Hospital documented how inadequately the house staff treated patients with acute pain. Moreover, after noticing that the patients were still in pain despite having received analgesic medication, the junior physicians were reluctant to prescribe additional drugs. The doses of narcotics that were prescribed were 50 to 65% of the amounts established as necessary to relieve severe pain. A similar study by Charap [8] showed that most house officers held the belief that a time-based (PRN) medication regimen was ideal because it reduced the likelihood of overdose and forestalled the development of tolerance. In a comprehensive review of postoperative pain management, Utting and Smith [6] cited a variety of papers, editorials, and letters to support their contention that, even in this enlightened, modern age, postoperative pain is still treated improperly. It is regrettable that so many patients experience intense pain following surgery, not because such discomfort is unpreventable but because physicians are reluctant to prescribe an adequate dose of analgesic! There is impressive evidence that lack of knowledge among surgical house staff and nurses of the pharmacology of analgesic drugs is the primary reason for inadequate management of postoperative pain.ADVERSE PHYSIOLOGICAL EFFECTS OF UNRELIEVED PAINAcute pain from a surgical incision or trauma causes several adverse physiological effects within the pulmonary, cardiovascular, gastrointestinal, muscular, and urinary systems [9]. The ability to cough is considerably reduced, due to spasm within the surgical wound and surrounding tissue. Involuntary splinting of the respiratory muscles fosters sputum retention, atelectasis, lobar collapse, hypoxia, hypercapnia, and abnormal V/Q relationships [10,11]. Pain heightens sympathetic activity, thereby increasing myocardial work and oxygen consumption. Such neurohumoral overactivity may provoke myocardial ischemia and compromise regional blood flow to the kidneys, brain, and liver. Gastric stasis can lead to electrolyte abnormalities and malnutrition. Prolonged confinement to bed decreases blood flow and increases platelet aggregation which may result in deep vein thrombosis and pulmonary embolism. There is also substantial evidence showing that proper control of postoperative pain and prevention of the “stress response” have a beneficial effect on the patient's overall recovery [9].FACTORS THAT INFLUENCE THE NATURE OF POSTOPERATIVE PAINThe intensity and duration of postoperative pain depend to a large exterit on the following factors:Site and type of incision—probably the most important factors determining the severity of pain. Intrathoracic, high abdominal, and flank incisions are associated with excruciating pain and muscle spasm, especially during deep breathing and coughing.Patient's age—postoperative pain varies significantly in patients of different ages. Twenty-and thirty-year-old patients experience more pain following similar operations than do patients in their fifties, sixties, and seventies [12,13].Cultural, socioeconomic factors, and psychological makeup profoundly influence the pain experienced after surgical operations.Preoperative physical condition and the pharmacological preparation of the patient significantly alter the extent of postoperative pain.Intraoperative anesthetic management can modulate memory and the extent of discomfort felt during the postoperative period.Perhaps most important of all, empathetic care given by the physicians and nurses in the recovery period can lessen the pain and suffering. Nurses must be conscientious about giving pain medications on time if incisional pain is to be controlled effectively.Acute postoperative pain fosters anxiety, fear, a sense of helplessness, and sleep deprivation [14]. Fear about what was found atoperation, the prognosis, and the financial and social impact of hospitalization and recovery all contribute to the patient's anxiety. There is a direct and parallel relationship between anxiety and pain. Thus, a vicious cycle of anxiety, sleep deprivation, pain, and helplessness develops [14]. If this situation is not resolved by proper relief, attempts to subdue pain with larger doses of narcotic are usually futile. In addition, if acute pain is allowed to persist for several days, helplessness transforms into anger, depression, demoralization, and inability to cope with the illness.ROLE OF ANESTHESIOLOGIST-CHALLENGE AND OPPORTUNITYThe special knowledge and skills of the anesthesiologist, although well recognized in recent years, have traditionally been confined to the operating room. Paradoxically, it is customary to delegate responsibility for managing postoperative pain to the most junior members of the surgical team. House officers, even at the most modern institutes in the West, have little knowledge of pain mechanisms or pathways or how to interrupt them, and often have incorrect or inadequate information on the pharmacodynamics and pharmacokinetics of analgesic drugs [7,8]. There exists widespread, unrealistic concern about addiction and respiratory complications. As a result, house staff and nurses frequently give inadequate doses of pain medication spaced too widely apart to effectively control postoperative pain [15].The situation constitutes a major shortcoming of modern medicine. We simply are not applying available information in the best interest of our fellow human beings. Dr. John Bonica, a distinguished authority in pain research and management, has pointed out repeatedly that pain therapy is an orphan field. He states correctly that the curricula of North American medical schools lack even a modicum of instruction regarding proper treatment of acute or chronic pain. Anesthesiologists have a responsibility to close this shameful gap. Their knowledge of pain pathways, and their training, experience, and technical skills in the use of analgesic drugs and local anesthetics, should be used outside the operating room to assure better postoperative pain control. I often hear fellow anesthesiologists remark that the important anesthesia services they provide in the operating room are unappreciated and that theirs is a “thankless job.” For those anesthesiologists who need to boost their self-esteem and job satisfaction, here is an opportunity to leave the confines of the operating room and to use their knowledge and expertise to control “demon pain.” Such efforts would be well rewarded and, in my opinion, worth the anesthesiologists’ time spent outside the surgical theatre.METHODS OF POSTOPERATIVE PAIN CONTROLEffective treatment of postoperative pain requires (1) attention to patients’ general comfort and well-being; and (2) application of specific pain-relieving measures. The former embodies assuring physical and mental rest and reducing anxiety. Placid surroundings and the judicious use of benzodiazapines potentiate the effects of analgesics and provide amnesia and sleep as well as an antiemetic effect.The following specific methods are available to achieve partial or complete relief of postoperative pain: (1) systemic (parenteral) administration of analgesics; (2) regional anesthesia via intraspinal injection; (3) peripheral nerve block with local anesthetics; (4) transcutaneous electrical stimulation; and (5) cryoanalgesia.Systemic Administration of AnalgesicsIntramuscular administration: Intramuscular administration of an opioid analgesic is the most popular clinical method for relieving postoperative pain and is still the most widely used. However, there is abundant evidence that this method is a quite unsatisfactory means of relieving significant pain [15–18]. The usual approach is to order a preconceived dose of some narcotic, to be given at some arbitrarily chosen time interval. Due to variable absorption from the injection site, the blood concentration of the drug fluctuates in phase with the dosing intervals [19]. As a result, the patient experiences alternating periods of severe pain, relative comfort, and somnolence/ unconsciousness [15, 20].Discovery of opiate receptors within the central nervous system improved our understanding of analgesic action, while studies of the pharmacodynamics/pharmacokinetics of systemically administered analgesics have suggested new clinical techniques for their use. Further studies ultimately clarified why plasma concentrations after intramuscular injection were so unpredictable. Often the time interval between when a patient needs pain relief and when an analgesic effect is achieved with an intramuscular analgesic injection is quite variable and often surprisingly long! Austin and Stapleton [16] found that, in an individual patient receiving multiple same-dose intramuscular injections of narcotic, the peak concentration of the drug could fluctuate four-fold because of uneven absorption. These authors concluded that such fluctuations in plasma concentration “result in variable clinical responses.” Clearly, it is difficult to predict the dose of an intramuscular narcotic which will produce a sufficiently high plasma concentration to achieve satisfactory subjective analgesia. Today there are better ways to attain that goal, and following is a description of some of these methods:Intravenous analgesia. Well-planned intermittent or continuous intravenous (IV) administration of analgesic drugs can avoid the variability in peak plasma concentration associated with the intramuscular injection of analgesics, so that a sustained response can be attained [17,21]. The advantages of IV injection of analgesics are: (1) rapid onset of action makes it possible to attain prompt relief; (2) early determination of the effective dose can be made, which then guides precise titration of the drug to meet the individual needs of the patient; and (3) the plasma level declines promptly when the infusion is stopped, thus simplifying the management of side effects.Relief can be achieved quickly by giving the patient a “loading dose” of the analgesic under close observation for 15 to 20 minutes. Subsequent incremental doses of the drug should be given slowly—morphine, 1-5 mg, or meperidine, 10-25 mg, diluted in 5 to 10 ml of normal saline solution. Initially these incremental doses can be given at 10-to 20-minute intervals. Once good analgesia is achieved, the interval can be increased to 30 to 45 minutes to maintain a steady state. In spite of its proven efficacy, intermittent intravenous injection does have two major disadvantages:Analgesia is relatively short-lived due to the rapid decline in the plasma level of the drug as it is taken up by tissue and eliminated from the body.The technique is somewhat impractical because frequent injections are required and because of the need to monitor the patient closely; both of these requirements place substantial demand on house staff and nursing personnel.A better approach is to provide a stable analgesic drug plasma concentration by continuous infusion at a rate which matches its elimination from the circulation [17]. This method abolishes the wide swings in drug concentration seen with intermittent injections. Still, continuous infusion requires careful patient monitoring and periodic adjustment of the infusion rate to suit individual patients’ needs. In a study by Mather et al [22], meperidine administration by continuous drip resulted in sustained satisfactory pain relief in all patients and volunteers. These authors reported that patients were not only comfortable enough to sit up in bed but also relaxed enough to read. Another study by Stapleton et al [21] provided pharmacokinetic data about meperidine infusion in patients following hysterectomy. They administered an initial loading dose followed by a maintenance infusion. All patients were pain-free after four hours.It is my practice to administer, over a 15-minute period, an IV loading dose of 5 to 15 mg of morphine, depending on the age and emotional status of the patient and the site of operation. After careful evaluation of the effect on the patient's respiratory rate and the extent of pain relief, I start an IV morphine drip at 2.5 to 8 mg/hr (25 mg of morphine is mixed in 100 ml of normal saline, concentration = 0.25 mg/ml). The patient initially receives 5 to 10 ml/hr under careful observation. The IV drip rate is altered every 10 to 15 minutes during the first 30 minutes according to the response. After 30 minutes, the drip rate is adjusted to between 5 and 6 mg of morphine per hour; after two hours, the infusion rate is decreased to one-half that amount for another two hours. Subsequently a maintenance dose of 2 to 3 mg/hr is usually sufficient to control pain for 24 to 36 hours. During the first several hours, the pain must be monitored closely to evaluate the extent of pain relief and any associated depression of respiration; these factors are the crucial determinants of the ultimate infusion rate.Patient controlled analgesia. In 1968, Sechzer [23] first suggested that analgesics, given intravenously on the patient's demand, would improve pain relief with a smaller drug dosage than could be achieved with conventional intramuscular narcotic therapy. In another study, the same author also showed that patients’ postoperative analgesic requirements were cyclical and that, although the needs of the individual patient were fairly consistent, there was considerable variation in need between patients [24]. This simply underscores the fact that IV administration of repeated small doses of analgesic must be highly individualized and therefore is often impractical because of the demand it places on the nursing staff.In the early 1970s, the idea of giving the responsibility of postoperative pain management to patients themselves resulted in a revolution in acute pain management [25, 26]. Instruments were devised that could inject precise doses of analgesic upon patient demand. These devices were tested and improved to the extent that patient-controlled anesthesia (PCA) became a practical and successful technique. Good analgesia was achieved with a relatively low total amount of drug. Both patient and physician acceptance was good and nursing personnel were relieved of a real burden.PCA is clearly more effective than traditional intramuscular narcotic administration. By repeated IV injection of small doses of analgesic, a fairly constant blood concentration is achieved [27]. In 1982, Bennett et al [28] reported better postoperative pain control and decreased narcotic consumption with PCA than with intramuscular injections.For the PCA technique to be successful it must be thoroughly explained to the patient. He or she must know not only how to use the infusion device but also must accept less than complete relief of pain. Rather, he or she is encouraged to use the device in a “prophylactic manner,” so as to avoid any full-blowrr, distressing pain.To initiate PCA, the patient receives a loading dose of morphine or meperidine in the operating or recovery room. As soon as pain is evident, the patient starts the PCA device; the initial incremental dose setting for morphine is 1 mg (meperidine, 10 mg) per request, with a “lockout” period of 8 minutes. After about five doses, if the patient still has significant pain, the demand dose is increased to 1.5 mg of morphine (15 mg of meperidine). If, after another hour, the patient still feels pain, the “lockout” interval is reduced to 6 minutes. With this protocol, a steady plasma concentration of narcotic is achieved quickly and individual analgesic consumption remains almost constant throughout the PC A period. Most patients can achieve comfort when PCA is employed.Regional Analgesia Achieved with Intraspinal NarcoticIn 1973, shortly after Pert and Synder [29] identified opiate receptors in the spinal cord, Wang et al [30] reported prolonged relief of cancer pain after intrathecal injection of only 0.5 to 1.0 mg of morphine. These two discoveries opened a new chapter in the management of acute and chronic pain. Many studies have since revealed excellent relief of postoperative pain by intraspinal administration or morphine [31–34]. Other reports have shown that, apart from providing excellent pain relief, epidural narcotic analgesia also reduces overall morbidity and mortality and decreases the stay of high-risk patients in the intensive care unit (ICU) and hospital [35,36].Lipid solubility of the narcotic drugs seems to be the most important factor that determines the onset, spread, and duration of intraspinal anesthesia [37]. Morphine, a water-soluble narcotic, has a slow onset of action, good dermatomal spread, and longer duration of action compared with more lipid-soluble drugs such as fentanyl. It must be stressed, however, that the duration of action of intraspinal narcotics also depends on the dose, the patient's age and condition, the level of injection, the pain intensity, and even socioeconomic and cultural factors.Lipid solubility has other important implications for the clinical application of intraspinal narcotics. Lipid-soluble drugs diffuse rapidly through the dura mater to reach the lipid-rich spinal cord [38]. Also, due to rapid uptake by the lumbar spinal cord, less drug reaches the cervical segments, thereby limiting the ultimate extent (spread) of the analgesia achieved [39]. A study by Sjostrom et al [39] examined whether the quality of pain relief or the spinal level achieved was altered when the same dose of morphine was given in a 1-ml or 10-ml volume; they concluded that no difference could be identified.The epidural narcotic dose is selected on the basis of the age and physicial condition of the patient, the surgical procedure, the available monitoring capabilities, and the experience of the physician. In fit patients, the initial doses of epidural morphine and meperidine are: morphine, 0.03-0.1 mg/kg, and meperidine, 0.1-0.3 mg/kg.Pain relief with morphine begins within 25 to 30 minutes and with meperidine, within 5 to 10 minutes. An initial dose of epidural morphine may be expected to last for 6 to 18 hours; duration of meperidine action usually lasts 6 to 8 hours. Because elderly patients require substantially smaller amounts, doses in such patients are calculated with this formula [40]: 24-hr dose (mg) = 18 -(age × 0.15). One third of this dose is given as an initial bolus and subsequent doses are adjusted according to the effectiveness and duration of the initial dose.Several side effects (complications) are associated with the use of intraspinal narcotics, due either to the technique itself or the narcotic's action in the epidural space. Accidental durai puncture during placement of the catheter may result in so-called spinal headache. Persistent backache occasionally occurs even after an atraumatic epidural puncture. There is also a small risk of infection from invasion of the epidural space. However, the most serious complication of the epidural narcotic technique is respiratory depression, even apnea. It must be anticipated that any patient who receives an intraspinal narcotic is at such risk. There is clear evidence that subarachnoid narcotic administration, particularly with morphine, imposes a higher risk (5.5%) than does the epidural method (0.33%) [41]. A 1982 Swedish survey of subarachnoid and epidural administration of narcotics showed that respiratory depression developed within six hours in patients over 70 years old. In contrast, a study by Brownridge [42] on 2000 cesarean section patients who received 50 mg of meperidine found that only one patient suffered respiratory depression. Although the hazard is slight, patients who receive epidural narcotics should be admitted to the ICU or step-down unit whenever possible [43]. Respiratory monitors and high-intensity nurse surveillance are necessary to prevent potentially serious complications. Careful patient selection, effective nurse education, proper monitoring equipment, and availability of informed medical personnel are important additional means of reducing the risk of respiratory depression. When epidural narcotics are used with these safeguards, they provide excellent pain relief and speed postoperative recovery even in very sick, high-risk surgical patients.Other less significant side effects, such as nausea, vomiting, urinary retention, and pruritus, can be troublesome in some patients. Such problems respond well to symptomatic therapy; antiemetics, antihistamines, and low-dose naloxone are mainstays of treatment.Neural Blockage with Local AnestheticsPeripheral nerve blockage with local anesthetic agents was among the earliest techniques used to relieve postoperative pain. In addition to easing the patient's discomfort, nerve block has other benefits. For example, the breathing pattern is normalized when pain and muscle spasm are prevented or relieved [44, 45]. The patient can breathe deeply as well as increase his vital capacity, functional residual capacity, and peak expiratory flow rate, thereby preventing atelectasis and ventilation/perfusion mismatch (hypoxemia) [46]. Other beneficial effects of nerve block include reduced need for narcotic, facilitation of early ambulation to forestall venous thrombosis, and early restoration of appetite. All of these help shorten the convalescent period.Several methods of nerve blockade are used, depending on the site and extent of the surgery. The most popular techniques are epidural, intercostal, paravertebral, and sacral nerve block. Whatever method is chosen, it is very important that the physician possess appropriate technical skill and be familiar with the proper dose and volume of the local anesthetic to be used. Knowledge of adverse local anesthetic reactions and the effective methods to treat them are necessary if local anesthetic block is to be used safely for postoperative pain control.Segmental regional analgesia is not without its disadvantages. Therefore the risk/benefit ratio must be considered before any of these techniques can be employed. With intercostal block, the risk of pneumothorax and toxic reaction from absorbed drug are always present. It is safer to perform this block under direct vision at the end of surgery—for example, after an intrathoracic operation. The complications and disadvantages of epidural local anesthetic block are the same as those for any other situation in which the epidural approach is used: the associated sympathetic nerve blockade may produce significant hypotension, especially when a wide segmental area is anesthetized or when the patient's fluid status (hydration) is depleted. Elastic stockings and abdominal binders are useful to reduce pooling in the splanchnic and peripheral vascular beds and thus to lessen the likelihood of hypotension.Local anesthetic complications can be reduced by adding narcotics to the local anesthetic solution. This improves the effectiveness of the local agents and modulates the sympathetic and motor blockade [47]. The total dose of both drugs can be further reduced by infusing dilute solutions. A smaller narcotic dose also minimizes the chance of respiratory depression and urinary retention. Such combination therapy is particularly effective in relieving pain associated with coughing, deep breathing, and early ambulation.Transcutaneous Electrical Nerve StimulationThe concept of using counter-irritation to obtain pain relief is quite old. Since ancient times man has used nonpainful sensory stimulation to divert attention from acute and chronic pain. A classic example is massage of an aching muscle or joint.Renewed interest in the counter-stimulation technique arose after Melzack and Wall [48] published their theory of gate control in 1965. Their theory asserts that certain cells in the substantia gelatinosa of the dorsal horn act as gates that modulate (suppress) noxious stimuli coming into the central nervous system over large-diameter afferent nerves. Thus, painful stimuli are blocked whenever the gate is closed. However, these gates remain open to activity (traffic) or persistent stimulation of the small A delta and C fibers.The rationale for the use of electricity to produce analgesia is based, at least in part, on this gate control theory. Also, animal experiments have shown that electrical stimulation or electrodes implanted in the brainstem cause release of endorphins and enkephlin-like material into the cerebrospinal fluid which, in turn, produces analgesia [49]. In 1976, Adams [50] discovered that the analgesia produced by brain stimulation could be reversed by giving naloxone. An additional explanation for the analgesia produced by electrical stimulation was offered by Melzack, who suggested the existence of a powerful descending inhibitory system in the region of the periaqueductal gray matter of the aqueduct of Sylvius. According to this theory, nociceptive sensory impulses that reach the posterior horn of the spinal cord are transmitted to the midbrain and cortical areas to activate the inhibitory fibers, which then block further noxious stimuli at the level of the spinal cord [51]. Whether a biochemical mechanism is involved in this process has not been determined, but there is speculation that enkephalins may be released into the substantia gelatinosa and may be responsible for the pain relief produced by electrical stimulation.Many investigators have used counter-irritant sensory input to provide postoperative pain relief [52–55]. Solomon et al [54] found that, when surgical patients used transcutaneous electrical stimulation (TENS), they required much less narcotic medication. Other investigators noted improved pulmonary function after thoracotomy when TENS was used [53,55]. Tyler [56] reviewed this subject thoroughly in 1982 and cited several other studies which claimed that TENS was a useful modality for postoperative pain control.In spite of the substantial clinical evidence of the effectiveness of TENS, for reasons that are not clear, the modality does not enjoy considerable popularity among surgeons, anesthesiologists, or nursing staff. This apathy exists despite the fact that the TENS device is simple to use and produces no side effects. Disposable sterile adhesive electrodes are applied about 2.5 cm on either side of the surgical wound immediately after the skin closure. The current is turned on as soon as the patient feels pain. The pocket-sized stimulator delivers either a square or spikewave form. For most types of postoperative pain, the stimulus pattern usually consists of current pulses of 2 to 5 Hz at nonpainful intensities of 15 to 50 ma. A basic principle of TENS use is to activate large myelinated nerve fibers located at various depths in the painful tissue. It is important not to stimulate or activate the thin (C) fibers that would, according to the gate theory, open the gate and permit pain impulses to reach the higher centers.CryoanalgesiaIt has been known for centuries that cold has analgesic properties [57]. In 1976, Lloyd et al [58] used cold to relieve postoperative pain for several days, even for several weeks in some cases. There is experimental evidence that A-delta and C fibers are damaged by cold, which probably explains why pain is abolished. However, spontaneous nerve recovery usually occurs after a few weeks. Duration of pain relief seems to depend on the completeness of nerve impairment. This cryolesion technique has been used primarily to obtund thoracotomy incision pain [59]. In a study carried out by Glynn et al [60], 29 patients received intercostal cryolésion nerve block prior to closure of their thoracotomy incisions. When compared to a control group of patients who received only intramuscular pain medication, the cryoanalgesia group required significantly smaller doses of pain medication at much longer intervals. The technique is relatively simple but does require special equipment. Also, precise positioning of the cryoprobe (needle) is essential to achieving an effective block. Attempts to achieve percutaneous cryoanalgesia have not been gratifying; results are much better when the nerve(s) is blocked under direct vision [60].The Acute Pain ServiceBy the nature of orientation of their specialty, anesthesiologists have traditionally provided important service in the control of pain during surgery. In the process of learni