Acute Postoperative Pain Management

Anesthesiologists continue to practice pain medicine and contribute significantly to the scientific evolution of this most important subspecialty in modern health care. As the public becomes more aware of the incredible techniques that are now available to manage acute, chronic, and cancer pain, the expectation that there will be painless surgery and postoperative recovery increases. Thus, health care professionals must stay abreast of the advances in acute and chronic pain management and strive always to provide contemporary care. We have a potent arsenal of modalities that can effectively minimize the patient’s postoperative pain. Doing so prevents unnecessary patient discomfort, lengthy hospital stays, undue medical expenses, poor clinical outcomes, and extensive utilization of already overburdened health care resources (1–3). The clinical practice guidelines promulgated by the Agency for Health Care Policy and Research from 1992 encouraged clinicians to focus on providing effective acute postoperative pain management and proposed a systematic approach to doing so (4). The American Society of Anesthesiologists (ASA) has promulgated practice guidelines for acute pain management because this aspect of our contemporary practice is so essential (5). So significant are the benefits from treating pain effectively that the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) is commanding that all institutions develop pain management programs as a criterion for regaining certification. The proposed guidelines identify the responsibilities of both the institution and the clinical staff, as well as delineate the patient’s rights. The JCAHO standards change the emphasis to patient satisfaction as an essential element that drives the clinical activity of health care professionals. The documentation of the preoperative assessment of the patient as to knowledge about and preferences for pain management techniques, as well as the teaching provided and an amplified postoperative evaluation protocol, become paramount in establishing hospital policy and clinical care. The ASA Committee on Pain Medicine considers the following as important for measurement of the effectiveness of pain intervention: subjective pain report, patient satisfaction, patient health perception, productivity (as to social, recreational, and vocational function), functionality in daily living, medical findings, mental health, health care utilization, and cost. These data are a powerful database that will continue to be validated. Todd and Brown (6) add vitality to this discussion in raising this timely question: how can we most firmly establish the true advantages of regional anesthesia and analgesia? Pathophysiology of Postoperative Pain Surgery represents a form of premeditated injury to the body. We understand that surgical injury provokes changes in the peripheral and the central nervous system (CNS) that must be dealt with therapeutically to define effective care and to positively influence outcome (2,3,7–12). Many patients believe that there will be no escape from the pain that follows their surgery, and for some this attitude actually becomes a coping strategy. What the patient believes and understands about the pain is a crucial factor that influences his or her reaction to all of the other therapy provided. Thus, the education of all involved with the patient’s care is fundamental to successful pain management. The physical processes of incision, traction, and cutting of tissue stimulate free nerve endings and specific nociceptors (7,8,10–12). The threshold for activation and the activity of these receptors is modified by the local release of chemical mediators of inflammation and sympathetic amines released within the surgical stress response. Substances such as bradykinin, serotonin, and histamine both sensitize and stimulate the receptors, whereas arachidonic acid derivatives only sensitize them. The influence of the sympathetic nervous system is appreciated, though the exact mechanisms of its interaction are not well defined. Problem 1 in postoperative pain is this peripheral sensitization, which is characterized by the decreased activation threshold of receptors, a shortened response latency to the point that there can be spontaneous pain (pain without an obvious stimulus), and an e-aggerated response within the peripheral nervous system to a given stimulus (i.e., the patient stays in pain long after the surgeon has e-amined the healing incision). Clinically, the patient manifests primary hyperalgesia, meaning that even gentle stroking of the incisional area causes e-quisite pain. Secondary hyperalgesia results when the elaborated chemicals and vascular response sensitize adjacent receptors such that pain spreads, i.e., the patient’s skin is painful and sensitive to even light touch away from the incision. Ordinarily, A-δ and c-fibers transmit nociceptive information from the periphery to the CNS (2,7,8,10). The input from A-δ fibers is associated with sharp, localized pain that is rapidly conveyed (because these fibers are myelinated), whereas that related to the c-fibers is usually aching, throbbing, diffuse, and more slowly transmitted (because these fibers are unmyelinated). A-δ and c-fibers make up about 70–90 of a peripheral nerve. What percentage function under normal circumstances and what percentage act as “reserve cabling” (so-called silent primary afferent fibers) is not known . Problem 2 relates to the reality that A-α and A-β fibers can be induced to carry nociceptive input to the CNS when peripheral sensitization occurs. This input does not necessarily undergo the usual inhibition in the dorsal horn, as does A-δ or c-fiber input, because A-α and A-β fibers do not terminate in the same levels of the dorsal horn (the substantia gelatinosa), as do the A-δ and c-fibers. An ancillary problem that is a consequence of these two problems is that there is a constant bombardment of the CNS with no-ious input: this overwhelms the CNS’s innate capability to filter or ameliorate painful input and fuels ongoing plasticity in the CNS response (13). Problem 3 occurs when the no-ious input begins to be processed by the CNS (9,13). Spinal reflexes (which require no integration of input within the CNS), such as muscle spasm and sympathetic stimulation, are provoked. Supraspinal reflexes that involve the integration of nociceptive input from a few spinal segments incite the mediators of the stress response. The surgical stress response (SSR) peaks in the postoperative period and has major effects on the cardiac, coagulation, and immune systems of the body (7). Although regional anesthesia and analgesia do not inhibit the local release of stress mediators into the bloodstream, Brodner et al. (14) have shown that blocking the SSR results in earlier tracheal extubation and ambulation, thus augmenting recovery and decreasing cost. They studied patients undergoing abdominothoracic esophagectomy surgery. Group 1 was a retrospective cohort of patients who had an epidural placed at T6 through T9 before surgery, followed by general anesthesia. An untitrated (to analgesia) epidural infusion of bupivacaine and sufentanil was provided after surgery for 5 days. Group 2 patients had a preinduction level of T4 established by the use of an epidural bupivacaine/sufentanil mixture, and an intraoperative infusion via the epidural was maintained. After surgery, Group 2 patients had the epidural infusion rate varied to achieve effective analgesia. Patients in Group 2 demonstrated superior pain relief, faster extubation, earlier mobilization, earlier achievement of intensive care unit (ICU) and step-down unit discharge criteria, and less metabolic disturbance. The authors concluded that this multimodal approach to pain management, which most likely blocked the SSR, improved patient outcome and decreased the cost of care. The multimodal therapy concept applied has been touted as being essential to gaining the poten-tial benefits of regional anesthesia and analgesia (1–3,5,7,11,14). The summation of the adverse effects described so far generates the pathophysiological consequences of acute pain listed in Table 1 (Problem 4). Because each of these consequences can detrimentally influence postoperative morbidity and mortality, Table 1 is also a compelling listing of reasons why postoperative pain must be treated effectively (3,4,7,15). Every body system can be negatively affected by inadequately treated pain, and there is the potential for multisystem failure as more individual systems are overstressed. Contemporary literature provides insight into the physiologic impact of epidural analgesia used to clinical advantage. The most painful incisions include those on the chest wall, the upper abdomen, the back, the major joints, and the anorectal area. All are regions of the body we can block with regional anesthesia or analgesia.Table 1: Pathophysiologic Consequences of PainThe original benefit of epidural anesthesia was documented in patients undergoing hip replacement (16) and lower extremity vascular surgery (17,18). Presumably because of the increased blood flow from the technique (and perhaps the effect of local anesthetics on the rheology of the blood), lower rates of deep venous thromboses were manifested. Chaney (19) raised the issue of the benefits to the cardiac surgery patient, and Loick et al. (20) have presented the positive impact of thoracic epidural anesthesia on lessening myocardial ischemia. De Leon-Casasola et al. (21) reported on the cardiac and pulmonary consequences of thoracic epidural anesthesia and analgesia. Ballantyne et al. (22) performed a telling metaanalysis on seven postoperative analgesic therapies as to their impact on pulmonary outcome. Epidural analgesia had a significant effect on decreasing pulmonary morbidity. Groudine et al. (23) showed that IV lidocaine was effective in speeding the return of bowel function and shortening a patient’s hospital stay, but one cannot directly correlate the blood levels of local anesthetic from this study with those encountered during continuous epidural infusions. Steinbrook (24) provides a thorough review of the positive consequences that epidural analgesic techniques have on recovery of gastrointestinal function. As experience has been gained with the technique of epidural anesthesia and analgesia and numerous reports are published, attention must be paid to both the constancy and the contents of the drugs being administered to most ac-curately interpret the clinical significance of the literature. As if the above enumeration of problems alone isn’t enough, the no-ious input from acute injury also triggers a state of sensitization of the CNS response, called wind-up (Problem 5) (2,7,8,10,12). The neurotransmitter release at the dorsal horn that is precipitated by repetitive nociceptive input conditions the CNS such that there is enhanced responsiveness, i.e., A-α and A-β input is painful, secondary hyperalgesia occurs because of an expansion of receptive fields in the area of the primary incision, or unilateral input produces hyperalgesia on the contralateral side of the body. Experimental evidence shows that the duration of wind-up in the CNS response long outlasts that of the provocative stimulus, although the exact correlation is still a matter of debate (25–27). The process of wind-up is not prevented by general anesthesia but is modified by opioid administration in experimental animal paradigms (28). The primary excitatory neurotransmitters are glutamate and aspartate. The intensity, consistency, or both of the noxious input recruits N-methyl-d-aspartate (NMDA) receptor activation among other receptors (AMPA, ACPD). Knowing this about the neuropharmacology of the spinal cord has led to research aiming at modifying or blocking NMDA receptors to effect pain control and to the concept of preemptive analgesia. Most research efforts have devoted attention to the blockade of NMDA receptors with ketamine. A nice review of the evolution of the change of our use of this drug is provided by Kohrs and Durieu- (29). Less postoperative pain was documented when epidural ketamine was administered by Choe et al. (30) in patients having upper abdominal surgery, by Wong et al. (31) in patients undergoing total knee replacement, and by Chia et al. (32) in patients using patient-controlled epidural analgesia (PCEA) after major intrathoracic or upper abdominal surgery, whereas Kucuk et al. (33) did not identify a preemptive analgesic effect in patients after abdominal surgery. More recent research has pursued the use of dextromethorphan, another NMDA receptor blocker, for its preemptive effect, with mixed results reported thus far (Kawamata et al. (34), positive; Grace et al. (35), negative). Given the redundancy in the neurotransmitter receptor systems in the CNS, it is little surprise that blocking one component of the system in a variety of clinical situations does not result in uniform effects. The entire concept of preemptive analgesia fostered by the above realities is predicated on treating the pain before it is provoked by anticipating the mechanism of its causation and preventing the peripheral and central sensitization with carefully chosen therapy (36–38). Though the concept of preemptive analgesia is very appealing, and electrophysiologic and whole animal studies support the use of preemptive techniques to prevent peripheral and central sensitization, clinical benefit in humans has been only variably achieved thus far. Kissin (39) eruditely notes that proving preemptive analgesia can be expected to be difficult because of the necessity of meeting a number of criteria: a preestablished, universal definition of what preemptive analgesia is; assurance of complete afferent input blockade; partial preemptive effects in control groups; standardizing the intensity of the noxious input; and agreeing on appropriate outcome measures. Numerous studies have proposed preemptive effects of epidural analgesia (31,32,36,37,40,41).Gottschalk et al. (42) have most recently continued the notion of preemptive analgesia in their study of patients who had undergone radical prostatectomy surgery. 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This must result in a significant of health care is to and of the most in medical in recent has been that of the opioid receptors The that the primary of opioid is in the substantia of the dorsal horn of the spinal cord led to the clinical of and epidural for pain management to neurotransmitter release and to dorsal horn central sensitization is that those of preventing wind-up are are of administration for the IV are are provided by using patient-controlled analgesia in the successful use of this include the patient to with IV before the that the patient control of the using appropriate and and using a et al. showed that patients having more pain before surgery used more in the after surgery. 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