DESPITE recent advances in our understanding of the physiology of acute pain, the development of new opioid and nonopioid analgesics and novel methods of drug delivery, and more widespread use of pain-reducing minimally invasive surgical techniques, pain after surgical procedures remains a challenge for many practitioners.1Not surprisingly, recent surveys in the United States and Europe have emphasized the insufficient quality of postoperative pain management and the need for further improvements.2,3The increasing implementation of standardized pain evaluation and treatment protocols, and the use of multimodal analgesic techniques, are hopeful signs that improvements in pain management are likely to continue in the years ahead. What then are the major unresolved issues in the management of acute postoperative pain, and how should surgical patients be managed based on the available evidence from the peer-reviewed medical literature?
The concept of multimodal “opioid-sparing” analgesic techniques (so-called balanced analgesia) was introduced more than 15 yr ago,4with the aim of improving analgesia by combining analgesics with additive or synergistic effects. Theoretically, the use of a combination of analgesics from different pharmacologic drug classes for managing perioperative pain should improve the safety and efficacy of pain therapy due to the differing mechanisms of action and the side-effect profiles of the individual drugs. Although only a limited number of well-conducted, prospective randomized clinical trials have demonstrated improved clinical outcomes with respect to analgesia and opioid-related side effects with multimodal (vs . single) therapy,5,6meta-analyses of single-modality, nonopioid analgesics have demonstrated clinically significant reductions (20–40%) in postoperative nausea and vomiting and sedation.7However, beneficial effects of multimodal therapy with respect to other common side effects (e.g. , bowel and bladder dysfunction and ventilatory depression) and improvement in dynamic analgesia have been less consistently reported. Clearly, a need exists for large-scale clinical investigations of drugs (and class) specific side effects when analgesics are administered as part of combination therapies in the postoperative period. Although opioid-related side effects (e.g. , postoperative nausea and vomiting, urinary retention, ileus, constipation, sedation, and ventilatory depression) have been extensively described in the literature, nonopioid analgesics such as acetaminophen, classic and cyclooxygenase selective nonsteroidal antiinflammatory drugs (NSAIDs), ketamine, and gabapentanoids also have their own unique side-effect profiles (e.g. , hepato- and renal toxicity, coagulation, confusion, sedation, and dizziness), which may be exacerbated when they are administered as a part of a multimodal regimen after surgery. The benefit–risk ratio for analgesic drug combinations is, therefore, largely dependent on the type of surgery (i.e. , risk of rebleeding after tonsillectomy, renal failure after vascular surgery, and ileus after colon surgery).
Despite available evidence showing the benefits of multimodal analgesic techniques,4–6major surveys have reported that these techniques are underused in clinical practice.2,3What is needed to improve the perioperative pain management is to first implement the existing evidence-based recommendations regarding the use of individual nonopioid analgesics (namely, NSAIDs, cyclooxygenase-2 inhibitors, acetaminophen, gabapentanoids, ketamine, and local and regional anesthetic techniques) when supplemented by opioid analgesics on an as needed basis.8Second, practicing clinicians need to use rational analgesic drug combinations to achieve reductions in opioid-related side effects, leading to improved early outcomes and more rapid resumption of normal activities of daily living (e.g. , mobilization, recovery of bowel function, and return to work).6In this context, clinicians should be aware that previous guidelines for perioperative pain management failed to consider procedure-specific issues. For example, different types of surgical procedures (e.g. , orthopedic, abdominal, thoracic, and laparoscopic) have their own unique postoperative pain characteristics and clinical consequences (e.g. , immobilization, paralytic ileus, urinary retention, and impairment of pulmonary function). Therefore, a procedure-specific approach is strongly recommended. As an example, continuous epidural analgesia is beneficial in reducing dynamic pain, ileus, and postoperative nausea and vomiting compared with other analgesic techniques after major abdominal procedures.‡However, epidural analgesia is clearly not appropriate for many other types of abdominal surgery procedures (e.g. , open hysterectomy, laparoscopic colon resection, adrenalectomy, or nephrectomy). In addition, analgesic drugs or techniques may have different side-effect profiles depending on the type of surgical procedure (e.g. , bleeding after ears-nose-throat, hip and plastic surgery with nonselective NSAIDs [but not with cyclooxygenase-2 inhibitors], ventilatory depression after thoracotomy procedures with opioid-based techniques [but not with regional analgesics techniques], and postoperative ileus after colon resection with opioid analgesics). Therefore, the practicing clinician needs to be aware of the available procedure-specific evidence for optimizing multimodal pain management (table 1). Recently, updated evidence has been made available for several common orthopedic, abdominal, and thoracic procedures on the PROSPECT Web site‡and published in recent review articles on this topic.9,10
Perioperative Analgesia and Postoperative Outcomes
Most clinicians inherently expect that better postoperative pain relief will lead to improved clinical outcomes such as reduced organ dysfunction, decreased morbidity, and shorter hospital stay. However, a recent review of the published literature reported a disappointing lack of major benefits with respect to clinically meaningful outcome measures.11The common explanation for this failure to demonstrate the expected improvement in clinical outcome is that many analgesic outcome studies have had major deficiencies in protocol design because they focused on surrogate endpoints (e.g. , changes in pain scores at rest, quantitative opioid sparing, and length of the recovery room and/or hospital stay) rather than more clinically meaningful endpoints (e.g. , resumption of dietary intake, recovery of bowel and bladder function, and resumption of normal physical activities).12Furthermore, by incorporating updated evidence-based care principles, recent evidence suggests that providing effective analgesia in the early postoperative period may lead to clinically important benefits with respect to long-term recovery (e.g. , less chronic pain).13
In future evaluations of perioperative analgesic regimens, the assessments should therefore be performed within the context of modern fast-track surgery rehabilitation paradigms where the benefits of an optimal procedure-specific analgesic regimen has been integrated into an enhanced recovery care program with early oral feeding, mobilization, and adjustments in other principles of surgical care (e.g. , drains, catheters, tubes, and monitoring) consistent with the existing evidence in the peer-reviewed literature.14,15In this context, the anesthesiologist(s) and acute pain management team responsible for the patient's analgesic therapy can play an important role in improving the patient's surgical outcomes.15The specific issue regarding the role of acute pain management in influencing persistent (chronic) postsurgical pain remains highly controversial despite the emerging relationship between early and persistent postoperative pain.13,16Unfortunately, most clinical trials have used only multimodal analgesia for a short period of time after surgery. Future studies should therefore include a highly effective multimodal treatment for as long as the surgical stimulus (inflammatory response) continues after the operation. The transition of acute postoperative pain into a chronic pain state is a complex process that involves psychologic, physiologic, and social–environmental factors.17
The potential role of more prolonged multimodal opioid-sparing analgesia in improving long-term functional outcomes after major surgery is of major importance to patients and healthcare providers.18Recent surveys would suggest that subacute pain lasting several weeks postoperatively represents another often neglected area of clinical investigation, with relatively sparse scientific data.19In addition, recent developments in fast-tracking methodology have emphasized the need for improved analgesia to enhance recovery and reduce the length of the hospital stay, medical and surgical morbidity, and the period of postdischarge convalescence.14,15
The ability to identify patients with both high and low risk of developing clinically significant pain after surgery will enhance both the efficacy and safety of analgesic therapies. A recent study20reported that the most important predictors of postoperative pain after ambulatory surgery were (1) the presence of preoperative pain, (2) patient and physician expectations regarding the level of pain after the operation, (3) patient fear regarding the short-term outcome of their surgery, and (4) the age of the patient. Interestingly, hypervigilance (i.e. , a strong attention bias toward pain) proved to be a powerful predictor of acute postoperative pain.21In patients undergoing painful foot and ankle surgery,22preoperative pain and anticipated postoperative pain were independently predictive of their level of pain during the first 72 h after surgery. In patients undergoing major abdominal surgery,23American Society of Anesthesiologists physical status, age, acute preoperative or chronic pain, and high trait anxiety levels and depressive mood states were factors associated with an increased risk of developing moderate-to-severe pain after surgery.
The Way Forward
Given the large disparity between the amount of pathophysiologic data on the mechanisms responsible for acute pain and the subsequent translation of this scientific evidence into clinical practice,2,3the most immediate way forward is to begin by routinely implementing procedure-specific, evidenced-based pain management protocols in the perioperative period (table 1).14,18However, these procedure-specific analgesic care maps need to be combined with a fast-track recovery strategy14,15to obtain the desired improvements in patient outcomes. This approach represents a logical extension of the traditional acute pain service.24Although the existing evidence in the literature fails to support the concept that improvement in pain management automatically leads to enhanced recovery and reduced morbidity,11it is clear that improvements in patient satisfaction can be consistently achieved.6,24
In this context, integrated collaborations are necessary between the departments of anesthesiology and surgery, acute pain management teams, and the postsurgical nursing staff to achieve the full benefits of improved analgesic regimens.14,15Thus, as suggested in the recent national surveys examining acute pain management practices,2,3implementation of evidenced-based guidelines for pain management alone is not sufficient to achieve the desired improvements in patient outcomes. Therefore, a clear need exists for more effective communication among leaders from the different medical and nursing disciplines, which participate in the perioperative care process, and hospital administrators, insurance companies, and governmental and regulatory bodies. Another approach would be to increase public awareness of the existing possibilities for improved pain management and educating surgical patients and family members regarding steps that they can take to improve the quality of perioperative analgesia and facilitate the recovery process.
Therefore, the most immediate solutions to improving the quality of pain management may be at an organizational level. Further clinical research is clearly needed to better delineate the essential components of procedure-specific, multimodal, nonopioid analgesic regimens.9,10In the future, simple and more rational approaches directed toward the periphery (i.e. , the surgical wound and surrounding tissues) may offer the greatest promise for advancing acute pain management.25The potential for clinical improvement in pain-related outcomes by a peripheral approach is exciting because it is inherently simple, and targets pain at the site of origin before centrally mediated changes can occur in the spinal cord or the cerebral cortex. Clinical examples include use of catheter delivery systems of local anesthetics at the incision site for improving pain control and recovery after major cardiac surgery.26In the future, local application of long-acting local analgesic formulations (e.g. , depo-bupivacaine and extended-release [saber] bupivacaine), and topical capsaicin,27may eventually obviate the need for these cumbersome and expensive catheter delivery systems.
Novel receptor populations on sensory nerve endings (e.g. , transient receptor potential vanilloid 1 binding sites) may prove to be useful targets for developing new analgesic adjuvants to add to the current armamentarium of opioid and nonopioid analgesic compounds. Capsaicin, the active ingredient in chili peppers, produces prolonged inhibition of C-fibers by interacting with transient receptor potential vanilloid 1 binding sites and has recently been reported to produce sustained pain relief lasting 3–4 days after surgery.27Another potential new class of analgesic drugs are the selective cannabinoid receptor-1 agonists. Preliminary clinical data suggest that even “old drugs” (e.g. , glucocorticoid steroids [methylpredinsolone, dexamethasone]) may provide sustained analgesic effects without clinically significant side effects in the perioperative period.
Another very important area for future clinical research includes the need to develop a more in-depth understanding of the basis of the large interindividual variability in the pain response to similar noxious surgical stimuli.28,29In the future, an improved and individualized approach to acute pain management may be possible if we can determine a patient's pain threshold before the operation.28In the low pain responders (i.e. , high pain threshold), less aggressive and simpler approaches could be implemented postoperatively, whereas more sophisticated invasive pain management techniques would be reserved for the high-pain responders. Overly aggressive use of opioid analgesics (e.g. , basal infusions) in low pain responders has contributed to significant morbidity and even mortalities after surgery.30Previous studies using preoperative nociceptive testing with thermal (heat) or electrical stimuli and psychosocial testing procedures have suggested practical approaches to evaluating high versus low pain responders.28,29In the future, genetic research may also increase the ability of clinicians to identify high and low pain responders before surgery or specific genotypes that may influence the pharmacokinetics of analgesics.31
Pharmacogenetics is an intriguing area for future investigations aimed at improving pain management. For example, Janicki et al. 32reported an association between functional polymorphism of the μ-opioid receptor gene in patients with acute and chronic pain. Although the presence of the minor allele did not affect opioid use in the management of acute pain, the gene was less common in chronic pain patients with high opioid analgesic requirements. Chou et al. 33have reported an association between μ-opioid receptor gene polymorphism and the variation in the morphine requirement after lower abdominal surgery. Therefore, genetic variation in the μ-opioid receptor may contribute to interindividual differences in postoperative pain and the need for opioid analgesic medication. Recently, Tan et al. 34reported that ethnicity and μ-opioid receptor genotype were independent and significant contributors to individual variations in pain perception and postoperative opioid usage. Genetically mediated interindividual variation may also influence the analgesic response of patients to NSAIDs and cyclooxygenase-2 inhibitor drugs.35The ability to identify these genetic polymorphisms may eventually prove to be useful to clinicians in optimizing the use of both opioid and nonopioid analgesic medications.
Other potentially important areas for future research in acute pain management relate to the influence of metabolic factors, aging and sex (gender) on patient responses to analgesic medications. Although the proportion of population in the elderly age category continues to increase at a rapid rate, surprisingly few clinical studies have carefully examined the effect of aging on the response to opioid and nonopioid analgesic medications in the postoperative period. Similarly, few well-controlled studies have examined the role of gender in the management of acute postoperative pain, because it is difficult to conduct comparative studies because of the potential confounding effect of different types of surgical procedures performed in men and women.36
Finally, the concept of “preemptive analgesia” (as distinct from “preventive analgesia”) needs to be carefully reexamined because data from randomized trials on the timing issue (i.e. , initiating analgesia before vs. after the surgical stimulus) have produced confusing findings.37,38Studies that compared the same dose of an analgesic given before versus after the surgical stimuli have failed to document advantages of the so-called preemptive approach.39Although preoperative administration is clearly better than giving a placebo, few well-controlled studies have actually compared perioperative versus postoperative administration of analgesic drugs. Sun et al. 40recently demonstrated that perioperative administration of the NSAID cyclooxygenase-2 inhibitor celecoxib was no better than simply administering the drug after surgery. It is clearly important to achieve effective analgesia in the early postoperative period and then ensure that an effective “preventative” analgesic regimen is continued into the postdischarge period for as long as the nociceptive input from the wound persists after surgery.4,12,17However, additional information is clearly needed regarding the optimal duration of the postdischarge treatment on a procedure-specific basis, and these recommendations should be modified based on individual patient pain response factors.
Despite the tremendous progress that has been made in our understanding of the pathophysiologic basis of acute pain, there remains a need for clinicians to implement evidence-based procedure-specific multimodal analgesic protocols, which are modified to meet the needs of individual patients to enhance the quality of postoperative pain management. Importantly, there is a critical need for collaborations between the various heathcare providers involved in perioperative patient care (e.g. , anesthesiologists, surgeons, nurses, and physiotherapists) to integrate improved perioperative pain management with the recently described fast-track recovery paradigms.14,15This type of combined approach is well documented to improve the quality of the recovery process and reduce the hospital stay and postoperative morbidity, leading to a shorter period of convalescence after surgery. Rather than simply performing more meta-analysis and systematic reviews of the pain management literature,12clinical investigators need to return to the hard work of performing prospective, randomized clinical trials on a procedure-specific basis, evaluating the use of different analgesic combinations as part of multimodal analgesic treatment regimens in the postoperative period.