Perioperative management of chronic pain patients with opioid dependency.
Introduction
Surgical patients suffering from chronic pain and who receive chronic opioid treatment present a complex challenge in the perioperative period. They may experience more severe acute pain and more opioid related complications than opioid naive controls.
The number of patients treated chronically with opioids has increased steadily over the past decade; currently about 10% of all chronic-pain patients are treated with opioids. As these patients are no longer confined to terminally ill cancer patients, growing numbers of these patients are facing surgical interventions. (There are no published data reporting the percentage of chronic pain patients being treated with opioids that undergo surgical intervention. More studies are required to estimate this.) Accordingly, most anesthesiologists can expect to be confronted with opioid-dependent patients in routine anesthesia practice and should acquire specific knowledge and skills to effectively manage the perioperative and acute pain-management issues that arise.
In this article, we discuss the perioperative anesthesia and pain management of patients with chronic pain receiving chronic opioid administration. The chronic abuse of illicit narcotics is an allied (and occasionally overlapping) example of chronic opioid dependency. The irregularity of administration, the occasional inconsistency of purity of opioid preparation and most importantly the lack of an underlying chronic pain disorder, however, make this clinical scenario different from the chronic-pain patient receiving chronic opioid administration and will not be discussed in depth.
Chronic pain patients
The International Association for the Study of Pain defines chronic pain as: ‘pain without apparent biological value that has persisted beyond the normal tissue healing time usually taken to be 3 months’. Chronic pain of moderate to severe intensity occurs in 19 to 37% of the population. Prevalence rates for chronic pain are higher in women and older age groups. Additionally, chronic pain may be a symptom of underlying disease, which may require surgical intervention. Chronic pain, however, should not be regarded only as a symptom, but be recognized as a syndrome of disease state.
Chronic pain patients present a unique challenge to the anesthesiologist. They are characterized by depression, anxiety, lack of energy and appetite. Patients with chronic pain are frequently on complex medication regimens, including multiple analgesic drugs [opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), cyclooxygenase-2 inhibitors (COXIBs)] in addition to antidepressants, anticonvulsants, muscle relaxants, [alpha]-adrenergic agonists, and benzodiazepines. All of these medications may have significant interactions with drugs administered during surgery and anesthesia and should be taken into consideration. An accurate drug history may be difficult to obtain.
Opioid dependency
Until recently, opioids were used only for the relief of acute pain and for the chronic treatment of cancer pain in terminally ill patients. With the extension of opioid treatment to nonterminally ill chronic patients, the number of patients prescribed with chronic opioids has increased dramatically. In an Australian study of patients with chronic pain who were referred to pain centers, 83% of patients had already been prescribed with opioids by their general practitioner at the time of their referral. In the United States, the annual sale of opioids to ambulatory patients increased by approximately 130% from 1999 to 2003, with a two-fold increase relative to the same period in the previous decade. Additional factors contributing to this growing trend in opioid therapy for chronic pain include physician education, leading to an increased understanding and acceptance of opioids by patients and physicians alike and an awareness of the problem of under medication and inadequate pain control. Several studies have shown that chemically addicted patients have lower pain thresholds and higher pain sensitivity with consequent inadequate acute pain control.
Opioid-dependent patients exhibit increased sensitivity during cold pressor and thermal testing. It has been hypothesized that constant opioid receptor activity produces hyperalgesia, which renders these patients less capable to cope with acute pain.
The anesthesiologist confronted with patients receiving chronic opioid therapy should be able to anticipate, diagnose, and treat the different potential scenarios of breakthrough pain, overdose, physical dependence, tolerance, withdrawal, and abuse.
Patients treated in drug addiction programs should be able to provide accurate information as to the daily opioid consumption. Many of the opioid abusers have cross-addiction to nicotine, cocaine, benzodiazepine, marijuana, and alcohol and may have communicable bloodborne infectious diseases that should be brought to the notice of all members of the medical team.
The solution
Perioperative management of the chronic pain patients with opioid dependency.
Preoperative management
The opioid-dependent patient should receive their regular dose of opioid on the morning of surgery. Patients who have not received their baseline opioids may be treated with an equivalent loading dose of opioid administered preoperatively as an oral elixir or intravenously either at the time of anesthetic induction or during the operative procedure.
Some authors have suggested that patients receiving chronic opioid administration are at increased risk of acid aspiration caused by the delayed gastric emptying and decreased bowel motility known to be associated with opioid administration. While there are no studies that have assessed the risk of aspiration in the opioid-maintained chronic pain patient, it would seem prudent to consider them at higher risk for gastric aspiration.
A preoperative cardiogram has been recommended for patients receiving oral methadone in doses greater than 200 mg/day especially in medical conditions that may predispose to QT interval prolongation. This recommendation is based on previous reports that have revealed that methadone administered in high doses (more than 200 mg/day) may be associated with ventricular arrhythmias.
Systemic nonopioid analgesia
Nonopioid analgesic drugs may be used to provide multimodal analgesia. Agents that induce analgesia by a nonopioid mechanism have been recognized for many years, but have gained increased popularity. While most of these drugs have not been evaluated specifically in opioid-dependent patients, multiple studies have documented their opioid-sparing effects in postoperative pain management.
Perioperative administration of NSAIDs is recommended for all patients unless specifically contraindicated. Recent developments of new parenteral forms of paracetamol and NSAIDs make this form of treatment more practical in the perioperative period.
Ketamine, a phencyclidine derivative, is a potent nonopioid N-methyl--aspartate (NMDA) receptor antagonist and has been used as an effective analgesic in patients with high tolerance to opioids. Its desired analgesic properties may be counterbalanced by its hallucinogenic and other psychomimetic effects, but these are minimal when administered in low doses.
Carr et al. recently examined the safety and efficacy of intranasal ketamine, for the treatment of breakthrough pain (BTP) in opioid-dependent patients with chronic pain who were unresponsive to opioid rescue. This randomized, double-blind, placebo-controlled, crossover study demonstrated significant analgesic efficacy of intranasal ketamine when compared with intranasal placebo for BTP in these patients. The use of ketamine in the perioperative management of opioid-dependent patients has not been well defined but initial data seems to be encouraging.
Clonidine and dexmedetomidine elicit analgesia by agonism of the [alpha]-adrenergic receptor. They are available in parenteral and other forms of administration and are associated with a reduction in postoperative opioid use and improved analgesia.
Gabapentin and pregabalin are sodium-channel blockers, anticonvulsant agents that have been shown to be effective in the treatment of chronic neuropathic pain. Recent studies demonstrated that premedication with gabapentin reduced postoperative opioid analgesic requirements without increasing side effects.
Systemic opioid analgesia
The opioid analgesia may be administrated before and/or during the operation and in the postoperative period.
Preoperative
Chronic pain patients most commonly use oral opioids. Following surgery patients will occasionally be required to alter the opioid or change the route of administration. If an oral opioid used preoperatively is changed to be administered intravenously the dose of opioid can usually be reduced. This finding is more prominent with opioids that have lower bioavailability with oral administration such as morphine as opposed to methadone and oxycontin. Anesthesiologists should be able to transfer from one opioid to the other and from one route of administration to another, using equianalgesic doses of opioids.
Oral opioids are available in both sustained-release and immediate-release forms and they can be administered by a number of routes, including oral, parenteral, rectal, sublingual, transdermal, and transmucosal. Morphine and other opioids with short half-lives require frequent administration to maintain analgesia. Immediate-release morphine, oxycontin, and similar products provide about 4 h of pain relief and need to be dosed accordingly. Controlled-release formulations such as morphine, fentanyl patches or oxycontin provide alternatives to frequent opioid administration. Medications with longer half-lives, for example methadone and some forms of slow release morphine, provide analgesia for 12 to 24 h.
Patients treated with a transdermal fentanyl patch should usually be advised to continue this treatment as fentanyl patches administer controlled amounts of drug and provide background analgesia. In major surgery, however, or in cases in which major alterations in patient body temperature or intravascular fluid volume are predicted, the controlled release of fentanyl may be unpredictable and the removal of the transdermal patch is usually advised. In these cases, an appropriate equianalgesic dose of a systemic opioid should be administered. Hypothermia has been shown in volunteers to decrease fentanyl absorption from the patch, while the application of a local heat source over the area of the patch has been shown to increase fentanyl absorption [44]. Potential changes in the rates of absorption of fentanyl from patches should be remembered and the application of a warming blanket directly over the patch should be avoided.
Intraoperative and postoperative
Intraoperative and postoperative opioid requirements are difficult to determine in any patient caused by variability among patients. Furthermore, the patient's pain stimulus may be decreased after surgery, leading to a relative opioid overdose and subsequent respiratory depression. Some authors suggest that after any surgical procedure that may be associated with substantial pain relief, the dose of opioids administered should be reduced to 25–50% of the preoperative amount.
Methods that have been described to determine an individual's response to opioid include the use of spontaneous ventilation, as an endpoint for opioid loading during anesthesia, and the use of a preoperative fentanyl challenge test.
The maintenance of spontaneous ventilation during general anesthesia allows a simple and reliable endpoint to gauge the individual response to systemic opioid administration. Ideally, muscle relaxation should be avoided, or paralysis reversed early enough before the end of surgery to enable the use of this technique. Opioids may be titrated to any desired respiratory rate, although it is recommended to maintain the respiratory rate above 12 to 14 breaths/min.
Davis et al. recently reported using a preoperative fentanyl challenge as a tool to estimate postoperative opioid requirements in opioid consumers. In this study, 20 surgical patients receiving chronic opioid administration received a fentanyl infusion of 2 µg/kg/min preoperatively and the total accumulated dose until respiratory depression (respiratory rate less than 5 breaths/min) was measured. Pharmacokinetic simulations were used to estimate the effect site concentration at the time of respiratory depression. As existing data suggest that analgesia occurs at a threshold that is approximately 30% of the concentration required to produce respiratory depression, on the basis of the preoperative fentanyl challenge test, the patient-controlled analgesia (PCA) protocol was designed to administer 30% of the estimated concentration. This group reported that the postoperative PCA settings that were predicted by the preoperative fentanyl challenge test did not need significant adjustments and met analgesic requirements. While the practicality of using the fentanyl challenge in a clinical setting may be questioned, the use of a simple preoperative assay to predict postoperative analgesic needs in this patient population is compelling.
Rehabilitation–detoxification should not be considered in the immediate perioperative period. In some situations, a gradual reduction in opioid consumption should be considered following surgery, such as when the ‘pain generator’ has been surgically excised, but not in the immediate postoperative period.
Rapp et al. reported that chronic opioid users typically had higher pain scores following surgery yet had a more frequent incidence of sedation compared with opioid naïve patients. Although preoperative assessment of opioid equianalgesic equivalence should be used as a primary guide, these comparisons are poor predictors of postoperative analgesic requirements. Then, when using systemic opioids for the postoperative pain management of opioid-dependent patients, frequent and repeated clinical monitoring is essential to deliver the correct dose of drug. No substitute exists for vigilant clinical assessment, including respiratory rate, heart rate (and oxygen saturation), sedation, degree of pupil dilatation, and the Visual Analog Scale pain score.
Intravenous PCA provides effective postsurgical analgesia and allows adjustment of individual opioid requirement. Although the practice of allowing opioid-dependent patients, and even substance abusers, to use intravenous PCA to control postoperative pain was initially considered highly controversial, it is now accepted practice.
Patients who experience inadequate postoperative analgesia despite the administration of high doses of opioids should be transferred to an alternative opioid in order to activate different subtypes of the mu opioid receptor to which morphine tolerance has not developed. Oral or intravenous methadone has been advocated in opioid-dependent patients caused by its unique NMDA receptor antagonistic and [alpha]-adrenergic agonistic properties.
Regional analgesia
Regional analgesia offers an additional route for the administration of anesthesia and analgesia, either opioid or nonopioid mediated.
Although there are few data that formally favors regional anesthesia over general anesthesia for this patient population, clinical judgment and expert opinion usually recommend regional anesthesia and analgesia whenever possible. The anesthesiologist caring for these challenging patients must be skilled in various regional analgesia procedures that can minimize pain perception and be a substitute for systemic opioids. The different peripheral and neuraxial regional analgesia techniques have been discussed in detail elsewhere.
Neuraxial anesthesia and analgesia
Neuraxial administration of opioids provides more effective postoperative analgesia and may produce fewer side effects than systemic opioids. Even so, the neuraxial dose of the opioid should be adjusted as systemic and epidural opioid requirements increase in the same range in patients with prior opioid exposure.
A combination of low-dose epidural opioid with a local anesthetic is the standard of care in many institutions for improved postoperative pain management. The addition of a local anesthetic to the opioid is particularly important in the opioid-dependent patient, as neuraxial opioid analgesia may be decreased by down-regulation of spinal opiate receptors, while the local anesthetic activity is not affected by the opioid dependence.
Irrespective of the opioid selected and the local anesthetic concentration, the epidural opioid dose should equal the preoperative opioid dose unless baseline opioids are administered systemically.
Epidural and intrathecal opioid infusions delivered by internally implanted devices are usually maintained throughout the perioperative period and are used to maintain baseline pain control.
Peripheral blocks
New developments (such as stimulating catheters, ultrasound guided blocks, better designed needles and portable delivery systems) for use with continuous peripheral blocks have made this technique more practical for postoperative analgesia. Recent reports on continuous peripheral nerve blocks have demonstrated well tolerated and effective pain relief, even in ambulatory patients treated at home. Patients treated with peripheral blocks administrating local anesthetics should receive their daily maintenance dose of opioids as a base line and may substitute breakthrough pain with additional opioids.
Conclusion
Whenever possible, anesthesiologists should employ multimodal pain management therapy. Unless contraindicated, all patients should receive an around-the-clock regimen of NSAIDs, COXIBs, or acetaminophen. In addition, regional blockade with local anesthetics should be considered. Dosing regimens should be administered to optimize efficacy while minimizing the risk of adverse events. The choice of medication, dose, route, and duration of therapy should be individualized.
Anesthesiologists providing perioperative analgesia services should do so within the framework of an Acute Pain Service, and participate in developing standardized institutional policies and procedures. An integrated approach to perioperative pain management that minimizes analgesic gaps includes ordering, administering, and transitioning therapies, and transferring responsibility for perioperative pain therapy, as well as outcomes assessment and continuous quality improvement.
Acute pain control is considered nowadays a humanitarian issue whereas not providing effective relief of acute pain may be considered a breach of fundamental human rights. Chronic pain patients who are opioid-dependent are more likely to complain of severe pain postoperatively, but are also vulnerable to complications of opioid overdose. Individualized pain management, and vigilant clinical monitoring are the keys to successful postoperative pain management in these challenging patients.
Surgical patients suffering from chronic pain and who receive chronic opioid treatment present a complex challenge in the perioperative period. They may experience more severe acute pain and more opioid related complications than opioid naive controls.
The number of patients treated chronically with opioids has increased steadily over the past decade; currently about 10% of all chronic-pain patients are treated with opioids. As these patients are no longer confined to terminally ill cancer patients, growing numbers of these patients are facing surgical interventions. (There are no published data reporting the percentage of chronic pain patients being treated with opioids that undergo surgical intervention. More studies are required to estimate this.) Accordingly, most anesthesiologists can expect to be confronted with opioid-dependent patients in routine anesthesia practice and should acquire specific knowledge and skills to effectively manage the perioperative and acute pain-management issues that arise.
In this article, we discuss the perioperative anesthesia and pain management of patients with chronic pain receiving chronic opioid administration. The chronic abuse of illicit narcotics is an allied (and occasionally overlapping) example of chronic opioid dependency. The irregularity of administration, the occasional inconsistency of purity of opioid preparation and most importantly the lack of an underlying chronic pain disorder, however, make this clinical scenario different from the chronic-pain patient receiving chronic opioid administration and will not be discussed in depth.
Chronic pain patients
The International Association for the Study of Pain defines chronic pain as: ‘pain without apparent biological value that has persisted beyond the normal tissue healing time usually taken to be 3 months’. Chronic pain of moderate to severe intensity occurs in 19 to 37% of the population. Prevalence rates for chronic pain are higher in women and older age groups. Additionally, chronic pain may be a symptom of underlying disease, which may require surgical intervention. Chronic pain, however, should not be regarded only as a symptom, but be recognized as a syndrome of disease state.
Chronic pain patients present a unique challenge to the anesthesiologist. They are characterized by depression, anxiety, lack of energy and appetite. Patients with chronic pain are frequently on complex medication regimens, including multiple analgesic drugs [opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), cyclooxygenase-2 inhibitors (COXIBs)] in addition to antidepressants, anticonvulsants, muscle relaxants, [alpha]-adrenergic agonists, and benzodiazepines. All of these medications may have significant interactions with drugs administered during surgery and anesthesia and should be taken into consideration. An accurate drug history may be difficult to obtain.
Opioid dependency
Until recently, opioids were used only for the relief of acute pain and for the chronic treatment of cancer pain in terminally ill patients. With the extension of opioid treatment to nonterminally ill chronic patients, the number of patients prescribed with chronic opioids has increased dramatically. In an Australian study of patients with chronic pain who were referred to pain centers, 83% of patients had already been prescribed with opioids by their general practitioner at the time of their referral. In the United States, the annual sale of opioids to ambulatory patients increased by approximately 130% from 1999 to 2003, with a two-fold increase relative to the same period in the previous decade. Additional factors contributing to this growing trend in opioid therapy for chronic pain include physician education, leading to an increased understanding and acceptance of opioids by patients and physicians alike and an awareness of the problem of under medication and inadequate pain control. Several studies have shown that chemically addicted patients have lower pain thresholds and higher pain sensitivity with consequent inadequate acute pain control.
Opioid-dependent patients exhibit increased sensitivity during cold pressor and thermal testing. It has been hypothesized that constant opioid receptor activity produces hyperalgesia, which renders these patients less capable to cope with acute pain.
The anesthesiologist confronted with patients receiving chronic opioid therapy should be able to anticipate, diagnose, and treat the different potential scenarios of breakthrough pain, overdose, physical dependence, tolerance, withdrawal, and abuse.
The most important step is identifying the chronically opioid-dependent patient in the first place. Chronic pain patients tend to underestimate and underreport their medication use. This tendency is more frequent for opioid analgesics than for other medications. Not identifying the fact that the patient is an opioid consumer in the preoperative period may induce opioid withdrawal symptoms and uncontrolled pain intraoperatively and postoperatively. While self-reporting and a focused history may be the best means to determine the dose and duration of opioid exposure for chronic pain patients, self-reporting is much less reliable in cases of substance abuse, addicts may either exaggerate, downplay or deny the dose, frequency, purity, and route of opioid administration.
Patients treated in drug addiction programs should be able to provide accurate information as to the daily opioid consumption. Many of the opioid abusers have cross-addiction to nicotine, cocaine, benzodiazepine, marijuana, and alcohol and may have communicable bloodborne infectious diseases that should be brought to the notice of all members of the medical team.
The solution
Perioperative management of the chronic pain patients with opioid dependency.
Preoperative management
The opioid-dependent patient should receive their regular dose of opioid on the morning of surgery. Patients who have not received their baseline opioids may be treated with an equivalent loading dose of opioid administered preoperatively as an oral elixir or intravenously either at the time of anesthetic induction or during the operative procedure.
Preoperative evaluation of the chronic pain patient is necessary to identify risk factors, make anesthetic choices, and plan perioperative analgesia management. This time should also be used for patient education.
Some authors have suggested that patients receiving chronic opioid administration are at increased risk of acid aspiration caused by the delayed gastric emptying and decreased bowel motility known to be associated with opioid administration. While there are no studies that have assessed the risk of aspiration in the opioid-maintained chronic pain patient, it would seem prudent to consider them at higher risk for gastric aspiration.
A preoperative cardiogram has been recommended for patients receiving oral methadone in doses greater than 200 mg/day especially in medical conditions that may predispose to QT interval prolongation. This recommendation is based on previous reports that have revealed that methadone administered in high doses (more than 200 mg/day) may be associated with ventricular arrhythmias.
Systemic nonopioid analgesia
Nonopioid analgesic drugs may be used to provide multimodal analgesia. Agents that induce analgesia by a nonopioid mechanism have been recognized for many years, but have gained increased popularity. While most of these drugs have not been evaluated specifically in opioid-dependent patients, multiple studies have documented their opioid-sparing effects in postoperative pain management.
Perioperative administration of NSAIDs is recommended for all patients unless specifically contraindicated. Recent developments of new parenteral forms of paracetamol and NSAIDs make this form of treatment more practical in the perioperative period.
Ketamine, a phencyclidine derivative, is a potent nonopioid N-methyl--aspartate (NMDA) receptor antagonist and has been used as an effective analgesic in patients with high tolerance to opioids. Its desired analgesic properties may be counterbalanced by its hallucinogenic and other psychomimetic effects, but these are minimal when administered in low doses.
Carr et al. recently examined the safety and efficacy of intranasal ketamine, for the treatment of breakthrough pain (BTP) in opioid-dependent patients with chronic pain who were unresponsive to opioid rescue. This randomized, double-blind, placebo-controlled, crossover study demonstrated significant analgesic efficacy of intranasal ketamine when compared with intranasal placebo for BTP in these patients. The use of ketamine in the perioperative management of opioid-dependent patients has not been well defined but initial data seems to be encouraging.
Clonidine and dexmedetomidine elicit analgesia by agonism of the [alpha]-adrenergic receptor. They are available in parenteral and other forms of administration and are associated with a reduction in postoperative opioid use and improved analgesia.
Gabapentin and pregabalin are sodium-channel blockers, anticonvulsant agents that have been shown to be effective in the treatment of chronic neuropathic pain. Recent studies demonstrated that premedication with gabapentin reduced postoperative opioid analgesic requirements without increasing side effects.
Systemic opioid analgesia
The opioid analgesia may be administrated before and/or during the operation and in the postoperative period.
Preoperative
Chronic pain patients most commonly use oral opioids. Following surgery patients will occasionally be required to alter the opioid or change the route of administration. If an oral opioid used preoperatively is changed to be administered intravenously the dose of opioid can usually be reduced. This finding is more prominent with opioids that have lower bioavailability with oral administration such as morphine as opposed to methadone and oxycontin. Anesthesiologists should be able to transfer from one opioid to the other and from one route of administration to another, using equianalgesic doses of opioids.
Oral opioids are available in both sustained-release and immediate-release forms and they can be administered by a number of routes, including oral, parenteral, rectal, sublingual, transdermal, and transmucosal. Morphine and other opioids with short half-lives require frequent administration to maintain analgesia. Immediate-release morphine, oxycontin, and similar products provide about 4 h of pain relief and need to be dosed accordingly. Controlled-release formulations such as morphine, fentanyl patches or oxycontin provide alternatives to frequent opioid administration. Medications with longer half-lives, for example methadone and some forms of slow release morphine, provide analgesia for 12 to 24 h.
Patients treated with a transdermal fentanyl patch should usually be advised to continue this treatment as fentanyl patches administer controlled amounts of drug and provide background analgesia. In major surgery, however, or in cases in which major alterations in patient body temperature or intravascular fluid volume are predicted, the controlled release of fentanyl may be unpredictable and the removal of the transdermal patch is usually advised. In these cases, an appropriate equianalgesic dose of a systemic opioid should be administered. Hypothermia has been shown in volunteers to decrease fentanyl absorption from the patch, while the application of a local heat source over the area of the patch has been shown to increase fentanyl absorption [44]. Potential changes in the rates of absorption of fentanyl from patches should be remembered and the application of a warming blanket directly over the patch should be avoided.
Intraoperative and postoperative
Intraoperative and postoperative opioid requirements are difficult to determine in any patient caused by variability among patients. Furthermore, the patient's pain stimulus may be decreased after surgery, leading to a relative opioid overdose and subsequent respiratory depression. Some authors suggest that after any surgical procedure that may be associated with substantial pain relief, the dose of opioids administered should be reduced to 25–50% of the preoperative amount.
Methods that have been described to determine an individual's response to opioid include the use of spontaneous ventilation, as an endpoint for opioid loading during anesthesia, and the use of a preoperative fentanyl challenge test.
The maintenance of spontaneous ventilation during general anesthesia allows a simple and reliable endpoint to gauge the individual response to systemic opioid administration. Ideally, muscle relaxation should be avoided, or paralysis reversed early enough before the end of surgery to enable the use of this technique. Opioids may be titrated to any desired respiratory rate, although it is recommended to maintain the respiratory rate above 12 to 14 breaths/min.
Davis et al. recently reported using a preoperative fentanyl challenge as a tool to estimate postoperative opioid requirements in opioid consumers. In this study, 20 surgical patients receiving chronic opioid administration received a fentanyl infusion of 2 µg/kg/min preoperatively and the total accumulated dose until respiratory depression (respiratory rate less than 5 breaths/min) was measured. Pharmacokinetic simulations were used to estimate the effect site concentration at the time of respiratory depression. As existing data suggest that analgesia occurs at a threshold that is approximately 30% of the concentration required to produce respiratory depression, on the basis of the preoperative fentanyl challenge test, the patient-controlled analgesia (PCA) protocol was designed to administer 30% of the estimated concentration. This group reported that the postoperative PCA settings that were predicted by the preoperative fentanyl challenge test did not need significant adjustments and met analgesic requirements. While the practicality of using the fentanyl challenge in a clinical setting may be questioned, the use of a simple preoperative assay to predict postoperative analgesic needs in this patient population is compelling.
Rehabilitation–detoxification should not be considered in the immediate perioperative period. In some situations, a gradual reduction in opioid consumption should be considered following surgery, such as when the ‘pain generator’ has been surgically excised, but not in the immediate postoperative period.
Rapp et al. reported that chronic opioid users typically had higher pain scores following surgery yet had a more frequent incidence of sedation compared with opioid naïve patients. Although preoperative assessment of opioid equianalgesic equivalence should be used as a primary guide, these comparisons are poor predictors of postoperative analgesic requirements. Then, when using systemic opioids for the postoperative pain management of opioid-dependent patients, frequent and repeated clinical monitoring is essential to deliver the correct dose of drug. No substitute exists for vigilant clinical assessment, including respiratory rate, heart rate (and oxygen saturation), sedation, degree of pupil dilatation, and the Visual Analog Scale pain score.
Intravenous PCA provides effective postsurgical analgesia and allows adjustment of individual opioid requirement. Although the practice of allowing opioid-dependent patients, and even substance abusers, to use intravenous PCA to control postoperative pain was initially considered highly controversial, it is now accepted practice.
Patients who experience inadequate postoperative analgesia despite the administration of high doses of opioids should be transferred to an alternative opioid in order to activate different subtypes of the mu opioid receptor to which morphine tolerance has not developed. Oral or intravenous methadone has been advocated in opioid-dependent patients caused by its unique NMDA receptor antagonistic and [alpha]-adrenergic agonistic properties.
Regional analgesia
Regional analgesia offers an additional route for the administration of anesthesia and analgesia, either opioid or nonopioid mediated.
Although there are few data that formally favors regional anesthesia over general anesthesia for this patient population, clinical judgment and expert opinion usually recommend regional anesthesia and analgesia whenever possible. The anesthesiologist caring for these challenging patients must be skilled in various regional analgesia procedures that can minimize pain perception and be a substitute for systemic opioids. The different peripheral and neuraxial regional analgesia techniques have been discussed in detail elsewhere.
Neuraxial anesthesia and analgesia
Neuraxial administration of opioids provides more effective postoperative analgesia and may produce fewer side effects than systemic opioids. Even so, the neuraxial dose of the opioid should be adjusted as systemic and epidural opioid requirements increase in the same range in patients with prior opioid exposure.
A combination of low-dose epidural opioid with a local anesthetic is the standard of care in many institutions for improved postoperative pain management. The addition of a local anesthetic to the opioid is particularly important in the opioid-dependent patient, as neuraxial opioid analgesia may be decreased by down-regulation of spinal opiate receptors, while the local anesthetic activity is not affected by the opioid dependence.
Irrespective of the opioid selected and the local anesthetic concentration, the epidural opioid dose should equal the preoperative opioid dose unless baseline opioids are administered systemically.
Epidural and intrathecal opioid infusions delivered by internally implanted devices are usually maintained throughout the perioperative period and are used to maintain baseline pain control.
Peripheral blocks
New developments (such as stimulating catheters, ultrasound guided blocks, better designed needles and portable delivery systems) for use with continuous peripheral blocks have made this technique more practical for postoperative analgesia. Recent reports on continuous peripheral nerve blocks have demonstrated well tolerated and effective pain relief, even in ambulatory patients treated at home. Patients treated with peripheral blocks administrating local anesthetics should receive their daily maintenance dose of opioids as a base line and may substitute breakthrough pain with additional opioids.
Conclusion
Whenever possible, anesthesiologists should employ multimodal pain management therapy. Unless contraindicated, all patients should receive an around-the-clock regimen of NSAIDs, COXIBs, or acetaminophen. In addition, regional blockade with local anesthetics should be considered. Dosing regimens should be administered to optimize efficacy while minimizing the risk of adverse events. The choice of medication, dose, route, and duration of therapy should be individualized.
Anesthesiologists providing perioperative analgesia services should do so within the framework of an Acute Pain Service, and participate in developing standardized institutional policies and procedures. An integrated approach to perioperative pain management that minimizes analgesic gaps includes ordering, administering, and transitioning therapies, and transferring responsibility for perioperative pain therapy, as well as outcomes assessment and continuous quality improvement.
Acute pain control is considered nowadays a humanitarian issue whereas not providing effective relief of acute pain may be considered a breach of fundamental human rights. Chronic pain patients who are opioid-dependent are more likely to complain of severe pain postoperatively, but are also vulnerable to complications of opioid overdose. Individualized pain management, and vigilant clinical monitoring are the keys to successful postoperative pain management in these challenging patients.
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