Chapter 37 Perioperative Pain Management
1. What factors correlate with the severity of postoperative pain?
2. What are some potential adverse physiologic effects of acute postoperative pain?
3. What are some potential benefits of the effective management of acute postoperative pain?
4. What are the principles of multimodal perioperative analgesia?
Neurophysiology of pain
7. What are nociceptors? How are they stimulated?
8. What is the neurologic pathway of afferent pain impulses?
9. Where along the neurologic pathway of afferent pain impulses can modulation of the painful stimulus occur?
10. How can the modulation of painful stimuli occur in the periphery? What pharmacologic agents may be particularly useful for the modulation of painful stimuli in the periphery?
11. How can the modulation of painful stimuli occur at the level of the spinal cord?
12. How can the modulation of painful stimuli occur above the level of the spinal cord?
13. Name some excitatory and inhibitory neurotransmitters believed to have a role in the modulation of painful stimuli.
14. What is the difference between preemptive analgesia and preventative analgesia?
Analgesia delivery systems
15. Name some routes for the administration of analgesic drugs.
16. What is the limitation of the oral administration of analgesic agents for the management of acute postoperative pain? When is this route of administration appropriate?
17. What benefit does the intramuscular administration of analgesic agents have over oral administration? What are some problems with this method of administration?
18. Does ketamine have a role in the perioperative period? What are the side effects of low dose ketamine therapy?
19. How is a patient taking oral buprenorphine managed preoperatively, intraoperatively, and postoperatively?
20. What are the advantages and disadvantages of the subcutaneous, transdermal, and transmucosal administration of opioids?
21. Describe patient-controlled analgesia (PCA). What is the lockout interval?
22. What are some of the advantages of patient-controlled analgesia?
23. How do neuraxially administered opioids exert their effect?
24. What are some of the potential benefits of neuraxial opioids for postoperative analgesia?
25. What are some of the potential adverse effects of neuraxial opioids for postoperative analgesia? What different potential adverse effects may be caused by neuraxial infusion of local anesthetics?
26. What is the early depression of ventilation that may be seen with the neuraxial administration of an opioid believed to be due to?
27. What is the delayed depression of ventilation that may be seen with the neuraxial administration of an opioid believed to be due to? Why might this effect be more pronounced with morphine than with fentanyl?
28. Which patients may be most at risk for delayed depression of ventilation from the administration of a neuraxial opioid?
29. What characteristic of an opioid administered into the intrathecal space determines its time of onset and its duration of action?
30. What are the disadvantages of a single-dose administration of opioid in the intrathecal space for the management of acute postoperative pain?
31. What may be the reason for the clinical impression that the incidence of side effects associated with intrathecally administered opioid is higher than the incidence of side effects associated with the epidural administration of opioid for postoperative analgesia?
32. Why does the epidural administration of opioid require more drug than the intrathecal administration of the same opioid? What dose of epidural opioid is equipotent to the same opioid administered in the intrathecal space?
33. Why is it believed that fentanyl produces a more segmental band of anesthesia than morphine when administered in the epidural space?
34. How do the resulting plasma concentrations of fentanyl compare when the same dose of fentanyl is administered intravenously versus epidurally?
35. Why might a local anesthetic be added to the opioid for administration in the epidural space for the management of postoperative pain?
36. What is the concern regarding the concurrent use of neuraxial analgesia and anticoagulants? What are some general concepts regarding this issue covered in the American Society of Regional Anesthesia guidelines?
37. What factors increase the risk of postoperative epidural abscess associated with epidural analgesia?
Alternative approaches to management of Acute postoperative pain
38. What is an advantage and a disadvantage of peripheral nerve blocks for the management of acute postoperative pain?
39. What are the advantages and disadvantages of the intraarticular administration of analgesics?
40. Are there any unique benefits of the paravertebral blockade technique?
41. What are the advantages of perioperative continuous perineural catheters in both upper and lower extremity surgeries?
42. What is the role of clonidine as an adjuvant in peripheral nerve blockade?
43. How is intrapleural regional analgesia achieved? What is an advantage and a disadvantage of this technique for the management of acute postoperative pain?
44. What are the indications for a transverse abdominis plane block? What advantages does this peripheral block offer?
Answers*
1. Factors that positively correlate with severity of postoperative pain include preoperative opioid intake, anxiety, depression, pain level, and the duration of surgery. Factors that are negatively correlated include the patient’s age and the level of the surgeon’s operative experience. A perioperative plan should be developed that encompasses these factors to lessen the severity of the patient’s postoperative pain. (650)
2. Potential adverse physiologic effects of acute postoperative pain include hypoventilation, atelectasis, ventilation-to-perfusion mismatching in the lungs, hypercapnia, pneumonia, systemic hypertension, tachycardia, cardiac dysrhythmias, myocardial ischemia, deep vein thrombosis, decreased immune function, ileus, nausea and vomiting, urinary retention, hyperglycemia, sodium and water retention, insomnia, fear, and anxiety. Poorly controlled postoperative pain may also be a factor in developing chronic postsurgical pain. (650-651, Table 40-1)
3. Some potential benefits of the effective management of acute postoperative pain include improvement in patient comfort, a decrease in perioperative morbidity, enhanced postoperative rehabilitation, and a possible decrease in chronic postsurgical pain. It may also reduce cost by shortening the time spent in postanesthesia care units, intensive care units, and hospitals. (650)
4. The goals of multimodal analgesia include sufficient diminution of the patient’s pain to instill a sense of control over their pain, enable early mobilization, allow early enteral nutrition, and attenuate the perioperative stress response. The secondary goal of this approach is to maximize the benefit (analgesia) while minimizing the risk (side effects of the medication being used). (653-654)
5. The goals of an acute pain management service are to evaluate and treat postoperative pain to minimize the period of recuperation, decrease duration of hospital stay, improve patient satisfaction, and to inhibit the development of chronic (persistent) pain through early intervention. (653-654)
Neurophysiology of pain
6. Nociception is used to describe the recognition and transmission of painful stimuli. Pain is described as an unpleasant sensory and emotional experience caused by actual or potential tissue damage. (652)
7. Nociceptors are the free nerve endings of afferent myelinated A-delta and unmyelinated C nerve fibers. Nociceptors are stimulated by thermal, mechanical, or chemical tissue damage. (652)
8. Nociceptors, on stimulation, send axonal projections to the dorsal horn of the spinal cord and synapse on second-order neurons there. The axonal projections of the second-order neurons cross to the contralateral half of the spinal cord and ascend the spinothalamic tract to the thalamus in the brain. In the thalamus, these second-order neurons synapse with third-order neurons that send axonal projections to the sensory cortex. Before reaching the thalamus, the second-order neurons divide and also send axonal branches to the reticular formation and periaqueductal gray matter. (652)
9. Modulation of the painful stimulus can occur at almost every level along the afferent neurologic pain pathway. It can occur at the site of stimulation of the nociceptors or at any synapse. In addition, modulation of nociception can even occur by the inhibition of the afferent sensory pathways by descending inhibitory pathways originating at the level of the brainstem. (652)
10. Modulation of painful stimuli can occur in the periphery by decreasing or eliminating the endogenous mediators of inflammation in the vicinity of the nociceptor. Examples of endogenous mediators of inflammation include prostaglandins, histamine, bradykinin, serotonin, acetylcholine, lactic acid, hydrogen ions, and potassium ions. These endogenous inflammatory mediators sensitize and excite nociceptors, leading to the conduction of the painful stimulus. Pharmacologic agents that are particularly useful for the modulation of painful stimuli in the periphery are aspirin and nonsteroidal antiinflammatory agents (NSAIDs). These agents modulate painful stimuli by decreasing the synthesis of prostaglandins. (652, Table 40-2)
11. The modulation of painful stimuli can occur at the level of the spinal cord through the effects of excitatory or inhibitory neurotransmitters in the dorsal horn of the spinal cord. (652)
12. The modulation of painful stimuli can occur above the level of the spinal cord through the effects of a descending inhibitory pathway that originates in the brainstem. The descending inhibitory pathway synapses in the substantia gelatinosa region of the spinal cord. There are at least two types of descending inhibitory pathways, the opioid and α-adrenergic pathways. The opioid descending pathway releases endorphins and enkephalins, whereas the α-adrenergic descending pathway releases norepinephrine. Both these pathways work by hyperpolarizing the nerve fibers of the ascending pain pathway and potentially negate the action potential that would otherwise have resulted from the stimulation of the nerve by the painful stimulus. Neurotransmitters or second messenger effectors (e.g., substance P, protein kinase C-γ) may also play important roles in spinal cord sensitization and chronic pain. (652, Table 40-3)
13. Examples of pain modulating neurotransmitters include glutamate, aspartate, vasoactive intestinal polypeptide, cholecystokinin, gastrin-releasing peptide, angiotensin, and substance P. Examples of inhibitory neurotransmitters that are believed to modulate painful stimuli include enkephalins, endorphins, and somatostatin. (652, Table 40-3)
14. The precise definition of preemptive analgesia is one of the major controversies in perioperative pain medicine, and contributes to the confusion regarding its clinical relevance. The concept is that the development of central or peripheral sensitization of pain transmission after a traumatic injury can result in amplification of the pain response in the postoperative period. Preemptive analgesia can be defined as an analgesic intervention initiated before the noxious stimulus develops in order to block peripheral and central pain transmission. Preventive analgesia can be functionally defined as an attempt to block pain transmission prior to the injury (incision), during the noxious insult (surgery itself), and after the injury and throughout the recovery period. Unfortunately, few trials have examined the concept of preventive analgesia in a rigorous fashion. Confining the definition of preemptive analgesia to only the immediate preoperative or early intraoperative (incisional) period may not be clinically relevant or appropriate because the inflammatory response may last well into the postoperative period and continue to maintain peripheral sensitization. (654)
Analgesia delivery systems
15. Routes for the administration of analgesic drugs include oral, transmucosal, transdermal, intramuscular, intrapleural, intravenous, subcutaneous, rectal, neuraxial, and by injection to block a peripheral nerve. (654, Table 40-4)
16. The limitation of the oral administration of analgesic agents for the management of acute postoperative pain is the lack of ability to titrate it effectively to pain and the prolonged amount of time it takes to reach its peak effect. Patients are also limited by their perioperative NPO status. The oral route of administration for analgesic agents is appropriate when the pain the patient is experiencing has decreased and there is no longer a need for rapid adjustments in the level of analgesia. (655-656)
17. The intramuscular injection of analgesic agents has a more rapid onset and more rapidly reaches its peak effect than the oral route of administration of analgesic agents. There are some problems with the intramuscular administration of analgesics, however. Following intramuscular administration, the plasma concentration of the drug can vary among patients by three to five times, making dosing of the drug difficult. The use of this route has been replaced primarily by intravenous patient-controlled analgesia dosing, which provides a more standardized dosing interval. (656)
18. Ketamine can be effective in small doses for postoperative analgesia partly due to its NMDA antagonistic properties, which can attenuate central sensitization and opioid tolerance. Low-dose ketamine infusions have a low incidence of hallucinations or cognitive impairment. Ketamine is comparable to opioids with regard to its side effects of dizziness, itching, nausea, or vomiting. The use of ketamine in patients at high risk for the development of chronic postsurgical pain should be considered. (656)
19. Buprenorphine is commonly used for detoxification or maintenance therapy for patients with opioid abuse disorders (addiction). It is now more frequently being prescribed for the treatment of pain in non-addicts as well. It poses additional challenges to the anesthesiologist in the operative setting because of its pharmacodynamics and pharmacokinetics. Buprenorphine is a partial agonist at the μ-opioid receptor, and when used with a full agonist, such as morphine or fentanyl, it acts as an antagonist. Therefore the analgesia the patient experiences is less than what the patient would normally experience for a given dose of morphine or fentanyl. The pharmacokinetics of buprenorphine are somewhat unpredictable, making it hard to predict when its partial agonist properties will have worn off after the last dose of buprenorphine taken prior to surgery. This uncertainty leads to the risk of unexpected respiratory depression from the full opioid agonist as the buprenorphine unbinds from the opioid receptor.
20. Opioids can be administered through subcutaneous, transdermal, and transmucosal routes. Subcutaneous delivery can be an effective method for patients without intravenous access or who need long-term access at home. Subcutaneous therapy is primarily used for cancer patients. Transdermal fentanyl results in a variable range of serum concentrations and analgesic response across patient populations and requires 24 to 48 hours to reach peak levels. These limitations can lead to adverse outcomes for patients in the perioperative period because of side effects such as respiratory depression. The primary indication for transmucosal opioid therapy is for an adult opioid-tolerant oncology patient for breakthrough pain. (656-657)
21. Patient-controlled analgesia (PCA) is a method of delivering an opioid for analgesia to a patient. In this form of analgesic delivery, the patient controls his or her own administration of the opioid by pressing a button connected to a pump. The pump is programmed to deliver a preset small intravenous dose of opioid when triggered by the patient. The lockout interval is the interval of time that must pass after the last self-administered dose before the patient can deliver another small dose of opioid to himself or herself. (654)
22. There are several advantages of patient-controlled analgesia. These include high patient acceptance and for patients a sense of control, improved titration of drug, and subsequent patient comfort with less total drug administered, less sedation, improved sleep at night, and a more rapid return to physical activity after surgery. (654-655)
23. The analgesic site of action of the neuraxial administration of opioids can be primarily spinal or systemic, depending on their lipid solubility. There are mechanistic differences between continuous epidural infusions of lipophilic (e.g., fentanyl, sufentanil) and hydrophilic (e.g., morphine, hydromorphone) opioids. For continuous epidural infusions of lipophilic opioids the analgesic site of action is not clear, although several randomized clinical trials suggest that it is systemic. Hydrophilic opioid epidural infusions have a primarily neuraxial mechanism of action. (657)
24. Potential benefits of the neuraxial administration of opioids for postoperative analgesia include superior pain control, improved postoperative pulmonary function, decreases in cardiovascular complications, decreases in infectious complications, and decreases in total hospital costs. (657)
25. Potential adverse effects of the neuraxial administration of opioids for postoperative analgesia include pruritus, urinary retention, nausea and vomiting, sedation, and early and delayed depression of ventilation. Local anesthetic infusions are more likely to cause hypotension and motor block than opioid infusions. (657-658)
26. The early depression of ventilation that is seen with the neuraxial administration of opioids usually occurs in the first 2 hours after the administration of the opioid. Early respiratory depression is believed to occur as a result of vascular uptake and redistribution of the opioid. (657-658)
27. The delayed depression of ventilation that is seen with the neuraxial administration of opioids usually occurs 6 to 24 hours after the administration of the opioid. It is believed to be due to the cephalad spread of the opioid in the cerebrospinal fluid to the medullary centers of the brain. The medullary centers are in the area of the fourth cerebral ventricle. This effect may be more pronounced with the less lipid-soluble opioids, such as morphine, than with the more lipid-soluble drugs, such as fentanyl. The more lipid soluble the opioid is, the more readily it will attach to opioid receptors on the spinal cord. This makes less medication available for diffusion to the brain. The opposite occurs with the less lipid-soluble drug, leaving more drug available for diffusion to the medullary centers. (657-658)
28. Patient characteristics contribute to the risk of depression of ventilation from the administration of neuraxial opioid. Factors that increase the risk for the depression of ventilation include larger dose, geriatric age group, concomitant administration of systemic opioids or sedatives, the possibility of prolonged or extensive surgery, the presence of comorbidities, and thoracic surgery. (657-658)
29. The lipid solubility of intrathecally administered opioids is the primary determinant of its time of onset and duration of action. The onset time is shorter with more lipid-soluble drugs, and the duration of action is shorter. Conversely, less lipid-soluble drugs have a longer onset time and a prolonged duration of action. (657)
30. Typically, the intrathecal administration of opioid is administered as a single dose in conjunction with a local anesthetic block for a surgical procedure. Disadvantages of a single dose intrathecal administration of opioid for the management of acute postoperative pain include the lack of titratability and the need for other analgesic options after the initial intrathecal opioid effect subsides. (657)
31. The clinical impression that intrathecal opioid results in a higher incidence of side effects when compared with the epidural administration of the same opioid probably comes as a result of the administration of excessive doses of opioid in the intrathecal space. The same receptors are being stimulated in both cases, so theoretically equipotent doses at the receptor should result in similar desired and undesired effects. (657)
32. The epidural administration of opioid requires more medication to be administered than if it were administered intrathecally because the drug must diffuse across the dura to reach the spinal cord and exert its effect. In addition, fat, connective tissue, and the epidural veins all take up opioid that is deposited in the epidural space. In contrast, the intrathecal administration of opioid places the opioid directly at its site of action. The dose of epidurally administered opioid is approximately 10 times the dose of intrathecally administered opioid to produce an equipotent effect. (657)
33. Fentanyl administered in the epidural space is believed to produce a more segmental band of anesthesia than morphine because of its increased lipid solubility. The increased lipid solubility of fentanyl causes it to bind to opioid receptors in the spinal cord adjacent to the area in which it enters the intrathecal space. Morphine, being more hydrophilic, binds less readily and instead diffuses in the intrathecal space. This results in a wider distribution of anesthesia with morphine than with fentanyl when administered in the epidural space. (657)
34. The plasma concentration of fentanyl when administered intravenously is similar to the plasma concentration of fentanyl when the same dose is administered epidurally. This is thought to occur from the systemic absorption of fentanyl from the epidural space by the vasculature in the epidural space. This implies that at least part of the analgesic effect of fentanyl administered epidurally is through its systemic effects. (657)
35. Local anesthetic added to the opioid solution for administration in the epidural space results in a synergistic analgesic effect. This is believed to occur because of the blockade of painful stimuli at two different sites at the spinal cord. The opioid administered acts by binding to opioid receptors. The local anesthetic administered acts at the nerve roots and in the dorsal root ganglia by blocking the transmission of afferent impulses. The synergistic effect of these two classes of drugs allows for a decreased dose of each to be administered to the patient. This has the added benefit of a decreased risk of the potential side effects of both drugs. (657)
36. The concern regarding the concurrent use of neuraxial analgesia and anticoagulants is for the formation of a spinal or epidural hematoma. The incidence of spinal or epidural hematoma related to neuraxial analgesia is rare, but can be catastrophic and requires immediate surgical attention. General concepts for the management of neuraxial analgesia with anticoagulation include: (1) the timing of neuraxial needle or catheter insertion or removal should reflect the pharmacokinetic properties of the specific anticoagulant, (2) frequent neurologic monitoring is essential, (3) concurrent administration of multiple anticoagulants may increase the risk of bleeding, and (4) the analgesic regimen should be tailored to facilitate neurologic monitoring, which may be continued in some cases for 24 hours after epidural catheter removal. (658)
37. Factors that increase the risk of postoperative epidural abscess associated with epidural analgesia include a longer duration of anesthesia and the presence of coexisting immunocompromising or complicating disease such as malignancy or trauma. The overall incidence of postoperative epidural abscess associated with epidural analgesia is extremely rare, however. (658)
Alternative approaches to management of acute postoperative pain
38. An advantage of peripheral nerve blocks for the management of acute postoperative pain is their ability to provide good management of postoperative pain while not affecting the patient systemically. Thus the patient is not at risk for any of the negative effects of systemic opioids. A disadvantage of peripheral nerve blocks for postoperative pain is their relatively short duration of action. (659)
39. Intraarticular injection of opioids may provide analgesia for up to 24 hours postoperatively and prevent the development of chronic postsurgical pain. However, superiority of this delivery method over systemic administration has not been demonstrated. Continuous intraarticular administration of bupivacaine has been associated with chondrolysis in the glenohumeral joint. (659)
40. Paravertebral blockade has been directly correlated with improved outcomes for patients undergoing breast surgery. This technique has also been found to decrease the development of chronic postsurgical pain, as well as the acute pain associated with the procedure. (659)
41. Continuous perineural catheters for upper extremity procedures have been associated with increased pain relief with minimal opioid supplementation with increased patient satisfaction and sleep quality. Continuous catheters for major foot and ankle surgery are also associated with an earlier discharge. (659-660)
42. Clonidine is beneficial in extending the duration of preoperative blockade, but has less utility with perineural catheters. The mechanism is most likely peripheral α2-adrenergic receptor-mediated and dose-dependent. Clonidine is a better preemptive analgesic when added to a local anesthetic block than when used as a single drug. Side effects, including hypotension, bradycardia, and sedation, are less likely to occur with lower doses. (659)
43. Intrapleural regional analgesia is most frequently used for the management of acute postoperative pain after a thoracotomy. It is achieved by the injection of a local anesthetic solution through a catheter placed in the intrapleural space. The catheter is often placed intraoperatively by the thoracic surgeon one interspace lower than that of the surgical incision. The local anesthetic diffuses to the intercostal nerves and produces a multilevel, unilateral intercostal nerve block. Unfortunately, this technique provides little analgesia for patients unless it is actually placed in the paravertebral space from the intrathoracic approach. An advantage of this technique for postoperative pain management is the potential for pain relief without hemodynamic changes associated with epidural analgesia. A disadvantage of this technique is that the local anesthetic may be lost through the pleural drainage tubes that are placed after a thoracotomy. Complications associated with this technique include pneumothorax and high plasma concentrations of local anesthetic. The majority of local anesthetic infused into the intrapleural space flows to the dependent aspect of the patient, which is most often the lung bases where analgesia is not needed. The efficacy of this technique for postoperative pain management is therefore highly variable and has mostly been abandoned. This technique is less frequently used than epidural catheters or paravertebral blocks. (Chapter 40, 10)
44. The transverse abdominis plane block has been used for many abdominal procedures, including abdominal hysterectomy, cesarean section, and laparoscopic cholecystectomy. Theoretical advantages of this technique over other modalities include avoidance of both neuraxial involvement and lower extremity blockade, decreased urinary retention, and decreased systemic side effects. Ultrasound guidance has made this a more reliably achieved peripheral blockade. (660)
