Chapter 31 Pain Management for the Postoperative Cardiac Patient
Adequate postoperative analgesia prevents unnecessary patient discomfort, may decrease morbidity, may decrease postoperative hospital length of stay, and thus may decrease cost. Because postoperative pain management has been deemed important, the American Society of Anesthesiologists has published practice guidelines regarding this topic.1 Furthermore, in recognition of the need for improved pain management, the Joint Commission on Accreditation of Healthcare Organizations has developed new standards for the assessment and management of pain in accredited hospitals and other health care settings.2 Patient satisfaction (no doubt linked to adequacy of postoperative analgesia) has become an essential element that influences clinical activity of not only anesthesiologists but also all health care professionals.
Achieving optimal pain relief after cardiac surgery is often difficult. Pain may be associated with many interventions, including sternotomy, thoracotomy, leg vein harvesting, pericardiotomy, and/or chest tube insertion, among others. Inadequate analgesia and/or an uninhibited stress response during the postoperative period may increase morbidity by causing adverse hemodynamic, metabolic, immunologic, and hemostatic alterations. Aggressive control of postoperative pain, associated with an attenuated stress response, may decrease morbidity and mortality in high-risk patients after noncardiac surgery and may also decrease morbidity and mortality in patients after cardiac surgery. Adequate postoperative analgesia may be attained via a wide variety of techniques (Table 31-1). Traditionally, analgesia after cardiac surgery has been obtained with intravenous opioids (specifically morphine). However, intravenous opioid use is associated with definite detrimental side effects (nausea/vomiting, pruritus, urinary retention, respiratory depression), and longer-acting opioids such as morphine may delay tracheal extubation during the immediate postoperative period via excessive sedation and/or respiratory depression. Thus, in the current era of early extubation (“fast-tracking”), cardiac anesthesiologists are exploring unique options other than traditional intravenous opioids for control of postoperative pain in patients after cardiac surgery.3 No single technique is clearly superior; each possesses distinct advantages and disadvantages. It is becoming increasingly clear that a multimodal approach/combined analgesic regimen (utilizing a variety of techniques) is likely the best way to approach postoperative pain (in all patients after surgery) to maximize analgesia and minimize side effects. When addressing postoperative analgesia in cardiac surgical patients, choice of technique (or techniques) is made only after a thorough analysis of the risk/benefit ratio of each technique in the specific patient in whom analgesia is desired.
| Local anesthetic infiltration |
| Nerve blocks |
| Opioids |
| Nonsteroidal anti-inflammatory agents |
| α-Adrenergic agents |
| Intrathecal techniques |
| Epidural techniques |
| Multimodal analgesia |
PAIN AND CARDIAC SURGERY
Surgical or traumatic injury initiates changes in the peripheral and central nervous systems that must be addressed therapeutically to promote postoperative analgesia and, it is hoped, positively influence clinical outcome (Boxes 31-1 and 31-2). The physical processes of incision, traction, and cutting of tissues stimulate free nerve endings and a wide variety of specific nociceptors. Receptor activation and activity are further modified by the local release of chemical mediators of inflammation and sympathetic amines released via the perioperative surgical stress response. The perioperative surgical stress response peaks during the immediate postoperative period and exerts major effects on many physiologic processes. The potential clinical benefits of attenuating the perioperative surgical stress response (above and beyond simply attaining adequate clinical analgesia) have received much attention during the past decade and remain fairly controversial. However, it is clear that inadequate postoperative analgesia and/or an uninhibited perioperative surgical stress response has the potential to initiate pathophysiologic changes in all major organ systems, including the cardiovascular, pulmonary, gastrointestinal, renal, endocrine, immunologic, and/or central nervous systems, all of which may lead to substantial postoperative morbidity.
Persistent pain after cardiac surgery, although rare, can be problematic.4 The cause of persistent pain after sternotomy is multifactorial, yet tissue destruction, intercostal nerve trauma, scar formation, rib fractures, sternal infection, stainless-steel wire sutures, and/or costochondral separation may all play roles. Such chronic pain is often localized to the arms, shoulders, or legs. Postoperative brachial plexus neuropathies may also occur and have been attributed to rib fracture fragments, internal mammary artery dissection, suboptimal positioning of patients during surgery, and/or central venous catheter placement. Postoperative neuralgia of the saphenous nerve has also been reported after harvesting of saphenous veins for coronary artery bypass grafting (CABG). Younger patients appear to be at higher risk for developing chronic, long-lasting pain. The correlation of severity of acute postoperative pain and development of chronic pain syndromes has been suggested (patients requiring more postoperative analgesics may be more likely to develop chronic pain), yet the causative relationship is still vague.
POTENTIAL CLINICAL BENEFITS OF ADEQUATE POSTOPERATIVE ANALGESIA
Inadequate analgesia (coupled with an uninhibited stress response) during the postoperative period may lead to many adverse hemodynamic (tachycardia, hypertension, vasoconstriction), metabolic (increased catabolism), immunologic (impaired immune response), and hemostatic (platelet activation) alterations. In patients undergoing cardiac surgery, perioperative myocardial ischemia (diagnosed by electrocardiography and/or transesophageal echocardiography) is most commonly observed during the immediate postoperative period and appears to be related to outcome. Intraoperatively, initiation of CPB causes substantial increases in stress response hormones (e.g., norepinephrine, epinephrine) that persist into the immediate postoperative period and may contribute to myocardial ischemia observed during this time. Furthermore, postoperative myocardial ischemia may be aggravated by cardiac sympathetic nerve activation, which disrupts the balance between coronary blood flow and myocardial oxygen demand. Thus, during the pivotal immediate postoperative period after cardiac surgery, adequate analgesia (coupled with stress-response attenuation) may potentially decrease morbidity and enhance health-related quality of life.5
TECHNIQUES AVAILABLE FOR POSTOPERATIVE ANALGESIA
Local Anesthetic Infiltration
Pain after cardiac surgery is often related to median sternotomy (peaking during the first 2 postoperative days). One method that may hold promise is continuous infusion of local anesthetic (Box 31-3). In a prospective, randomized, placebo-controlled, double-blind clinical trial, White and associates6 studied 36 patients undergoing cardiac surgery. Intraoperative management was standardized. All patients had two indwelling infusion catheters placed at the median sternotomy incision site at the end of surgery (one in the subfascial plane above the sternum, one above the fascia in the subcutaneous tissue). Patients received 0.25% bupivacaine (n = 12), 0.5% bupivacaine (n = 12), or normal saline (n = 12) via a constant rate infusion through the catheter (4 mL/hr) for 48 hours after surgery. Average times to tracheal extubation were similar in the three groups (5 to 6 hours). Compared with the control group (normal saline), there was a statistically significant reduction in verbal rating scale pain scores and patient-controlled analgesia (PCA) using intravenous morphine in the 0.5% bupivacaine group. Patient satisfaction with their pain management was also improved in the 0.5% bupivacaine group (vs. control). However, there were no significant differences in PCA morphine use between the 0.25% bupivacaine and control groups. Although tracheal extubation time and the duration of the intensive care unit (ICU) stay (30 hours vs. 34 hours, respectively) were not significantly altered, time to ambulation (1 day vs. 2 days, respectively) and duration of hospital stay (4.2 days vs. 5.7 days, respectively) were lower in the 0.5% bupivacaine group than in the control group.
Nerve Blocks
With the increasing popularity of minimally invasive cardiac surgery, which utilizes nonsternotomy incisions (minithoracotomy), the use of nerve blocks for the management of postoperative pain has increased as well (Box 31-4).7 Thoracotomy incisions (transverse anterolateral minithoracotomy, vertical anterolateral minithoracotomy), owing to costal cartilage trauma tissue damage to ribs, muscles, or peripheral nerves, may induce more intense postoperative pain than that resulting from median sternotomy. Adequate analgesia after thoracotomy is important because pain is a key component in alteration of lung function after thoracic surgery. Uncontrolled pain causes a reduction in respiratory mechanics, reduced mobility, and increases in hormonal and metabolic activity. Perioperative deterioration in respiratory mechanics may lead to pulmonary complications and hypoxemia, which may in turn lead to myocardial ischemia/infarction, cerebrovascular accidents, thromboembolism, and delayed wound healing, leading to increased morbidity and prolonged hospital stay. Various analgesic techniques have been developed to treat postoperative thoracotomy pain. The most commonly used techniques include intercostal nerve blocks, intrapleural administration of local anesthetics, and thoracic paravertebral blocks. Intrathecal techniques and epidural techniques are also very effective in controlling post-thoracotomy pain.
Thoracic paravertebral block involves injection of local anesthetic adjacent to the thoracic vertebrae close to where the spinal nerves emerge from the intervertebral foramina (Fig. 31-1). Thoracic paravertebral block, compared with thoracic epidural analgesic techniques, appears to provide equivalent analgesia, is technically easier, and may harbor less risk. Several different techniques exist for successful thoracic paravertebral block and have been extensively reviewed.8 The classic technique, most commonly used, involves eliciting loss of resistance. Injection of local anesthetic results in ipsilateral somatic and sympathetic nerve blockade in multiple contiguous thoracic dermatomes above and below the site of injection (along with possible suppression of the neuroendocrine stress response to surgery). These blocks may be effective in alleviating acute and chronic pain of unilateral origin from the chest and/or abdomen. Bilateral use of thoracic paravertebral block has also been described. Continuous thoracic paravertebral infusion of local anesthetic via a catheter placed under direct vision at thoracotomy is also a safe, simple, and effective method of providing analgesia after thoracotomy. It is usually used in conjunction with adjunct intravenous medications (opioid or other analgesics) to provide optimum relief after thoracotomy.
Opioids
Beginning in the 1960s, large doses of intravenous opioids have been administered to patients undergoing cardiac surgery (Box 31-5). Because even very large amounts of intravenous opioids do not initiate “complete anesthesia” (unconsciousness, muscle relaxation, suppression of reflex responses to noxious surgical stimuli), other intravenous/inhalation agents must be administered during the intraoperative period. Analgesia is the best known and most extensively investigated opioid effect, yet opioids are also involved in a diverse array of other physiologic functions, including control of pituitary and adrenal medulla hormone release and activity, control of cardiovascular and gastrointestinal function, and the regulation of respiration, mood, appetite, thirst, cell growth, and the immune system. A number of well-known and potential side effects of opioids (nausea and vomiting, pruritus, urinary retention, respiratory depression) may limit postoperative recovery when opioids are used for postoperative analgesia.
