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Dr. Castellano is Assistant Professor of Anesthesiology, Acute Pain Service, and Dr. Durbin is Medical Director, Respiratory Care, Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.
Correspondence to: Charles G. Durbin, Jr, MD, Department of Anesthesiology, University of Virginia Health Science Center, Box 100710, Charlottesville, VA 22908–0710; e-mail: CGD8V{at}virginia.edu
Pain following surgery remains a significant clinical problem. Frequently, systemic opioids are used in inadequate doses due to severe side effects and fear of respiratory depression. Patients undergoing intrathoracic procedures are especially at risk of inadequate analgesia. The consequences of persistent pain include hypertension, sympathetic hyperactivity, poor pulmonary toilet, atelectasis, and pneumonia. Recently, interest has emerged in the use of epidural infusions of local anesthetics and narcotics to improve analgesia in high-risk patients following thoracic surgery. With every intervention, there is a series of risks that must be weighed against the potential for a desired outcome. Inadequate or spotty analgesia, nerve or spinal cord injury, back pain, local infection, epidural abscess, inadvertent subarachnoid injection, respiratory arrest, and spinal cord compression from epidural hematoma are possible complications from epidural analgesia. Most of these are rare, reversible, or insignificant. Spinal cord compression from a hematoma or abscess is frequently not reversible. Systemic anticoagulation is presumed to increase the incidence of developing an epidural hematoma related to the epidural catheter; however, there is little objective evidence to quantitate the magnitude of this increased risk. In fact, there are no published reports of epidural hematomas complicating thoracic epidural analgesia in patients following cardiac surgery employing cardiopulmonary bypass and systemic anticoagulation. In this issue of CHEST (see page 551), the article by Ho et al is a mathematical attempt to bracket the upper and lower likelihood of this potentially catastrophic event occurring. While interesting, the analysis by Ho et al provides little evidence to reassure the prudent clinician that epidural placement is safe in cardiac surgery patients who have undergone anticoagulation.
The potential usefulness of thoracic epidural analgesia in cardiac surgery patients has been addressed in multiple studies.1 2 3 However, fear of epidural hematoma formation has led to reluctance among anesthesiologists to place epidural catheters in these patients who receive high-level anticoagulation. Clinicians who are proponents of this analgesic technique highlight the benefits that a thoracic epidural blockade can provide to the cardiac surgery patient. As mentioned above, these include reduction in the stress response, sympatholysis with increased coronary perfusion, excellent pain management in the postoperative period, and overall reduction in systemic opioid medications. In addition, Stenseth et al4 reported improvement in pulmonary function and improved stability of the postoperative hemodynamics in coronary artery bypass patients. These are all well-established potential benefits of thoracic epidural analgesia. Before endorsing use of this technique for all cardiac surgery patients, a careful examination of the clinical details of the technique, risks, and published experience is necessary.
Ho et al have presented a statistical analysis suggesting that, at most, one epidural hematoma secondary to catheter placement will occur for every 1,520 patients following coronary artery bypass surgery. His analysis is based on the fact that there are no reported epidural hematomas in the 1,500 or so reported uses of epidural analgesics in cardiac surgery patients. He states that the actual risk might be considerably lower if the risk of epidural hematoma in cardiac patients is identical to all patients receiving epidurals (without anticoagulation), estimated to be 1 in 50,000 to 1 in 250,000. Whether or not to embrace epidural analgesia in cardiac surgery patients revolves on the question that dominates all clinical decision-making: Is the patient benefit worth the increased risk involved? Is this estimated incidence small enough to encourage cardiac anesthesiologists to place thoracic epidural catheters, thus creating an expanded clinical database to further define the true risk?
An epidural hematoma is one of the most serious complications that can occur in regional anesthesia, which usually has profound detrimental neurologic consequences that are often permanent. Although uncommon, epidural hematomas have been documented as occurring in patients who have undergone anticoagulation without catheters, and even spontaneously in patients with malignancies that have developed coagulopathies secondary to their disease. Nakaya et al5 reported a case of a spinal epidural hematoma occurring spontaneously after open heart surgery. The painless presentation coupled with the slow onset of symptoms serve to emphasize the need for close neurologic surveillance in patients after coagulation. Even though the epidural space was not entered in this instance, the hematoma produced neurologic symptoms that did not resolve following decompression. Once an epidural hematoma begins forming and symptoms are noted, there is a window of opportunity for surgical intervention that may avert a poor outcome. Lawton et al6 underscored the importance of rapid diagnosis of a hematoma and associated the neurologic outcome to the rapidity of surgical evacuation. Patients undergoing decompressive laminectomy within 12 h had a much improved neurologic outcome as compared to those treated beyond the 12-h window. The diagnosis is based on the presence of back pain and identifying progressive sensory and motor loss in the area below the lesion. Patients who are unable to be carefully followed and evaluated for subtle changes because of mechanical ventilation, use of sedatives, or who are unstable following surgery are at greater risk of permanent sequelae if a hematoma develops. The onset of a hematoma in the epidural space can be very subtle, and initially may present only as a mild sensory deficit prior to profound motor deterioration. An alert patient followed with appropriate neurologic evaluations at periodic intervals is most likely to have the problem detected promptly.
The risk of his complication can be reduced by careful patient selection. Sanchez and Nygard7 reported 558 cardiac surgery patients who had epidural catheters placed following strict guidelines. These included performing the procedure the day prior to surgery, using a paramedian approach, obtaining an initial normal coagulation profile, carefully screening preoperative drug use, and limiting attempts at placement to two tries. There were no epidural hematomas reported in this study. This represents a highly selected group of patients. In other cardiac surgery patients, including those presenting for emergency procedures and those who are unstable, these catheter placement protocols are impossible to follow. In the article by Ho et al, this high-risk group is excluded, and the authors state that the analysis applies to those patients undergoing "conventional" cardiac surgery, presumably only those patients in whom the guidelines can be followed.
Thoracic epidural analgesia does have a therapeutic role in patients with unstable angina. The beneficial result of increased coronary perfusion is documented in multiple studies.8 9 There may be specific benefits in patients with ischemic pain unresponsive to conventional treatment measures who are not surgical candidates. Epidural pain management consists of several options. Catheter location is one choice. There may be less risk of permanent neurologic damage should a hematoma form in the lumbar area. Lumbar or thoracic epidural analgesia can be achieved with narcotics alone or by using continuous infusions. Brodsky et al10 reported that continuous lumbar infusion of hydromorphone provided excellent pain relief for patients following thoracotomy. This is a particularly difficult group in which to manage postoperative pain, as they have severe pain coupled with poor lung function. A lumbar catheter with narcotic infusion will not provide the sympathetic block that a thoracic catheter with dilute local anesthetic infusions would produce. However, thoracic pain can be managed with this lower (lumbar) catheter technique.
An alternative to preoperative placement of an epidural catheter would be the placement of the catheter following surgery after reversal of heparin. A normal coagulation status should be verified by laboratory methods prior to catheter insertion. Although attractive in theory, no studies reporting the risk of complications with this approach have yet been published.
The reason for the study by Ho et al is that thoracic epidural analgesia may be very beneficial in a selected population of cardiac surgery patients and that the risks may be acceptable. When epidural analgesia is conducted under strict protocols with appropriate neurologic monitoring, the potential for permanent neurologic damage from an epidural hematoma is judged to be acceptably low. Using lumbar epidural catheters in patients who have undergone anticoagulation is not a new concept and has been used for many years. Patients with advanced peripheral vascular disease of the lower extremities undergoing vascular surgical procedures have benefited from the sympathectomy produced by continuous lumbar epidural infusions of local anesthetics. Infusions of heparin are used concurrently in many of these patients. These patients are monitored appropriately and are selected based on institution protocols for detection of adverse events. The catheters are only removed when coagulation status has returned to normal.
A final issue is whether epidural analgesia is needed at all following cardiac surgery through a median sternotomy. Most cardiac surgery patients are easily managed with minimal doses of narcotics and will not require thoracic epidural analgesia for postoperative pain relief or to improve cardiac function. The risk of epidural use is lowest for the group that will not significantly benefit from it. More severely ill patients with coexisting disease that would potentially benefit from the multiple effects of epidural blockade are better candidates, but may have a higher risk of complications. Multicenter studies should be developed with consistent guidelines for patient selection, catheter placement, and neurologic surveillance techniques to assess this risk. Even if the risk of epidural hematoma is as low as 1 case in 1,500, this rate is still distressingly high, given the severity of this complication. More severely ill patients, should a complication arise, would require a second emergent surgical procedure (for decompression) in the immediate postoperative period, with incumbent increased morbidity and mortality.
The debate over the value and risk of epidural analgesia in the cardiac surgery patient will continue. The article by Ho et al has provided an important qualitative milestone and is based on the currently available literature. Further study is needed to determine if the risks are worth the benefits.
References
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