CON: Conscious Neuraxial Anesthesia is a Viable Alternative to General Anesthesia in Cardiac Surgery

Peggy T. Y. Li, MBChB & Anthony M. H. Ho, MD, FRCPC, FCCP

Department of Anaesthesia and Intensive Care
The Chinese University of Hong Kong
Prince of Wales Hospital
Shatin, NT, Hong Kong, SAR, PRC

"... As to diseases, make a habit of two things - to help, or at least to do no harm." - Hippocrates in the Epidemics, Bk 1, Sect XI

The combined use of general anesthesia (GA) and thoracic epidural anesthesia/analgesia (TEA) in cardiac surgery may lead to earlier tracheal extubation, decreased pulmonary complications and arrhythmias, and im-proved analgesia, although improvement in mortality and myocardial in-farction rates as compared to GA alone has yet to be demonstrated.1 In the 1980s, the off-pump technique in coronary artery bypass grafting (CABG) was revived. In 1998, the first CABG in a premedicated but conscious patient without GA was performed with TEA.2 Thus far, limited experience suggests that conscious cardiac surgery may be safe and may have advantages.2-9 There are, however, many concerns that must be addressed before the technique of awake cardiac surgery can be considered viable.

Anesthetic concerns

An overriding concern is the possibility of neuraxial hematoma. The incidence of neuraxial hematoma in the non-cardiac-surgery population that receives epidural anesthesia is one in 143,000.10 The risk of hematoma after full- or half-dose heparin for cardiac surgery is probably higher. Based in part on a zero occurrence, this risk may range from 1:1,500 to 1:150,000.11 Since the publication of that paper in 2000, at least two cases of epidural hematoma in patients having TEA for cardiac surgery have been reported.12,13 Despite surgical decompression, one of them remained paraplegic.13 In addition, there have been two reports of spontaneous epidural hematoma after cardiac surgery without epidural instrumentation.14,15 The possibility thus exists that hematoma could spontaneously occur at sites of epidural placement. There have also been two other patients suffering from this complication after epidural catheterization intended for cardiac surgery scheduled for the next day.16,17 Conceivably, if surgery had immediately followed, the consequence would likely have been worse.

Performing spinal decompression after CABG is daunting. The patient remains at risk of coronary insufficiency, has multiple tubes attached, and may be unstable.

We also speculate that the need to withdraw the epidural catheter under reasonable hemostatic conditions could lead to unnecessary transfusion with coagulation factors and platelets, especially after cardiopulmonary bypass (CPB). More postoperative blood tests may be needed to facilitate catheter withdrawal in valve cases in which anticoagulation is required postoperatively.

To minimize the risk of neuraxial hematoma, investigators inserted the epidural catheter the day before surgery, a move that makes same-day-admission impossible. Ensuring that the epidural is inserted at least an arbitrary hour before heparinization is seldom a problem, but is impossible if the patient becomes unstable and needs to go on CPB quickly. Postponing surgery due to a "bloody tap" (incidence of 3-4%) is inconvenient for all parties involved. There is also no guarantee that there will not be a "bloody tap" the next time around. All in all, no precaution would completely eliminate the risk of neuraxial hematoma when TEA is used in cardiac surgery.

Another potential problem is the failure to insert an epidural catheter. Three percent of patients in Karagoz's series could not be catheterized.2 Multiple attempts put the patient at risk of neuraxial complications18,19 even if no catheter is inserted, and no purported benefits of TEA could be derived.

Many cardiac patients have impaired ventricular function and/or are on ß-blockers. High TEA may cause extensive sympatholysis. Vasopres-sors used in such cases may have detrimental effects on the coronaries and grafts.20,21

Paralysis of the diaphragm is another potential complication if the TEA reaches C5 or higher. Due to intercostal blockade, any degree of diaphragmatic paralysis would be detrimental. Conversion to GA was needed in one of the seven patients in Meininger's report.7 An inadequate block may also necessitate conversion to GA,5 or require supplementation with local anesthetics at the jugular notch or xiphoid process level, as seen in 8% and 42% of the patients.2,6 Several questions are unanswered: What is the incidence of incomplete bilateral blocks? Does analgesia of the skin covering the sternum guarantee a stress-free sternotomy? Is impaired ventilation due to TEA less harmful than the effects of intubation and mechanical ventilation. Overall, titration of the epidural block to a satisfactory level may be tedious with no guarantee of success.

Surgical concerns

Spontaneous respiration can interfere with surgery. A patient undergoing aortic valve replacement needed CPB for over two hours due, in part, to the negative impact of the breathing pattern on surgical progress.8 Pneumothorax in cardiac surgery has reported incidences of 10% and 28%.2,3 Four of the 137 patients in Karagoz's series and two of Aybek's 31 patients required intubation because of it.2,3 Furthermore, two patients (out of 151) in one of the reports required conversion to GA because of coughing.4 Rarely, hemorrhage and cardiovascular instability may require conversion to GA, just when the clinicians need to focus on efficiently rectifying the problem(s).

For patients undergoing CABG with TEA, saphenous venous graft harvesting mandates a lumbar neuraxial block, thus increasing the risks of neuraxial complications, cardiovascular instability, and local anesthetic toxicity. Therefore, the majority of cases reported were one- or two-vessel bypasses using internal mammary arteries. In some cases, the radial artery was used. In summary, conscious cardiac surgery imposes significant limitations on surgical options and progress.

Patient concerns

Some patients would require intraoperative sedation,5,6 which must be titrated carefully because respiratory depression compounds the problem of muscle paralysis from the TEA. It is common for patients undergoing a high risk operation to be anxious. Having a chest opened and having to stay still for several hours are stressful. One could also imagine the anxiety (relief in some patients perhaps) evoked when told that surgery can only continue by converting to GA - a non-reassuring sign to some. Anxiety is undesirable in patients with coronary insufficiency. Even though patients expressed satisfaction after a successful CABG under TEA and sedation,4,5,7 one wonders if it was not due in part to the relief of surviving the experience. In other words, without comparison with a similar group of patients under GA, any claim of superior satisfaction after TEA is premature.

In summary, there are many potential problems, some extremely serious, associated with conscious neuraxial anesthesia for cardiac surgery. The potential gain seems relatively minimal, and for the most part, unproven. One case of emergency evacuation of spinal hematoma and/or paraplegia in a post-cardiac patient would negate all of the so-called benefits derived from many uncomplicated awake cardiac cases. Fast track and off-pump cardiac surgery have successfully evolved using GA alone. The use of TEA for conscious cardiac surgery, in spite of its theoretical advantages, represents a leap into the unknown that, for the moment, seems too risky to justify.

References

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