Abstracts

Rarely, injection of amobarbital during the Intracarotid Amytal procedure (IAP or Wada test) will fail to produce sufficient anesthesia for testing. After a sudden increase in the rate of such failures, we performed a retrospective chart review study on all patients receiving IAP[apos]s at UCLA over a 2 1/2 year period. Our goal was to identify any common characteristics in the medication lot, demographics, seizure history, or medication usage than could explain these cases. We determined all subject demographics, seizure history, perfusion patterns, current and recent medications, treating physician, and length of anesthesia during the IAP as measured by return of grip strength in successive cases. Gennder, age, seizure duration, treating physician, date of exam, perfusion patterns and medications were compared across individuals with and without reduced anesthesia. Anesthesia failures were found to be exclusively explained by concurrent or very recent use of Topiramate, Zonisamide, or antihypertensive agents, all of which have carbonic anhydrase inhibition properties. Approximately 75% of patients taking either Zonisamide or Topiramate showed reduced or absent anesthesia. No patients not taking one of these medications showed a reduced period of anesthesia during the IAP. Following withdrawal from these medications, a minimum of 8 weeks off the medications was necessary in the majority of cases before an average length of anesthesia during the IAP was found. Differences in anesthesia average times for patient taking and not taking carbonic anhydrase inhibiting drugs were very significant (p[lt].0000001). We now systematically withdraw patients from these medications prior to performing the IAP. We suggest that the mechanism of action common to all medications associated with reduced anesthesia have an action of carbonic anhydrase inhibition. Both amobarbital and carbonic anhydrase inhibitors appear to act on the GABA-A receptor channel , suggesting a possible mechanism for this interaction. Such an interaction is supported by animal studies of carbonic anhydrase inhibition and barbiturates. These results have important implications for clinical care for patients undergoing IAP exams.