Rationale: The Wada Test is often
carried out in presurgery
patients to lateralize language and to exclude possible amnesia after
surgery. For the past 15 years, we have used sodium amobarbital (Amytal)
for this purpose. We recently switched to sodium methohexital (Brevital)
and we report our observations on the differences between the two
Methods: Because of the relatively short action of sodium methohexital, we make two successive injections (3 mg then 2 mg), separated by about 60 sec (modeled after the Gainesville FL procedure; Eileen Fennell personal communication). Our current practice is to wait until the patient shows some signs that the injected hemisphere is recovering, such as grip strength in the contralateral hand or the beginning of language behavior after injection of the dominant hemisphere, before making the second injection. Language tests are given after the first injection; memory items are presented after the second. It is important to monitor motor recovery after the second injection in case it is necessary to make a third injection (2 mg). On some occasions, we have had to make as many as three more 2 mg injections to have time for all the memory items. We always test both hemispheres. In the present poster, we have analyzed the recovery times to EEG and behavioral baselines in 16 of the 24 patients who received sodium methohexital (NB: The data below are from patients who received 4 mg then 3 mg injections; we are in the process of analyzing the data from 3-2 mg injections).
Results: Recovery to baseline EEG after paired injections of sodium methohexital took about 4.8 minutes (286 +/- 70 sec; range: 180-420 sec), versus about 7.8 minutes (465 +/- 121 sec) following an injection of 125 mg of sodium amobarbital (see Selwa et al., 1997, Epilepsia, 38:1294-1299). This difference of about 3 minutes is highly significant (p<0.0001). Time to EEG baseline was similar for the first and second hemispheres (284 +/- 80 sec and 289 +/- 60 sec). Behavioral and neurological changes were the same as with sodium amobarbital, but rapid and complete recovery from the effects of sodium methohexital meant that we could proceed immediately to the second hemisphere and could repeat the procedure without incremental drowsiness.
Conclusion: Our experience with sodium methohexital suggests that this anesthetic can be used successfully in the Wada test for language and memory. The behavioral results are the same as those with sodium amobarbital, and sodium methohexital has the added advantage of faster recovery with little or no incremental drowsiness.