Rationale: The Wada Test is often
carried out in presurgery
epilepsy
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
anesthetics.
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 almost 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.