Abstracts

Rationale: The intracarotid amobarbital (Wada) test is an integral part of the pre-surgical evaluation for temporal lobe surgery, in order to obtain information regarding speech and memory function of each hemisphere. Although the average dose of amobarbital is between 85mg to 125mg, at our institution the dosage of amobarbital is often titrated to suppress the targeted hemisphere. The purpose of this study was to evaluate for interhemispheric differences in required amobarbital doses in patients with medically refractory seizures.Methods: A total of 106 patients who underwent Wada testing at our center were retrospectively reviewed. Each patient received the first dose of amobarbital in the internal carotid artery on the side of the suspected seizure focus followed by the contralateral side in thirty minutes. The dosage of amobarbital was titrated to induce paralysis of the contralateral arm as well as language dysfunction. Cerebral suppression was also verified by simultaneous EEG recording, which demonstrated burst of delta activity ipsilateral to the injected side. Patients with significant cross circulation based on angiography or EEG were excluded from the study. In addition, patients who had unilateral injection or had extra-temporal seizure focus were excluded. Results: Thirty-nine patients (16 male) with right-sided seizure onset were included in the first analysis and fifty-three patients (26 male) with left-sided seizure were included in the second analysis. Five patients with right-sided onset and nine patients with left-sided onset were excluded in the study due unilateral injection. For individuals with right-sided seizure onset, the mean dose of the first injection (right-side injection) was 112.4 mg (± 29.87) and the mean dose on the second injection (left-side injection) was 101.9 (± 25.43). This difference was statistically significant [t(39)= 2.75 , p < .01]. For individuals with left-sided seizure onset, the mean first injection (left-side injection) was 116.6 mg (± 28.78) and the mean second injection (right-sided injection) was 116.9 mg (± 32.61). This was not a statistically significant difference [t(53)= -.1 , p > .01]. Of patients with right-sided seizure onset, thirty-eight (97%) were left hemisphere dominant based on language evaluation. In comparison patients with left-sided seizure onset, 50 (94%) had left hemisphere dominance. Conclusions: This study demonstrates that there may be an interhemispheric difference in amobarbital dosage needed to induce functional suppression dependant on the side of seizure focus. In our study, patients with a right-sided seizure focus needed less total dose of amobarbital to suppress the left hemisphere, suggesting the dosage should be titrated in each hemisphere individually. Although it is not clear, hemispheric dominance may have played a role in the difference of the required dosage. Therefore, a Wada protocol with titrated amobarbital dosage can avoid excessive suppression of the targeted hemisphere.