Abstracts

Rationale: The intracarotid amobarbital procedure, also known as the Wada test, has emerged as the gold standard for determination of language and memory dominance for risk stratification prior to temporal lobe epilepsy surgery.  Amobarbital is introduced via the internal carotid arteries of each hemisphere independently, then the patient is tested via language and memory cues.  Temporary anesthetization of each cerebral hemisphere allows for evaluation of relative contribution made by each temporal lobe to support language as well as memory function. Amobarbital’s supply chain issues have forced many epilepsy centers to use other short-acting anesthetics for Wada tests including methohexital, pentobarbital, etomidate and propofol.  This retrospective study was undertaken to compare methohexital with amobarbital in their effect on EEG suppression, impairment of motor function and verbal and visuospatial memory test scores.

Methods: Retrospective review of patient charts undergoing pre-surgical testing for drug-resistant epilepsy using the institutional electronic medical records. Included were epilepsy surgery candidates who underwent Wada testing with one dose of either amobarbital 100 mg  or methohexital 3 mg per injection between 2018 – 2020. Associated with injection the following parameters were recorded: impairment of language and motor function, duration of EEG suppression, time to return to full strength, and scores of verbal and visuospatial memory testing. Duration of EEG slowing and time for patient to recover to full strength was compared with use of amobarbital or methohexital.

Results: Ten patients were included, 1 female patient and 9 male patients, all with suspected temporal lobe epilepsy. One patient with right temporal lobe and 9 patients with left temporal lobe seizures.  Five patients received amobarbital and 5 patients methohexital.  Methohexital and amobarbital produced instant contralateral weakness and in the dominant hemisphere language suppression. EEG slowing and time to return to full motor strength were of longer duration with use of amobarbital (Figure 1). Comparison of verbal and visuospatial test results showed that scores were similar for both groups (Figure 2). Results may have been affected by the small sample size of 10. 

Conclusions: Use of methohexital in place of amobarbital appears to be an adequate option for Wada testing.  Methohexital was used in 5 patients in our institution with successful lateralization of language and memory functions with memory scores not different from what would be expected when using amobarbital. Given that supply chain constraints are not expected to be alleviated, the use of methohexital can be considered for Wada procedures.

Funding: None