Abstracts

For 45 years the intracarotid amobarbital procedure (IAP) has been used to lateralize cerebral dominance for speech and evaluate memory in each hemisphere independently. This has been done by anesthetizing one hemisphere briefly while the awake hemisphere performs simple speech and memory tests. The drug most used in this procedure was sodium amobarbital. Due to repeated shortages and other problems, attempts have been made to find another anesthetic agent. Methohexital (brevital) has been used with some success, and propofol has been tried. However, methohexital is not readily available and is so short-lived that re-injection is usually required. Propofol is contained in a lipid emulsion. We report our experience using etomidate, a widely-used agent for the induction of anesthesia. Patients requiring IAP to evaluate memory or for speech lateralization were tested. A catheter was placed in the internal carotid artery and an angiogram was performed prior to the procedure. EEG was recorded and read online by an EEGer. The drug was injected under the supervision of an anesthetist using an algorithm that would reproduce local plasma levels identical to those achieved by a usual systemic dose (0.3 mg/kg over 30 to 60 sec). Administration was by bolus followed by an infusion, which was maintained during the initial speech and memory tests. Upon termination of infusion, cognitive testing continued until all tests were completed and baseline levels were observed on EEG, handstrength, and language (in dominant hemisphere injections). Six patients (10 hemispheres) were tested. In all cases a satisfactory contralateral hemiplegia followed injection without affecting the ipsilateral hemibody. EEG slow waves were confined to the injected hemisphere in 4 injections, with some contralateral slowing in 6, consistent with our usual EEG findings in IAP. Dysarthria was observed in nondominant hemisphere injections, and global aphasia with preserved attention and cooperation in dominant injections. These phenomena remained throughout the period of infusion. After ending the infusion a gradual return to baseline was observed for about four minutes, allowing speech testing as the aphasia cleared, passing through a stage of dysphasia and then recovery. Trembling of the contralateral arm was observed during the drug effect in 8 of 10 injections. No patient complained of discomfort, and most had no memory of weakness, visual defects or speech disturbance that had occurred during the drug effect. Etomidate administration by bolus followed by infusion offers more than a viable alternative to the traditional IAP; it presents a considerable improvement for performing all cognitive tests during an assured hemianesthesia of the injected hemisphere. We have observed no contraindications in patients tested so far.