Anesthetic care during thiopental tests to evaluate epileptic patients for surgical therapy

A thiopental test 2 weeks after insertion of intracranial electrodes may be used to evaluate patients with refractory epilepsy for surgical therapy. Barbiturates normally produce beta activity on the electroencephalogram. The absence of this response in a monitored brain region implies focal cerebral dysfunction. We describe a technique used to perform this test and the resultant morbidity. The thiopental test consists of intravenous injection of thiopental, 25 mg, every 30 s until either corneal reflexes are abolished, 1,000 mg of thiopental has been administered, or adverse events occur. In children, the dose is adjusted to approximately 0.3 mg/kg of thiopental every 20 s. A retrospective chart review was performed on 104 patients who underwent thiopental tests at the University of Pittsburgh Epilepsy Center. Records were systematically reviewed for thiopental dose, mean arterial blood pressure, heart rate, oxygen saturation in arterial blood, time to responsivity, need for airway intervention, and occurrence of nausea or vomiting. Thirty-six patients developed upper airway obstruction which required jaw lift maneuver, six patients were given 1,000 mg of thiopental without loss of corneal reflexes, and one patient briefly sustained an arterial saturation of 67%. Five patients exhibited electrographic seizures with clinical seizures evident in two patients. No permanent effects were evident in any patient as a consequence of the test. We conclude, with appropriate monitoring and personnel, that the thiopental test, as described, can be performed safely with acceptable morbidity.