Thiopental after brain ischemia in monkeys. Cardiovascular and electroencephalographic effects

The cardiovascular and electroencephalographic (EEG) effects of thiopental were investigated, with and without preceding global brain ischemia (GBI). Four groups of pigtailed monkeys were used: Group I received thiopental 90 mg/kg over 1 h after 16 min GBI. Group II received thiopental 90 mg/kg over 1 h without preceding brain ischemia. Group III received 90 mg/kg over 1, 3, 6, or 8 h with varying infusion rates and no brain ischemia. Group IV, after 16 min GBI, received thiopental 90 mg/kg over 12 h with a gradually reduced infusion rate, keeping thiopental serum levels around 120-140 mumol X l-1 throughout the infusion. Large doses of thiopental (Group II) produced serious cardiovascular side-effects. With co-existing brain ischemia (Group I), these side-effects were much worse; five of six animals not receiving lidocaine prophylaxis suffered circulatory arrest. A prolongation of the Q-T interval on the electrocardiogram may be of pathogenetic importance. In contrast, lower thiopental blood levels, sufficient to depress the EEG to burst suppression or isoelectricity, were well tolerated with and without preceding brain ischemia (Groups IV and III).