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).