How long was brain electrical activity suppressed when thiopental was given during hypothermic heart bypass?

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This three-group comparative study examined the duration of electroencephalographic (EEG) suppression in patients undergoing hypothermic cardiopulmonary bypass (CPB) at 25–30 °C under halothane–nitrous oxide anesthesia.

Group I (n = 8) received three intravenous doses of thiopental, each 8 mg/kg: at induction of anesthesia, immediately after CPB began, and just after coming off CPB. Group II (n = 5) received no thiopental. Group III (n = 4) received only one intravenous dose of thiopental, 8 mg/kg, during CPB.

In Group I, the combination of thiopental and hypothermia was associated with an unexpectedly prolonged duration of EEG suppression of 26.1 minutes, compared with 4.8 minutes in Group II during hypothermic CPB without thiopental. Group III was studied to rule out a possible cumulative effect of thiopental administration. Even with only a single dose given during CPB, EEG suppression lasted 29.3 minutes.

Mild cardiovascular depression occurred when thiopental was administered during induction of anesthesia, whereas administration after coming off CPB was associated with mild-to-moderate cardiovascular depression.

The authors concluded that thiopental and hypothermia, used together in modest doses during CPB, appear to produce profound depression of cerebral electrical activity and presumably cerebral metabolism.