The Neurologic Effects of Thiopental Therapy Following Experimental Cardiac Arrest in Cats

Abstract

To define the utility of high-dose barbiturate therapy following an episode of complete global cerebral ischemia, the effects of 60 mg/kg of thiopental given to cats 5 min after resuscitation from 12, 14 or 16 min of electrically induced ventricular fibrillation (VF) were studied. All aspects of the arrest, resuscitation with post-arrest care, were carefully controlled, with the EEG becoming isoelectric 20-25 s after the onset of VF, a 89-91% rate of successful resuscitation, and with an overall mean resuscitation time of 2.5 .+-. 0.2 min. For any given duration of VF, there were no differences (control vs. thiopental) in any pre- or post-arrest parameters (blood pressure, blood gases, electrolytes, etc.) A total of 68 resuscitated cats were entered into various treatment and control groups, and all but 1 group received 20-24 h of postresuscitation paralysis, mechanical ventilation and ICU [intensive care unit] support before being extubated. Cats received an additional 6 days of aggressive nursing care, and daily examinations were performed with the assignment of a neurologic deficit score (NDS) between 0 (normal) and 100 (brain dead). Autopsies were performed to determine the cause of death in animals which died before the end of the 7-day observation period. The early post-arrest period was marked by the occurrence of repetitive, rhythmic bursts of high-frequency EEG activity (? seizures) in 38% of control animals (16/42, all arrest times combined). Ten of these animals died as a result of severe neurologic injuries. Only 12% of treated cats (3/26) developed similar EEG patterns (P < 0.05) and there were no neurologic deaths in the thiopental groups. The differences in the incidence of neurologic deaths (control vs. thiopental) was significant (P < 0.02). The change in overall mortality did not quite reach significance (36 vs. 21%), and treatment had no effect on the incidence of deaths due to cardiovascular causes (e.g., myocardial infarctions). In spite of the effects on mortality, treatment had no effect on the neurologic function of survivors (assessed by NDS). Evidently, thiopental improved suvival rates by suppressing an unusual past-arrest EEG pattern (? anticonvulsant effect) but had no additional cerebral protective effects.