Cardiovascular Effects of Plasma Levels of Thiopental Necessary for Anesthesia

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Abstract
The cardiovascular effects of plasma levels of thiopental necessary for anesthesia were studied using systolic time intervals (STI). In 10 healthy patients anesthesia was induced with thiopental, 2-2.5 mg/kg, i.v. and maintained with an infusion of 1-1.5 mg/kg per min. STI and thiopental plasma levels were measured before induction and when corneal reflex and trapezius muscle response, indicators of anesthetic depth equivalent to response to surgical stimulation, were lost. Significant changes included an increase in heart rate with induction of anesthesia, a decrease in 1/pre-ejection period indexed for heart rate (1/PEP-I) at loss of corneal reflex, a decrease in systolic blood pressure and 1/PEP-I at loss of trapezius muscle response. No other variable was significantly different from control. Control values for STI were in the high-normal range, indicating some sympathetic stimulation. With induction of anesthesia these values decreased to a normal range. Free and total plasma levels were 5.4 and 37.6 .mu.g/ml at loss of corneal reflex; 6.1 and 41.6 .mu.g/ml at loss of trapezius muscle response. Thiopental causes less cardiac depression than inhalational agents at approximately the same anesthetic depth. In healthy patients plasma levels of thiopental producing surgical anesthesia result in minimal cardiac depression as determined by systolic time intervals.

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