The cardiovascular effects of slow (over two minutes) intravenous infusions of thiopentone 750 mg in conscious instrumented sheep breathing 100% oxygen were examined for 30 minutes following the start of the infusion.
The maximum rate of rise of left ventricular pressure (an index of myocardial contractility) decreased significantly from 1 to 10 minutes, to a minimum of 45% of baseline. Heart rate increased by up to 33% above baseline from 0.5 min onwards. Both mean arterial pressure and cardiac output were decreased from between 1 and 7 min. Left ventricular minute work was transiently decreased, but left coronary blood flow and myocardial oxygen consumption showed little or no change from baseline.
We conclude that in vivo, thiopentone administered at a relatively slow rate caused large reductions in myocardial contractility, and therefore cardiac reserve, in the absence of significant changes in myocardial blood flow or oxygen consumption.
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