THE EFFECTS OF SHORT INTRAVENOUS INFUSIONS OF THIOPENTONE ON MYOCARDIAL-FUNCTION, BLOOD-FLOW AND OXYGEN-CONSUMPTION IN SHEEP

The cardiovascular effects of slow (over two minutes) intravenous infu sions of thiopentone 750 mg in conscious instrumented sheep breathing 100% oxygen were examined for 30 minutes following the start of the in fusion, The maximum rare of rise of left ventricular pressure (an inde x of myocardial contractility) decreased significantly from I to 10 mi nutes, to a minimum of 45% of baseline. Heart rate increased by lip 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 ventr icular 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 rel atively slow I ate caused large reductions in myocardial contractility , and therefore cardiac reserve, in the absence of significant changes in myocardial bloodflow ol oxygen consumption.