The combined effect of halothane-induced hypotension and hypocapnia on canine myocardial blood-flow and oxygen consumption.

In eleven intact mechanically ventilated dogs anaesthetized with pentobarbitone, mean arterial pressure was reduced to 55% of the control value by ventilating with 1-1.5% halothane. At normocapnia this resulted in decreases in myocardial blood-flow and oxygen consumption to 47% and 55% of their respective control values and an increase in myocardial vascular resistance to 123% of control value. When hypocapnia (mean PaCO2=26 mm Hg) was superimposed on hypotension, myocardial blood-flow was further decreased to 38% of control value whereas oxygen consumption did not alter significantly. When halothane was discontinued, allowing recovery from hypotension, the rate of recovery of myocardial blood-flow and cardiac output was much slower than that of arterial pressure.