Pulmonary shunting and lung volume during hypotension induced with trimetaphan

In 10 dogs anaesthetized with pentobarbitone mean Pa02 decreased from the control value of 13.5 kPa to 10.2 kPa, cardiac output decreased by 33%, and right-to-left shunt doubled during hypotension induced with trimetaphan. There was no signficant change in functional residual capacity during the period of hypotension or recovery. The hypoxaemia resulted from an increase in ventilation/perfusion inequality, with a decrease in arterial saturation consequent upon a decrease in cardiac output with a constant shunt. During the recovery period, right-to-left shunting remained greater than the values obtained before induction of hypotension.