The effect of dopamine, atropine, phenylephrine and cardiac pacing on oxygen consumption during fentanyl-nitrous oxide anaesthesia in the dog.

In animals deeply anaesthetized with fentanyl and nitrous oxide the arterial blood pressure and heart rate were increased using dopamine, atropine, electrical pacing and phenylephrine in order to study the accompanying change in whole body oxygen consumption. Seven dogs (16-24 kg) were anaesthetized with fentanyl 1 microgram . kg-1 . min-1. After completing instrumentation a dopamine infusion was started at a rate of 39 micrograms . kg-1 .min-1. After the mean blood pressure reached 18.6 kPa the infusion was reduced to 10 micrograms . kg-1 . min-1 and maintained for 10 minutes. After waiting 45 minutes an infusion of atropine 20 micrograms . kg-1 . min-1 was started and when the heart rate reached 120 b/min the infusion was slowed to 1.25 micrograms . kg-1. min-1 and maintained for 10 minutes. Twenty-five minutes later the heart rate was increased to 150 beats/min and maintained at that level for 10 minutes using electrical pacing. The pacing was removed and an infusion of phenylephrine 5 micrograms . kg-1 . min-1 was started. When the blood pressure reached 21.3 kPa the infusion was reduced to 2.5 micrograms . kg-1 . min-1 and maintained for 10 minutes. The results show increases in oxygen consumption of 14 per cent with dopamine, 19 per cent with atropine, 16 per cent, and 14 per cent with phenylephrine. All changes were significantly different from the control values. The magnitude of change in whole body oxygen consumption was best predicted by either the cardiac output X blood pressure product or by the cardiac output alone.