Effects of vasodilators on rates of change of nasopharyngeal temperature and systemic vascular resistance during cardiopulmonary bypass in anaesthetized dogs.

The effects of various vasodilating agents on the rates of change of nasopharyngeal temperature and total systemic vascular resistance of anaesthetized dogs during cardiopulmonary bypass were studied. Intravenous administration of nitroglycerine (14 micrograms/kg per min, infused at 35 degrees C and 36 degrees C), sodium nitroprusside (5 micrograms/kg per min, infused at 36 degrees C) and phenoxybenzamine (1 mg/kg bolus, given at 32 degrees C and 36 degrees C) did not have any effect on the total cooling time or the rate of cooling from 36 degrees C to 18 degrees C. However, in dogs treated with phenoxybenzamine the time taken to rewarm to 36 degrees C was significantly shorter than those observed in the control, nitroglycerine or sodium nitroprusside treated animals. This difference in rewarming time was mainly due to the more even rate of rewarming induced by phenoxybenzamine. Moreover, a significantly greater reduction in systemic vascular resistance was observed in phenoxybenzamine treated animals than in the other treatment groups.