Cardiovascular functions in the dog rewarmed rapidly and slowly from deep hypothermia

¹ Department of Pharmacology, Tufts University School of Medicine, Boston, Massachusetts

Heart rate, blood pressure, cardiac output and cardiac minute work were measured in pentobarbitalized dogs prior to induction of hypothermia, at rectal temperatures of 25°C or 20°C and following rapid rewarming in warm water or slow rewarming by wrapping in heated sheeting. During rapid rewarming from either 25°C or 20°C no consistent failure in recovery of normal cardiovascular function was observed, although 1 out of 10 dogs did suffer cardiovascular collapse during rapid rewarming. Slow rewarming from 25° and 20°C resulted in consistent failure of some or all of these functions to recover to prehypothermic levels. Moreover, 5 out of 15 slowly rewarmed dogs suffered cardiovascular collapse during the rewarming process. In five dogs slowly rewarmed from 20°C saline was infused into the superior vena cava. This procedure resulted in moderate increases in blood pressure but dramatic increases in cardiac output and minute work (200% and 270%, respectively), thereby negating myocardial failure as the primary cause of the occasionally observed cardiovascular failure.