Norepinephrine plus phentolamine improves regional blood flow during experimental low cardiac output syndrome.

A complication of cardiac surgical procedures is postoperative low cardiac output syndrome. Treatment with norepinephrine plus phentolamine (N + P) is beneficial, but the effect of these agents on regional organ blood flow has not been evaluated. Therefore, in 6 dogs with long-term instrumentation, pentobarbital was infused to simulate low cardiac output (32 + 10% of the conscious control level). Infusions of N + P at 0.2, 0.5, and 1.0 microgram/kg/min restored cardiac pump performance to conscious control levels. Regional blood flows, determined with tracer-labeled microspheres, were substantially reduced in the low cardiac output state but increased to values not markedly different from control levels in all organs studied except stomach fundus during infusion of N + P. The pressure-work index, an indirect measure of myocardial oxygen consumption, did not increase to more than the conscious level except at the highest dose. The data demonstrate that simultaneous infusion of N and P is capable of successfully improving cardiac pump performance with restoration of vital organ perfusion and without evidence of excessive myocardial oxygen consumption.