High dose naloxone does not improve cerebral or myocardial blood flow during cardiopulmonary resuscitation in pigs.

In a prospective, randomized, placebo-controlled, double-blind trial we tested the hypothesis that naloxone given during cardiopulmonary resuscitation (CPR) enhances cerebral and myocardial blood flow. Twenty-one anesthetized, normoventilated pigs were instrumented for measurements of right atrial and aortic pressures, and regional organ blood flow (radiolabeled microspheres). After 5 min of untreated fibrillatory arrest, CPR was commenced using a pneumatic chest compressor/ventilator. With onset of CPR, an i.v. bolus of 40 micrograms/kg b.w. of epinephrine was given, followed by an infusion of 0.4 micrograms/kg per min. After 5 min of CPR, either naloxone, 10 mg/kg b.w. (group N, n = 11) or normal saline (group S, n = 10) was given i.v. Prior to, and after 1, 15, and 30 min of CPR, hemodynamic and blood flow measurements were obtained. After 30 min of CPR, mean arterial pressure was significantly higher in group N (26 +/- 5 vs. 13 +/- 3 mmHg, P < 0.05). Groups did not differ with respect to myocardial perfusion pressure or arterial blood gases at any time during the observation period. Regional brain and heart blood flows were not different between N and S at any point of measurement. We conclude that high-dose naloxone does not augment cerebral or myocardial blood flow during prolonged closed-chest CPR.