Lack of efficacy of naloxone in a fixed-volume hemorrhage model.

Animal studies using a reservoir model of hemorrhagic shock have shown the narcotic antagonist naloxone to be of value in reversing the hemodynamic effects of severe hemorrhage. We conducted a study to evaluate the ability of naloxone to limit the deleterious effects of a fixed-volume hemorrhage. Fifteen mongrel dogs were bled 50% of their estimated blood volumes during one hour. This was followed by a one-hour stabilization period; reinfusion during a 30-minute period; and finally, an additional one-hour monitoring period. Eight dogs received 2 mg/kg IV naloxone 30 minutes prior to hemorrhage and 2 mg/kg/hr for the duration of the study. Seven control dogs received an equivalent volume of saline without naloxone. Pulmonary capillary wedge pressure, central venous pressure, cardiac output, heart rate, blood pressure, arterial and mixed venous blood gases, and serum lactate were measured at 19 intervals throughout the study period. Mean arterial pressure, cardiac index, and systemic vascular resistance were calculated for each sampling period. With the exception of serum lactates, which were higher in the naloxone group, there were no significant differences between the groups in the mean values calculated for each sampling interval (P less than .05, two-tailed independent t test). Furthermore, the changes in hemodynamic parameters observed during the hemorrhage, stabilization, reinfusion, and monitoring periods were not significantly different. We conclude that in this fixed-volume hemorrhage model, naloxone does not prevent or reverse hemodynamic deterioration.