Early Norepinephrine Infusion Delays Cardiac Arrest After Hemorrhagic Shock in Rats

Background: Severe hemorrhagic shock often results in cardiac arrest due to vital organ hypoperfusion, especially of the heart. Although fluid resuscitation is the mainstay of management in hemorrhagic shock, treatment of cardiac arrest in association with severe hemorrhagic shock is unclear. Objective: This study was designed to determine the effect of early infusion of norepinephrine on hemodynamics and survival in hemorrhagic shock. Methods: Twelve Sprague-Dawley rats were bled to about 35% of estimated blood volume for 30 min and randomized to one of two groups: the study group received norepinephrine (10 μg/kg/min) in 5% dextrose solution (n = 6); the control group received the same volume of 5% dextrose (n = 6) concurrently with Lactated Ringer's solution. After 30 min of resuscitation, half of the shed blood was transfused in both groups. Time to cardiac arrest and mean arterial pressure (MAP) were compared between the two groups. Results: MAP during the resuscitation period was higher in the norepinephrine group than in the control group. Five of 6 rats in the norepinephrine group but none of the control group survived until the transfusion period (83.3% vs. 0.0%, respectively; p = 0.003). Median time to cardiac arrest was significantly longer in the norepinephrine group (67.0 min, interquartile range [IQR] 60.0-77.0) than in controls (41.0 min, IQR 40.0-47.0; p = 0.002). Conclusions: Early use of norepinephrine in a rat model of hemorrhagic shock increased mean arterial pressure during the resuscitation period and delayed the onset of cardiac arrest.