Review of: Little CM, Marietta MH, Peng K, et al: "Vasopressin alone or with epinephrine may be superior to epinephrine in a clinically relevant porcine model of pulseless electrical activity cardiac arrest." American Journal of Emergency Medicine. 24(7):810-814, 2006.
This study examines the effect of vasopressin alone, epinephrine alone and the combination of vasopressin and epinephrine on several clinical parameters of pigs with PEA following cardiac arrest.
The primary outcome variable was coronary artery perfusion pressure and atrial filling pressures. Survival was not measured because of the limited number of pigs they had to work with.
The combination of the two drugs resulted in significantly higher coronary artery pressures, which is postulated to result in improved coronary perfusion and subsequently higher cardiac arrest survival. Interestingly, those patients that failed to respond to epinephrine alone had a significant response to the subsequent administration of vasopressin.
The 2005 guidelines further extended the role of vasopressin by including it in the treatment of asystole in place of epinephrine. It had been placed in the V-fib/V-tach algorithm in the 2005 guidelines. The idea was that the two agents were interchangeable.
However, further research indicates that the clinical effects of epinephrine and vasopressin differ in how they work by stimulating different receptors in the vasculature. European studies have shown that vasopressin significantly increases coronary artery pressure and therefore might improve the outcomes in cardiac arrest. No one had looked at using vasopressin as a pressor agent in the context of pulse-less electrical activity (PEA).
One of the postulated advantages of vasopressin over epinephrine is that epinephrine increases myocardial oxygen consumption and therefore would lead to worsening cardiac function. Vasopressin appears to exert more of an effect on the vasculature, resulting in higher aortic and coronary artery pressures. I suspect that this and similar research may lead to changes in the PEA algorithm.