Arginine vasopressin versus norepinephrine: will the stronger one win the race?

In the current issue of Critical Care, Friesenecker and colleagues present a well-designed comparative study on the microvascular effects of arginine vasopressin (AVP) and norepinephrine (NE) in a physiological, unanesthetized hamster model. The authors clearly demonstrate that AVP, but not NE, has marked vasoconstrictive effects on large arterioles, whereas the impact on small arterioles is comparable for both vasopressors. However, it remains unclear if these results, per se, reflect a stronger vasopressive potential of AVP versus NE, as macrohemodynamic variables were not different between study groups. Since the authors did not investigate the effects of AVP and NE in vasodilatory shock states, the microcirculatory response in sepsis or systemic inflammatory response syndrome remains inconclusive. The same authors previously reported that AVP infusion in patients suffering from vasodilatory shock carries the risk for ischemic skin lesions. This in turn raises the question whether the quality of vasopressors should be judged by their potency.