Vasopressin in vasodilatory shock: is the heart in danger?

In the previous issue of Critical Care Müller and colleagues reported that arginine vasopressin (AVP) (either 0.005 U/kg/min or titrated to a mean arterial pressure of 90 mmHg) after porcine myocardial ischemia reduced the cardiac output and the brain, coronary and kidney blood flow [1]. The fall in blood flow was compensated for by a marked increase in oxygen extraction. In particular, while left heart systolic contraction was not affected, AVP impaired diastolic relaxation and ventricular compliance. Neither the ischemic period nor the subsequent AVP infusion influenced the plasma troponin T level. The authors conclude that using AVP should be cautioned during cardiac surgery and AVP should be withheld in ischemic heart failure.How does Müller and colleagues' study compare with the existing literature? The observed cerebral and renal vaso-constriction confirms findings by Malay and colleagues: incremental AVP – similar to the pure α-agonist phenylephrine-dose-dependently reduced organ blood flow [2]. Müller and colleagues unfortunately did not measure portal venous flow, but it is tempting to speculate that the increased hepatic arterial flow reflects a well-maintained hepatic arterial buffer response, which at least partially compensated for the most likely reduced portal venous flow. In fact, low doses of the AVP analogue terlipressin during long-term, hyperdynamic porcine endotoxemia restored this otherwise impaired physiologic adaptation [3].The myocardial effects reported by Müller and colleagues deserve particular attention: in good agreement with their results, ample literature is available that the dose-dependent vasoconstrictor properties of AVP are also present in the coronary circulation [4-8]. Nevertheless, direct afterload-independent (that is, unrelated to systemic vasoconstriction) myocardial effects of AVP are a matter for debate: both positive inotrope properties [6,9] and negative inotrope properties [4,8,10,11] have been reported in isolated hea