Critical Care Medicine

Answer 4 Continuous infusion at low doses reduces the catecholamine infusion requirement. Vasopressin is a peptide synthesized in the hypothalamus and released from the posterior pituitary. Vasopressin produces a wide range of physiologic effects, including blood pressure maintenance. Acting through vascular V1-receptors, the endogenous hormone directly induces vasoconstriction in hypotensive patients but does not significantly alter vascular smooth muscle constriction in humans with normal blood pressure. Landry and colleagues8 demonstrated that patients with septic shock had inappropriately low levels of serum vasopressin compared with patients with cardiogenic shock, who had normal or elevated levels. In addition, they demonstrated that supplementing a low-dose infusion of vasopressin in septic shock patients allowed for the reduction or removal of the other catecholamine vasopressors. This was seen despite a reduction in cardiac output. Although these results were duplicated in subsequent studies, none evaluated outcomes such as length of stay or mortality until recently. A randomized double-blind study comparing vasopressin versus norepinephrine for the treatment of septic shock demonstrated no difference in 28-day mortality between the 2 treatment groups.9 Subgroup analysis of patients with severe septic shock, defined as requiring 15 µg/min of norepinephrine or its equivalent, also did not demonstrate a mortality benefit. However, patients with less severe septic shock (ie, requiring 5–15 µg/min of norepinephrine) experienced a trend toward lower mortality when treated with low-dose (0.01–0.03 U/min) vasopressin. REFERENCES 8. Landry DW, Levin HR, Gallant EM, et al. Vasopressin deficiency contributes to the vasodilation of septic shock. Circulation 1997;95:1122–5. 9. Russell JA, Walley KR, Singer J, et al; VASST Investigators. Vasopressin versus norepinephrine infusion in patients with septic shock. N Engl J Med 2008; 358:877–87 Click here to return to the questions

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