Use of methylene blue for catecholamine-refractory vasoplegia from protamine and aprotinin.

We present two cases of catecholamine-refractory and vasopressin-refractory vasoplegic syndrome associated with intraoperative anaphylaxis during cardiac surgery. One case was related to the administration of protamine and the other case to the administration of aprotinin. Both cases were successfully managed using intravenous methylene blue. The use of methylene blue blocks accumulation of cyclic guanosine monophosphate by competitively inhibiting the enzyme guanylate cyclase. This results in reduced responsiveness of the vasculature to cyclic guanosine monophosphate-mediated vasodilators, such as nitric oxide. This report provides a description of severe anaphylaxis induced by different agents, in which the use of methylene blue was associated with a significant clinical response.