Hydroxocobalamin as a Rescue Treatment for Refractory Vasoplegic Syndrome After Prolonged Cardiopulmonary Bypass

VASOPLEGIC SYNDROME is a form of vasodilatory shock that occurs in 5% to 25% of patients during or after cardiopulmonary bypass (CPB).(1) The incidence of vasoplegic syndrome is related directly to the duration of CPB.(2) Vasoplegic syndrome typically is characterized by moderate-to-profound hypotension (mean arterial pressure [MAP] < 50 mmHg), normal or elevated cardiac index (> 2.4 L/min/m(2)), reduced systemic vascular resistance (< 800 dyne s/cm(5)), and a markedly attenuated response to vasoconstrictors.(3) Vasoplegic syndrome persisting for more than 24 hours despite medical therapy is associated with substantial increases in morbidity and mortality.(3) Abnormal nitric oxide-mediated dilatation of vascular smooth muscle resulting in arterial and venous vasodilatation appears to play an essential role in the pathophysiology of vasoplegic syndrome.(4) Alpha(1)-adrenoceptor agonists, vasopressin, and the nitric oxide scavenger methylene blue are the current mainstays of vasoplegic syndrome treatment,(5,6) but these interventions may not always be effective and are associated with a substantial risk of adverse side effects. For example, methylene blue (doses exceeding 5-7 mg/kg/day) interferes with pulse oximetry; may cause serotonin syndrome, methemoglobinemia, or hemolysis in susceptible patients; and has been linked to neuronal apoptosis.(5,7) Hydroxocobalamin (vitamin B-12a) consistently increases arterial pressure when used for the treatment of acute cyanide poisoning while producing few other adverse clinical effects.(8-10) The hypertensive effect of hydroxocobalamin most likely occurs as a result of alterations in nitric oxide metabolism,(8,11-13) although other mechanisms also have been implicated.(14-16) A single previous report documented the utility of hydroxocobalamin for the treatment of vasoplegic syndrome during CPB.(17) The authors describe the successful use of hydroxocobalamin for treatment of vasoplegic syndrome after prolonged cardiopulmonary bypass that was refractory to administration of vasoconstrictors and methylene blue.