Thrombocytopenia accompanying a reaction to protamine sulfate

Catastrophic pulmonary vasoconstriction, an idiosyncratic reaction to protamine, occurred following cardiopulmonary bypass in a patient with mitral regurgitation. One minute following intravenous injection of 10 mg of protamine, systemic blood pressure decreased precipitously, accompanied by elevated pulmonary arterial pressure, decreased left atrial pressure, and a dilated and poorly contracting right ventricle. These changes spontaneously reversed over five minutes. Rechallenge with protamine was uneventful. Platelet count decreased from 76,000/mm3 to 12,000/mm3. Transient thrombocytopenia occurs predictably in dogs given protamine rapidly. Suggested mechanisms of idiosyncratic pulmonary vasoconstriction in patients should consider the role of the associated thrombocytopenia.