The effect of vasopressin on oxygen availability

Vasopressin has been used with increasing frequency to control gastrointestinal bleeding, the beneficial effect being attributed to marked splanchnic vasoconstriction. Because vasopressin may result in impaired cardiac function and because other potent vasoconstrictive substances have been shown to increase the pulmonary shunt and decrease arterial oxygenation, this study was undertaken to determind the effect of vasopressin on oxygen availability. Ten healthy anesthetized mechanically ventilated dogs received a five hour intravenous vasopressin infusion, 0.005 U/kg/min. The heart rate decreased moderately and briefly. The mean systemic arterial pressure increased and then decreased, both minimally. The pulmonary shunt and the arterial oxygen content decreased slightly. The total systemic resistance increased and the stroke volume decreased, both substantially. The pulmonary artery wedge pressure gradually increased. The oxygen availability decreased markedly. This study demonstrated that a vasopressin infusion causes a marked decrease in oxygen availability due primarily to a decreased stroke volume and, to a lesser extent during the first hour, to a decreased heart rate. The pulmonary shunt did not increase. Increased systemic resistance followed by a gradual increase in the pulmonary wedge pressure suggests that the decreased stroke volume resulted, at least in part, from an increased afterload and left ventricular failure. It is suggested that until the effect of vasopressin on the cardiopulmonary systems and hence oxygen availability is fully studied in critically ill patients, that it be used with caution and with appropriate hemodynamic monitoring.