Systolic pressure variation predicts the response to acute blood loss

Study Objective: To evaluate systolic pressure variation (SPV), defined as the difference between the maximum and minimum systolic blood pressure measured during a controlled mechanical respiratory cycle, as a predictor of the cardiac output (CO) response to an acute decrease in ventricular preload. Design: Prospective study with each subject serving as his or her own control. Setting: Cardiac surgery operating rooms of a university medical center. Patients: 15 adults with good ventricular function undergoing coronary artery bypass grafting. Intervention: During stable anesthetic conditions and before surgical stimulation, 500 ml of blood was removed from each patient over 10 minutes. Measurements and Main Results: CO, central venous pressure (CVP), pulmonary artery diastolic pressure, and pulmonary artery occlusion pressure (PAOP), and SPV before and after phlebotomy were recorded. Phlebotomy was associated with significant decreases in CVP, PAOP, and CO, and an increase in SPV. Of these variables, SPV was the best predictor of the percent decrease in CO resulting from blood loss. Conclusion: SPV is a dynamic measurement, which, by revealing the response to small cyclical changes in left ventricular preload that occur during the controlled mechanical respiratory cycle, is a better predictor than central filling pressures of the response of CO to acute decreases in preload that occur as a result of acute blood loss.