A Novel Assessment of Peripheral Tissue Microcirculatory Vasoreactivity Using Vascular Occlusion Testing During Cardiopulmonary Bypass

OBJECTIVE: Cardiac surgery and cardiopulmonary bypass are associated with release of inflammatory mediators and microcirculatory alterations that result in organ dysfunction. Near-infrared spectroscopic measurement of tissue oxygen saturation (StO2) and the vascular occlusion test (VOT) were utilized in a study of elective cardiac surgical patients as a novel, noninvasive method of assessing microcirculatory vasoreactivity during nonpulsatile cardiopulmonary bypass (CPB). The objective of this pilot study was to determine whether differences in microcirculatory function and vasoreactivity could be measured in cardiac surgery using StO2 and VOT. DESIGN: A prospective, observational trial. SETTING: Tertiary care teaching hospital. PARTICIPANTS: Thirteen patients undergoing elective cardiac surgery using tepid, nonpulsatile cardiopulmonary bypass. INTERVENTIONS: Patients had continuous regional oxygen saturation monitoring using near-infrared spectroscopy and vascular occlusion tests performed in the perioperative period before, during, and after cardiopulmonary bypass. MEASUREMENTS AND MAIN RESULTS: Occlusion slope and hyperemic area did not vary significantly. Mean reperfusion slope was significantly lower during cardiopulmonary bypass (2.4%/second) compared to before and after bypass (4.1 and 3.5%/second, respectively). Reperfusion slope decreased as a function of CPB duration. CONCLUSIONS: This pilot study demonstrates a significant difference in reperfusion slopes during cardiopulmonary bypass when compared to prebypass and postbypass, suggesting impaired peripheral microvascular reactivity. Reperfusion slopes also exhibited a successive decline with duration of CPB, implying worsening microcirculatory dysfunction that returned to baseline values in all patients within 1 hour of separation from CPB. This noninvasive technique has potential to optimize circulatory parameters during cardiopulmonary bypass.