Changes of Microvascular Vasomotion and Oxygen Metabolism during Cooling and Rewarming Period of Cardiopulmonary Bypass

Abstract

Microcirculation plays an important role in keeping a stable tissue metabolism during cardiopulmonary bypass (CPB). The relationship between microvascular vasomotion (MV) and total body’s oxygen metabolism with temperature alteration during CPB remains unclear. Is there a relationship, or is the autoregulation a consequence of CO2, pressure and/or blood flow? The purpose of this study was to investigate the effect of temperature alteration on cutaneous MV and the total body’s oxygen metabolism during CPB. Sixteen consecutive patients scheduled for elective cardiac valve replacement surgery were included in this study. The pump flow varied from 1.8–3.0 L/m-2min-1 to maintain venous oxygen saturation above 65% and mean arterial blood pressure above 60 mmHg. At a nasopharyngeal temperature of 30°C, oxygen consumption (VO2) and oxygen extraction (O2 ext) were measured during the cooling and rewarming periods. MV and skin microcircular flow (SMF) were monitored dynamically at the middle of two sides of the eyebrow with a laser Doppler flowmeter simultaneously VO2 and O2 ext at 30°C were significantly lower during the cooling period (VO2, 49.9 ± 17.7 mL/m-2/min-1; O2 ext, 19.3 ± 6.2%) than that during the rewarming period (VO2, 133.3 ± 40.0 mL/ m-2/min-1; O2 ext, 35.2 ± 9.2%) (p < .05). SMF was significantly depressed during CPB (p < .05). SMF during the cooling period (50.2% ± 10.1%) was significantly less than that during the rewarming period (79.5% ± 12.3%) (p < .05). MV was significantly less active during CPB than that before CPB (5.8 ± 1.2 cyc/ min)(p < .05), whereas there was no significant difference in MV between the cooling (3.7 ± 1.8 cyc/min) and the rewarming period (4.1 ± 1.5 cyc/min) and (p > .05). SMF and MV were depressed during hypothermic CPB, and there was some recovery during the rewarming period. Compared to baseline, SMF and MV were still significantly reduced during the warming period, indicating microvascular function was abnormal. Some measures should be taken for improvement of microvascular function during CPB.