EFFECT OF HYPOTHERMIA ON RECTAL MUCOSAL PERFUSION IN INFANTS UNDERGOING CARDIOPULMONARY BYPASS

We have examined the effect hypothermia on gut mucosal infants, aged 1 .4-45 weeks, pulmonary bypass (CPB). After induction of anaesthesia, a laser Doppler probe was inserted 8 cm into the patient's rectum to al low monitoring of rectal mucosal perfusion (''flux'') throughout opera tion. Steady-state observation periods (5 min with no change in temper ature or mean arterial pressure (MAP)) were achieved after 10 min on C PB at 35 degrees C, after CPB-induced cooling to 15-25 degrees C, imme diately before rewarming and after rewarming to 35 degrees C. Througho ut these periods flow rate was 100 ml kg(-1) min(-1), packed cell volu me was kept constant and Pace, maintained at 5.3 +/- 0.5 kPa. No vasoa ctive drugs were used. Initial warm and rewarm MAP values (46 mm Hg) w ere significantly lower (P = 0.008) than during the cold CPB periods ( 63 and 64 mm Hg). Mean flux in the first cold period (152) was signifi cantly lower (P = 0.001) than that in the first warm CPB period (211). Post-rewarm flux (127) was significantly lower than all other CPB flu x values (P = 0.004). We con elude that although hypothermia significa ntly reduced mucosal blood flow, rewarming produced even greater reduc tions in mucosal perfusion that may prove crucial in the development o f mucosal hypoxia.