Influence of moderate-hypothermia on renal and cerebral haemodynamics and oxygenation during experimental cardiopulmonary bypass in sheep.

Abstract

Cardiac surgery requiring cardiopulmonary bypass (CPB) can result in renal and cerebral injury. Intra-operative tissue hypoxia could contribute to such organ injury. Hypothermia, however, may alleviate organ hypoxia. Therefore, we tested whether moderate-hypothermia (30o C) improves cerebral and renal tissue perfusion and oxygenation during ovine CPB. Ten sheep were studied while conscious, under stable anaesthesia and during 3 hours of CPB. In a randomised within-animal cross-over design, 5 sheep commenced CPB at a target body temperature of 30 o C (moderate-hypothermia). After 90 minutes, body temperature was increased to 36 o C (standard-procedure). The remaining 5 sheep were randomised to the opposite order of target body temperature. Compared with the standard-procedure, moderately-hypothermic CPB reduced renal oxygen delivery (-34.8 ± 19.6%, P = 0.003) and renal oxygen consumption (-42.7 ± 35.2%, P = 0.04). Nevertheless, moderately-hypothermic CPB did not significantly alter either renal cortical or medullary tissue PO2 . Moderately-hypothermic CPB also did not significantly alter cerebral perfusion, cerebral tissue PO2 , or cerebral oxygen saturation compared with the standard-procedure. Compared with anaesthetised state, standard-procedure reduced renal medullary PO2 (-21.0 ± 13.8 mmHg, P = 0.014) and cerebral oxygen saturation (65.0 ± 7.0 to 55.4 ± 9.6%, P = 0.022) but did not significantly alter either renal cortical or cerebral PO2 . Ovine experimental CPB leads to renal medullary tissue hypoxia. Moderately-hypothermic CPB did not improve cerebral or renal tissue oxygenation. In the kidney, this is probably because renal tissue oxygen consumption is matched by reduced renal oxygen delivery.