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

Abstract

Aim Cardiac surgery requiring cardiopulmonary bypass (CPB) can result in renal and cerebral injury. Intraoperative tissue hypoxia could contribute to such organ injury. Hypothermia, however, may alleviate organ hypoxia. Therefore, we tested whether moderate hypothermia (30°C) improves cerebral and renal tissue perfusion and oxygenation during ovine CPB. Methods Ten sheep were studied while conscious, under stable anesthesia, and during 3 h of CPB. In a randomized within‐animal cross‐over design, five sheep commenced CPB at a target body temperature of 30°C (moderate hypothermia). After 90 min, the body temperature was increased to 36°C (standard procedure). The remaining five sheep were randomized to the opposite order of target body temperature. Results 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 the anesthetized state, the 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. Conclusion 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.

Differential responses of cerebral and renal oxygenation to altered perfusion conditions during experimental cardiopulmonary bypass in sheep

“…Recently, we observed little or no impact of moderate hypothermia on cerebral rSO 2 or PO 2 , or renal cortical or medullary tissue PO 2 . 20 In the current study, we found that both cerebral rSO 2 and renal PO 2 were improved by increasing pump flow, either when target MAP was maintained at mm Hg or when it was increased from 65 to 80 mm Hg. Both were also relatively unaffected by the use of partially pulsatile flow.…”

Associations Between Systemic and Cerebral Inflammation in an Ovine Model of Cardiopulmonary Bypass

“…In a clinically relevant large mammalian model of CPB, 18,19 we investigated the magnitude of systemic- and neuroinflammatory activation by CPB above the changes due to GA and surgical trauma alone. While the surgical trauma was not of the same magnitude as a median sternotomy, it is broadly analogous to that sustained during minimally invasive cardiac surgery before the institution of CPB.…”

Intraoperative hemodynamics and risk of cardiac surgery‐associated acute kidney injury: An observation study and a feasibility clinical trial

“…The relative effects of changes in pump flow, 8,19 arterial pressure, 8,19 pulsatility of flow and pressure, 19 blood haemoglobin concentration 45 and body temperature 46 Approximately one-third of eligible patients (10 of 32) did not consent to participation in the trial. While this level of recruitment might be viewed as suboptimal, given the difficulties the COVID-19 pandemic created for the function of elective cardiac surgery in our centre in Melbourne (Australia), we see this level of recruitment as satisfactory.…”