Oxygenation Within the First 120 H Following Coronary Artery Bypass Grafting. Influence of Systemic Hypothermia (32 Degrees C) or Normothermia (36 Degrees C) During the Cardiopulmonary Bypass: a Randomized Clinical Trial

Background: Lung function is often impaired after cardiac surgery performed under cardiopulmonary bypass (CPB). Normothermic CPB has become more common, but it remains unknown whether it reduces post-operative lung function compared with hypothermic CPB. The aim of this study was to investigate oxygenation within the first 120 h after systemic hypothermia and normothermia under CPB.

Methods: Thirty patients undergoing coronary artery bypass grafting (CABG) were randomized to either hypothermic (32 degrees C) or normothermic (36 degrees C) CPB. Oxygenation was studied by a simple method for the estimation of intrapulmonary shunt and ventilation-perfusion (V/Q) mismatch pre-operatively and 4, 48 and 120 h post-operatively by changing Fio2 in four to six steps. V/Q mismatch was described with DeltaPo2 (normal values, 0-2.38 kPa).

Results: Shunt and V/Q mismatch (DeltaPo2) increased post-operatively in both groups (P<0.01), with no differences between the groups, and with the nadir values 48 h after surgery, i.e. shunt of 15% (5.8-25%) and DeltaPo2 of 3.0 kPa (0.8-14 kPa) [values given as median (range)].

Conclusions: Impaired oxygenation is prevalent and prolonged following CABG, with equal intensity after hypothermic and normothermic CPB.