EFFECT OF INHALED OXYGEN CONCENTRATION ON PULMONARY GAS EXCHANGE DURING OFF-PUMP CORONARY BYPASS GRAFTING

Aim of study - supra-physiologic level of PaO2, securing oxygen reserves and preventing perioperative hypoxia, may offset the reduced oxygen delivery during cardiac surgery. However, high FiO2 will speed up gas absorption in low V/Q regions, promote atelectasis formation and increase pulmonary shunt fraction. PaO2/FiO2, P(a-Et)CO2 and PEtCO2/PaCO2 are the variables linked to CO2 and O2 exchange impairment. The aim of our study was to assess pulmonary gas exchange performance while ventilating patients with different FiO2 during OPCABG. The seventy patients were randomly equally distributed in two groups: H (High) and L (Low). The patients in the group H were ventilated with FiO2 0.8 and the patients in the group L _ with FiO2 0.5. PaO2/FiO2 ratio, P(a-Et)CO2 gradient and PEtCO2/PaCO2 ratio were checked at the start and the end points of operations. PaO2/FiO2 decreased, P(a-Et)CO2 increased and PaCO2/PEtCO2 decreased at the end of operations compared with the start values in both groups. PaO2/FiO2, P(a-Et)CO2 and PaCO2/PEtCO2 ware different between H and L groups. The difference became statistically significant at the end of operations. (PaO2/FiO2 326±65 vs 290±63 p=0.020; P(a-Et)CO2 5.7±2.3 mmHg vs 7.5±2.4 mmHg p=0.003; PaCO2/PEtCO2 0.84±0.05 vs 0.80±0.06 p=0.001). The groups were comparable according to the outcomes such as hemodynamic and laboratory data, duration of postoperative mechanical ventilation and ICU length of stay. FiO2 0.8 was associated with more derangements of pulmonary gas exchange compared with FiO2 0.5. Although FiO2 did not have an impact on the outcomes we studied, using FiO2 0.5 seems to be safer in patients undergoing OPCABG.