Influence of Inhaled Oxygen Level on Pulmonary Function and Gas Exchange in Off-Pump Coronary Artery Bypass Grafting Patients

Purpose: Off-pump coronary artery bypass grafting (OPCAB) is widely used for treating advanced coronary artery disease; however, postoperative pulmonary complications remain a challenge.The inspired oxygen fraction (FiO₂) during surgery may impact pulmonary gas exchange and respiratory efficiency.This study compared the effects of two intraoperative FiO₂ levels (0.5 vs. 0.8) on pulmonary gas exchange in OPCAB patients using PaO₂/FiO₂ ratio, P(a-Et)CO₂ gradient, and PEtCO₂/PaCO₂ ratio.Methods: A prospective observational study was conducted at Hameed Latif Hospital, Lahore, involving 76 adult patients undergoing elective OPCAB.Participants were randomly allocated to receive either FiO₂ = 0.5 (Group L) or FiO₂ = 0.8 (Group H) during mechanical ventilation.Arterial blood gas and end-tidal CO₂ measurements were obtained 30 minutes after induction and at the end of surgery.Data were analyzed using SPSS v25, with p < 0.05 considered significant.Results: At surgery completion, Group L (FiO₂ = 0.5) showed a significantly higher PaO₂/FiO₂ ratio (322.5 ± 49.7 vs. 282.9± 37.0, p < 0.05), lower P(a-Et)CO₂ gradient (4.1 ± 1.0 vs. 7.0 ± 1.1 mmHg, p < 0.01), and higher PEtCO₂/PaCO₂ ratio (0.879 ± 0.027 vs. 0.803 ± 0.032, p < 0.01) compared to Group H, indicating better ventilation-perfusion matching and CO₂ elimination.Conclusion: Ventilation with FiO₂ = 0.5 during OPCAB results in more favorable pulmonary gas exchange than FiO₂ = 0.8, minimizing ventilation-perfusion mismatch.Further randomized trials are warranted to refine intraoperative oxygen management in cardiac surgery.