The Cardiovascular Changes Induced by Inspired Oxygen Fraction in Patients Undergoing on-pump Coronary Artery Surgery

Background: The inspiratory gas during open heart surgery with on-pump technique usually consists of 100% oxygen without any N2O because the risks of bubble embolism during these procedures. We sought to establish whether the cardiovascular effects of increased FiO2 are also present in cardiac surgery patients. Patients and Methods: The present study was a randomized double- blind clinical trial on sixty adult patients (40-70 years) with the cardiac ejection fraction (EF) of more than 40% and ASA II or III undergoing elective on-pump coronary artery bypass. They received either a mixture of 50% O2 with 50% air (case group=30) or 100% oxygen (control group=30) throughout the anesthesia. Data were analyzed by SPSS software using t-test and Q-square as well as non parametric tests wherever appropriate. Results: The mean values of systolic, diastolic and mean blood pressure as well as HR and CI were similar in the case and control groups (p > 0.05) at all times of measurement. The mean PaO2 was significantly higher in the control group (p < 0.05). The mean pH was statistically higher in the control group but not clinically noticeable. The control group required more inotropic drug support than the case group (16 vs. 8 patients respectively). Likewise, the mean venous pressure was higher in the control group compared with the case group. Conclusions: Exposing patients during and after coronary artery surgery to hyperoxia induced significant hemodynamic changes which required more extensive studies with invasive CI measurements and larger groups.