The cardiovascular effects of inspired oxygen fraction in patients undergoing on-pump coronary artery surgery

Increased inspired oxygen fraction (FiO2) has significant negative hemodynamic effects in conscious volunteers. The aspiratory gas during open heart surgery with on-pump technique usually consists of 100% oxygen without any N2O because of the risks of bubble embolism during these procedures. We sought to establish the effected of inspired pure oxygen in comparison to 50% oxygen in patients. During anesthesia in cardiac coronary bypass surgery. In a clinical trial study, sixty adult patients (40-70 y/o) with ASA II or III undergoing elective on-pump coronary artery bypass were elected. They received either a mixture of 50% O2 with 50% air (case group=30) or 100% of oxygen (control group=30) throughout the anesthesia. Cardiac index (CI) was measured by non invasive cardiac output (NICO) technique using end tidal PCO2. Measurements of systolic, diastolic and mean blood pressure as well as heart rate (HR) and central venous pressure (CVP), PaO2, arterial PH and CI were obtained at pre-bypass, post bypass, end of surgery and 2 hours after ICU admission. Intra operative requirements for isotropic drugs were also evaluated. Data were analyzed by SPSS software using X2, t, ANOVA and ManWithny tests, P<0.05 was considered as significant. No differences were found between the two groups with regard to age, sex pump time, operation time and body mass index and preoperative ejection fraction (EF). 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 control group required more isotropic drug support than the case group (16 vs. 8 patients respectively; P<0.05). Likewise, the mean CVP was higher in the control group compared with the case group (P<0.05). Hyperoxia increases CVP and isotropic requirements during cardiac surgery in anaesthetized patients. Therefore, exposing patients during and after coronary artery surgery to hyperoxia induces significant hemodynamic change as which require more extensive studies with invasive CI measurements and larger groups.