Does Baseline Pao2/Fio2 Affect the In-Hospital Outcome in Patients Undergoing Coronary Artery Bypass Grafting?

Background: Oxygen saturation and the PaO2 are the direct risk factors for post -operative respiratory outcome in patients undergoing prolonged surgery under general anaesthesia. However the effect of preoperative PaO2 and PaO2/FiO2 ratio on the postoperative course of the patient undergoing coronary artery bypass grafting is not known. Hypothesis: Pre-operative PaO2 and PaO2/FiO 2 ratio have a significant effect on the postoperative outcome among the patients undergoing coronary artery bypass grafting. Study design: Prospective clinical study Setting: Tertiary health care centre Materials and Methods: One hundred and fifty eight consecutive patients with a EURO Score of <6 undergoing routine first time coronary artery bypass grafting were selected for this study. Patients with ventricular dysfunction, Chronic Obstructive Pulmonary Disease (COPD), renal or hepatic dysfunction, patients on mechanical ventilation, on preoperative Intra Aortic Ballon Pump (IABP) and those who had to undergo emergency surgery were excluded from the study. All patients were managed by the same anaesthesia and surgical team and the anaesthesia management protocol was similar for all the patients. The pre-operative PaO2/FiO2 ratio (base line) for all patients was noted before anaesthesia induction in room air. The primary outcome measures were duration of mechanical ventilation, ICU stay and hospital stay. The secondary outcome measures were requirement of inotropes, arrhythmias, requirement of IABP, cardiogenic shock, perioperative myocardial infarction, sepsis, respiratory failure , any other organ dysfunction and death .The total duration of follow up period was one month. Statistical analysis: Seventeen subjects were subsequently dropped because of incomplete data. Consequently, the data for 141 subjects were used for the analysis. The various methods used were Student T test, Spearman’s coefficient correlation, bi-variate and univariate logistic regression analysis. In each case a p value of <0.05 was considered to be significant. Results: There exists a positive correlation between preoperative PaO2/FiO2 ratio and duration of intubation (r = -0.5607, p = 0.001) as well as Intensive Care Unit (ICU) stay (r = -0.2564, p = 0.002). PaO2/FiO2 ratio also has a positive correlation with the use of inotropes (p=0.03) and frequency of death (p=0.014) in the patients undergoing CABG . Conclusion: Low pre-operative PaO2/FiO2 ratio has a direct impact on the in-hospital outcome among the patients undergoing coronary arterybypass grafting.