Predictive risk factors for pulmonary oxygen transfer in patients undergoing coronary artery bypass grafting

The ratio of arterial oxygen tension to inspired oxygen fraction (PaO2/FiO2) is a useful indicator for weaning patients from mechanical ventilation and a reliable predictor of pulmonary dysfunction after cardiac surgery. The aim of this study was to elucidate the patient characteristics and variables that affect the PaO2/FiO2 ratio. Between 1994-1998, 167 patients who underwent coronary artery bypass grafting (CABG) were examined retrospectively. Spearman's correlation coefficients were calculated between the PaO2/FiO2 ratio and intubation period, and length of ICU stay. Patients were then divided into two groups with a PaO2/FiO2 ratio < 350 and PaO2/FiO2 ratio > or = 350. Univariate analysis of the putative risk factors was performed. A logistic regression model was developed to evaluate factors that would influence the PaO2/FiO2 ratio. A significant correlation was observed between the PaO2/FiO2 ratio and intubation period, and length of ICU stay. Univariate predictors of a PaO2/FiO2 ratio < 350 were low body weight, low preoperative PaO2 long operation time, high FiO2, low postoperative PaO2 history of smoking, hypertension and opening of pleura (p < 0.05). Excellent prediction was found with a model consisting of preoperative PaO2 and hypertension.

The results of this study suggest that patients with a low preoperative PaO2 or hypertension may need more careful peri- and postoperative management since these factors are closely associated with the PaO2/FiO2 ratio.