Predictive Risk Factors for Pulmonary Oxygen Transfer in Patients Undergoing Coronary Artery Bypass Grafting

Abstract

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 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.
Conclusion: 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.