Preoperative prediction of postoperative respiratory outcome: Coronary artery bypass grafting

Objective: The hypothesis that traditionally defined preoperative risk factors predict prolonged mechanical ventilation after coronary artery bypass graft surgery (CABG) was tested in our cohort. The predictive power of these factors was quantified, and specific patient subsets destined for prolonged mechanical ventilation after CABG surgery were defined. Design: Five hundred thirteen consecutive patients undergoing CABG were prospectively evaluated. Preoperative pulmonary evaluation included clinical historic data, standard spirometry, and arterial blood gas. Preoperative cardiac parameters included clinical parameters and left ventricular function assessment. Nonthoracic organ (renal, endocrine, pancreas, liver) function was assessed. Setting: University-based, tertiary, referral center. Interventions: None (observational only). Outcomes measured: Duration of mechanical ventilation, duration of surgical ICU stay, and mortality. Results: Multivariate regression analyses revealed that for the patient undergoing routine elective surgery and the patient undergoing urgent surgery, prolonged mechanical ventilation and death were rare events (8.3% and 2.0%, respectively). The combination of reduced left ventricular ejection fraction and the presence of selected preexisting comorbid conditions (clinical congestive heart failure, angina, current smoking, diabetes) served as modest risk factors for prolonged mechanical ventilation; their absence strongly predicted an uncomplicated postoperative respiratory course. No pulmonary diagnosis, mechanical lung function, or blood gas parameter substantially contributed to predicting adverse outcome. Classification and regression tree subgroup analysis refined specific factors important in specific subgroups. Conclusion: With the exception of left ventricular ejection fraction, no preoperative factors emerge as good predictors across all subgroups. This series suggests that pulmonary diagnosis, lung mechanics, and blood gas parameters do not offer the clinician global rules in predicting postoperative respiratory outcome, nor should they be used as exclusion criteria for CABG surgery.