Predictors of weaning after 6 weeks of mechanical ventilation

Study objective: To identify variables associated with weaning outcome in long-term ventilator-dependent patients. Using those variables, to construct models to predict weaning success and to test the accuracy of those models. Design: Retrospective medical record review. Setting: Regional weaning center (RWC). Patients: An initial group of 421 and a subsequent group of 170 consecutive patients referred for attempted weaning after 6 weeks of mechanical ventilation. Measurements and results: Data obtained on admission to our facility were analyzed for correlation with weaning outcome. In the initial patient group, selected variables which correlated with weaning success were alveolar-arterial oxygen pressure difference (P[A-a] O2), BUN, BUN/creatinine ratio (each with p≤0.001), and female gender (p=0.04). We used these variables in logistic regression models to predict weaning success in this population. We then tested the models in the 170-patient validation group using both standard and receiver operating characteristic (ROC) curve analysis. The ROC analysis indicated 59% accuracy using P(A-a)O2 alone and 68% accuracy using all previously mentioned variables. We used data from all 565 patients with known outcome and omitted BUN/creatinine ratio to fashion a simple scoring system to predict weaning success with 70% accuracy using PA-a)O2, BUN, and Gender-the A+B+G score. Conclusion: In patients suffering prolonged mechanical ventilation, models incorporating simple measurements allowed construction of a score to predict weaning success at our RWC.