INSPIRATORY PRESSURE MAXIMAL INSPIRATORY PRESSURE RATIO - A PREDICTIVE INDEX OF WEANING OUTCOME

Objective: To compare the accuracy of P(I)/P(I)max ratio and other commonly used indices in predicting weaning outcome. Design: A prospective study. Setting: Intensive care unit. Patients: 31 stable intubated patients ready to undergo weaning trial. Methods: A simple method was developed to measure the P(I) and P(I)max in intubated patients. The accuracy of P(I)/P(I)max ratio and other commonly used indices in predicting outcome were compared. All indices were measured prior to weaning trial using standardized methods. Measurements and results: Minute ventilation of the successful patients (13.00 +/- 0.67 (SE) l/min) was not significantly different from the failure patients (10.64 +/- 1.26 l/min, p = 0.10). The P(I) and P(I)max for the successful patients (11.48 +/- 1.25 cmH2O and 47.77 +/- 4.48 cmH2O, respectively) and the unsuccessful patients (14.32 +/- 2.31 cmH2O and 40.16 +/- 4.55 cmH2O, respectively) were also not significantly different (p = 0.28 and 0.24, respectively). The P(I)/P(I)max ratio was lower for the weaning successes (0.26 +/- 0.03) than for the weaning failures (0.36 +/- 0.04, p < 0.05). The threshold value of 0.3 for P(I)/P(I)max provided the best separation between weaning success and failure patients. The combined usage of rapid shallow breathing index and P(I)/P(I)max ratio provided the highest accuracy with sensitivity of 0.81 and specificity of 0.93. Conclusion: The P(I)/P(I)max ratio provided a good separation between the patients who were successfully weaned and those who failed. It provides additional discriminative power to f/V(T).