Inspiratory pressure/maximal inspiratory pressure ratio: a predictive index of weaning outcome

Abstract

Objective: To compane the accuracy of PI/ PImax 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 PI and PImax in intubated patients. The accuracy of PI/PImax 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 PI and PImax for the successful patients (11.48±1.25 cmH2O and 47.77±4.48 cm H2O, 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 PI/PImax 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 PI/PImax provided the best separation between weaning success and failure patients. The combined usage of rapid shallow breathing index and PI/PImax ratio provided the highest accuracy with sensitivity of 0.81 and specificity of 0.93. Conclusion: The PI/PImax ratio provided a good separation between the patients who were successfully weaned and those who failed. It provides additional discriminative power to f/VT. © 1993 Springer-Verlag.