• K L Yang.
• Division of Pulmonary and Critical Care Medicine, University of Texas Health Science Center, Houston.
• Intensive Care Med. 1993 Jan 1;19(4):204-8.

ObjectiveTo compare the accuracy of PI/PImax ratio and other commonly used indices in predicting weaning outcome.DesignA prospective study.SettingIntensive care unit.Patients31 stable intubated patients ready to undergo weaning trial.MethodsA 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 ResultsMinute 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 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 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.ConclusionThe 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.

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