Comparison of Maximal Inspiratory Pressure,Tracheal Airway Occlusion Pressure,and Its Ratio in the Prediction of Weaning Outcome: Impact of the Use of a Digital Vacuometer and the Unidirectional Valve

Abstract

OBJECTIVE:

To investigate the predictive value of the maximal inspiratory pressure obtained by a digital vacuometer using a unidirectional valve (P_ImaxUV) as to weaning outcome, and to compare its performance with the respiratory drive using airway occlusion pressure at 0.1 second (P_0.1), and P_0.1/P_ImaxUV.

METHODS:

Patients on mechanical ventilation for > 24 hours who fulfilled the weaning criteria were prospectively enrolled. Measurements of P_ImaxUV and P_0.1 were accomplished with a digital vacuometer with a unidirectional valve that allows only exhalation. Measured values were electronically recorded and stored on the digital vacuometer measurement device. Cutoff points for the used parameters were: absolute values of P_ImaxUV > 30 cm H₂O, P_0.1 < 2.3 cm H₂O, and P_0.1/P_ImaxUV < 0.10. Receiver operating characteristic curves were calculated to compare the predictive values of the indexes.

RESULTS:

One hundred three subjects completed the test. The areas under the receiver operating characteristic curve were 0.79 ± 0.04, 0.65 ± 0.05, and 0.74 ± 0.04 for P_ImaxUV, P_0.1, and P_0.1/P_ImaxUV, respectively. The area under the receiver operating characteristic curve for P_ImaxUV was higher than for P_0.1 and P_0.1/P_ImaxUV, but statistical significance was only found against P_0.1 (P = .007).

CONCLUSIONS:

Every studied index had only a modest performance regarding prediction of weaning outcome. Of note, P_ImaxUV values obtained by digital technology using a unidirectional valve performed better than historically reported using a conventional techniques, surpassing P_0.1 and P_0.1/P_ImaxUV in this regard.