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.

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 H(2)O, P(0.1) < 2.3 cm H(2)O, 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.