• Leonardo Cordeiro de Souza, Cyro Teixeira da Silva, and Jocemir Ronaldo Lugon.
• Universidade Federal Fluminense, Niterói, Rio de Janeiro, Brazil. leonardo.uti@gmail.com
• Resp Care. 2012 Feb 1;57(2):257-62.

BackgroundThe measurement of the maximal inspiratory pressure (P(Imax)) is of great importance in choosing the time for the start of weaning.ObjectiveTo measure the inspiratory pressure in mechanically ventilated patients suitable for weaning to determine the point at which the P(Imax) is achieved within 60 seconds of observation, and analyze factors associated with P(Imax) values.MethodsMeasurement of P(Imax) was accomplished with a digital vacuometer with a unidirectional valve, which allows only exhalation (P(ImaxUV)). With this technique, values are registered and stored, remaining accessible whenever necessary. All patients were on mechanical ventilation, and met the criteria recommended by the American Thoracic Society/European Respiratory Society in 2007 to undergo weaning trial.ResultsEighty-four from the 87 enrolled patients completed the test. No patients reached the P(ImaxUV) in the first 20 seconds of observation. P(ImaxUV) was achieved between 20.1 and 40 seconds in 12 patients (14.0%), and between 40.1 and 60 seconds in 72 cases (86.0%). In a multivariate analysis model in which age, sex, days of mechanical ventilation, APACHE score, and respiratory drive (measured as airway-occlusion pressure 0.1 s after the start of inspiratory flow [P(0.1)]) were included, only age (P = .006) and P(0.1) (P = .003) were significantly associated with the values of P(ImaxUV).ConclusionsWithin an observation period of 60 seconds, the majority of patients reached the maximal inspiratory peak between 40.1 and 60 seconds. Older patients were found to have lower P(ImaxUV) values, whereas higher values for P(0.1) strongly correlated with higher P(ImaxUV) values. These findings are potentially useful to improve successful weaning prediction in the future, but further studies are needed to better clarify this issue.

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