Sustained maximal inspiratory manoeuvres can be used to predict extubation outcome after prolonged periods of mechanical ventilation

Abstract

Rationale: Maximal inspiratory pressure (MIP) is an accepted effort-dependent measure of global inspiratory muscle strength. Although numerous studies have examined its ability to predict weaning /extubation outcome after mechanical ventilation, MIP has generally been found to have lower specificity than is clinically acceptable. The Respiratory Trainer (RT2) is a new device originally conceived as a methodology for training the inspiratory muscles. It generates three measures of inspiratory muscle function including a new measure called prolonged MIP (PMIP) area. This is calculated as the area under the curve produced by sampling maximal inspiratory pressure at 16 Hz during a sustained inspiratory manoeuvre.Methods: Twenty-seven intubated adults who had required prolonged mechanical ventilation (48 hours plus) and were deemed ready for extubation were measured using the RT2 prior to extubation. Differences in PMIP area measures between extubation success and failure outcome groups were then sought using independent samples t tests. Sensitivity and specificity of different levels of PMIP area to predict outcome were also calculated using ROC curves.Results: Significant differences in PMIP area were found between the extubation success and failure groups (t = 7.371, p <0.001). A PMIP area cut-off point of 57.5 pressure-time units gave a sensitivity and specificity of 1.0 for extubation outcome prediction.Conclusion: PMIP area measures were significantly different in the extubation success and failure outcome groups. This work suggests that PMIP area may have a role in predicting extubation outcome after prolonged periods of mechanical ventilation