Improving Our Understanding of Respiratory Muscle Training to Facilitate Weaning From Mechanical Ventilation in the ICU

A majority of mechanically ventilated patients develop respiratory muscle weakness during critical illness.

The potential value of implementing rehabilitative interventions for respiratory muscle conditioning are supported by observations showing that respiratory muscle weakness is associated with prolonged duration of mechanical ventilation, difficult weaning, and increased ICU mortality.

Despite a strong theoretical rationale and some evidence supporting its use, mechanistic studies evaluating physiological adaptations that occur in respiratory muscles of mechanically ventilated patients in response to different training regimens have not been performed so far. Consequently, the characterization of IMT modalities and of the optimal approach to IMT remain largely uncertain.

To date, the great part of the studies on the topic employed an external mechanical threshold device to perform trainings, in general adopting loads ranging between 10-50% of maximal inspiratory strength (i.e. maximal inspiratory pressure (PImax)). Intermittent spontaneous breathing periods (e.g. using partially assisted or spontaneous modes of ventilation) are also frequently applied as an activating stimulus to the respiratory muscles during periods of mechanical ventilation.

A tapered flow resistive load (TFRL) device (POWERbreathe KH2, HaB International, UK) has been already tested and implemented at University Hospital Leuven as a way of loading respiratory muscles in ICU patients. The TFRL approach represents a potential more optimal way of loading the respiratory muscles in patients on prolonged mechanical ventilation. Such a loading approach allows higher inspiratory tidal volumes to be reached and higher work and power generation during trainings, by adapting to changes in length-tension characteristics of the inspiratory muscles during inspiration.