Manual hyperinflation or bagging is a physiotherapy technique commonly used on mechanically ventilated patients on intensive care. The way it is performed appears to vary widely, and in the past there has been little or no monitoring of what is actually happening during the technique in terms of what airway pressures and tidal volumes are being delivered to the patient. Conclusive evidence from large scientific studies of the benefits and side effects of manual hyperinflation are to date still lacking.