© 2016 John Wiley & Sons LtdAims and objectives: To assess the consistency and safety of manual hyperinflation delivery by nurses of variable clinical experience using a resuscitator bag during physiotherapy treatment. Background: Manual hyperinflation involves the delivery of larger than normal gas volumes to intubated patients and is routinely used by nurses in collaboration with physiotherapists for the management of retained sputum. The aim is to deliver slow deep breaths with an inspiratory hold without unsafe airway pressures, lung volumes or haemodynamic changes. In addition, nursing staff should be able to ‘feel' differences in resistance and adjust their technique accordingly. Design: Prospective observational study utilising the simulation of a mechanically ventilated patient. Methods: Thirty-three nurses delivered manual hyperinflation to a SimMan3G mannequin who had three distinct lung scenarios applied (normal; asthma; Acute Respiratory Distress Syndrome) in randomised order during simulated physiotherapy treatment. Respiratory rate, tidal volume (Vt), mean inspiratory flow rate (Vt/Ti), and peak airway pressure data were generated. Results: Over all scenarios, mean respiratory rate = 12·3 breaths/minute, mean Vt = 638·6 mls, mean inflation time = 1·3 seconds and peak airway pressure exceeded 40 cm H2O in 41% of breaths, although only in 10% of breaths during the ‘normal' lung scenario. Conclusions: Experienced nurses were able to manually hyperinflate ‘normal' patients in a simulated setting safely. Despite their knowledge of barotrauma, unsafe airway pressures were delivered in some scenarios. Relevance to clinical practice: Training with regard to safe airway pressures, breath hold and adequate volumes is recommended for all nurses undertaking the procedure. Nurses and physiotherapists must closely monitor the patient's condition during manual hyperinflation thereby recognising changes with regard to lung compliance and airway resistance, with nurses responding by altering their technique. The addition of a pressure manometer in the circuit may improve patient safety when performing manual hyperinflation.