['Manual hyperinflation (MH) can be performed as part of airway management in intubated and mechanically ventilated patients to mobilize airway secretions. Although previous studies demonstrated MH to be associated with hemodynamic and respiratory instability, we hypothesized MH to cause fewer adverse events (AEs) when performed by experienced and trained nurses in stable critically ill patients.', 'The incidence and type of AEs associated with MH were studied in a 28-bed mixed medical-surgical Intensive Care Unit. A difference in mean arterial pressure (MAP) or heart rate (HR) >15%, a decrease in peripheral oxygen saturation (SpO2) >5%, and a change in end-tidal (et)-CO2 >20% were considered AEs. A decrease of MAP to ≤60 mmHg, any new arrhythmia, and a decrease of SpO2 ≤90% were all considered severe AEs. Also, all changes in medication were considered severe AEs.', 'A total of 107 MH maneuvers in 74 patients, performed by 57 nurses, were observed and analyzed. A total of 17 MH maneuvers (16%) were associated with any AE; 7 maneuvers (6%) were associated with a severe AE. Overall, MH did not affect MAP. MH caused a statistically significant but clinically irrelevant increase of HR (from 87±24 to 89±22 bpm). In one patient the MAP dropped from 70 mmHg to 60 mmHg, requiring adjustment of vasopressor therapy; one patient developed ventricular tachycardia requiring electric cardioversion. In general, MH did not affect SpO2. In one patient SpO2 dropped below 90%, requiring additional oxygen supply for 10 minutes. MH caused a statistically significant but clinically irrelevant increase of et-CO2 levels (from 4.4±0.9 to 4.5±1.0 kPa). Five patients developed anxiety/agitation during or shortly after MH, mandating additional sedation in four patients. Occurrence of (severe) AEs was not associated with any specific patient or MH characteristic.'] Is manual hyperinflation associated with a low rate of adverse events when performed by experienced and trained nurses in stable critically ill patients -- a prospective observational study?