Normobaric hypoxia training in military aviation and subsequent hypoxia symptom recognition

Altitude hypoxia episodes are increasingly common in military aviation. Hypoxia training is mandatory for fighter pilots, but evidence-based data on the effects of training are scarce. The purpose of this study was to validate the normobaric hypoxia (NH) training effect. Data were collected from 89 pilots from the Finnish Air Force (FINAF). This survey was conducted in a tactical F/A-18C Hornet simulator in two sessions under normobaric conditions, in which the pilots performed flight missions and breathed 21% oxygen (O₂) in nitrogen (N₂), and blinded to the pilot, the breathing gas was changed to a hypoxic mixture containing either 8, 7 or 6% O₂ in N₂. The time taken to notice hypoxia symptoms and peripheral capillary O₂ saturation was measured. A mean of 2.4 years after the initial training, pilots recognised their hypoxic symptoms 18 s quicker with 8% O₂ mixture, 20 s quicker with 7% O₂ and 10 s quicker with 6% O₂. Our data indicate that NH training in a flight simulator helps pilots to recognise hypoxia symptoms earlier, and may, thus, enhance flight safety. Practitioner Summary: We show that hypoxia training enhances pilots’ ability to recognise symptoms of acute normobaric hypoxic exposure up to 2.4 years after an initial NH training session. Based on these data, refreshment NH training is nowadays mandatory every 3 years in the FINAF as opposed to the North Atlantic Treaty Organisation (NATO) Standardisation Agreement (STANAG) requirement of 5-year intervals between hypoxia trainings. Abbreviations: O₂: oxygen; TUC; time of usefull consciousness; SpO₂: peripheral capillary oxygen saturation; NATO: North Atlantic Treaty Organization; STANAG: stanrdization agreement; HH: hypobaric hypoxia; NH: normobaric hypoxia; FINAF: finnish air force; N₂: nitrogen; ECG: electrocardiogram; CI: confidence interval; SD: standard deviation.