Abstract
BackgroundRisk prediction of acute mountain sickness, high altitude (HA) pulmonary or cerebral edema is currently based on clinical assessment. Our objective was to develop a risk prediction score of Severe High Altitude Illness (SHAI) combining clinical and physiological factors. Study population was 1017 sea-level subjects who performed a hypoxia exercise test before a stay at HA. The outcome was the occurrence of SHAI during HA exposure. Two scores were built, according to the presence (PRE, n = 537) or absence (ABS, n = 480) of previous experience at HA, using multivariate logistic regression. Calibration was evaluated by Hosmer-Lemeshow chisquare test and discrimination by Area Under ROC Curve (AUC) and Net Reclassification Index (NRI).ResultsThe score was a linear combination of history of SHAI, ventilatory and cardiac response to hypoxia at exercise, speed of ascent, desaturation during hypoxic exercise, history of migraine, geographical location, female sex, age under 46 and regular physical activity. In the PRE/ABS groups, the score ranged from 0 to 12/10, a cut-off of 5/5.5 gave a sensitivity of 87%/87% and a specificity of 82%/73%. Adding physiological variables via the hypoxic exercise test improved the discrimination ability of the models: AUC increased by 7% to 0.91 (95%CI: 0.87–0.93) and 17% to 0.89 (95%CI: 0.85–0.91), NRI was 30% and 54% in the PRE and ABS groups respectively. A score computed with ten clinical, environmental and physiological factors accurately predicted the risk of SHAI in a large cohort of sea-level residents visiting HA regions.
Highlights
An increased number of sea-level residents visit areas above 4000 m of altitude for leisure, sport or work
A 30% Net Reclassification Index (NRI) indicates that 30% of subjects were correctly reclassified when adding the physiological variables into the predictive model
Desaturation was not included in the physio-clinical model due to close correlation with history of Severe High Altitude Illness (SHAI) leading to overadjustement and default of calibration
Summary
An increased number of sea-level residents visit areas above 4000 m of altitude for leisure, sport or work They may suffer from severe acute mountain sickness, high altitude pulmonary or cerebral edema, especially when they are not yet acclimatized to the hypoxic environment [1]. We assessed several clinical, environmental and physiological independent risk factors of SHAI in a cohort of 1326 sea-level residents who came to an outpatient mountain medicine consultation and underwent a hypoxic exercise test before a stay at altitude above 4000 m [2]. The main risk factors evidenced were previous history of SHAI, low ventilatory and cardiac response to hypoxia at exercise, speed of ascent above 400 m per day in the acclimatization period, high desaturation during exercise in hypoxia, history of migraine, geographical location (Aconcagua, Mont-Blanc, Ladakh), female gender, regular endurance training and age under 46 years old. Calibration was evaluated by Hosmer-Lemeshow chisquare test and discrimination by Area Under ROC Curve (AUC) and Net Reclassification Index (NRI)
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