Non-invasive positive pressure ventilation during sleep at 3800m

Ascent to high altitude results in hypobaric hypoxia and some individuals will develop Acute Mountain Sickness, which has been shown to be associated with low mean oxyhemoglobin saturation during sleep at high altitude. Previous research has shown that applying increased positive end-expiratory pressure by the use of expiratory valves in a face mask while awake, results in a reduction in AMS symptoms and higher oxyhemoglobin saturation. Therefore, in this research we aimed to compare sleeping oxyhemoglobin saturation and the incidence and severity of Acute Mountain Sickness in seven subjects sleeping for two consecutive nights at 3800m above sea level either using either non-invasive positive pressure ventilation, that delivered positive inspiratory and expiratory airway pressure via a face mask, or sleeping without assisted ventilation. The Lake Louise Score was used on both mornings, within an hour of waking, to assess the presence and severity of Acute Mountain Sickness. We found significant differences in the mean and minimum sleeping oxyhemoglobin saturation and the Lake Louise Score between subjects who used positive pressure ventilation during sleep and those who did not. We also found a significant difference between the mean sleeping SaO2 of those subjects who developed AMS and those who did not on the night spent without positive pressure ventilation. Key words: hypobaric hypoxia, acute mountain sickness, non-invasive positive pressure ventilation, Lake Louise Score, sleeping oxyhemoglobin saturation.