Active management of the casualty's airway during the ascent is necessary only as far as avoiding or correcting any position that tends to close the airway, such as extreme flexion of the neck. Expanding gases will generally pass passively out of the airway during rescue from depth, and pulmonary barotrauma is rare. A gradual and natural outflow of expanding air during the ascent may help prevent aspiration of water into the lungs. There is no evidence that compressing the chest to promote exhalation is more effective than simply maintaining an open airway.