Bedside blood gas analysis in airborne rescue operations.

The alveolar partial oxygen pressure (Pao(2)) recorded from 20 ventilated patients was found to decrease by 16 mm Hg during airborne rescue helicopter transport at an average altitude of 1780 feet mean sea level. The initial departure altitude was 192 feet, and the flight ascended to 2200 feet above ground level. Hence, the Pao(2) drop in patients was exclusively attributable to cruising altitude (atmospheric pressure = -42 mm Hg). Pathophysiological alterations include drops in the oxygenation index (-50 mm Hg), arterial partial oxygen pressure (-34 mm Hg), and heart rate (+7 beats per minute) and are attributable to growing disproportions in ventilation and perfusion. The absolute Pao(2) level does depend largely on the Fio(2) value.