Transconjunctival Oxygen Monitoring as a Predictor of Hypoxemia During Helicopter Transport

As the use of helicopters for air transport of critically ill patients increases, the availability of monitoring devices for physiological parameters during flight becomes important. It has long been known that arterial P_O2 (Pa_O2) decreases during unsupplemented, non-pressurized flight. In this study, the authors examined the use of the transconjunctival oxygen (cjO₂) monitor for assessing the adequacy of arterial oxygenation during helicopter flight in four healthy volunteers. Arterial Pa_O2 as measured by conventional blood gas analysis was compared with cjO₂ at ground level, 5,000 feet, and 10,000 feet altitude. Mean Pa_O2 dropped significantly from 93.5 to 81.5 to 58.5 mm Hg, respectively (P < 0.001, analysis of variance with repeated measures). Mean cjO₂ also decreased significantly from 63.8 to 52.0 to 34.8 mm Hg, respectively (P < 0.001, analysis of variance with repeated measures). Within individual subjects, cjO₂ was an accurate predictor of Pa_O2 (P < 0.001, multiple regression analysis). The relationship between cjO₂ and Pa_O2 was linear with a regression coefficient of 1.147. The authors conclude that the transconjunctival O₂ monitor may be useful for monitoring the adequacy of arterial oxygenation during helicopter flight in hemodynamically stable patients. The results of study also support the use of supplemental oxygen in all patients subjected to helicopter transport.