The ability of pulse oximetry to screen for hypoxemia and hypercapnia in patients breathing room air.

This study was designed to determine whether high room-air pulse oximetry can rule out hypoxemia or moderate hypercapnia. Based on retrospective analysis of 513 arterial blood gas results, oxygen saturation cutpoints were derived. Coincidentally, a room-air oxygen saturation (RAO2 sat) value of 96% was selected as a cutpoint to screen for both hypoxemia (PaO2 < 70 mm Hg) and moderate hypercapnia (PaCO2 > 50 mm Hg). These tests were validated prospectively by using a convenience sample of 213 Emergency Department patients in whom room-air arterial blood gas sampling was ordered. To detect hypoxemia, the sensitivity of RAO(2) sat < or = 96% was 1.0 [0.95-1.0, 95% confidence interval (CI)] and specificity was 0.54 (0.45-0.64, 95% CI). To detect hypercapnia, the sensitivity of RAO(2) sat < or = 96% was 1.0 (0.7-1.0) and specificity was 0.31 (0.25-0.38, 95% CI). We concluded that RAO(2) sat > or = 97% rules out hypoxemia and may also rule out moderate hypercapnia.