Operation Everest II: comparison of four instruments for measuring blood O2 saturation.

The bias and precision of four different methods for determining O2 saturation (SO2) were evaluated during a study of hypobaric hypoxia conducted with seven male subjects exposed progressively over a 40-day period to simulated altitudes from sea level (760 Torr) to 8,840 m (240 Torr). SO2 of arterial and mixed venous blood samples were measured with the Instrumentation Laboratory 282 CO-oximeter (CO-OX), the Radiometer ABL-300 (ABL), and the Lex-O2-Con-K (LEX). Noninvasive measurements of arterial SO2 were made with a Hewlett-Packard 47201A ear oximeter (EAR-OX). The CO-OX method was used as a secondary standard for comparison with the other methods because it has been validated against the classical Van Slyke method over a wide physiological range (Maas et al., Clin. Chim. Acta 29: 303-309, 1970). The LEX results most closely approximated but consistently underestimated those of the CO-OX: LEX = 0.93 CO-OX -0.86, standard error of the estimate (SEE) = 5.17, r = 0.98, n = 670. The ABL method appeared to combine two linear trends: for SO2 greater than 75%, ABL = 0.84 CO-OX +14.4, SEE = 1.77, r = 0.97, n = 369; less than 75%, ABL = 0.98 CO-OX +5.9, SEE = 4.44, r = 0.97, n = 486. The EAR-OX results were found to approximate those of the CO-OX at SO2 values only greater than 65%: EAR-OX = 1.07 CO-OX -6.12, SEE = 7.71, r = 0.98, n = 326.(ABSTRACT TRUNCATED AT 250 WORDS)