Accuracy of oxyhemoglobin saturation monitors during simulated altitude exposure of men with chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) are at risk for hypoxemia during air travel. We assessed the comparative performance of oxyhemoglobin saturation (%O2Hb) monitors on these patients during hypobaric exposure. We measured %O2Hb by arterial catheter blood co-oximetry (COOX) and compared these values to those from a transmittance ear oximeter and a reusable digital pulse oximeter. Additionally, we examined the effect of oxygen supplementation (4 L/min) on %O2Hb. A total of 18 ambulatory males with severe COPD were exposed to 8,000 ft (565 mm Hg) in a hypobaric chamber. Multiple measures of %O2Hb were made with each monitor at sea level and at 8,000 ft, with and without supplemental oxygen. By COOX, %O2Hb fell at altitude to clinically significant levels, and was subsequently corrected with supplemental oxygen. Saturations measured by the transmittance ear oximeter were very close to the COOX, underestimating the true value by only 0.6% at altitude (p less than 0.05), while the reusable digital pulse oximeter over-estimated %O2Hb alinearly by a mean of 3.8% at altitude.