Pulse Oximetry and Arterial Oxygen Saturation during Cardiopulmonary Exercise Testing

Abstract

ABSTRACT Introduction/Purpose Peripheral capillary oxygen saturation (SpO 2 ) is used as surrogate for arterial blood oxygen saturation. We studied the degree of discrepancy between SpO 2 and arterial oxygen (SaO 2 ) and identified parameters that may explain this difference. Methods We included patients who underwent cardiopulmonary exercise testing at Cleveland Clinic. Pulse oximeters with forehead probes measured SpO 2 and arterial blood gas samples provided the SaO 2 both at rest and peak exercise. Results We included 751 patients, 54 ± 16 yr old with 53% of female gender. Bland–Altman analysis revealed a bias of 3.8% with limits of agreement of 0.3% to 7.9% between SpO 2 and SaO 2 at rest. A total of 174 (23%) patients had SpO 2 ≥ 5% of SaO 2 , and these individuals were older, current smokers with lower forced expiratory volume in the first second and higher partial pressure of carbon dioxide and carboxyhemoglobin. At peak exercise ( n = 631), 75 (12%) SpO 2 values were lower than the SaO 2 determinations reflecting difficulties in the SpO 2 measurement in some patients. The bias between SpO 2 and SaO 2 was 2.6% with limits of agreement between −2.9% and 8.1%. Values of SpO 2 ≥ 5% of SaO 2 ( n = 78, 12%) were associated with the significant resting variables plus lower heart rate , oxygen consumption, and oxygen pulse. In multivariate analyses, carboxyhemoglobin remained significantly associated with the difference between SpO 2 and SaO 2 both at rest and peak exercise. Conclusions In the present study, pulse oximetry commonly overestimated the SaO 2 . Increased carboxyhemoglobin levels are independently associated with the difference between SpO 2 and SaO 2 , a finding particularly relevant in smokers.