Ascha M; Bhattacharyya A; Ramos JA; Tonelli AR.

Medicine & Science in Sports & Exercise. 50(10):1992-1997, 2018 Oct.
VI 1

INTRODUCTION/PURPOSE: Peripheral capillary oxygen saturation (SpO2) is
used as surrogate for arterial blood oxygen saturation. We studied the
degree of discrepancy between SpO2 and arterial oxygen (SaO2) 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
SpO2 and arterial blood gas samples provided the SaO2 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 SpO2 and SaO2 at rest. A total of 174
(23%) patients had SpO2 >= 5% of SaO2, 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%) SpO2 values were lower than the SaO2
determinations reflecting difficulties in the SpO2 measurement in some
patients. The bias between SpO2 and SaO2 was 2.6% with limits of agreement
between -2.9% and 8.1%. Values of SpO2 >= 5% of SaO2 (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 SpO2 and SaO2 both at rest and peak exercise.
CONCLUSIONS: In the present study, pulse oximetry commonly overestimated
the SaO2. Increased carboxyhemoglobin levels are independently associated
with the difference between SpO2 and SaO2, a finding particularly relevant
in smokers.