Pulse Oximetry and Arterial Oxygen Saturation during Cardiopulmonary Exercise Testing

Abstract

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.

Conflict of interest statement

Conflict of Interest Statements:

Mona Ascha BS: The author has no significant conflicts of interest with any companies or organization whose products or services may be discussed in this article.

Anirban Bhattacharyya MD: The author has no significant conflicts of interest with any companies or organization whose products or services may be discussed in this article.

Jose A Ramos RT: The author has no significant conflicts of interest with any companies or organization whose products or services may be discussed in this article.

Adriano R Tonelli MD, MSc: The author has no significant conflicts of interest with any companies or organization whose products or services may be discussed in this article.

Figures

Figure 1. Bland-Altman plots testing the differences between SpO2 and SaO2 at rest and peak exercise

Plots show the mean difference and 95% confidence interval between SpO2 and SaO2, labeled by smoking status (current smoker, ex-smoker and never smokers). Panel A: determinations at rest. Panel B: determinations at peak exercise.