Pulse Oximetry for Monitoring Patients with COVID-19 at Home. Potential Pitfalls and Practical Guidance

Abstract

During the ongoing coronavirus disease (COVID-19) pandemic, reports in social media and the lay press indicate that a subset of patients are presenting with severe hypoxemia in the absence of dyspnea, a problem unofficially referred to as "silent hypoxemia." To decrease the risk of complications in such patients, one proposed solution has been to have those diagnosed with COVID-19 but not sick enough to warrant admission monitor their arterial oxygenation by pulse oximetry at home and present for care when they show evidence of hypoxemia. Though the ease of use and low cost of pulse oximetry makes this an attractive option for identifying problems at an early stage, there are important considerations with pulse oximetry about which patients and providers may not be aware that can interfere with successful implementation of such monitoring programs. Only a few independent studies have examined the performance of pocket oximeters and smart phone-based systems, but the limited available data raise questions about their accuracy, particularly as saturation falls below 90%. There are also multiple sources of error in pulse oximetry that must be accounted for, including rapid fluctuations in measurements when the arterial oxygen pressure/tension falls on the steep portion of the dissociation curve, data acquisition problems when pulsatile blood flow is diminished, accuracy in the setting of severe hypoxemia, dyshemoglobinemias, and other problems. Recognition of these issues and careful counseling of patients about the proper means for measuring their oxygen saturation and when to seek assistance can help ensure successful implementation of needed monitoring programs.

Keywords: COVID-19; hypoxemia; oxygen saturation; pulse oximetry.

Figures

Figure 1.

Examples of data plots from Bland-Altman analysis. (A) An example on an ideal monitoring device. The bias is close to zero and the levels of agreement are narrow. (B) An example of monitoring device with poor performance. Compared with A, the bias is further away from zero and the limits of agreement are wider. (C) Another example of a monitoring device with poor performance. The differences between the monitor and the gold standard are markedly larger at the low end of the measured values than at the high end. Increased spread in values at the low end of the spectrum of oxygen saturation is a known feature of pulse oximeters. SD = standard deviation.

Figure 2.

The hemoglobin-oxygen dissociation curve. The light-gray shaded area highlights the flat portion of the curve where the oxygen saturation remains relatively stable as the partial pressure of oxygen (Po2) falls. The dark-gray shaded area highlights the steeper portion of the curve where small changes in the Po2 lead to large fluctuations of the oxygen saturation. Point A denotes the average Po2 for a healthy person with normal lung function living at sea level, whereas Point B denotes the average Po2 for a healthy person living at ∼1,600 m in elevation. This position lies closer to the steeper portion of the dissociation curve than in an individual at sea level.