Working accuracy of pulse oximetry in COVID-19 patients stepping down from intensive care: a clinical evaluation

Philip, Keir Elmslie James; Bennett, Benjamin; Fuller, Silas; Lonergan, Bradley; McFadyen, Charles; Burns, Janis; Tidswell, Robert; Vlachou, Aikaterini

INTRODUCTION: UK guidelines suggest that pulse oximetry, rather than blood gas sampling, is adequate for monitoring of patients with COVID-19 if CO(2) retention is not suspected. However, pulse oximetry has impaired accuracy in certain patient groups, and data are lacking on its accuracy in patients with COVID-19 stepping down from intensive care unit (ICU) to non-ICU settings or being transferred to another ICU. METHODS: We assessed the bias, precision and limits of agreement using 90 paired SpO(2) and SaO(2) from 30 patients (3 paired samples per patient). To assess the agreement between pulse oximetry (SpO(2)) and arterial blood gas analysis (SaO(2)) in patients with COVID-19, deemed clinically stable to step down from an ICU to a non-ICU ward, or be transferred to another ICU. This was done to evaluate whether the guidelines were appropriate for our setting. RESULTS: Mean difference between SaO(2) and SpO(2) (bias) was 0.4%, with an SD of 2.4 (precision). The limits of agreement between SpO(2) and SaO(2) were as follows: upper limit of 5.2% (95% CI 6.5% to 4.2%) and lower limit of −4.3% (95% CI −3.4% to −5.7%). CONCLUSIONS: In our setting, pulse oximetry showed a level of agreement with SaO(2) measurement that was slightly suboptimal, although within acceptable levels for Food and Drug Authority approval, in people with COVID-19 judged clinically ready to step down from ICU to a non-ICU ward, or who were being transferred to another hospital’s ICU. In such patients, SpO(2) should be interpreted with caution. Arterial blood gas assessment of SaO(2) may still be clinically indicated.