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

UK guidelines suggest that pulse oximetry, rather than blood gas sampling, is adequate for monitoring of patients with COVID-19 if CO₂ 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.

We assessed the bias, precision and limits of agreement using 90 paired SpO₂ and SaO₂ from 30 patients (3 paired samples per patient). To assess the agreement between pulse oximetry (SpO₂) and arterial blood gas analysis (SaO₂) 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.

Mean difference between SaO₂ and SpO₂ (bias) was 0.4%, with an SD of 2.4 (precision). The limits of agreement between SpO₂ and SaO₂ 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%).

In our setting, pulse oximetry showed a level of agreement with SaO₂ 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, SpO₂ should be interpreted with caution. Arterial blood gas assessment of SaO₂ may still be clinically indicated.