Is pulse oximeter a reliable tool for non-critically ill patients with COVID-19?

Guidelines recommend using a pulse oximeter rather than arterial blood gas (ABG) for COVID-19 patients. However, significant differences can be observed between oxygen saturation measured by pulse oximetry (SpO₂ ) and arterial oxygen saturation (SaO₂ ) in some clinical conditions. We aimed to assess the reliability of the pulse oximeter in patients with COVID-19.

We retrospectively reviewed ABG analyses and SpO₂ levels measured simultaneously with ABG in patients hospitalised in COVID-19 wards.

We categorised total 117 patients into two groups, in whom the difference between SpO₂ and SaO₂ was ≤4% (acceptable difference) and >4% (large difference). A large difference group exhibited higher neutrophil count, C-reactive protein, ferritin, fibrinogen, D-dimer and lower lymphocyte count. Multivariate analyses revealed that increased fibrinogen, increased ferritin and decreased lymphocyte count were independent risk factors for a large difference between SpO₂ and SaO₂ . The total study group demonstrated the negative bias of 4.02% with the limits of agreement of -9.22% to 1.17%. The bias became significantly higher in patients with higher ferritin, fibrinogen levels and lower lymphocyte count.

Pulse oximeters may not be sufficient to assess actual oxygen saturation, especially in COVID-19 patients with high ferritin and fibrinogen levels and low lymphocyte count with low SpO₂ measurements.