Discordance Between Invasive and NonInvasive Oxygen Saturation in Critically Ill COVID-19 Patients

Objectives To investigate discordance in oxy-hemoglobin saturation measured both by pulse oximetry (SpO 2 ) and arterial blood gas (ABG, SaO 2 ) among critically ill coronavirus disease 2019 (COVID-19(+)) patients compared to COVID-19(-) patients. Methods Paired SpO 2 and SaO 2 readings were collected retrospectively from consecutive adult admissions to four critical care units in the United States between March and May 2020. The primary outcome was the rate of discordance (|SaO 2 -SpO 2 |>4%) in COVID-19(+) versus COVID-19(-) patients. The odds each cohort could have been incorrectly categorized as having a PaO 2 /FiO 2 above or below 150 by their SpO 2 : Fractional inhaled oxygen ratio (pulse oximetry-derived oxyhemoglobin saturation:fraction of inspired oxygen ratio [SF]) was examined. A multivariate regression analysis assessed confounding by clinical differences between cohorts including pH, body temperature, renal replacement therapy at time of blood draw, and self-identified race. Results There were 263 patients (173 COVID-19(+)) included. The rate of saturation discordance between SaO 2 and SpO 2 in COVID-19(+) patients was higher than in COVID-19(-) patients (27.9% vs 16.7%, odds ratio [OR] 1.94, 95% confidence interval [CI]: 1.11 to 2.27). The average difference between SaO 2 and SpO 2 for COVID-19(+) patients was −1.24% (limits of agreement, −13.6 to 11.1) versus −0.11 [–10.3 to 10.1] for COVID-19(–) patients. COVID-19(+) patients had higher odds (OR: 2.61, 95% CI: 1.14-5.98) of having an SF that misclassified that patient as having a PaO 2 :FiO 2 ratio above or below 150. There was not an association between discordance and the confounders of pH, body temperature, or renal replacement therapy at time of blood draw. After controlling for self-identified race, the association between COVID-19 status and discordance was lost. Conclusions Pulse oximetry was discordant with ABG more often in critically ill COVID-19(+) than COVID-19(–) patients. However, these findings appear to be driven by racial differences between cohorts.