Abstract
Pulmonary involvement in COVID-19 is frequently associated with alterations in oxygenation. The arterial partial pressure of oxygen (PaO(2)) is the most clinically used variable to assess such oxygenation, since it decisively influences the oxygen transported by hemoglobin (expressed by its percentage of saturation, SaO(2)). However, two recent studies conducted respectively in silico and using omic techniques in red blood cells of COVID-19 patients have suggested that SARS-CoV-2 could decrease the affinity of oxygen for the hemoglobin (which would imply that PaO(2) would overestimate SaO(2)), and also reduce the amount of this carrier molecule. OBJECTIVE: To evaluate this hypothesis in blood samples from COVID-19 patients. METHODS: Blood gases of all COVID-19 patients performed in our laboratory in two months were included, as well as those from two control groups: synchronous patients with negative PCR for SARS-CoV-2 (SCG) and a historical group (HCG). Both SaO(2) and venous saturations (SvO(2)) measured by cooximetry (COX) were compared separately with those calculated using the Kelman (K), Severinghaus (SV) and Siggaard-Andersen (SA) equations in each group. RESULTS: Measured and calculated SaO(2) and SvO(2) were practically equivalent in all groups. Intraclass correlation coefficients (ICC) for SaO(2) in COVID-19 were 0.993 for COX-K and 0.992 for both COX-SV and COX-SA; being 0.995 for SvO(2) for either COX-K, COX-SV or COX-SA. Hemoglobin and ferritin were slightly higher in COVID-19 compared to SCG and HCG (hemoglobin, p < 0.001 for both; ferritin, p < 0.05 for SCG and p < 0.001 for HCG). CONCLUSION: Under clinical conditions SARS-CoV-2 does not have an appreciable influence on the affinity of oxygen for the hemoglobin, nor on the levels of this carrier molecule. Therefore, PaO(2) is a good marker of blood oxygenation also in COVID-19.