Abstract
Critical COVID-19 is a life-threatening disease characterized by severe hypoxemia with complex pathophysiological mechanisms that are not yet completely understood. A pathological shift in the oxyhemoglobin curve (ODC) was previously described through the analysis of p50, intended as the oxygen tension at which hemoglobin is saturated by oxygen at 50%. The aim of this study was to analyze Hb-O2 affinity features over time in a cohort of critically ill COVID-19 patients, through the analysis of ODC p50 behavior. A retrospective analysis was performed; through multiple arterial blood gas (ABG) analyses, each p50 was calculated and normalized according to PaCO2, pH and temperature; patients’ p50 evolution over time was reported, comparing the first 3 days (early p50s) with the last 3 days (late p50s) of ICU stay. A total of 3514 ABG analyses of 32 consecutive patients were analyzed. The majority of patients presented a left shift over time (p = 0.03). A difference between early p50s and late p50s was found (20.63 ± 2.1 vs. 18.68 ± 3.3 mmHg, p = 0.03); median p50 of deceased patients showed more right shifts than those of alive patients (24.1 vs. 18.45 mmHg, p = 0.01). One-way ANOVA revealed a p50 variance greater in the early p50s (σ2 = 8.6) than in the late p50s (σ2 = 3.84), associated with a reduction over time (p < 0.001). Comparing the Hb-O2 affinity in critically ill COVID-19 patients between ICU admission and ICU discharge, a temporal shift in the ODC was observed.
Highlights
The oxyhemoglobin dissociation curve (ODC) is a sigmoid curve representing the relationship between arterial hemoglobin saturations (SaO2 ) at different arterial blood oxygen tensions (PaO2 ) [1,2]; the continuous correlation between SaO2 and PaO2 is reported as hemoglobin–oxygen (Hb-O2 ) affinity
We described the p50 shift over time, plotting p50 values for each arterial blood gas analysis and representing the ODC temporal change
A total of 29 (87.8%) patients were men, with a mean age of 62 years (SD 11.7); 12 (36.3%) patients were affected with diabetes, 14 (42.4%) with arterial hypertension, 3 (9%) with chronic obstructive pulmonary disease (COPD), 5 (15.1%) with obstructive sleep apnea syndrome (OSAS) and 5 patients (15.1%) presented with a diagnosis of pulmonary embolism at intensive care unit (ICU) admission
Summary
The oxyhemoglobin dissociation curve (ODC) is a sigmoid curve representing the relationship between arterial hemoglobin saturations (SaO2 ) at different arterial blood oxygen tensions (PaO2 ) [1,2]; the continuous correlation between SaO2 and PaO2 is reported as hemoglobin–oxygen (Hb-O2 ) affinity. Various biochemical variables can physiologically influence the Hb-O2 affinity, leading to an ODC shift and to a consequent p50 change [5], with right and left shifts occurring in relation to changes in blood pH, PaCO2 , temperature and 2,3-biphosphoglycerate (2,3-BPG) plasma concentration (Bohr/Haldane effect). The ODC shift can be induced by other physiological or pathological conditions, such as aging [6], diabetes mellitus [7], anesthesia [8] and respiratory failure [9]. Considering these variables, an equation to represent the corrected
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