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Carbon monoxide (CO) is naturally synthesized in the body and plays an important role in the regulation of physiological functions such as vasodilation, angiogenesis, vascular remodeling, protection against tissue damage, and modulation of the inflammatory response. Approximately 85% of CO is produced by heme oxygenase and is excreted from the body through the respiratory system. In critical diseases such as acute respiratory failure, chronic obstructive pulmonary disease, acute pulmonary embolism, and acute myocardial infarction, low initial endogenous carboxyhemoglobin (COHb) level has been associated with high mortality and poor prognosis . The leading causes of morbidity and mortality in COVID-19 are acute respiratory failure, microthombi, and cardiac involvement.