CRP and coronary artery disorder: The other factors responsible for HFNO failure include being aged over 60, comorbidities (ischemic heart disease, chronic kidney disease, malignant neoplasm, obesity), several biomarkers (C-reactive protein, procalcitonin, creatinine, LDH), duration of symptoms before hospital admission ≤ 9 days and before administering HFNO therapy ≤ 4 days.