BACKGROUND: ROX index (SpO2 / FiO2) / respiratory rate, which is the ratio of peripheral oxygen saturation (SpO2) and inspired oxygen fraction (FiO2) divided by respiratory rate, to predict failure of HFNO therapy and intubation in patients with a rapid, easy-to-use, rapidly administered pneumonia. index used not to delay. This is a rating. HFNO reduces the need for endotracheal intubation in patients with acute hypoxic respiratory failure due to pneumonia. It has been suggested that HFNO may reduce the need for invasive mechanical ventilation compared to conventional oxygen therapy. Recently, experience has been reported that HFNO therapy also reduces the need for endotracheal intubation in patients with COVID-19 pneumonia. However, there are studies showing that insisting on HFNO and delaying intubation increase mortality in patients with acute respiratory distress syndrome (ARDS) and acute respiratory failure. In this study; We aimed to investigate the validity of the ROX index in predicting HFNO failure in patients with COVID-19 pneumonia admitted to the intensive care unit.

MATERIAL - METHOD: The population of the research consists of patients who will be hospitalized in the COVID-19 intensive care unit of Health Sciences University Ankara Atatürk Chest Diseases and Thoracic Surgery Training and Research Hospital for 3 months. According to a study conducted in Italy, 87% of COVID-19 patients hospitalized in intensive care go to intubation (6). Adult patients (≥18 years old) with acute respiratory failure due to COVID-19 pneumonia, positive PCR on nasopharyngeal swab, and HFNO when admitted to the intensive care unit will be included in this study. Patients under the age of 18 who received non-invasive or invasive mechanical ventilation therapy before HFNO will not be included in the study. Patients with chronic lung disease will be excluded from the study. RT-PCR tests will be performed with serial samples for detection of viral RNA. Demographic, clinical, treatment and laboratory data of the patients will be recorded. ROX score, APACHE 2 scores, Pneumonia Severity Index (PSI) score, CURB-65 and SOFA score will be calculated and recorded. In addition, the day of hospitalization in the intensive care unit, intensive care and hospital mortality, intubation time, invasive mechanical ventilation day, time of exit from the intensive care unit and discharge from the hospital will be recorded.

ORGANİZATİON AND ANALYSİS OF RESEARCH DATA The sample number of the study was calculated with the OpenEpi online computer program. The number of samples calculated with α= 0.05, d=5 and 87% frequency in the 95% confidence interval is 122. SPSS 23.0 statistical package program will be used for statistical analysis of research data. As a statistical analysis, in the descriptive findings section, categorical variables will be presented as numbers and percentages, and continuous variables will be presented as mean±standard deviation (min-max) for data showing normal distribution and median (IQR; 25-75). For categorical variables for non-normally distributed data, whether there is a frequency difference between groups will be compared using appropriate chi-square tests. Continuous variables will be compared with the normal distribution using Student's t test or Mann-Whitney U test. ROC analysis will be performed to determine whether the ROX index has a good cut-off value in making the intubation decision of COVID-19 patients. Statistical significance level will be accepted as p\<0.05.