key: cord-0898998-6y5okoyr authors: Kumar, Ashutosh; Aggarwal, Richa; Khanna, Puneet; Singh, Akhil kant; kumar, Rakesh; Soni, Kapil Dev; Trikha, Anjan title: Correlation of the SpO2/FiO2 (S/F) ratio and the PaO2/FiO2 (P/F) ratio in patients with COVID-19 pneumonia date: 2021-11-18 journal: Med Intensiva DOI: 10.1016/j.medin.2021.10.005 sha: aa8b4009bcf2dd4357d165476bbaf49dd542bfd7 doc_id: 898998 cord_uid: 6y5okoyr nan Conception and design of the study 4. Rakesh kumar 3 Drafting the article or revising it critically for important intellectual content Drafting the article or revising it critically for important intellectual 6. AnjanTrikha 4 Revising it critically for important intellectual content and final approval of the version to be submitted The clinical spectrum of SARS-CoV-2 infection varies widely ranging from asymptomatic infection to severe viral pneumonia with respiratory failure. 1 Some patients of COVID, who develop respiratory failure have hypoxemia but without signs of respiratory distress also termed as "silent hypoxemia". This silent hypoxemia may be responsible for the quick deterioration because it gives a false sense of well-being even when the oxygen debt is actually increasing. 2, 3 This mandates regular monitoring of oxygen levels in these patients. SpO2/FiO2 (S/F) ratio has been found to have good correlation with PaO2/FiO2 (P/F) ratio in adult and pediatric patients with pneumonia, acute respiratory distress syndrome (ARDS) and acute lung injury in various studies. [4] [5] [6] However, in COVID patients, there can be discordance between S/F ratio and P/ F ratio due to multiple reasons like shift of oxyhemoglobin dissociation curve to left or right , inaccuracy of SpO2 at lower levels of saturation and during critical illness. 7 Moreover, the linear correlation between SpO2 and FiO2 is lost when SpO2 is 100 % and even the PaO2 cannot be estimated when SpO2 is 100 %. The aim of this study was to assess the correlation between S/F and the P/F ratios in patients with COVID pneumonia requiring oxygen therapy and to find whether initial S/F ratio on We examined whether initial S/F ratio can indicate the requirement of IMV. In our study, 19 out of 60 patients required IMV later in the course of the disease ( ventilated group) and 41 did not (non ventilated ) . We compared these two groups ( table 1) . There were no differences in the demographic characteristics, initial S/F ratio and P/F ratio, in the two groups, however, the ventilated group patients were significantly more tachycardiac and tachypneic on admission pointing to the fact that patients were able to maintain oxygenation in the initial phase of the disease at the expense of tachypnea and use of accessory muscles. The median initial S/F ratio [147.5 (71-333)] in our cohort was much lower than in the study by Choi et al 21 (287.5 and 452.4 ) indicating patients were more hypoxemic and in advanced disease in our study probably owing to the delayed presentation to hospital in our cohort. Moreover, factors other than oxygenation e.g . secondary infections, altered sensorium could be reasons for deterioration and mechanical ventilation. Furthermore, it is imperative to note that some patients with COVID may not have dyspnea despite being hypoxemic, and therefore clinical monitoring of vitals gains paramount importance in these patients. They require aggressive management in order to halt further deterioration. In conclusion, S/F ratio can be used as surrogate of P/F ratio in patients with COVID pneumonia and can be highly useful in resource limited settings during this pandemic. However, initial S/F ratio on admission can not indicate the need of invasive ventilation later in the course of the disease. Keywords-S/F ratio; P/F ratio; COVID -19 , pneumonia 0.739 HR -Heart rate ; RR-Respiratory rate ; SBP-systolic blood pressure; DBP-Diastolic blood pressure; S/F ratio -SpO2/FiO2; P/F ratio-PaO2/FiO2 ; NRBM-non rebreathing mask ; HFNChigh flow nasal cannula; NIV-non invasive ventilation Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study Misconceptions of pathophysiology of happy hypoxemia and implications for management of COVID-19 The pathophysiology of 'happy' hypoxemia in COVID-19 Comparison of the SpO2/FiO2 ratio and the PaO2/FiO2 ratio in patients with acute lung injury or ARDS Comparison of the Spo2/Fio2Ratio and the Pao2/Fio2Ratio in Patients With Acute Lung Injury or Acute Respiratory Distress Syndrome Hospital Incidence and Outcomes of the Acute Respiratory Distress Syndrome Using the Kigali Modification of the Berlin Definition Why COVID-19 silent hypoxemia is baffling to physicians Utility of SpO2/FiO2 ratio for acute hypoxemic respiratory failure with bilateral opacities in the ICU The Association between Mortality and the Oxygen Saturation and Fraction of Inhaled Oxygen in Patients Requiring Oxygen Therapy due to COVID-19-Associated Pneumonia Competing interest -The authors have no competing interests to declare.