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. 2022 May 30:27:38.
doi: 10.4103/jrms.jrms_558_21. eCollection 2022.

Estimating the best fraction of inspired oxygen for calculation of PaO2/FiO2 ratio in acute respiratory distress syndrome due to COVID-19 pneumonia

Leila Kadkhodai  1   2 , Mahmoud Saghaei  1   2 , Mohammadreza Habibzadeh  1   2 , Babak Alikiaii  1   2 , Seyed Jalal Hashemi  1   2
Affiliations

Estimating the best fraction of inspired oxygen for calculation of PaO2/FiO2 ratio in acute respiratory distress syndrome due to COVID-19 pneumonia

Leila Kadkhodai et al. J Res Med Sci. .

Abstract

Background: The ratio of partial pressure of oxygen in arterial blood (PaO2) to the fraction of inspiratory oxygen concentration (FiO2) is an indicator of pulmonary shunt fraction. PaO2/FiO2 (P/F) ratio is used to classify severity of acute respiratory distress syndrome (ARDS). With the same shunt fraction, P/F ratio decreases with increases in FiO2 which may lead to errors in classifying severity of ARDS. The effect of FiO2 on P/F ratio has not been investigated in COVID-19 pneumonia. In this study, we estimated the best FiO2 for the calculation of P/F ratio in a sample of patients with ARDS due to COVID-19 pneumonia.

Materials and methods: Blood gas and ventilatory data of 108 COVID-19 ARDS patients were analyzed in a cross-sectional observational study. Using Oxygen Status Algorithm the calculated shunt fraction served a basis for calculating P/F ratio for different FiO2. The severity of ARDS determined by P/F ratios at each FiO2s was compared with the shunt-based severity to find the optimum FiO2 for calculation of P/F ratio so the resulting classification has the best match with the reference classification.

Results: A FiO2 of 1.0 for calculation of P/F ratio and ARDS classification showed the best match with shunt-based ARDS classification. A regression model was obtained with the PaO2, patient's original FiO2, Hemoglobin concentration, and SaO2 as the independent predictors of the P/F ratio for the FiO2 of 1.0.

Conclusion: This study shows a FiO2 of 1.0 as the best value for correct calculation of P/F ratio and proper classification of ARDS.

Keywords: Acute respiratory distress syndrome; COVID-19; P/F ratio; mechanical ventilation; oxygenation indices; pulmonary shunt.

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Conflict of interest statement

There are no conflicts of interest.

Figures

Figure 1
Figure 1
Proportions of correct and wrong ARDS classifications among different types of P/F ratios. ARDS = Acute Respiratory Distress Syndrome; FiO2 = Fraction of Inspiratory Oxygen
See this image and copyright information in PMC

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