Comparison of SpO2 / FiO2 Ratio and PaO2 / FiO2 Ratio as Diagnostic Criteria in Patients with ALI and ARDS

Author(s): Venkata Praveen Janipalli1 , Praveen Kumar Moturi2

BACKGROUND PaO2 / FiO2 ratio has been the main criterion in defining ALI / ARDS (Acute Lung Injury / Acute Respiratory Distress Syndrome). This study is particularly aimed at utilising SpO2 / FiO2 ratio as an alternative diagnostic criterion of ALI / ARDS. METHODS Fifty patients with ALI / ARDS were included in the study. SpO2, PaO2 values, and serum electrolytes were measured using pulse oximetry and arterial blood gas analysis along with simultaneous measurement of FiO2. RESULTS SpO2 / FiO2 and PaO2 / FiO2 ratio showed a good linear correlation. By quantifying the linear regression equation, the threshold value of SpO2 / FiO2 ratio was calculated. Evidence gathered from the study demonstrated strong association between SpO2 / FiO2 and PaO2 / FiO2 ratio and it is proposed that SpO2 / FiO2 ratio calculation should be the norm to characterise oxygen impairment in ALI / ARDS, rather than just using it as an alternative diagnostic criterion. CONCLUSIONS Threshold values of SpO2 / FiO2 ratio can be used as an alternative to PaO2 / FiO2 ratio in the early diagnosis of ALI and ARDS.