Background: ARDS is an acute hypoxemic respiratory failure whose early recognition is vital in implementing lung-protective ventilation strategy.PaO2/FiO2 (P/F) ratio is one of the parameters in ARDS diagnosis. This ratio is measured by arterial blood gas sampling. Since, this is an invasive procedure, this ratio can be substituted with Spo2/Fio2(S/F) ratio where SpO2 is measured by pulse oximetry. Therefore, SF ratio may be used as a reliable non-invasive alternative to the PF ratio.

Aims and Objectives: Deriving relationship between S/F and P/F ratios in ARDS patients and there by using S/F ratios as surrogate marker for P/F ratio.

Materials and Methods: 70 patients admitted in ICU of Kempegowda Institute of Medical Sciences and Research Centre, Bengaluru who met the criteria for ARDS, were intubated and receiving mechanical ventilation.

Results: Relationship between SF and PF ratio can be described by the regression equation SF =57+0.61 (P/F)[P <0.001].Based on this equation a PF ratio of 200 corresponds to an SF ratio of 181 [P <0.001]. The SF cut off 181 had 72% sensitivity and 81% specificity for the diagnosis of ARDS.

Conclusions: SF ratio is a reliable non-invasive surrogate for PF ratio for ARDS with the advantage of replacing invasive arterial blood sampling by non-invasive and continuously available pulse oximetry.

Keywords: ARDS, pulse oximetry, SpO2/FIO2 ratio, PaO2/FIO2 ratio.

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Dr Basanth Kumar S

Professor, Department of General Medicine, Kempegowda Institute of Medical Sciences and Research Centre, Bengaluru-560004