Utility of Pulse Oximetry Oxygen Saturation (SpO2) with Incorporation of Positive End-Expiratory Pressure (SpO2 ∗10/FiO2 ∗PEEP) for Classification and Prognostication of Patients with Acute Respiratory Distress Syndrome.

Abstract

Background: Conventionally, PaO₂/FiO₂ (P/F ratio) has been used to categorize severity of acute respiratory distress syndrome (ARDS) and prognostication of outcome. Recent literature has shown that incorporation of positive end-expiratory pressure (PEEP) into the P/F ratio (PaO₂ ∗10/FiO₂ ∗PEEP or P/FP∗10) has a much better prognostic ability in ARDS as compared to P/F ratio. The aim of this study was to correlate SpO₂ ∗10/FiO₂ ∗PEEP (S/FP∗10) to PaO₂ ∗10/FiO₂ ∗PEEP (P/FP∗10) and evaluate the utility of S/FP∗10 as a reliable noninvasive indicator of oxygenation in ARDS to avoid repeated arterial blood sampling.

Aim: To evaluate if pulse oximetry is a reliable indicator of oxygenation in ARDS patients by calculating SpO₂ ∗10/FiO₂ ∗PEEP (S/FP∗10). The primary objective was to determine the correlation of S/FP∗10 to P/FP∗10 ratio in ARDS patients. The secondary objective was to determine the cut-off value of S/FP∗10 ratio to predict severe ARDS and survival.

Methods: Patients aged 18-80 years on invasive mechanical ventilation (MV) diagnosed with ARDS as defined by the Berlin definition were included. The values of PaO₂, FiO₂, and SpO₂ were collected at three different time points. They were at baseline, i.e., after intubation and initiation of MV (within one hour of intubation), day one (1-24 hours of MV), and day three (48-72 hours of MV). The primary outcome was survival at the end of intensive care unit (ICU) stay.

Results: A total of 85 patients with ARDS on invasive MV were included. The data points were obtained at baseline, day one, and day three of MV. S/FP∗10 ratio has an excellent correlation to P/FP∗10 ratio at baseline and day three of invasive MV (r = 0.831 and 0.853, respectively; p < 0.001) and has a strong correlation on day one of invasive MV (r = 0.733, p < 0.001). S/FP∗10 ratio ≤116 at baseline has excellent discriminant function to be categorized as severe ARDS as per Berlin definition (AUC: 0.925, p < 0.001, 90% sensitivity, 93% specificity, CI: [0.862-0.988]). The increase in S/FP∗10 ratio by ≥64.40 from baseline to day three of MV is a good predictor of survival (AUC: 0.877, p < 0.001, 73.5% sensitivity, 97% specificity, CI: [0.803-0.952]).

Conclusion: S/FP∗10 has a strong correlation to P/FP∗10 in ARDS patients. S/FP∗10 ≤116 has an excellent discriminant function to be categorized as severe ARDS. The S/FP∗10 ratio on day three of MV and the change in S/FP∗10 ratio from baseline and day one to day three of MV are good predictors of survival in ARDS patients. This trial is registered with CTRI/2020/04/024940.