Clinical Performance of Sp o2 /F io2 and Pa o2 /F io2 Ratio in Mechanically Ventilated Acute Respiratory Distress Syndrome Patients: A Retrospective Study.

Abstract

The present study aims to evaluate the severity classification of acute respiratory distress syndrome (ARDS) in mechanically ventilated patients according to peripheral oxygen saturation by pulse oximetry (Sp o2 )/F io2 ratio compared with Pa o2 /F io2 ratio and the relationship between Sp o2 /F io2 ratio and venous admixture. Retrospective observational study. Medical-surgical ICU. A cohort of 258 mechanically ventilated patients with ARDS already enrolled in previous studies. None. Gas exchange, Sp o2 , and respiratory mechanics were measured on ICU admission and during the positive end-expiratory pressure (PEEP) trial. Radiological data from CTs were used to compute lung recruitability and to assess different lung compartments. A nonlinear association was found between Sp o2 /F io2 and Pa o2 /F io2 . Considering the possible confounding factors of the pulse oximeter on the relationship between Sp o2 /F io2 and Pa o2 /F io2 ratio, arterial pH, and Pa co2 had no effect. Sp o2 /F io2 and Pa o2 /F io2 ratio demonstrated a moderate agreement in classifying ARDS severity (intraclass correlation coefficient = 0.63). Between the correspondent classes according to Sp o2 /F io2 vs. Pa o2 /F io2 ratio-derived severity classifications, there was no difference in terms of respiratory mechanics, gas exchange, lung radiological characteristics and mortality in ICU, and within two levels of PEEP. A Sp o2 /F io2 ratio less than 235 was able to detect 89% of patients with a venous admixture greater than 20%, similarly to a Pa o2 /F io2 ratio less than 200. Sp o2 /F io2 ratio can detect oxygenation impairment and classify ARDS severity similarly to Pa o2 /F io2 ratio in a more rapid and handy way, even during a PEEP trial. However, our results may not be applicable to different patient populations; in fact, the pulse oximeter is merely a monitoring device and the information should be personalized by the physician on the patient's characteristics and conditions.