Accuracy of PaO2/FiO2 calculated from SpO2 for severity assessment in ED patients with pneumonia. Issue 5 (22nd May 2015)

• Record Type: Journal Article
• Authors: Sanz, Francisco; Dean, Nathan; Dickerson, Justin; Jones, Barbara; Knox, Daniel; Fernández‐Fabrellas, Estrella; Chiner, Eusebi; Briones, María Luisa; Cervera, Ángela; Aguar, María Carmen; Blanquer, José
• Is Part Of: Respirology. Volume 20:Issue 5(2015)
• Page Start: 813
• Page End: 818
• Publication Date: 2015-05-22
• Subjects: Respiratory organs -- Diseases -- Periodicals; Respiratory organs -- Periodicals; 612.2
• DOI: 10.1111/resp.12560
• Languages: English
• ISSNs: 1323-7799

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <sec id="resp12560-sec-0001" sec-type="section"> <title>Background and objective</title> <p>Assessment of oxygenation in patients with community‐acquired pneumonia is critical for treatment. The accuracy of percutaneous oxygen saturation (SpO<sub>2</sub>) determined by pulse oximetry is uncertain, and it has limited value in patients receiving supplemental oxygen. We hypothesized that calculation of partial arterial oxygen concentration/inspired oxygen faction (PaO<sub>2</sub>/FiO<sub>2</sub>) from SpO<sub>2</sub> by the Ellis or Rice equations might adequately correlate with PaO<sub>2</sub>/FiO<sub>2</sub> measured by arterial blood gases.</p> </sec> <sec id="resp12560-sec-0002" sec-type="section"> <title>Methods</title> <p>We studied 1004 patients with pneumonia in the emergency department with simultaneous measurement of SpO<sub>2</sub> and PaO<sub>2</sub> from two cohorts from Valencia, Spain and Utah, USA. We compared SpO<sub>2</sub> with measured SaO<sub>2</sub>, compared the equations' accuracy in calculating PaO<sub>2</sub>/FiO<sub>2</sub> and determined how often patients would be misclassified at clinically important thresholds. We compared estimated PaO<sub>2</sub>/FiO<sub>2</sub> to measured PaO<sub>2</sub>/FiO<sub>2</sub> using the Spearman correlation.</p> </sec> <sec id="resp12560-sec-0003" sec-type="section"> <title>Results</title> <p>Pairwise correlation of SpO<sub>2</sub> with SaO<sub>2</sub> was moderate (rho = 0.66; <italic>P</italic> < 0.01). Both equations performed similarly among patients with lower PaO<sub>2</sub>/FiO<sub>2</sub> ratios. The Ellis equation estimated PaO<sub>2</sub>/FiO<sub>2</sub> from SpO<sub>2</sub> more accurately than the Rice equation in patients with PaO<sub>2</sub>/FiO<sub>2</sub> ≥200. Simple agreement between calculated and measured P/F was 91% and 92%, respectively.</p> </sec> <sec id="resp12560-sec-0004" sec-type="section"> <title>Conclusions</title> <p>The Ellis equation was more accurate than the Rice equation for estimating PaO<sub>2</sub>/FiO<sub>2</sub>, especially at higher levels of P/F ratio. Estimation of PaO<sub>2</sub>/FiO<sub>2</sub> from SpO<sub>2</sub> is accurate enough for initial oxygenation assessment. Ellis and Rice equations could misclassify 20% and 30% of patients, respectively, at higher levels of PaO<sub>2</sub>/FiO<sub>2</sub>. For patients with abnormal oxygenation falling near thresholds for clinical decision making, arterial blood gas measurement preferably on room air is more accurate.</p> </sec> </abstract>