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Volume 17 Supplement 4

Sepsis 2013

SaO2/FiO2 ratio as risk stratification for patients with sepsis


The PaO2/FiO2 ratio is a well-known parameter to assess respiratory dysfunction, used in Sequential Organ Failure Assessment (SOFA) [1]. This study aims to determine whether the SaO2/FiO2 ratio can be used in the assessment of respiratory impairment and as a predictor of ICU mortality in patients with sepsis and to evaluate its correlation with PaO2/FiO2.

Materials and methods

A retrospective cohort study conducted in the ICU of Hospital Santa Luzia, Brasilia, DF, Brazil, during 5 months. An arterial blood sample was collected at the time of admission. Patients with sepsis were divided into two groups: survivors group (SG) and nonsurvivors group (NSG). Correlation with SaO2/FiO2 and PaO2/FiO2 was evaluated with the Pearson correlation coefficient. Accuracy of SaO2/FiO2 and PaO2/FiO2 to predict ICU mortality was measured with the area under the receiver operating characteristic curve.


A total of 118 patients with sepsis were enrolled. The mean age was 66 ± 21 years, SAPS3: 50 ± 14, APACHE II: 13 ± 8, PaO2/FiO2: 317 (IQ 233 to 426) and SaO2/FiO2: 362 (IQ 247 to 453). ICU mortality was 17.8% (n = 21). The main sites of infections were respiratory (57%, n = 67), urinary (19%, n = 23) and cutaneous (8.5%, n = 10). Nonsurvivor patients had lower SaO2/FiO2 (258 vs. 366, P = 0.00) and PaO2/FiO2 (285 vs. 354, P = 0.04). PaO2/FiO2 and SaO2/FiO2 had a good correlation (r = 0.645, P = 0.00). The relative risk of death in patients with SaO2/FiO2 <400 was 1.81 (95% CI: 1.47 to 2.24), SaO2/FiO2 <300 was 2.5 (95% CI: 1.54 to 4.05), SaO2/FiO2 <200 was 2.45 (95% CI: 1.27 to 4.71). The sensitivity for ICU mortality of SaO2/FiO2 <300 was 28% and of SaO2/FiO2 <200 was 35%. The specificity for ICU mortality of SaO2/FiO2 <300 was 90% and of SaO2/FiO2 <200 was 86% (95% CI: 93.5 to 100.0%). The area under the ROC curve for SaO2/FiO2 was 0.776 (95% CI: 0.677 to 0.875) and for PaO2/FiO2 was 0.655 (95% CI: 0.507 to 0.804) (Figure 1).

Figure 1

ROC curve for SaO 2 /FiO 2 and PaO 2 /FiO 2 .


A low SaO2/FiO2 was associated with mortality in this group of patients and had a good correlation with PaO2/FiO2. SaO2/FiO2 <300 showed high specificity for mortality. Further analysis is necessary to the validation of less invasive measures such as pulse oximetry saturation (SpO2/FiO2 ratio) in the assessment of patients with sepsis.


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    Pandharipande P, Shintani A, Hagerman H, St Jacques P, Rice T, Sanders N, Ware L, Bernard G, Ely E: Derivation and validation of Spo2/Fio2 ratio to impute for Pao2/Fio2 ratio in the respiratory component of the Sequential Organ Failure Assessment score. Crit Care Med. 2009, 37: 1317-1321. 10.1097/CCM.0b013e31819cefa9.

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Correspondence to Adriell Ramalho Santana.

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Santana, A.R., de Sousa, J.L., Amorim, F.F. et al. SaO2/FiO2 ratio as risk stratification for patients with sepsis. Crit Care 17, P51 (2013).

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  • Risk Stratification
  • Retrospective Cohort
  • Characteristic Curve
  • Retrospective Cohort Study
  • Pulse Oximetry