title: Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS.
abstract: BACKGROUND
  The diagnostic criteria for acute lung injury (ALI) and ARDS utilize the Pao(2)/fraction of inspired oxygen (Fio(2)) [P/F] ratio measured by arterial blood gas analysis to assess the degree of hypoxemia. We hypothesized that the pulse oximetric saturation (Spo(2))/Fio(2) (S/F) ratio can be substituted for the P/F ratio in assessing the oxygenation criterion of ALI.
  
  
  METHODS
  Corresponding measurements of Spo(2) (values </= 97%) and Pao(2) from patients enrolled in the ARDS Network trial of a lower tidal volume ventilator strategy (n = 672) were compared to determine the relationship between S/F and P/F. S/F threshold values correlating with P/F ratios of 200 (ARDS) and 300 (ALI) were determined. Similar measurements from patients enrolled in the ARDS Network trial of lower vs higher positive end-expiratory pressure (n = 402) were utilized for validation.
  
  
  RESULTS
  In the derivation data set (2,613 measurements), the relationship between S/F and P/F was described by the following equation: S/F = 64 + 0.84 x (P/F) [p < 0.0001; r = 0.89). An S/F ratio of 235 corresponded with a P/F ratio of 200, while an S/F ratio of 315 corresponded with a P/F ratio of 300. The validation database (2,031 measurements) produced a similar linear relationship. The S/F ratio threshold values of 235 and 315 resulted in 85% sensitivity with 85% specificity and 91% sensitivity with 56% specificity, respectively, for P/F ratios of 200 and 300.
  
  
  CONCLUSIONS
  S/F ratios correlate with P/F ratios. S/F ratios of 235 and 315 correlate with P/F ratios of 200 and 300, respectively, for diagnosing and following up patients with ALI and ARDS.
authors.affiliation: MSc, Division of Allergy, Pulmonary, and Critical Care Medicine, T-1218 MCN, Nashville, TN 37232-2650, USA. todd.rice@vanderbilt.edu
authors.forename: Todd W
authors.initials: TW
authors.lastname: Rice
authors.forename: Arthur P
authors.initials: AP
authors.lastname: Wheeler
authors.forename: Gordon R
authors.initials: GR
authors.lastname: Bernard
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Hayden
authors.forename: David A
authors.initials: DA
authors.lastname: Schoenfeld
authors.forename: Lorraine B
authors.initials: LB
authors.lastname: Ware
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D011175:Positive-Pressure Respiration / Q000379:methods*; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D011659:Pulmonary Gas Exchange; D015203:Reproducibility of Results; D012128:Respiratory Distress Syndrome / Q000097:blood / Q000175:diagnosis / Q000628:therapy; D012720:Severity of Illness Index; D013990:Tidal Volume; D016896:Treatment Outcome