title: Pulse oximetry saturation to fraction inspired oxygen ratio as a measure of hypoxia under general anesthesia and the influence of positive end-expiratory pressure.
abstract: OBJECTIVE
  In ICU patients with acute lung injury, the pulse oximetry saturation (Spo(2)) to fraction of inspired oxygen (Fio(2)) (S/F) ratio is a reliable surrogate measure for the P/F (Pao(2)/Fio(2)) ratio. Our goal was to determine the correlation of the S/F to the P/F in a large sample of patients undergoing general anesthesia and the influence of positive end-expiratory pressure (PEEP) on this measure.
  
  
  METHODS
  We studied adult general anesthetics performed with arterial blood gas analysis. Intraoperative data were collected from an anesthesia information system. The S/F ratios corresponding to P/F ratios of 300 were determined.
  
  
  RESULTS
  A total of 4439 values were collected. Linear correlation between S/F and P/F was identified (r = 0.46; P < .01) with a P/F of 300 corresponding to an S/F of 206. The correlation was stronger in patients with 5 to 9 cm PEEP (r = 0.52; P < .01), more than 9 cm H(2)O PEEP (r = 0.68; P < .01), and a P/F ratio of 300 or less (r = 0.61; P < .01).
  
  
  CONCLUSIONS
  The S/F correlates with the P/F in our cohort of patients undergoing general anesthesia, especially those ventilated with PEEP more than 9 cm H(2)O and/or with P/F less than 300. It has use as a noninvasive measure to screen for increased pulmonary dysfunction and to trend oxygenation during a general anesthetic.
authors.affiliation: Department of Anesthesiology, University of Michigan Health System, Ann Arbor, MI 48109, USA.
authors.forename: Ravi S
authors.initials: RS
authors.lastname: Tripathi
authors.forename: James M
authors.initials: JM
authors.lastname: Blum
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Rosenberg
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Tremper
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000768:Anesthesia, General; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D011175:Positive-Pressure Respiration; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D010100:Oxygen