title: Do changes in pulse oximeter oxygen saturation predict equivalent changes in arterial oxygen saturation?
abstract: BACKGROUND
  This study investigates the relation between changes in pulse oximeter oxygen saturation (SpO2) and changes in arterial oxygen saturation (SaO2) in the critically ill, and the effects of acidosis and anaemia on precision of using pulse oximetry to predict SaO2.
  
  
  METHODS
  Forty-one consecutive patients were recruited from a nine-bed general intensive care unit into a 2-month study. Patients with significant jaundice (bilirubin >40 micromol/l) or inadequate pulse oximetry tracing were excluded.
  
  
  RESULTS
  A total of 1085 paired readings demonstrated only moderate correlation (r= 0.606; P < 0.01) between changes in SpO2 and those in SaO2, and the pulse oximeter tended to overestimate actual changes in SaO2. Anaemia increased the degree of positive bias whereas acidosis reduced it. However, the magnitude of these changes was small.
  
  
  CONCLUSIONS
  Changes in SpO2 do not reliably predict equivalent changes in SaO2 in the critically ill. Neither anaemia nor acidosis alters the relation between SpO2 and SaO2 to any clinically important extent.
authors.affiliation: Intensive Care Unit, Birmingham Heartlands and Solihull NHS Trust (Teaching), Birmingham Heartlands Hospital, Birmingham, UK.
authors.forename: Gavin D
authors.initials: GD
authors.lastname: Perkins
authors.forename: Daniel F
authors.initials: DF
authors.lastname: McAuley
authors.forename: Simon
authors.initials: S
authors.lastname: Giles
authors.forename: Helen
authors.initials: H
authors.lastname: Routledge
authors.forename: Fang
authors.initials: F
authors.lastname: Gao
mesh_terms: D000138:Acidosis; D000368:Aged; D000369:Aged, 80 and over; D000740:Anemia / Q000503:physiopathology*; D001158:Arteries; D016638:Critical Illness; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D006113:United Kingdom
chemical_list: D010100:Oxygen