title: Confirmation of the pulse oximetry gap in carbon monoxide poisoning.
abstract: OBJECTIVE
  To demonstrate the degree to which pulse oximetry overestimates actual oxyhemoglobin (O2Hb) saturation in patients with carbon monoxide (CO) poisoning. This phenomenon has been reported in fewer than 20 humans in the English medical literature.
  
  
  METHODS
  A retrospective chart review of 191 patients evaluated for CO poisoning at a regional hyperbaric center identified 124 patients 10 years of age and older who had had both arterial blood gas and pulse oximetry measurements and who had received either high-flow oxygen through a nonrebreather mask or 100% inspired oxygen through an endotracheal tube. Blood gas measurements, including direct spectrophotometric determination of O2Hb and carboxyhemoglobin (COHb) saturation values, were compared with finger-probe pulse oximetry readings.
  
  
  RESULTS
  Measured O2Hb saturation (mean +/- SD, 88.7 +/- 10.2%; range, 51.4% to 99.0%) decreased linearly and predictably with rising COHb levels (10.7 +/- 10.4%; range, .2% to 46.4%). Pulse oximetry saturation (99.2% +/- 1.3%; range, 92% to 100%) remained elevated across the range of COHb levels and failed to detect decreased O2Hb saturation. The pulse oximetry gap, defined as the difference between pulse oximetry saturation and actual O2Hb saturation (10.5% +/- 9.7%; range, 0% to 40.6%), approximated the COHb level.
  
  
  CONCLUSIONS
  There is a linear decline in O2Hb saturation as COHb saturation increases. This decline is not detected by pulse oximetry, which therefore overestimates O2Hb saturation in patients with increased COHb levels. The pulse oximetry gap increases with higher levels of COHb and approximates the COHb level. In patients with possible CO poisoning, pulse oximetry must be considered unreliable and interpreted with caution until the COHb level has been measured.
authors.affiliation: R Adams Cowley Shock Trauma Center, University of Maryland Medical System, Baltimore, USA.
authors.forename: W P
authors.initials: WP
authors.lastname: Bozeman
authors.forename: R A
authors.initials: RA
authors.lastname: Myers
authors.forename: R A
authors.initials: RA
authors.lastname: Barish
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002249:Carbon Monoxide Poisoning / Q000097:blood* / Q000188:drug therapy; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000008:administration & dosage; D010108:Oxyhemoglobins / Q000032:analysis*; D015203:Reproducibility of Results; D012189:Retrospective Studies
chemical_list: D010108:Oxyhemoglobins; D010100:Oxygen