Carbon monoxide poisoning: pulse oximetry missed raised carboxyhaemoglobin levels and hypoxia.

Clinical bottom line (level 4)

  1. Pulse oximetry was inaccurate in patients with carbon monoxide poisoning.
  2. Among patients with suspected smoke inhalation or carbon monoxide poisoning, a direct blood gas measurement of the Sao2 level would be necessary.
Bozeman et al: Annals of Emergency Medicine 1997; 30: 608-611
Expires July 2003

The study

Setting: trauma and hyperbaric centre, USA

124 patients (aged range 11 to 83 years; mean 40, 70% male) evaluated for carbon monoxide exposure

Excluded if
  • <10 years old
  • no prior treatment with high-flow oxygen



    • Independent unblinded reference standard, applied in ?all patients from a consecutive ?appropriate spectrum.
    Reference standard:
    • arterial blood gas
    Diagnostic test: finger probe oximetry saturation

    The evidence

    • Pulse oximetry remained >92% in all patients despite CO haemoglobin ranging from 0.2% to 47%.
    • Oxyhaemoglobin saturation fell linearly as CO haemoglobin levels rose (range 54% to 99%; mean 89%).

    Comments

    1. More modern 'three phase' pulse oximeters may be able to eliminate this oximetry gap.

    Citation

    1. Bozeman WP, Myers RAM, Barish RA, et al: Confirmation of the pulse oximetry gap in carbon monoxide poisoning. Annals of Emergency Medicine 1997; 30: 608-611
    Search Terms: carbon monoxide, carbon monoxide poisoning and poisoning in Cochrane and Ovid Medline
    Contributor: Joel Ray and Chris Ball, July 2000
    Reviewer: Michael Christian

    Clinical Question.
    Patient suspected smoke inhalation
    Intervention or Exposure pulse oximetry
    Outcome diagnosis of CO poisoning