Carbon monoxide poisoning: venous blood gases accurately reflected arterial measurements of carboxyhaemoglobin levels.

Clinical bottom line (level 4)

  1. Venous blood gas carboxyhaemoglobin levels accurately reflected arterial carboxyhaemoglobin values.
Touger et al: Annals of Emergency Medicine 1995; 25: 481-483
Expires July 2003

The study

Setting: emergency department, municipal hospital with hyperbaric chamber, USA

61 patients (aged median 36 years, 62% male) suspected carbon monoxide poisoning who presented to the hyperbaric centre for care

Independent unblinded reference standard, applied in all patients from a consecutive appropriate spectrum.
Reference standard:
  • arterial blood gas
Diagnostic test: venous blood gas measurement of CO haemoglobin within five minutes of arterial blood gas

The evidence

  • carboxyhaemoglobin levels - mean (SD):
    • arterial sample- 7.2% (8.5%)
    • venous sample- 6.9% (8.2%)
    • mean difference - 0.30% (95% CI -2.7% to 3.3%)
  • correlation coefficient between arterial and venous CO Hb: 0.99 (95% CI: 0.99 to 0.99)

Comments

  1. Arterial blood gases are taken not only to measure carboxyhaemoglobin, but also to check oxygen partial pressures, since pulse oximetry is inaccurate in carbon monoxide poisoning. Venous sampling can give NO indication of severe hypoxia - this may require a second (arterial) stab.
  2. Only 8 out of 61 subjects had a HbCO greater than 20%, raising the possibility that the results may have differed had more patients with toxic ranges of HcCO been included in the study.

Citation

  1. Touger M, Gallagher EJ, Tyrell J: Relationship between venous and arterial carboxyhaemoglobin levels in patients with suspected carbon monoxide poisoning. Annals of Emergency Medicine 1995; 25: 481-483
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 CO poisoning
Intervention or Exposure venous blood gas (VBG)
Comparison arterial blood gas (ABG)
Outcome carboxyhaemoglobin tension