Relationship between venous and arterial carboxyhemoglobin levels in patients with suspected carbon monoxide poisoning

STUDY OBJECTIVE: To test the hypothesis that venous carboxyhemoglobin (V-COHb) levels accurately predict arterial (A-COHb) levels.

DESIGN: Prospective comparison of A-COHb and V-COHb levels in patients with suspected carbon monoxide (CO) poisoning.

SETTING: Municipal hospital emergency department with contiguous multiplace hyperbaric chamber staffed 24 hours a day.

PARTICIPANTS: Unselected convenience sample of 61 adults with suspected CO toxicity.

INTERVENTION: Simultaneous sampling of arterial and venous blood.

RESULTS: Correlation between V-COHb and A-COHb showed an r value of .99 (95%CI, .99 to .99), and an r2 value of .98. Agreement between V-COHb and A-COHb levels was examined by use of a plot of arteriovenous differences against the mean of the two measurements. The mean arteriovenous difference was .15% COHb (95%CI, .13% to .45%), with 95% of the differences ranging from 2.4% COHb to -2.1% COHb.

CONCLUSION: Venous COHb levels predict arterial levels with a high degree of accuracy. Patients with suspected CO poisoning can be screened with the use of venous blood, without the need for arterial puncture.