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. [Touger M, Gallagher EJ, Tyrell J: Relationship between venous and arterial carboxyhemoglobin levels in patients with suspected carbon monoxide poisoning. Ann Emerg Med April 1995;25:481-483.].