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Benefit of Hyperbaric Oxygen Therapy for Acute Carbon Monoxide Poisoning

Compared with sham treatment, hyperbaric oxygen therapy significantly reduced cognitive sequelae in patients with CO poisoning and should now be considered as the standard therapy.

The common wisdom is that carbon monoxide (CO) poisoning causes cognitive sequelae and that hyperbaric oxygen therapy mitigates this effect. Previous studies, most of which were methodologically flawed, have yielded conflicting results. In this large, prospective, double-blind trial, investigators compared the rate of cognitive sequelae in patients with CO poisoning who were randomized to treatment with hyperbaric oxygen or normobaric oxygen (sham treatment).

Patients were eligible if they had had CO exposure within the past 24 hours plus elevated carboxyhemoglobin levels, symptoms of CO poisoning, or metabolic acidosis; of 460 patients evaluated, 152 were enrolled. Patients underwent 3 treatment sessions in a hyperbaric chamber during a 24-hour period. In the hyperbaric-oxygen group, patients received oxygen at 3 atmospheres absolute (ATA) for approximately 1 hour and at 2 ATA for another hour during the first session and at 2 ATA for 2 hours in the next 2 sessions. In the sham-treatment group, patients received normobaric oxygen in the first session and air in the next 2 sessions. All sessions included 5-minute "air protection" periods to prevent hyperoxic seizures. Extensive psychological and psychometric testing was conducted after the first and third sessions and at 2, 6, 26, and 52 weeks.

Cognitive sequelae at 6 weeks (the primary endpoint) were less frequent in the hyperbaric-oxygen group than in the sham-treatment group (25.0% vs. 46.1%; odds ratio, 0.39; P=0.007). The difference was significant even among patients who did not complete all 3 sessions and was maintained at 52 weeks. Notably, the presence of cerebellar dysfunction before treatment was a strong predictor of cognitive sequelae (OR, 5.7; P=0.005). Carboxyhemoglobin levels were normal in almost all patients before treatment, highlighting that the benefit of treatment is the prevention of the damage caused by CO exposure rather than the removal of CO.

Comment: The results of this first-ever sham-controlled trial of hyperbaric oxygen therapy for CO poisoning should silence those who have questioned the efficacy of this therapy on the basis of previous studies' designs. An editorialist notes that this study "provides a reliable foundation on which to base decisions regarding management." Questions remain about which patients to treat (although this study's findings suggest treating, at the very least, all patients with cerebellar dysfunction) and what is the optimal treatment regimen. Every emergency department should develop a written plan for management of patients with CO exposure.

— J. Stephen Bohan, MS, MD, FACP, FACEP

Published in Journal Watch Emergency Medicine October 29, 2002

Citation(s):

Weaver LK et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med 2002 Oct 3; 347:1057-67.

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Thom SR. Hyperbaric-oxygen therapy for acute carbon monoxide poisoning. N Engl J Med 2002 Oct 3; 347:1105-6.

• Original article (Subscription may be required)
• Medline abstract (Free)

From time to time, a study is published that is of such importance to physicians that it warrants special attention and should lead to an immediate reappraisal of a current practice or to the adoption of a new approach. When such articles are identified by the editorial boards of the Journal Watch publications, they will receive the designation "Landmark Article." We encourage our readers to obtain the full text of these articles and review them carefully.