Hyperbaric Oxygen for Carbon Monoxide Poisoning
December 1, 2002 3 minutes read
Abstract & Commentary
Source: Weaver LK, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med 2002;347:1057-1067.
It is a well-known fact among emergency physicians that acute carbon monoxide (CO) poisoning can result in cognitive sequelae. These cognitive sequelae occur in 25-50% of patients with loss of consciousness or with CO levels above 25%. The value of hyperbaric oxygen therapy for the treatment of CO-poisoned patients, and its ability to prevent long-term cognitive sequelae, has been debated for years among toxicology and hyperbaric experts. This study from the University of Utah addressed this difficult issue.
Patients were eligible for enrollment if they had a documented CO exposure, or an "obvious exposure," with either loss of consciousness (LOC), confusion, headache, malaise, fatigue, forgetfulness, dizziness, visual disturbances, nausea, vomiting, cardiac ischemia, or metabolic acidosis. Patients were excluded if more than 24 hours had elapsed from the time of exposure, they were younger than 16 years of age, they were moribund, or were pregnant. Patients were then randomized to either three hyperbaric chamber sessions (at 3, 2, and 2 atmospheres) or one treatment with normobaric oxygen and two treatments with normobaric room air over the next 24 hours. All patients underwent a battery of neuropsychological tests after the first and third chamber sessions and at two weeks, six weeks, six months, and 12 months. The primary endpoint of the study was the occurrence of cognitive sequelae at six weeks post-treatment.
The trial was designed to include 100 patients in each group, with interim data analyses scheduled after each 25 patients per group. A total of 76 patients actually were enrolled in each group, but the trial was stopped after the third interim analysis, as hyperbaric oxygen was judged to be efficacious. Of the 76 enrolled in each group, complete data were available up to six weeks on 75 patients in the hyperbaric group and 72 patients in the normobaric group. On an intention-to-treat basis, cognitive sequelae occurred in fewer of the patients in the hyperbaric group than the normobaric group (25% vs. 46.1%, p < 0.01). Cognitive sequelae also were fewer on an intention-to-treat basis in the hyperbaric group at 12 months (18.4% vs. 32.9%, p = 0.04), although these data are not as compelling due to more patients lost to follow-up and other confounding factors.
The authors conclude that the treatment of patients with acute, symptomatic CO poisoning with three hyperbaric oxygen treatments within a 24-hour period appears to lower the incidence of cognitive sequelae at six weeks and 12 months.
Commentary by Jacob W. Ufberg, MD
This is a very well-planned and -executed study that, in my mind, tips the scales heavily in favor of the use of hyperbaric oxygen therapy for patients with acute CO poisoning, specifically the hyperbaric regimen used in this study. This regimen was based on a report that suggested better outcomes after more than two treatments. The authors chose to complete the treatments over 24 hours to limit patient compliance issues.
One very interesting piece of data is that while the two groups had mean CO levels of about 25% initially, both groups had mean CO levels near the normal range by the time of initiation of hyperbaric oxygen therapy. This suggests that the hyperbaric therapy may offer therapeutic mechanisms independent of its ability to hasten carboxyhemoglobin dissociation.
Dr. Ufberg, Assistant Professor of Emergency Medicine, Assistant Residency Director, Department of Emergency Medicine, Temple University School of Medicine, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.
The value of hyperbaric oxygen therapy for the treatment of CO-poisoned patients, and its ability to prevent long-term cognitive sequelae, has been debated for years among toxicology and hyperbaric experts. This study from the University of Utah addressed this difficult issue.
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