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Abstract & Commentary
Synopsis: In a large randomized, controlled trial of patients referred for hyperbaric oxygen treatment following acute carbon monoxide poisoning, those who received hyperbaric treatments did no better by any measure, and had worse outcomes by several measures, than those who received sham treatments with normobaric oxygen.
Source: Scheinkestel CD, et al. Med J Aust 1999;170: 203-210.
Hyperbaric oxygen (hbo) treatment is widely used in carbon monoxide (CO) poisoning, both to accelerate the displacement of CO from hemoglobin and to prevent neurologic or neuropsychiatric sequelae. In this randomized, controlled trial conducted in Melbourne, Australia, patients referred to a multiplace hyperbaric oxygen (HBO) facility because of acute CO poisoning were randomized to receive either HBO or sham treatments in the chamber with normobaric oxygen. All other aspects of therapy were the same in the two groups. One-hundred-minute HBO treatments were administered daily for three days, with all patients receiving supplemental oxygen between treatments. Those with persistent neurologic or neuropsychologic abnormalities at the end of the three-treatment series received an additional three treatments. Patients were stratified by circumstances of poisoning (suicidal or accidental) and by need for intubation and mechanical ventilation. Scheinkestel and associates administered seven different neuropsychological tests to all patients in assessment of both short-term (at conclusion of series of treatments) and delayed (after 1 month) outcomes.
During the 28-month study period, 191 patients (mean age 36 years, 82% men) were enrolled in the study. Patients with cutaneous burns, children, and pregnant women were excluded. Although patients with all grades of poisoning were included, 73% were classified as having severe poisoning and 26% were initially mechanically ventilated. The two patient groups were well matched by all the criteria examined by Scheinkestel et al.
Overall mortality was 3%. Persistent neurologic sequelae were judged to be present in 71% of the patients at hospital discharge and in 62% at one-month follow-up. More patients in the HBO group received additional treatments (28% vs 15%; P = 0.01). HBO patients had worse outcomes in the learning test at completion of treatment and a greater number of abnormal test results at completion of treatment than did the normobaric oxygen group. No outcome measure was worse in the normobaric oxygen group. Scheinkestel et al conclude that, under the circumstances of this trial in which both groups received high doses of oxygen, HBO offered no benefit and may even have worsened the outcome.
COMMENT BY DAVID J. PIERSON, MD, FACP, FCCP
The neuropsychiatric syndrome seen in some patients after CO poisoning has been difficult to study objectively and remains a source of controversy. Although both arms of the treatment regimen used in this Australian study likely differ from the way many patients are managed in this country, Scheinkestel et al are to be commended for the care and objectivity they brought to bear on the problem.
Although HBO is available in most larger U.S. cities, most patients with CO poisoning are treated by physicians who do not have direct access to HBO therapy, particularly in the emergency situation. This study provides reassurance to such physicians that outcomes from a rigorous treatment regimen using normobaric oxygen should be as good as those that include HBO. However, the results should not be extrapolated to an assumption that a shorter, less intensive supplemental oxygen exposure would yield clinical results as good as those observed in this study.
a. had 12% higher survival.
b. had 24% higher survival
c. had no difference in survival but 12% less neuropsychiatric sequelae.
d. had no difference in survival but 24% less neuropsychiatric sequelae.
e. None of the above