Hyperbaric O2 for the sick and the well with CO poisoning

A French study, large by hyperbaric oxygen trial standards, did not confirm that hyperbaric oxygen therapy improves recovery from pure CO poisoning. In addition, in comatose patients, repeating hyperbaric oxygen therapy resulted in worse outcomes compared to one session.

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INTRODUCTION: Although hyperbaric oxygen therapy (HBO) is broadly used for carbon monoxide (CO) poisoning, its efficacy and practical modalities remain controversial.
OBJECTIVES: To assess HBO in patients poisoned with CO.
DESIGN: Two prospective randomized trial on two parallel groups.
SETTING: Critical Care Unit, Raymond Poincaré Hospital, Garches, France.
SUBJECTS: Three hundred eighty-five patients with acute domestic CO poisoning.
INTERVENTION: Patients with transient loss of consciousness (trial A, n = 179) were randomized to either 6 h of normobaric oxygen therapy (NBO; arm A0, n = 86) or 4 h of NBO plus one HBO session (arm A1, n = 93). Patients with initial coma (trial B, n = 206) were randomized to either 4 h of NBO plus one HBO session (arm B1, n = 101) or 4 h of NBO plus two 2 HBO sessions (arm B2, n = 105). PRIMARY ENDPOINT: Proportion of patients with complete recovery at 1 month.
RESULTS: In trial A, there was no evidence for a difference in 1-month complete recovery rates with and without HBO [58% compared to 61%; unadjusted odds ratio, 0.90 (95% CI, 0.47-1.71)]. In trial B, complete recovery rates were significantly lower with two than with one HBO session [47% compared to 68%; unadjusted odds ratio, 0.42 (CI, 0.23-0.79)].
CONCLUSION: In patients with transient loss of consciousness, there was no evidence of superiority of HBO over NBO. In comatose patients, two HBO sessions were associated with worse outcomes than one HBO session.

Hyperbaric oxygen therapy for acute domestic carbon monoxide poisoning: two randomized controlled trials
Intensive Care Med. 2011 Mar;37(3):486-92

2 thoughts on “Hyperbaric O2 for the sick and the well with CO poisoning”

  1. To my mind, the design had a number of major problems:
    1) In the first trial, subjects were enrolled if they had syncope but “could not recall what happened”. I’m not sure what this means. Most toxicologists agree that there is not yet definitive evidence that HBO improves outcomes in any circumstance, but suggestive evidence if the patient has loss of consciousness at any time. Any effect in patients with real loss of consciousness at the scene could have been diluted out by the addition of the others.
    2) Trial B — initial coma — did not have a “no HBO” arm. I’m not sure that whether to use one or two HBO sessions is a pressing issue for most clinicians, and I find it hard to believe that 2 sessions significantly worsened outcome.
    3) The study’s end point — a self-assessment questionnaire and a “thorough” physical examination by a blinded “intensive care physician qualified in neurology” or the patient’s general practitioner — is vague and ill-defined, to say the least.
    So the key question is still unanswered — if a patient has loss of consciousness at the scene or on presentation, will he/she benefit from HBO. My own approach in these patients is that if transportation to an HBO center does not pose a risk, an HBO center should be consulted and HBO should be offered. We know a certain number of these patients will go on to have persistent neurological deficits, and it seems best to remove any doubt that this could have been prevented with a fairly safe procedure.

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