Hyperbaric oxygen for carbon monoxide poisoning? Eminence-based recommendations not evidence-based

October 31, 2012, 11:41 am

★★☆☆☆

Practice Recommendations in the Diagnosis, Management and Prevention of Carbon Monoxide Poisoning. Hampson NB et al. Am J Respir Crit Care Med 2012 Oct 18 [Epub ahead of print]

Abstract

When I first saw this paper I was really looking forward to reading it. I still find many aspects of managing carbon monoxide poisoning — especially those involving indications for hyperbaric oxygen (HBO) therapy — far from clear, and the abstract promised “consensus opinion of four recognized content experts in the field”. I should have recognized that placing this rather immodest claim up front was a warning sign that the road ahead would be strewn with eminence-based — not evidence-based — medicine.

Indeed, the “four recognized content experts” — Neil Hampson, Claude Piantadosi, Stephen Thom, and Lindell Weaver — have written many papers and chapters relating to CO poisoning. But anyone looking to this paper for unbiased guidelines should realize that all 4 approach the topic, not as medical toxicologists, but as hyperbaric medicine specialists. It would not be unreasonable to suspect that any guidelines provided by these authors might be weighted towards liberal use of HBO.

The authors begin by claiming that the evidence “is sufficient to draw firm conclusions about many aspects of the pathophysiology, diagnosis and clinical management of the syndrome [clinical CO poisoning], along with construction of evidence-based recommendations for best clinical practice related to CO poisoning”. Yet when it comes to HBO, they suggest:

Hyperbaric oxygen should at least be considered in all cases of serious acute CO poisoning and normobaric 100% oxygen continued until the time of hyperbaric oxygen administration.

This is anything but a “firm conclusion”. What is “serious” CO poison? For that matter, what does “should be at least considered” mean? In my experience, it’s a classic review article dodge, thrown in by authors who are hesitant to say “we really don’t know if this works”.

As for evidence for or against possible benefit from HBO in the treatment of CO poisoning, the authors throw out all existing literature as suffering from important flaws and limitations, except for one article that was — surprise! — co-authored by one of them. They don’t point out that their chosen paper had significant limitations if its own — in fact, there was no “Limitations” section discussing problems with the bizarre study design in the paper itself. In that paper, a study group of CO poisoning victims were treated with 3 sessions of HBO, and compared with controls receiving 1 session of normobaric oxygen plus 2 sessions of normobaric room air. This is obviously an unfair comparison — how do they know that the “hyperbaric” component caused any improved outcome, rather than just the increased exposure to oxygen. In addition, there were significant baseline differences between the groups favoring improved outcome in the HBO group.

In their “Key Message” summary (Table 1), the authors become more specific in their recommendations for HBO:

Poisoned patients with loss of consciousness, ischemic cardiac changes, neurological deficits, significant metabolic acidosis, or COHb >25% warrant HBO.

I would point out that there’s little evidence for any of this, except possibly loss of consciousness. In my opinion, if a patient is having ischemic EKG changes the risk of transport to an HBO facility likely outweighs any unproven benefit form HBO. Likewise, treating an isolated number (COHb > 25%) seems unwise. Finally, the undefined term “neurological deficits” is too vague to make treatment decisions on.

 

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