On the Shoulders of Giants
Hyperbaric oxygen therapy for carbon monoxide (CO) poisoning improved cognitive outcomes at 6 weeks and possibly at 12 months.
Why does this matter?
High flow oxygen reduces the half life of CO bound to hemoglobin, and hyperbaric oxygen reduces the half life even more. But it is not a simple task to perform hyperbaric oxygen (HBO) and not all centers have it available. This was a RCT to see what benefit HBO offered, if any. CO poisoning leads to long-term problems with memory, attention, concentration, and affect in about half of patients who lose consciousness or a have a CO level of 25%. And, of course, it may cause death. There was an interesting retrospective study from Taiwan earlier this year that suggested HBO may decrease mortality. Be sure to read the selections below in Another Spoonful. You need to have a sense of how this study fits in the broader scope of HBO for CO trials.
This was a RCT of 76 patients per group with CO poisoning, as evidenced by exposure history and: "loss of consciousness, confusion, headache, malaise, fatigue, forgetfulness, dizziness, visual disturbances, nausea, vomiting, cardiac ischemia, or metabolic acidosis," and a CO level at least 10. They received 3 HBO treatments vs. 3 normobaric treatments within 24 hours of CO exposure, most within an average of 6 hours. The 3 HBO treatments were all with O2; the first normobaric treatment was with supplemental O2, and the other 2 were not. Investigators were blinded to treatment assignment, and respiratory therapists controlled the chamber. They stopped the trial early, as they found that cognitive testing was significantly better at 6 weeks in the HBO group, NNT = 5. In the intention to treat group, HBO also showed improved cognitive outcome at 12 months.
Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med. 2002 Oct 3;347(14):1057-67.
- Speaking of deep dive, Life in the Fast Lane takes us deep into this study and several others on the subject of HBO and introduces a healthy skepticism on this topic.
- A Cochrane Review including this paper criticizes it for changing the original primary outcome, long-term cognitive sequelae, and for stopping early, which inflated the purported effect.