Here is an interesting article from the New England Journal of Medicine:

Hyperbaric Oxygen Treatments Reduced the Risk for Cognitive Sequelae after Acute Carbon Monoxide Poisoning

Weaver LK, Hopkins RO, Chan KJ, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med. 2002;347:1057-67. [PMID: 12362006][Abstract/Free Full Text]

This study examined oxygen therapy given in a hyperbaric chamber to patients referred with carbon monoxide poisoning. The results were so significant that the trial was stopped early so that all patients could benefit from the hyperbaric therapy. Traditionally, patients with carbon monoxide poisoning are treated with 100% oxygen delivered by a tightly fitting or nonrebreather face mask. This is done to displace carbon monoxide from hemoglobin by providing a high partial pressure of oxygen. Weaver and colleagues rationalized that patients with carbon monoxide poisoning may have lingering neuropsychological effects that may or may not be related to the carboxyhemoglobin level with which they present to the hospital and that hyperbaric oxygenation may have benefits above and beyond displacing carbon monoxide from hemoglobin molecules.

In this randomized, double-blind trial, the investigators assigned patients with symptomatic acute carbon monoxide poisoning to 3 hyperbaric oxygen treatments within a 24-hour period or 1 normobaric oxygen treatment plus 2 sessions of exposure to normobaric room air within a 24-hour period. The carbon monoxide poisoning was the result of various factors, including an indoor heating fire and a suicide attempt, and the patients had carboxyhemoglobin levels of at least 10% when enrolled in the study. The patients received the oxygen treatments from an endotracheal tube or from a high-flow reservoir through a face mask to prevent rebreathing. The investigators administered neuropsychological tests immediately after chamber sessions 1 and 3 and at 2 weeks, 6 weeks, 6 months, and 12 months after enrollment. The primary outcome was cognitive sequelae at 6 weeks after carbon monoxide poisoning.

When the investigators stopped the trial, they had enrolled 76 patients in each group. At 6 weeks, cognitive sequelae (poor functioning) affected 25% of the hyperbaric oxygen group (19 of 76 patients) and 46.1% of the normobaric oxygen group (35 of 76 patients), even after adjustment for variables. At 6 months and 12 months, corresponding rates were 21% versus 38% and 18% versus 33%, respectively.

Three hyperbaric oxygen treatments within a 24-hour period appeared to reduce the risk for cognitive sequelae after acute carbon monoxide poisoning. This strongly positive study suggests that, if possible, hyperbaric oxygenation should be provided for symptomatic patients with acute carbon monoxide poisoning. The ideal number of chamber sessions, however, is unknown. It is also not known how hyperbaric oxygenation works to eradicate carbon monoxide. In animal models, such oxygenation affects lipid peroxidation in the brain; it also alters brain glutamate levels the same way that hypothermia does. Therefore, benefits of hyperbaric oxygenation may be related to improving oxygenation of cells above and beyond the displacement of carbon monoxide from hemoglobin.