The recommended treatment for carbon monoxide (CO) poisoning is 100 percent nor-mobaric oxygen administered via a non-rebreather mask. Hyperbaric oxygen often is recommended, but previous small trials have shown conflicting results about possible benefits. Weaver and colleagues report on a larger randomized double-blind trial of hyperbaric oxygen.

Study participants were referred by various hospital emergency departments in Utah, Idaho, and Wyoming to LDS Hospital in Salt Lake City for treatment. Patients eligible for this study had a carboxyhemoglobin level of at least 10 percent or a known exposure to CO within the previous 24 hours and typical symptoms of poisoning (e.g., headache, confusion, visual disturbances, nausea, loss of consciousness).

Of the 332 patients who were initially eligible for the trial, 180 declined to participate, leaving 152 patients to be randomized into one of two treatment groups. Patients in one group received hyperbaric oxygen, while patients in the other group received normobaric oxygen. Both treatment sessions occurred in the hyperbaric chamber to help preserve blinding of the treatment assignment. Hyperbaric treatment consisted of three sessions during the first 24 hours. The first session used 3 atmospheres of pressure; the second and third sessions used 2 atmospheres of pressure. Patients randomized to normobaric treatment received 100 percent oxygen at sea level pressure.

Cognitive testing for sequelae of CO poisoning was conducted after the first and third chamber sessions, then at two weeks, six weeks, six months, and 12 months. Complete follow-up was unavailable for eight of 152 patients.

When tested for cognitive sequelae six weeks after treatment, problems were noted in 25 percent of subjects receiving hyperbaric oxygen compared with 46 percent of subjects receiving normobaric treatment, a difference that was statistically significant. This advantage persisted at six months (21 versus 38 percent), and at 12 months (18 versus 33 percent).

Hyperbaric treatment had some adverse effects. A full three sessions of hyperbaric pressure could not be accomplished in 18 percent of patients. The most common reason for stopping the first session was anxiety. Inability to equalize middle ear pressure was the most common reason for stopping the second and third sessions. One patient suffered a ruptured eardrum.

The authors conclude that use of hyperbaric oxygen for CO poisoning is associated with improved short- and long-term cognitive functioning compared with standard normobaric oxygen therapy.