This clinical trial from the UK looked at an unusual indication for hyperbaric oxygen. Many patients suffer mild neurologic injury following surgery involving cardiac bypass, the most common of which is surgery for coronary artery bypass grafts (CABG.) The kind of injuries seen are usually minimal changes in intellectual or behavioral function, but an occasional massive stroke does occur. Mild neurologic injury is common, affecting about six percent* of patients undergoing CABG. These neurologic events are believed to be caused both by atherosclerotic emboli and air emboli. Surgical manipulation of major blood vessels during surgery can dislodge atherosclerotic plaque and introduction of microscopic amounts of air into the circulation during bypass is virtually unavoidable. It is the plaque and air emboli that cause the neurologic injury, which fortunately is mild, most of the time. Although hyperbaric oxygen is useful for treating stroke, interesting animal studies have suggested that pretreatment with hyperbaric oxygen can actually prevent some of the neurologic injury that follows cardiac bypass. These authors took the next logical step and looked at patients.
The authors randomized 64 patients to either hyperbaric oxygen (2.4 ATA for 60 minutes) or hyperbaric air (1.5 ATA.) Each patient received three hyperbaric treatments in the 24 hours before surgery. Each group had detailed measurements of inflammatory markers both before and soon after surgery. Each group also had detailed neuropsychiatric testing preoperatively and four months postoperatively.
The results were striking. In the immediate postoperative period, the patients treated with hyperbaric oxygen had significantly lower amounts of inflammatory markers detectable. Neurologic injury, as measured by a battery of neuropsychiatric tests, was statistically more common in the hyperbaric air patients compared to the hyperbaric oxygen patients.
Essentially, three hyperbaric oxygen treatments given shortly before cardiac bypass conferred some resistance to brain ischemic injury. The authors discuss their findings in great detail, so I won’t go into it any further. I only want to ask one question. In view of the results of this study, the known lack of risk of hyperbaric oxygen, and the limited amount of brain tissue we all have, would anyone be willing to participate in another double-blind study of hyperbaric oxygen to prevent neurolgical injury from cardiac bypass surgery?
* New England Journal of Medicine, 1996:335:1857-1864.