Major symptoms (any history of loss of consciousness, amnesia, or myocardial ischemia) have traditionally been an indication for initial HBO treatment. -I4 While dramatic improvement in symptoms and signs is generally seen, there is continued debate as to whether HBO is better than NBO with regard to short- and long-term outcomes.19 Prospective, randomized studies comparing HBO and NBO have yielded conflicting results, possibly due to different entry criteria, the intensity of the outcome measure, and the duration of follow-up.2 2 and 22 There appears to be some benefit to HBO in reducing neurophysiologic sequelae, but that difference may be detectable only with specific testing and the benefit may disappear after 12 months of follow-up.
While the patient is being prepared for referral to a hyperbaric chamber, he or she should be maintained on 100% NBO. Traditional recommendations for HBO treatment for CO poisoning have sometimes stressed the use of HbCO criteria. This approach is no longer advocated because of the poor correlation between clinical symptoms, morbidity, mortality, and ED HbCO levels. In addition, there is no evidence that HBO treatment based on HbCO level alone is beneficial.
The added mortality or morbidity incurred by transport to an HBO treatment facility has been established to occur in less than 5 percent of cases so handled. Both monoplace and multiplace hyperbaric chambers have critical care capability for ventilator support of endotracheally intubated patients, blood pressure monitoring, central venous manometry, and cardiac monitoring. U.S. emergency physicians can find the location of the nearest hyperbaric chamber by calling the Divers Alert Network (DAN), Duke University, Durham, NC, at 1-919-684-8111.
Standard HBO treatment for CO intoxication uses 100% oxygen at 2.4 to 2.8 ATA for 90 min. Most patients with moderate symptoms respond to one treatment, although some may have persistent symptoms that require one or two more treatments during the first 24 h to fully resolve. Treatment costs for HBO are approximately $500 per session, in comparison to about $150 to $200 for 4 h of NBO in an ED.
In addition to enhancing the elimination of CO from the body, HBO treatment has several theoretical advantages over NBO treatment. HBO improves oxygen delivery to ischemic tissue and CO elimination from hemoglobin. HBO, not NBO, lessens CO-induced reperfusion injury by truncating lipid peroxidation and lessening leukocyte endothelial adherence in microvasculature. 91°
Complications of HBO treatment include a very low incidence of oxygen-induced seizures (approximately 1 per 1000 patients), ear and sinus barotrauma, pulmonary barotrauma, and vascular gas embolism. Pregnancy is not a contraindication to HBO treatment. The only absolute contraindication to HBO treatment is an untreated pneumothorax.
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