When is hyperbaric oxygen (HBO) therapy indicated in the treatment of smoke inhalation injury?

Updated: Oct 15, 2021
  • Author: Keith A Lafferty, MD; Chief Editor: Joe Alcock, MD, MS  more...
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In patients with CO poisoning from smoke inhalation, the main reason for use of hyperbaric oxygen (HBO) therapy is to prevent delayed neurological sequelae. Carboxyhemoglobin levels are poor indicators of the severity of intoxication; patients with significant toxicity may have low levels. In fact, at the time of the initial HBO treatment, patients enrolled in most studies have normal or near-normal carboxyhemoglobin levels.

At this time, 6 prospective, randomized controlled trials have compared HBO with normobaric oxygen (NBO) therapy for CO poisoning. Four of these studies show a benefit for CO poisoning; two do not. The data and conclusions drawn from these studies are conflicting and highlight the controversy surrounding the utility of HBO.

In a prospective, double-blind study that compared HBO with NBO in patients with symptomatic acute CO poisoning, Weaver and colleagues found that 3 HBO treatments decreased the incidence of cognitive sequelae by 46% at 6 weeks. [47] Furthermore, a benefit continued to be seen at 12-month follow-up. Essentially, for every 6 patients treated with HBO, one case of delayed neurologic sequelae could be avoided. The evidence of benefit with HBO was so strong that the study was halted before its scheduled completion.

Although there has been much debate regarding the accuracy of neuropsychometric testing, including the fact that patients who are depressed and who have attempted suicide with non-CO means perform as poorly as CO-exposed patients, such testing remains an objective means to evaluate cognitive function.

Neurologic abnormalities and a history of loss of consciousness are the primary clinical features used to define severe CO toxicity and are indications for HBO. In addition, HBO use is indicated in patients with any of the following:

  • Base excess lower than -2 mmol/L

  • CO level greater than 25% (or >15% in pregnancy, as fetal hemoglobin binds CO more tightly)

  • Signs of cerebellar dysfunction

  • Cardiovascular dysfunction

  • Pulmonary edema

  • Extremes of age

Note that the incidence of delayed neurologic sequelae increases with a more symptomatic initial clinical picture, in older patients, and in those with a prolonged exposure. [10]

The American College of Emergency Physicians Clinical Policies Subcommittee recommended in 2008 continued use of HBO in CO poisoning, especially in children and pregnant women, due to the conflicting results of previous studies. [48]

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