Hyperbaric Oxygen Therapy Quiz

Of the following answers, all except paraquat can be indications for HBO. In fact, HBO would likely cause patient harm for paraquat poisoning because paraquat generates more free radicals in the setting of hyperoxia.

The typical arterial oxygen tension is around 200 mmHg to 400 mmHg, which roughly equals 5 times oxygen tension when breathing room air. The mechanism of action of HBO therapy is to saturate the RBC’s and mitochondria to maximize oxygen delivery to the mitochondria, which are poisoned in critical CO exposure.

The proposed mechanism is that HBO reduces neuroinflammation by reducing levels of carboxyhemoglobin, reducing levels of nitrous oxide, and decreasing carboxymyoglobin levels (thereby increasing myocardial contractility). No study has shown displacement of CO from cytochrome oxidases, therefore answer 2 is incorrect. Several studies have shown that elevated atmospheric pressures have O2 have decreased neutrophil adherence to the endolthelium. Therefore answer 3 is incorrect. Answer 4 is incorrect because HBO likely decreases brain lipid peroxidation, which is a further marker of neuroinflammation.

The correct answer is decreased neuropsychiatric effects. The data have shown increased neuroinflammation and increased neuropsychiatric effects manifesting 2-50 days after carbon monoxide exposure. There has never been any mortality benefit demonstrated. Although carboxyhemoglobin is more rapidly decreased with HBO, this is not a patient center measure. Methemoglobinemia is not classically associated with carbon monoxide exposure. The data does not demonstrate an increased recovery time from coma and decreased ventilator time. Either this was not studied directly, or it was not significant.

The P450 pathway is the predominant mechanism for development of CO as a metabolite. Methylene chloride is found in paint stripper, industrial solvents, aerosol sprays, photographic film processing, and degreasing agents. All of the other answers are incorrect because they are not stoichiometrically balanced. Data is limited regarding the efficacy of HBO for methylene chloride toxicity; however, it may be of benefit.

There are not patient centered data supporting use of HBO for isolate cyanide exposures.

NAC repletes glutathione, which detoxifies radical products of Carbon Tetrachloride. HBO has not been shown to have patient centered outcomes resulting in improved outcomes. Therefore, IV NAC and supportive care is the best course of action.

Hyperbaric oxygen treatment is indicated because it has been shown to reduce the volume of the offending gas. In this case, it would most likely be O2. Theoretically, increased atmospheric pressure during HBO would lead to decreased size of any gas-air embolism.

The patient should be place in left lateral decubitus and Trendelenburg position to decrease the probability that gas-air emboli migrate to the cerebral circulation. Placing the the patient in the right lateral decubitus and Trendelenburg position may increase the probability of vomiting.

15% is the standard treatment threshold for HBO in a pregnant patient exposed to CO. 25% would be the threshold for any patient with CO exposure. Any syncope during exposure regardless of level should be considered for HBO therapy.