Hyperbaric oxygen exposure

Administration of hyperbaric oxygen following exposure to carbon tetrachloride improved survival from 31 to 96% in rats (Ellenhorn and Barceloux 1988). Hyperbaric oxygen has also been used in treating overdoses of carbon tetrachloride in humans and may correct regional tissue hypoxia and damage, as well as inhibit the P-450-dependent reductive dehalogentation of carbon tetrachloride to the metabolically active acute trichloromethyl radical in the liver. However, the effectiveness of this method has not been established in humans (Burkhart et al. 1991 Ellenhorn and Barceloux 1988). 

In cases of acute intoxication, removal of the individual from the exposure source and maintenance of respiration is essential, followed by administration of oxygen—the specific antagonist to CO— within the limits of oxygen toxicity. With room air at 1 atm, the elimination half-time of CO is about 320 minutes with 100% oxygen, the half-time is about 80 minutes and with hyperbaric oxygen (2-3 atm), the half-time can be reduced to about 20 minutes. 

Blood gases and serum electrolytes should be monitored and corrected as needed (Hall and Rumack, 1986 Vogel et al, 1981). Blood cyanide levels can confirm exposure, but due to the time needed to get the results, they are not clinically useful. Provide supplemental oxygen with assisted ventilation as indicated. Animal study results for hyperbaric oxygen therapy have been questionable (Way et al, 1972). Acidosis (pH <7.1) should be corrected with intravenous sodium bicarbonate, but acidosis may not resolve until after the administration of antidotes (Hall and Rumack, 1986). Benzodiazepines or barbiturates can be used to control seizures. 

Diagnosis is based primarily on history. Blood nitrites may indicate exposure if measured immediately after exposure (Reiffenstein et al. 1992). Treatment consists primarily of supportive measures. Some protocols call for managing symptoms with atropine, amyl nitrite, sodium nitrite, or hyperbaric oxygen (Gosselin et al. 1984 Reiffenstein et al. 1992). The efficacy of these treatments is unclear. 

B. Specific drugs and antidotes. Theoretically, administration of nitrites (see p 476) to produce methemoglobinemia may promote conversion of sulfide ions to sulfmethemoglobin, which is far less toxic. However, there is limited evidence for the effectiveness of nitrites, and they can cause hypotension and impaired oxygen delivery. Animal data and limited human case reports have suggested that hyperbaric oxygen (HBO, see p 482) may be helpful if provided early after exposure, but this therapy remains unproven. 

B. Carbon monoxide poisoning. Provide 100% oxygen by tight-fitting mask or via endotracheal tube. Consider hyperbaric oxygen therapy if the patient has serious poisoning (see Indications, above) and the patient can be treated within 6 hours of the exposure. Consult with a poison center ([800] 222-1222) or hyperbaric specialist to determine the location of the nearest HBO facility. Usually, three HBO treatments at 2.5-3 atm are recommended over a 24-hour period. 

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