Carbon dioxide tolerability and toxicity in rat and man: A translational study.

Due the increasing need for storage of carbon dioxide (CO) more individuals are prone to be exposed to high concentrations of CO accidentally released into atmosphere, with deleterious consequences. We tested the effect of increasing CO concentrations in humans (6-12%) and rats (10-50%) at varying inhalation times (10-60 min). In humans, a continuous positive airway pressure helmet was used to deliver the gas mixture to the participants. Unrestrained rats were exposed to CO in a transparent chamber. In both species regular arterial blood gas samples were obtained. After the studies, the lungs of the animals were examined for macroscopic and microscopic abnormalities. In humans, CO concentrations of 9% inhaled for >10 min, and higher concentrations inhaled for <10 min were poorly or not tolerated due to exhaustion, anxiety, dissociation or acidosis (pH < 7.2), despite intact oxygenation. In rats, concentrations of 30% and higher were associated with CO narcosis, epilepsy, poor oxygenation and, at 50% CO, spontaneous death. Lung hemorrhage and edema were observed in the rats at inhaled concentrations of 30% and higher. This study provides essential insight into the occurrence of physiological changes in humans and fatalities in rats after acute exposure to high levels of CO. Humans tolerate 9% CO and retain their ability to function coherently for up to 10 min. These data support reconsideration of the current CO levels (<7.5%) that pose a risk to exposed individuals (<7.5%) as determined by governmental agencies to ≤9%.