A study of the application of reduction gas analysis in determining the relationship between carboxyhaemoglobin and tissue co levels in brain, heart and skeletal muscle after extreme exposure to co poisoning in rats

Abstract

Little is known of tissue carbon monoxide (CO) changes after acute exposure because tissue levels are in the order of picomoles per milligram and the technology to measure such low concentrations has only become available relatively recently. This study tested three hypotheses: That tissue CO levels (1) vary among tissues after acute poisoning; (2) change over time; but (3) cannot be predicted by measuring carboxyhaemoglobin (COHb) levels. Twenty four healthy male Sprague-Dawley rats were exposed to 2500 ppm CO in air for 45 min. This non-lethal exposure achieved reproducible COHb values of 66 to 72%. Animals were allowed to recover breathing air and were sacrificed at 30 minute intervals for 150 minutes. An additional nine male animals served as unexposed controls. Accurate measurements of tissue CO levels were made in blood, brain, heart, and skeletal muscle samples. All samples were prepared using the validated technique described by Vreman et al., and Reduction Gas Analysis was used to determine the pmol CO per wet weight tissue. Co-oximetry and gas chromatography were performed on all blood samples. Predictably, blood CO content dropped following exposure, but tissue CO content did not follow the same trend in all tissues. This study supports the hypothesis of (1) tissue and (2) time-related variability of CO concentration in three body tissues after exposure and (3) documents lack of utility of COHb for predicting tissue CO tissue values.