What causes the bright red color of a dog's mucous membranes after smoke inhalation?

The bright red color observed in a dog's mucous membranes following smoke inhalation is primarily caused by carbon monoxide exposure. When carbon monoxide enters the bloodstream, it binds with hemoglobin in red blood cells, forming carboxyhemoglobin. This compound interferes with the blood's ability to carry oxygen, leading to a significant reduction in available oxygen for tissues, but it also changes the color of the blood. Carboxyhemoglobin has a bright cherry-red hue, which is why the mucous membranes of affected animals appear bright red.

In contrast, the other choices do not cause the same vivid discoloration of mucous membranes. Carbon dioxide does not lead to a bright red color; rather, it can cause respiratory acidosis and other physiological changes without a distinct change in color. Ash may contribute to irritation but does not alter the color of mucous membranes. Burns can cause local tissue damage and discoloration, but they result in different clinical signs and typically manifest as pallor or darkening rather than bright red coloration.