Carboxyhemoglobin (COHb) is a protein, resulting from the binding of hemoglobin with carbon monoxide which once in the blood tends to bind in this way.
Hemoglobin has an affinity two hundred and ten times higher for carbon monoxide, than for oxygen, displacing it easily. Because of the affinity of carbon monoxide for hemoglobin, there is a progressive formation of COHb; this formation depends on the duration of exposure to CO, the concentration of this gas in the inspired air and the alveolar ventilation.
CO is toxic because when carboxyhemoglobin is formed, it can no longer capture oxygen, since the CO-Hb bond is irreversible. Often carbon monoxide poisoning is included as a form of anemic hypoxia because there is a deficiency of hemoglobin available to transport oxygen.
The symptoms of CO poisoning are those of hypoxia of any kind, especially headache and nausea, but there is little stimulation of breathing. The cherry red color of the COHb causes no cyanosis. Death occurs when 70 to 80% of the circulating hemoglobin becomes COHb. The symptoms caused by chronic exposure to non-lethal concentrations of CO are those of progressive brain damage, which includes mental changes and sometimes a state similar to parkinsonism. Bibliography
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