By Yervand Kondrahjian | Staff Writer
Carbon monoxide (CO) is a highly toxic gas that is both colorless and odorless. It is formed as a result of incomplete combustion of organic matter. Approximately 40% of atmospheric CO is generated by natural sources such as volcanic eruptions, vegetal and animal degradation, and natural forest fires. The remaining 60% of CO is produced by human activities, such as the consumption of fossil fuels and tobacco smoke.
In addition to external sources, CO can also be produced endogenously. Normal levels of CO in plasma typically range from 1% to 5%, but can increase to 7% or 8% in smokers. The main endogenous source of CO in healthy individuals is the breakdown of the heme group from erythrocytes into biliary pigments, which is catalyzed by heme oxygenases (HO). Tissues such as the spleen, liver, and reticulo-endothelial system, which are the major locations for heme metabolism, can also contribute to CO production by expressing HO. It is estimated that the net rate of endogenous CO production is approximately 0.42 ml at standard temperature and pressure.
The toxicity of CO is related to its interaction with hemoglobin (Hb). CO is quickly absorbed by the lungs and once in the bloodstream, it binds rapidly to Hb with a higher affinity than oxygen. This results in the formation of carboxyhemoglobin (COHb). COHb compromises the transportation of oxygen to peripheral tissues, leading to a hypoxic situation.
The primary mechanism of toxicity caused by CO exposure is tissue hypoxia. Tissues with higher demand for oxygen, such as the brain and heart, are particularly vulnerable to the effects of CO.
CO intoxication is typically categorized as mild, moderate, or severe. Mild intoxication may cause symptoms such as nausea, dizziness, vision disturbances, headache, dilated cutaneous musculature, and occasionally cherry lips and skin. In moderate CO intoxication, confusion, chest pain, tachycardia, weakness, and dyspnea may also appear. Severe CO intoxication can cause hypotension, cardiac and respiratory arrest, seizures, coma, and even death.
The analysis of CO in blood has been of great interest for many years, and various techniques have been used for this purpose. Among these techniques, spectrophotometry is one of the most frequently employed for quantifying CO levels in blood.