Determination of carbon monoxide

Carbon monoxide (CO, carbon monoxide, carbon monoxide) is a colorless, tasteless, odorless gas that does not cause irritation, a product of incomplete combustion. It is a component of many industrial gases (blast furnace, generator, coke); the content of carbon monoxide in the exhaust gases of internal combustion engines can reach 1-13%.

When inhaled, carbon monoxide combines with the oxygen-binding sites of hemoglobin (its affinity for hemoglobin is 220 times greater than that of oxygen). The resulting product, HbCO, cannot bind oxygen. Moreover, the presence of HbCO reduces the dissociation of oxygen from the remaining oxyhemoglobin, which reduces the transport of oxygen to tissues. The brain and heart suffer the most. In healthy non-smoking adults, the HbCO level in the blood is less than 1%. This level corresponds to the endogenous formation of CO during heme catabolism. In smokers, the HbCO content reaches 5-10%. In people in an atmosphere containing 0.1% CO, the HbCO level in the blood can reach 50%.

The main signs of CO intoxication are associated with hypoxia and develop in the following sequence: psychomotor disturbances, headache and a feeling of pressure in the temporal region, confusion, tachycardia, dyspnea, fainting and coma. Deep coma, convulsions, shock and respiratory arrest develop later. Individual variability of clinical manifestations of intoxication at a specific concentration of HbCO in the blood is observed. At an HbCO level below 15%, symptoms of poisoning rarely occur; a collapse state and fainting may be observed at a concentration of approximately 40%; and at a concentration above 60%, a fatal outcome may occur.

In addition to determining HbCO in the blood, which requires special equipment, there is a simpler way to diagnose CO poisoning. Blood containing CO, when adding a 1% tannin solution, acquires a red tint, while blood that does not contain CO becomes gray.

Relationship between HbCO concentration in blood and clinical manifestations

HbCO concentration,%	Clinical manifestations
0-2	There are no symptoms
2-5	Found in moderate smokers, usually asymptomatic, but may cause decreased intelligence
5-10	Found in heavy smokers, accompanied by mild shortness of breath with tension
10-20	Shortness of breath with moderate exertion, mild headache
20-30	Headache, irritability, impaired self-control and memory, rapid fatigue
30-40	Severe headache, blurred vision, confusion, weakness, shortness of breath
40-50	Tachycardia, dyspnea, severe headache, confusion, fainting, ataxia, collapse
50-60	Coma, intermittent convulsions
More than 60	Respiratory failure and death if not treated
80	Quick death

When studying the acid-base balance, p _a O ₂ is normal, although in fact the oxygen content in the tissues is reduced, p _a CO ₂ may be normal or slightly reduced, and the pH is reduced (metabolic acidosis due to tissue hypoxia).

In acute intoxication, treatment should be aimed at maintaining respiratory function. Oxygen therapy with 100% oxygen is of great importance and should be started as early as possible. Its goal is to increase the oxygen content in the blood by maximizing its fraction dissolved in plasma. It should be remembered that at an air pressure of 1 atm, the half-life of CO is approximately 320 min, with inhalation of 100% oxygen it decreases to 80 min, and with hyperbaric oxygenation (2-3 atm) - to 20 min. The HbCO level should be determined every 2-4 hours and oxygen treatment should be continued until HbCO decreases to 10%.

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