Carbon monoxide poisoning (CO): symptoms, diagnosis, treatment
Last reviewed: 23.04.2024
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Carbon monoxide poisoning causes acute symptoms: headache, nausea, weakness, exertional angina, dyspnoea, loss of consciousness and to whom. Neurological symptoms can develop after a week. Diagnosis is based on the determination of the concentration of carboxyhemoglobin, the gas composition of the blood, including oxygen saturation. Treatment consists in inhalation of oxygen. Prevention is possible with the help of home CO detectors.
Carbon monoxide poisoning - one of the most frequent fatal poisonings, occurs when inhaled. CO is an odorless and colorless gas, a product of incomplete combustion of hydrocarbons. Typical sources of CO for poisoning - home ovens, fireplaces, heating appliances, kerosene burners, improperly ventilated cars. CO is formed by the combustion of natural gases (methane, propane). Upon inhalation of tobacco smoke, CO falls into the blood, but in a concentration insufficient for poisoning. The half-life of CO is 4.5 hours with inhalation of air, 1.5 hours with respiration 100% oxygen, 20 minutes with oxygen breathing at a pressure of 3 atm (pressure chamber).
The mechanisms of carbon monoxide poisoning are not completely uncovered. They include the displacement of oxygen from Hb due to the higher affinity of CO to hemoglobin, the shift of the hemoglobin dissociation curve to the left (reduction of oxygen release from erythrocytes in tissues), the suppression of mitochondrial respiration. It is also possible to have a direct toxic effect on the brain.
[Symptoms of Carbon Monoxide Poisoning
Clinical manifestations correlate with the concentration of carboxyhemoglobin in the blood. Many manifestations are nonspecific. Headache and nausea occur when the content of carboxyhemoglobin is 10-20% hemoglobin. The content of carboxyhemoglobin> 20% is usually accompanied by dizziness, general weakness, impaired concentration, and reduced criticality. The content> 30% causes dyspnea with physical activity, chest pain (in patients with ischemic heart disease) and impaired consciousness. A higher content leads to fainting, convulsions and loss of consciousness. With a content> 60%, arterial hypotension, coma, respiratory failure and death develop.
Many other symptoms are possible: visual impairment, abdominal pain, local neurological deficit. With severe poisoning, neuropsychiatric manifestations can develop in a few weeks. Because CO poisoning often occurs in household fires, patients may have combined airway damage, which increases the risk of developing respiratory failure.
Diagnosis of carbon monoxide poisoning
Because the symptoms are variable and nonspecific, the diagnosis is easy to miss. Because of the absence of specific symptoms of poisoning, many cases of mild severity are regarded as viral diseases. Doctors should be cautious about possible poisoning. If people living in the same house, especially with the stove heating system, have nonspecific symptoms, one must suspect poisoning with CO.
If there is a suspicion of CO poisoning, it is necessary to study the concentration of carboxyhemoglobin of the blood with a CO-oximeter, it is possible to use venous blood for analysis because of a slight arteriovenous difference. The gas composition of the blood is not routinely examined. The data of the gas composition of blood and pulse oximetry, both individually and together, are insufficient for the diagnosis of CO poisoning, since the O2 saturation level obtained reflects the dissolved oxygen, including in the composition of carboxyhemoglobin. Pulse oximetry does not distinguish normal hemoglobin from carboxyhemoglobin and therefore shows a false overestimation. Although elevated carboxyhemoglobin in the blood serves as an obvious proof of poisoning, it can be falsely low, as it rapidly falls after the gas exposure ceases, especially when oxygen is used (for example, in an ambulance). Metabolic acidosis may be an auxiliary feature. Other research methods can help to assess specific symptoms (eg, ECG for chest pain, CT for the presence of neurological symptoms).
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Prevention and treatment of carbon monoxide poisoning
Prevention includes checking the sources of home heaters for proper installation and the presence of an exhaust (ventilation) system. Pipes should be periodically inspected for possible leaks. Required CO-detectors, early warning of the presence of free CO in the room. If there is a suspicion of the presence of CO in the room, it is necessary to open windows, evacuate people, establish a source of CO. Victims should be evacuated away from the source of CO. Inhalation of 100% O through a mask and maintenance therapy is shown. Hyperbaric oxygenation (HBO) is indicated for patients with life-threatening cardiopulmonary complications, continuing pain behind the sternum, impairment of consciousness, loss of consciousness (regardless of the term), pregnant women affected with a carboxyhemoglobin content in the blood of more than 25%. The patient is placed in a chamber with a pressure of about 2-3 atm. The use of HBO reduces the risk of developing late neurologic symptoms. However, pressure chambers may not be nearby, which will require transportation of a patient with an unstable condition. The most effective use of HBO for about 4 hours from the time of poisoning. In general, the effectiveness of the method requires additional evidence. Consultation of the Center for the control of poisonings, or a specialist in HBO is required.
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