Carbon monoxide (CO) poisoning: symptoms, diagnosis, treatment

Carbon monoxide poisoning causes acute symptoms: headache, nausea, weakness, angina, dyspnea, loss of consciousness and coma. Neurological symptoms may develop weeks later. Diagnosis is based on determining the concentration of carboxyhemoglobin, blood gas composition, including oxygen saturation. Treatment consists of oxygen inhalation. Prevention is possible with home CO detectors.

Carbon monoxide poisoning is one of the most common fatal poisonings, and occurs when inhaled. CO is an odorless, colorless gas, a product of incomplete combustion of hydrocarbons. Typical sources of CO in poisoning are home stoves, fireplaces, heating devices, kerosene burners, and improperly ventilated cars. CO is formed during the combustion of natural gases (methane, propane). When inhaling tobacco smoke, CO enters the blood, but in a concentration insufficient for poisoning. The half-life of CO is 4.5 hours when inhaling air, 1.5 hours when breathing 100% oxygen, and 20 minutes when breathing oxygen under a pressure of 3 atm (pressure chamber).

The mechanisms of carbon monoxide poisoning are not fully understood. They include displacement of oxygen from Hb due to the higher affinity of CO for hemoglobin, a leftward shift in the hemoglobin dissociation curve (reduced release of oxygen from red blood cells in tissues), and inhibition of mitochondrial respiration. Direct toxic effects on the brain are also possible.

[ 1 ], [ 2 ], [ 3 ], [ 4 ]

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 carboxyhemoglobin content is 10-20% of hemoglobin. Carboxyhemoglobin content >20% is usually accompanied by dizziness, general weakness, impaired concentration, decreased criticality. Content >30% causes dyspnea during physical exertion, chest pain (in patients with coronary heart disease) and impaired consciousness. Higher content leads to fainting, convulsions and loss of consciousness. When the content is >60%, arterial hypotension, coma, respiratory failure and death develop.

Many other symptoms are possible: visual impairment, abdominal pain, local neurological deficit. In severe poisoning, neuropsychiatric manifestations may develop after several weeks. Since CO poisoning often occurs in house fires, patients may have combined damage to the respiratory tract, increasing the risk of respiratory failure.

Diagnosis of carbon monoxide poisoning

Because symptoms are variable and non-specific, the diagnosis can be easily missed. Because there are no specific symptoms of poisoning, many mild cases are considered viral diseases. Physicians should be alert for possible poisoning. If people living in the same house, especially with a stove heating system, develop non-specific symptoms, CO poisoning should be suspected.

If CO poisoning is suspected, the concentration of carboxyhemoglobin in the blood should be measured with a CO-oximeter; venous blood may be used for analysis due to the insignificant arteriovenous difference. Blood gas composition is not routinely analyzed. Blood gas composition and pulse oximetry data, either separately or together, are insufficient for the diagnosis of CO poisoning, since the resulting O2 saturation level reflects dissolved oxygen, including that contained in carboxyhemoglobin. Pulse oximetry does not distinguish normal hemoglobin from carboxyhemoglobin and therefore gives a falsely high result. Although elevated blood carboxyhemoglobin serves as clear evidence of poisoning, it may be falsely low, since it falls rapidly after exposure to the gas ceases, especially when oxygen is used (e.g., in an ambulance). Metabolic acidosis may be an auxiliary sign. Other research methods can help to evaluate specific symptoms (for example, ECG for chest pain, CT for neurological symptoms).

[ 5 ], [ 6 ], [ 7 ]

Prevention and treatment of carbon monoxide poisoning

Prevention includes checking home heating sources for proper installation and the presence of an exhaust (ventilation) system. Pipes should be periodically inspected for possible leaks. CO detectors are required to provide early warning of the presence of free CO in a room. If CO is suspected in a room, open windows, evacuate people, and identify the source of CO. Victims should be evacuated away from the source of CO. Inhalation of 100% O through a mask and supportive therapy are indicated. Hyperbaric oxygenation (HBO) is indicated for patients with life-threatening cardiopulmonary complications, persistent chest pain, impaired consciousness, loss of consciousness (regardless of the period), pregnant women, and victims with a blood carboxyhemoglobin content of more than 25%. The patient is placed in a chamber with an O pressure of 2-3 atm. The use of HBO reduces the risk of developing late neurological symptoms. However, a pressure chamber may not be nearby, which will require transporting a patient with an unstable condition. The most effective application of HBO is within approximately 4 hours of the poisoning. In general, the effectiveness of the method requires additional evidence. Consultation with the Poison Control Center or a specialist in HBO is required.