CARBON MONOXIDE (CO) POISONING

It is well known to us that Carbon Monoxide (CO) is a colorless, odorless and tasteless gas. There have been many cases reported of deaths due to carbon monoxide poisoning. It is very common in India and many other countries. It could be accidental, suicidal and rarely homicidal.

Carbon monoxide comes under the category of asphyxiant gases, An asphyxiant gas is a toxic or non toxic gas which causes respiratory blockage that can lead to asphyxia or death. Many gases like carbon dioxide, argon, helium, methane, hydrogen sulfide, phosgene, cyanide also comes under this category.

Properties

CO is a colorless, odorless and tasteless gas.

It is produced by incomplete combustion of carbonaceous materials.

After combining with chlorine it forms a toxic gas called phosgene.

Sources

Coal gas is a mixture of CO, methane and hydrogen.
It is also found in the gaseous products from charcoal fires, refineries, blast furnaces, gas refrigerators and household fires.
Other common sources of CO are tobacco smoke, automobile exhaust (1-7%), faulty heating units.

Mechanism of Action

Carbon Monoxide has very high affinity for hemoglobin as compared to oxygen. It combines with hemoglobin in blood and forms carboxyhemoglobin (COHb) and produces anemic hypoxia (reduced oxygen carrying capacity of blood). CO being a cellular poison disrupts the electron chain transfer at cellular level in mitochondria. Its combination with cytochrome P450 and inhibits the cellular respiration.

Signs and Symptoms

Acute symptoms include headache, dizziness, weakness, nausea and confusion.
Patients may display memory disturbance,
The CO poisoning depends on the concentration, duration of exposure. The elderly people are more vulnerable with respiratory diseases. At high altitude and high temperature the toxicity is more profound.
When carboxyhemoglobin exceeds 60 per cent, hypotension and a slowing of pulse and respiration is observed. When this level exceeds 70% survival is not possible.
In cases of chronic poisoning headache, nausea, fatigue, confusion and difficulty in sleeping, diarrhea and abdominal pain are seen.
Exposure of CO in pregnant ladies can give rise to still births.

Treatment

The patient should be removed from the source of exposure at once.
Maintain airway by fresh air and orthobaric oxygen by tight fitting face mask or endotracheal tube.
In severe poisoning cases, hyperbaric oxygen should be provided at PO2 of 2-3 atmospheric pressure.
Blood transfusion if required should be provided.
Cerebral edema is treated by mannitol 500 ml IV as 20% solution over 15 min, then followed by 500 ml of 5% dextrose over next 4 hours.

Postmortem Findings

External findings –

Cherry red coloration of the skin, mucous membranes, tissues and internal organs.

Lips and fingernails also appears to be of cherry red in color.

PM staining also appears to be of cherry red color.

Fine froth at the nostril or mouth.

Internal findings-

Lungs are congested and oedematous.

Petechial hemorahages to myocardial necrosis is seen in heart.

Neuronal hypoxic injury is the most pronounced in the gray matter of brain.

Medicolegal aspects of CO poisoning

It is a common mode of suicidal poisoning in Western world but rarely in India.
Accidental cases of CO poisoning by placing angeethi in rooms during winter, leakage of cooking gas, etc. is seen in India.
Putrefaction has no effect on carboxyhemoglobin, (as it is not a product of it) so its levels can be determined even several days of after death.
Heavy smokers can have COHb level upto 10%.