Carbon monoxide is a colorless, tasteless, non-irritative gas that is produced due to the incomplete combustion of carbon. It burns with a blue flame. It is lighter than air and can get readily absorbed across the alveolus and combines with hemoglobin. Its affinity for Hb is 200 to 300 times greater than that of oxygen. It displaces the bond between oxygen and hemoglobin and forms a stable compound named carboxyhemoglobin

Carbon monoxide poisoning occurs when it builds up in the bloodstream. This can lead to serious tissue damage or even death. CO acts as a chemical asphyxiant and produces death due to anemic anoxia. It is a potent cellular toxin. It inhibits electron transportation by blocking cytochrome A3 and cytochrome P-450, and therefore intracellular respiration. 

Death due to CO poisoning started long back in history especially during the times of mining coal. Later it started to be used as a weapon. The most famous one is when the nazis used vans filled with carbon monoxide gas at the Chelmno extermination camp as part of the holocaust during World War II. The development of the symptoms has a progression, roughly parallel to the rise in the saturation of the blood by CO.

Signs and Symptoms of Carbon Monoxide Poisoning

0 to 10 %No appreciable symptoms. 
10% to 20%Breathlessness on moderate exertion,  mild headache, weakness. 
20% to 30%Throbbing headache, irritability, emotional instability, disturbed judgment, defective Memory & rapid fatigue. 
30% to 40%Severe headache, nausea, vomiting, dizziness, dimness of vision, confusion, cherry-red color. 
40% to 50%Increasing confusion, sometimes hallucinations, severe ataxia, rapid respirations & collapse with attempts at exertion. Symptoms resemble alcoholic intoxication 
50% to 60%Syncope or comma with intermittent convulsions, rapid respiration, tachycardia with a weak pulse and pink or red discoloration of the skin. 
60 % to 70%Increasing depth of comma with incontinence of urine and feces. 
70 %  to 80%Profound comma with depressed or absent reflexes, a weak thready pulse, shallow and irregular respiration, and death. 
Above 80%Rapid death from respiratory arrest. 
  • The blood under the skin and in the tissues will be cherry-red due to carboxyhemoglobin.
  • Death is relatively rapid due to CO hence blisters are rare.
  • Bullae tend to be separate and isolated lesions. They are localized by external pressure and are seen in the regions of the calves, buttocks, wrists, and knees. The bullous fluid is usually thick and cellular and often an inflammatory reaction in the surrounding skin. 
  • Signs rarely involve the fingers and toes.
  • There is a tendency of the dying victim to wild, erratic swinging movements inside the room, disturbing clothing, and furniture which gives an impression of violent struggle (CO automatism).
  • Chronic Poisoning: Headache, confusion, weakness, visual disturbances, hypertension, hyperthermia, palpitations, atrial fibrillation, bundle branch blocks, mental retardation, psychosis, Parkinsonism, and incontinence.  

Postmortem Appearences in Carbon Monoxide Poisoning

  • The cherry-red coloration of the skin, mucous membranes, conjunctivae, nail beds, areas of hypostasis, blood, tissues, and internal organs.
  • Anemic person: Color may be faint or absent.
  • Dark-colored victims: Color may be masked, but may be seen in the inner aspect of lips, nail-beds, tongue, palms, and soles, inside the eyelids.
  • Cherry-red discoloration changes to dark-green, then to brown with the onset of decomposition.
  • Blistering of the skin of dependent areas.
  • Congestion of the lungs with pink fluid blood, and if the victim survived for some time, pulmonary edema with congestion is found.


Exposure to carbon monoxide is more dangerous to unborn babies because fetal blood cells take up carbon monoxide more rapidly than adult blood cells, children, and younger people because they take breaths more frequently than adults, people with heart disease, or breathing problems.

CO poisoning can cause permanent brain damage, cardiac complications, miscarriage. Postmortem findings help to determine the cause of death. 

Categories: Toxicology


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