Neurological or neuropsychiatric features including disorientation, apathy, mutism, irritability, inability to concentrate, personality change, Parkinsonism and parietal lobe lesions. This late stage is more common in those aged over 40. Some patients develop later symptoms perhaps after several weeks of apparent recovery from the incident. Carbon monoxide poisoning is likely to be suspected in circumstances where exposure to a source has taken place and symptoms improve when the patient has been removed from the source. Symptoms are likely to be mild and may include nausea, subjective weakness, headache and poor concentration/memory. The physical symptoms of carbon monoxide poisoning are subtle and low-level exposure may produce no abnormal physical signs. The neonate also has high levels of fetal haemoglobin. The fetus is more vulnerable to carbon monoxide toxicity because of the natural leftward shift of the dissociation curve of fetal haemoglobin, a lower baseline PaO 2, and levels of HbCO at equilibration that are 10-15% higher than maternal levels.Clinical features are nonspecific and so a high level of suspicion is required. The latter often results from a poorly serviced gas fire and the elderly are most at risk. Acute toxicity results from a single exposure but chronic carbon monoxide poisoning also needs to be recognised.Proximity to a conflagration such as a house fire - during the assessment and management of burns, do not forget the possibility of carbon monoxide poisoning and smoke inhalation too.Simply having the windows and doors of a garage open is not enough. Running a petrol or diesel engine in a confined space increases the risk.Any carbon-based fuel can be hazardous, including oil. Inadequately serviced fires - there is an increased risk in winter and a greater risk in the households which use solid fuel.A study in the USA in 2007 found an emergency department attendance rate of 50,000 annually, a significant increase on previous estimates. EpidemiologyĬarbon monoxide poisoning kills 50 people and seriously injures nearly 200 in the UK each year, but the overwhelming majority of cases go unrecognised, unreported, and untreated. The value of hyperbaric oxygen is, however, unclear. 100% oxygen reduces this to 30-90 minutes and 100% oxygen at hyperbaric pressure of 2.5 atmospheres reduces it to 15-23 minutes. The half-life in a normal atmosphere is 3 to 4 hours. It is a colourless, odourless gas and so cannot be detected by the normal senses.Ĭarbon monoxide is excreted through the lungs. Tobacco smoke also contains carbon monoxide. In someone who has escaped from a fire, both smoke inhalation and carbon monoxide poisoning must be considered, as must hydrogen sulphide poisoning. It is present in a car exhaust if oxygen is limited, as in a garage or with the choke engaged. Carbon monoxide binds even more avidly to cardiac myoglobin than to haemoglobin.Ĭarbon monoxide may result from the combustion of wood or fossil fuels such as gas, oil and coal with inadequate oxygen supply. It also binds to intracellular carriers of oxygen, causing tissue asphyxiation. In an atmosphere of 21% oxygen and 0.1% carbon monoxide, therefore, the blood will leave the lungs about 50% saturated with oxyhaemoglobin and 50% saturated with carboxyhaemoglobin.Īn ambient carbon monoxide level of 100 parts per million (ppm) produces 16% HbCO at equilibrium, which is sufficient to produce clinical symptoms. Carbon monoxide competes with oxygen to form carboxyhaemoglobin (HbCO) instead of oxyhaemoglobin but it has 210 times the affinity for haemoglobin. Carbon monoxide is produced by the incomplete combustion of carbon or carbon-containing compounds in an inadequate supply of oxygen.
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