Generality
Carbon monoxide (CO) intoxication is one of the most common causes of death from inhalation poisoning.
Carbon monoxide poisoning occurs subtly; in fact, this gas is colorless and odorless; furthermore, the symptoms manifested by intoxicated individuals are rather non-specific and generic.
Causes
The causes of carbon monoxide poisoning can be different. Generally, among the most common ones we find:
- Malfunctions in domestic heating systems (such as, for example, boilers, coal or wood burning fireplaces, etc.);
- Malfunctions of wood or gas powered appliances (such as, for example, the oven or gas water heaters);
- Fires;
- Malfunctions or inadequate ventilation inside cars.
Toxicity mechanism
Carbon monoxide poisoning occurs especially when this dangerous gas accumulates in poorly ventilated areas. This intoxication also takes place in a subtle manner, since the CO is an absolutely colorless, odorless, tasteless and non-irritating gas; all these features prevent the individual from recognizing the dangerous situation.
The carbon monoxide is then inhaled and rapidly absorbed in the lung, thus entering the bloodstream.
The mechanism by which poisoning is established is related to the ability of carbon monoxide to bind to hemoglobin - present in red blood cells - with an affinity greater than that of oxygen.
CO, therefore, having a high affinity for hemoglobin (Hb), displaces the binding of oxygen with the aforementioned protein, leading to the formation of carboxyhemoglobin (COHb).
Carboxyhemoglobin, as can easily be imagined, is not able to release oxygen to tissues as, on the other hand, happens with hemoglobin. Furthermore, the CO is able to bind to a particular enzyme involved in the cellular respiration mechanism: the tissue cytochrome oxidase, thus preventing the cells from using the remaining oxygen.
Briefly summarizing, carbon monoxide causes toxicity through the following mechanisms:
- Bond with hemoglobin which leads to the formation of carboxyhemoglobin;
- Impairment of hemoglobin's ability to release oxygen to tissues and organs;
- Inhibition of tissue cytochrome oxidase.
The combination of all these mechanisms leads to the lack of oxygen supply and lack of use, which leads to the onset of the various non-specific symptomatology that characterizes carbon monoxide intoxication.
Diagnosis
Often, the diagnosis of carbon monoxide poisoning is difficult to make, precisely because of the subtle way in which it is established and because of the non-specific symptoms.
If the doctor suspects possible carbon monoxide poisoning, he will immediately perform blood tests to evaluate the carboxyhemoglobin blood levels, in order to identify the actual presence and severity of the intoxication.
In addition to this, to confirm the diagnosis, the doctor may resort to performing other tests, such as blood gas analysis and pulse oximetry.
In the most serious intoxications, to assess the extent of damage caused by carbon monoxide poisoning, the doctor may also decide to carry out tests such as the electrocardiogram, CT scan, MRI and electroencephalogram.
Symptoms
To learn more: Symptoms Carbon monoxide intoxication ยป
As mentioned, the symptomology induced by carbon monoxide intoxication is rather non-specific and involves different parts of the body. However, these symptoms are all related to the poor supply of oxygen to various organs and tissues, which occurs during this particular type of intoxication.
The symptoms that can occur in the initial phase of carbon monoxide intoxication consist of:
- Nausea;
- He retched;
- Headache;
- Weakness;
- Asthenia;
- Dizziness;
- Dyspnea on exertion;
- Chest pain;
- tachypnea;
- Confusion and disorientation;
- Irritability;
- Difficulty concentrating;
- Tachycardia;
- Palpitations.
If carbon monoxide poisoning is severe, they can also arise:
- Convulsions;
- Vision and hearing disorders;
- Drowsiness;
- Ataxia;
- Hypotension;
- Generalized muscle stiffness;
- Cardiovascular arrest;
- Respiratory failure;
- Loss of consciousness;
- Coma and, in the most serious cases, death.
Furthermore, it should be remembered that sometimes - after several days or even weeks after the poisoning has taken place - late symptoms may occur, such as:
- Dementia;
- Parkinsonism;
- Psychosis;
- Mnesic alterations.
Types of intoxication
Carbon monoxide intoxications can be classified according to their severity, which is closely related to the levels of carboxyhemoglobin present in the patient's blood.
In this regard, we can distinguish:
- Suspected intoxication, characterized by blood carboxyhemoglobin levels of 2-5%. However, in these cases of suspected intoxication, it is good to remember that smokers have higher carboxyhemoglobin levels than non-smokers.
- Mild intoxication, in this case blood carboxyhemoglobin levels are 5-10%; this intoxication is characterized by decidedly non-specific symptoms, such as headache, generalized malaise and nausea.
- Moderate intoxication, in which blood carboxyhemoglobin levels increase to 10-25%; in this case, the symptoms that can occur are more pronounced and consist of: intense headache, dizziness, visual disturbances, retinal haemorrhages, intense red coloration of the mucous membranes, hypotension and tachycardia.
- Severe intoxication, in which blood carboxyhemoglobin levels are above 25-30%. In these cases, the symptomatology is decidedly serious and includes convulsions, coma, respiratory failure, cardiocirculatory arrest and death.
First Aid and Treatment
The first aid intervention, as well as the hospital treatment of carbon monoxide poisoning, are essential to safeguard the life of the patient and preserve it from the onset of permanent damage.
The task of the rescuers is basically to immediately remove the patient from the carbon monoxide source and to support the vital functions until he reaches the hospital center, at which level all the analyzes and all the treatments of the case will be performed.
In particular, the treatment of carbon monoxide poisoning involves the administration to the patient of 100% oxygen. In fact, very high concentrations of oxygen are able to reduce the half-life of carboxyhemoglobin, both at the blood level and at the tissue level. More in detail, the patient can undergo - depending on the case and according to the doctor's opinion - two different types of treatment:
- Normobaric oxygen therapy, consisting in the administration of 100% oxygen through the use of a special facial mask. In doing so, the half-life of carboxyhemoglobin is reduced to 60-90 minutes, compared with the 2-7 hours that would be required without oxygen.
Usually, this type of treatment is continued until the carboxyhemoglobin levels are less than 5%.
- Hyperbaric oxygen therapy, consisting in the administration of 100% oxygen in a hyperbaric chamber in which the pressure is higher than atmospheric (indicatively, 2.5-3 atmospheres). In this case, the half-life of carboxyhemoglobin - both in the blood and in the tissues - is drastically reduced to 30 minutes.
However, it should be remembered that hyperbaric oxygen therapy can only be undertaken in certain cases and that it is really effective only if it is performed as soon as possible after the carbon monoxide poisoning (indicatively, within 12 hours).
