How does activated charcoal work in the treatment of poisonings?
Reasons why activated carbon adsorbs molecules, mainly of the organic type. There are many different forms of pure carbon in nature. Some examples are diamond, graphite, carbon black, mineral coals or simple carbon used for roasting meat. The difference between each of them is in the structure formed by their carbon atoms.
One of the main characteristics of all forms of carbon is its eagerness to retain molecules of liquids, gases or vapors. This phenomenon is called adsorption: the solid, which in this case is the carbon, is the adsorbent and the molecule retained is the adsorbate.
The adsorption of activated carbon.
Adsorption on carbon is due to an imbalance of forces that is generated on every surface formed by carbon atoms. This imbalance is due to the fact that the carbon atoms tend to form their four bonds perfectly distributed in the three coordinates in space. Since this does not happen in the carbon atoms that form part of the solid surface, they tend to form Van der Waals type bonds with the molecules of the adjacent fluid. More specifically, the links between carbon and adsorbate are called the London Forces, which are the most common of the Van der Waals six forces in nature.
In seeking to harness the adsorptive property of carbon, man has found a way to produce porous carbons with a huge surface area. Since the adsorption capacity depends on the surface of the solid, when a carbon is activated, its adsorption capacity increases.
By way of comparison, a charcoal or a mineral coal has a surface area of about 10 m2 per gram; on the other hand, an activated carbon has an area of more than 500 m2 per gram.
As mentioned above, carbon tends to trap all kinds of molecules. However, it presents certain selectivity as it prefers:
a) To the least polar ones.
b) Those with a higher molecular weight.
c) Those least soluble in water.
d) Those with the most branched out molecules.
Therefore, if the carbon meets a mixture of molecules, it will prefer those that best meet the above characteristics. Organic molecules generally comply better than inorganic ones with these characteristics. Therefore, carbon whether activated or not, is considered to be an ALMOST UNIVERSAL ADSORBENT OF ORGANIC MOLECULE. An activated carbon effectively adsorbs molecules with a molecular weight greater than 55.
This does not mean that carbon does not adsorb inorganic substances. In fact, carbon adsorbs well inorganic substances that do not dissociate in an aqueous medium. This is because they are the least polar and, not being present as charged electrolytes, are susceptible to binding to carbon by Van der Waals forces.
The process of adsorption is the reason why a piece of carbon eliminates the odors given off by food inside a refrigerator. It is also he reason why, in ancient times, pieces of carbon were placed in the barrels in which the stored drinking water, in order to keep it free of the taste imparted by the wood. And it is also the reason why peasants eat carbonized tortillas when they get sick in their stomachs (the carbon prevents excess food or the intoxicated food from being adsorbed any further).
Activate carbon is a much more effective means of purification than unactivated carbon. The adsorption capacity of an activated carbon is between 20 and 90 percent of its own weight. In other words, 100 grams of activated carbon will retain between 20 and 90 grams of adsorbates.
The origin of the raw material of the activated carbon.
Activated carbon can be produced from any material of plant or animal origin: wood, coconut shell, bagasse, meat, cobs, blood, among thousands. It can also be produced from mineral coals, since these come from trees and plants.
There are two methods of activation: thermal and chemical. In the first one, the formation of the pores is achieved or by subjecting the previously carbonized material to a temperature close to 1000 °C (1832 °F) and in an atmosphere saturated with water vapor.
In the chemical method, the raw material is flooded in a solution of a dehydrating compound, such as zinc chloride or phosphoric acid. Dehydration causes the molecular chains to separate from each other.
The dehydrated material is then calcined at a relatively low temperature, thus obtaining a carbon that is already porous. As a final step in this method, the carbon is washed to remove the activating chemical compound; in this way, on the one hand, the chemical is recovered, and on the other, the carbon is purified to the extent possible.
Activated carbon in the treatment of poisoning
When a person becomes intoxicated due to the ingestion of an organic product, activated carbon can save his life. However, not just any activated carbon is the most effective for this application.
The carbon must comply with the following:
(a) Be microporous
(b) Preferably be of plant origin
(c) Preferably be thermally activated
As for the need for it to be microporous, this is because the toxic molecules that are absorbed into the body have a molecular diameter of less than 2 nanometers. In contrast, non-harmful molecules such as proteins and most fats are usually larger. Therefore, if a larger-pore carbon is used, I will adsorb these non-harmful molecules.
Coconut shell carbon is the most microporous of those found on the market. More than 95% of its pores are less than 2 nm in diameter, and therefore best meets the condition of microporosity.
As for the vegetable origin, it is a recommendation that is due to the fact that the raw material does not contain harmful contaminants. Coals of mineral origin should be avoided, as most of them contain heavy metals, sulfides and other dangerous elements that can dissolve in gastric juices.
The method of activation of the activated carbon.
Thermal activation is preferred, since chemical activation always leaves traces of the chemical in the resulting carbon. At present, the main chemicals used are zinc chloride and phosphoric acid. The first is made up of zinc, which is a toxic metal in low doses; the second comes from phosphate rock, which is a mineral and as such contains a wide range of impurities.
How does activated carbon work in poisoning or intoxication of the body?
In order to provide guidance to users of activated carbon as a method of detoxification, pharmacopoeias from different countries, including Mexico, have issued technical specifications that the carbon must meet.
Activated carbon can have different presentations, such as granules, pellets or powder. For its application in patients with severe intoxication, the carbon must be a powder smaller than mesh 200, that is, less than 74 microns. This is because the smaller the particles of the carbon, the faster it acts, and therefore the chances of successful treatment are increased. The increase in the speed of adsorption is due to a decrease in the length of the pores, which are filled by a capillary effect.
The effect of increasing the speed of adsorption by decreasing the particle size of the carbon is inversely proportional to the square of the particle size of the same. That is to say:
———- = ——–
v = velocity of the adsorption of the activated carbon of smaller particle size
V = velocity of the adsorption rate of the largest particle size activated carbon
d = average diameter of the smallest particle size activated carbon
D = average diameter of the largest particle size activated carbon
As an example, an activated carbon between 200 and 325 mesh (average diameter of 0.059 mm) adsorbs 3.57 times faster than one between 100 and 200 mesh (average diameter of 0.1115 mm).
On the other hand, powdered carbon is suitable to flow easily in a suspension along the hoses through which it is administered when the person is intubated.
The recommended dose of activated carbon for a patient with acute poisoning is one gram per kilogram of body weight. If this dose does not achieve an acceptable decrease in serum levels of the poison or in signs and symptoms, it should be repeated every four hours, up to a maximum of 36 hours.
In order to avoid intestinal constipation, it is important to administer together with the first dose of carbon, a sodium or magnesium sulphate cathartic, in a dose of 0.25 g of this salt per kg of body weight. In case of multidose of carbon, the dose of the cathartic must be repeated every 12 hours.
There is literature, laboratories and physicians who recommend and use sorbitol or mannitol as cathartics. However, experience has shown that with these there is an increased risk of hypernatremia (dehydration).
The effectiveness of carbon over a much longer period than the time in which the toxic is present in the
gastrointestinal tract, is because it retains metabolites of those toxins that follows the enterohepatic cycle and that, slowly, and over many hours, reach the duodenum (small intestine) in the bile flow. Likewise, carbon performs intestinal dialysis by causing enterohepatic circulation of the toxins that circulate in the blood and pass through the intestinal villi to the carbon.
Carbon does not cause biochemical side effects, as it is an insoluble, nonreactive, inert and nonabsorbable material in the body. So far, there are no reports indicating a dose beyond which carbon beyond which carbon causes serious problems of gastrointestinal irritation or acute constipation, as long as the cathartic is administered properly.
Activated carbon has been widely used in the treatment of intoxicated patients. There are many references on this subject (see references listed at the end of this document). In the United States of America, an activated carbon suspension is part of every paramedic´s medical kit. Activated carbon is indicated even in cases of comatose patients who, for obvious reasons, are administered by nasogastric tube. In case of convulsions or blockage of the gastrointestinal tract, this problem must be resolved and the carbon administered.
When administering carbon, due precautions must be taken to avoid bronchial aspiration since in 10 % of the cases, vomiting is induced involuntarily.
Activated carbon is contraindicated in the case of poisoning with aliphatic organic solvents (among these are the organic solvents normally used by society, outside the companies), not because it does not adsorb them, but because they are absorbed very little into the gastrointestinal tract, thus resulting in little toxicity. On the other hand, if vomiting occurs, bronchoaspiration would be the cause of an injury that could be serious or fatal.
It is obvious that the administration of activated carbon is also contraindicated in cases of ingestion of corrosive substances (muriatic acid, battery fluid) and caustics (soda, ammonia). Not only due to the fact that they are poorly adsorbable substances (inorganic, ionic in aqueous medium and of low molecular weight), but also because carbon would make endoscopy and cleaning difficult in post-traumatic intervention.
Other applications of carbon in the medical and pharmaceutical area
In the case of mild intoxication, and other gastrointestinal problems, such as indigestion, flatulence and meteorism, small amounts of carbon are administrated in capsule or tablet form. Although there are no serious studies that justify them, these products are also indicated in the case of bacterial or viral infections, since carbon adsorbs microorganisms, drags them and expels them from the intestinal tract. Another application of carbon consists of bandages that are applied directly to the skin in the case of bites or stings from poisonous animals (including bees and wasps) or in the case of skin irritation caused by plants.
A mixture of powdered carbon and water is prepared for this purpose. The water plays the role of the vehicle through which the toxic substance flows into the carbon. The only risk is that the carbon can tattoo the skin. To avoid this, a sufficiently tightly woven canvas is placed between the skin and the dressing.
Method of application in cases of acute intoxication.
Acute poisoning is one of the cases that occur in hospital emergency rooms. It can cause death, which in many cases is caused by children accidentally talking too much of one of the medications typically found in any family´s medicine cabinet.
There are other causes of poisoning. Some examples are: overdose of a drug; ingestion of pesticides, solvents, poisonous mushrooms or certain ornamental plants.
Activated carbon has the property of adsorbing organic molecules, including those that form the toxic compounds mentioned above.
Toxic compounds that enter the body orally, and are absorbed in the stomach and intestines, can follow various mechanisms before damaging organ and tissue cells.
Among these mechanisms are:
(a) Lipophilic compounds will tend to deposit in fatty tissues.
(b) The hydrophilic compounds will remain in the blood, until they reach a cell where they can be metabolized, thus damaging the cell.
(c) Compounds suffering from enterohepatic cycle, are biotransformed in the liver, to form activate metabolites that are transported by the bile to the small intestine.
When they get there, they are reabsorbed and transported by the blood to the cells they will damage.
In all three cases, the toxin requires some time to reach the cell it will damage. The greater the amount of the poison, the longer it will take for those molecules that are in excess of the body´s capacity for metabolism to metabolize. And that time, which is usually several hours, will allow the activated carbon to perform a purification that increases the chances of the patient being healed.
In the treatment of a patient with acute intoxication, the goal is to administer powdered activated carbon, in the amount and frequency that allows a continuous flow of carbon along the intestinal tract. In the intestinal lumen, the carbon will exert an attraction on the organic compounds circulating in the blood. These compounds will pass through the membranes from the blood to the carbon.
By decreasing the concentration of lipophilic compounds in the blood, according to the laws of thermodynamic, a potential will be generated that will cause the toxic compounds deposited in the fatty tissues to pass into the bloodstream. And again, these compounds will be attracted and adsorbed by the activated carbon.
As for the compounds that suffer from the enterohepatic cycle, when they reach the duodenum, transported from the liver by the bile, the activated carbon adsorbs them and prevents their reabsorption.
This whole process of purification performed by the carbon is an intestinal dialysis. It is important to point out that the treatment with activated carbon, in no way substitutes the general supportive and symptomatic measures that must be carried out simultaneously.
It should also be noted that activated carbon is not only indicated for oral intoxication. Based on the explanation of the mechanism by which it acts, it can be expected to cause intestinal dialysis even when the poisoning comes from parenteral absorption (injection, insect bite or sting). In fact, activated carbon is indicated for the case of stings and bites, although in this case, the problem usually lies in the fact that, the speed with which the poison affects the patient, makes a specific antidote necessary.
Treatment and dosage
The treatment is indicated for poisoning by: organic compounds whose molecular weight is greater than 55, and which have entered the body orally or parenterally.
1. In the event of seizures or a blockage of the intestinal tract, the problem must be resolved and treatment proceeded.
2. A suspension of activated carbon is prepared. The dose of carbon should be 1 g per kg of body weight of the patient.
3. The patient is intubated with a nasogastric tube, making sure that it reaches the stomach and not the lungs, and the suspension is administered. Be careful to avoid bronchial aspiration in case of vomiting. The procedure is repeated every four hours over a period of 24 to 36 hours. The treatment is terminated when the symptoms have resolved, or better yet, when the concentration of the toxin in the blood has decreased and reached a level considered to be non-harmful.
4. A saline cathartic should be administered at the beginning, middle and end of treatment. The cathartic is prepared with sodium or magnesium sulfate in an amount of 0.25 g per kg of body weight. The objective of this is to maintain adequate peristalsis and avoid accentuated constipation. Some authors have recommended mixing activated carbon with hyperosmolar solutions (sorbitol or mannitol) as cathartics. However, the accentuated catharsis resulting from this mixture has led to hypernatremia (severe dehydration), which is why this practice is not recommended.
As can be seen, the execution of the above method is simple, safe, non-invasive, low cost and only exceptionally causes undesirable side effects. There are variations in the method, however, they all agree on the basic principles.
The treatment is NOT indicated for poisoning by:
- Corrosive agents, such as strong acids (hydrochloric, sulphuric, nitric) or alkalis (soda). Carbon does not preferentially adsorb these compounds, due to their polarity and low molecular weight. On the other hand, when ingested, they cause burns and perforations in the esophagus and stomach, and the activated carbon would only complicate the problem and make endoscopic evaluation difficult.
- Oil derivatives (diesel, oils, kerosene, gasoline, diaphanous oil, etc.). Although carbon adsorbs them, these compounds do not cause important damaged and it is better not to take the risk of provoking vomit with the administration of carbon (it occurs in 10% of the cases), since bronchial aspiration can occur which would have important harmful effects.
- Organic compounds whose molecular weight is less than 55 (methanol, ethanol, formaldehyde, acrolein, etc.), since carbon does not adsorb them effectively.
- Compounds that ionize in aqueous solution, such as most metals, and inorganic compounds in general.
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