Intensive Care of Acute Poisoning - A. V. Hovenko 2010

General Characteristics of Acute Poisoning
Toxicokinetics of Oral Poisoning

Most frequently, toxic substances enter the body via the oral route. Their residence time in the gastrointestinal tract depends on the PHYSICOCHEMICAL PROPERTIES OF the poison as well as the functional state of The Stomach and intestines. The pH gradient across different segments of the GI tract determines the varying absorption rates of toxic compounds. Primarily, poison absorption occurs in the Small Intestine, where the pH is 7.5–8.0. However, certain poisons can be absorbed as early as in the Oral Cavity (nicotine, phenol, nitroglycerin, cyanides). Water-soluble substances (ethanol and other alcoholic medication solutions) are completely absorbed through the mucous membrane of the Oral Cavity and Esophagus, entering the systemic Circulation via the SUPERIOR VENA CAVA. Nevertheless, the likelihood of poisoning via this route is limited due to the brief contact time between the toxic substance and the mucous membrane. In such cases, the severity of poisoning depends on the toxicity of the substance. Ingestion of extremely potent substances—such as potassium cyanide, dichloroethane, and others—can lead to severe poisoning.

Toxic substances may remain in the stomach for a longer duration, which subsequently facilitates their absorption by the gastric mucosa and entry into the bloodstream, where they induce systemic toxic effects. The rate of gastric poison absorption is influenced by:

- the presence or absence of food;

- the COMPOSITION OF THE food;

- peristalsis and the rate of bowel emptying;

- the functional state of the mucosa secreting gastric juice;

- the degree of comminution or the liquid state of the potentially toxic substances.

Food masses present in the stomach can sorb and reduce the concentration of toxic substances, thereby hindering contact between the poison and the mucous membrane. Absorption of toxic substances in the stomach is hindered by a small volume of liquid, as well as a large bulk of dense food. Therefore, it is essential to consider whether ingestion occurred before or after a meal. In the former case, when the stomach is empty, toxic substances are absorbed more rapidly. At the same time, the digestive tract contains enzyme systems that break down Proteins and fats, releasing the toxic substances bound to them.

The primary site of substance absorption upon oral administration is the small intestine. Certain poisons (acids, alkalis, heavy metals, etc.) can directly damage the intestinal epithelium and impair absorption. Complexes of toxic substances with proteins are poorly absorbed in the small intestine. Slowed Blood flow and blood pooling in the intestinal area during Exotoxic Shock intensify the local toxic effect, which is caused by the equalization of poison concentration in the blood and the intestines. Enhanced intestinal peristalsis facilitates the rapid elimination of toxic substances from the body and reduces their absorption due to the short duration of contact between the poison and the intestinal mucosa. Upon absorption from the small intestine, substances first pass through the PORTAL VEIN SYSTEM into the Liver, where they undergo various chemical transformations. Sometimes they are partially or completely detoxified; in other cases, conversely, their toxicity may increase ("Lethal synthesis"). However, it should be borne in mind that when absorbed via Lymphatic vessels, the poison may bypass the hepatic barrier.

It should also be taken into account that non-ionized molecules of poisons or chemical compounds are highly lipophilic and therefore penetrate Cell membranes of the gastric, intestinal, and vascular walls much more easily due to the lipoprotein Structure of these membranes.

Thus, the absorption capacity of any chemical substance in the stomach and intestines depends on the following factors:

- lipid solubility;

- water solubility;

- degree of dissociation (ionization);

- molecular size;

- type of absorption.