Hypoxia

Hypoxia is oxygen deficiency, a condition that occurs when there is insufficient oxygen supply to the body's tissues or a violation of its utilization in the process of biological oxidation, accompanies many pathological conditions, being a component of their pathogenesis and clinically manifested by hypoxic syndrome, which is based on hypoxemia. We hope you have understood the terminology: hypoxia is a lack of oxygen supply to tissues, hypoxemia is insufficient oxygen content in the blood. Metabolic disturbance occurs at the membrane level: alveoli - blood; blood - cell membrane; intra-tissue oxygen exchange.

The Barcroft classification (1925) has found wide application; later classifications are alternative only in terminology, but the essence is the same.

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Types of hypoxia

Hypoxemia according to its genesis is divided into 4 types:

1. respiratory hypoxia caused by impaired pulmonary ventilation and gas exchange at the level of the alveolocapillary membrane;
2. hemic hypoxia caused by impaired oxygen transport to tissues due to anemia or hemoglobin binding (CO poisoning, cyanide poisoning);
3. circulatory hypoxia caused by impaired blood flow, microcirculation and gas exchange at the blood-tissue level;
4. hypoxia of combined genesis, when all three first components of hypoxemia are present. According to the rate of development and duration, there are: fulminant, acute, subacute and chronic hypoxemia.

Respiratory hypoxia can be caused by external factors due to: a decrease in the partial pressure of oxygen in the external environment when in a rarefied atmosphere, for example, at altitude (characterized by the development of De Acosta syndrome - shortness of breath, rapid breathing, cyanosis, dizziness, headache, hearing, vision, and consciousness impairment); hypercapnic conditions (with excess carbon dioxide in the atmosphere) in closed spaces, mines, etc. with poor ventilation, since hypercapnia in itself does not cause gas exchange disorders, on the contrary, it improves cerebral blood flow and myocardial blood supply, but with a lack of oxygen leads to the development of acidosis; hypocapnic conditions developing with hyperventilation of the lungs due to increased and frequent breathing, as a result of which carbon dioxide is washed out of the blood, with the development of alkalosis, while the respiratory center is suppressed. Internal factors may be caused by: alveolar hypoventilation due to asphyxia, inflammatory processes, bronchospasm, foreign bodies; reduction of the respiratory surface of the lungs due to destruction of alveolar surfactant, pneumothorax, pneumonia; pathology of respiratory mechanics due to disruption of the rib cage framework, damage to the diaphragm, spastic conditions of the respiratory muscles; disturbances of central regulation due to damage to the respiratory center due to trauma or brain disease or suppression by chemicals.

Circulatory hypoxia occurs in cardiovascular failure, when blood flow decreases in all organs and tissues, or in the case of local decrease in blood flow caused by angiospasm, erythrocyte stasis, thrombus formation, arteriovenous shunting, etc.

Hemic hypoxemia is determined by a decrease in circulating hemoglobin due to anemia or hemoglobin blockade by toxic substances, such as carbon monoxide, cyanides, lewisite, etc.

In a separate form, hypoxemia is extremely rare, since they are all connected by a pathogenetic chain, it is just that one of the types is a trigger, causing the addition of others. An example is acute blood loss: the hemic component causes a violation of blood flow, which, in turn, forms a "shock" lung with the development of the respiratory component "respiratory distress syndrome".

Lightning forms of hypoxia, for example, in cyanide poisoning, do not produce clinical manifestations of hypoxic syndrome, since death occurs instantly; moreover, in carbon monoxide and cyanide poisoning, bound hemoglobin gives the skin a pink, “healthy” color.

In the acute form (from several minutes to several hours), agonal syndrome develops, which is manifested by decompensation of the function of all organs and systems, and, above all, respiration, cardiac activity and the brain, since brain tissue is most sensitive to hypoxia.

In subacute (up to several days or weeks) and chronic, lasting for months and years, a pronounced clinical picture of hypoxic syndrome is formed. In this case, the brain also suffers first. Various neurological and mental shifts develop, with general cerebral symptoms and diffuse dysfunction of the central nervous system predominating.

Initially, active internal inhibition is disrupted: excitement and euphoria develop, critical assessment of one's condition decreases, motor restlessness appears. Then, and sometimes initially, symptoms of cerebral cortex depression appear: lethargy, drowsiness, tinnitus, headache, dizziness, general inhibition, up to impaired consciousness. There may be convulsions, involuntary urination and defecation. Sometimes consciousness clears up, but inhibition remains. Disturbances of craniocerebral and peripheral innervation gradually increase, focal symptoms are formed.

With prolonged hypoxia of the brain, mental disorders gradually develop: delirium, Korsakov's syndrome, dementia, etc.

Convulsions and hyperkinesis during hypoxia manifest themselves in various ways. Convulsions usually occur under the influence of an external stimulus, most often occur in the form of myoclonus: they begin with the face, hands, then other muscles of the limbs and abdomen are involved. Sometimes, with hypertonicity of the extensors, opisthotonus is formed. Convulsions, as with tetanus, are tonic and clonic in nature, but, unlike it, small muscles are involved in the process (with tetanus, the feet and hands are free), there is always a disturbance of consciousness (with tetanus, it is preserved).

From the side of other organs and systems, dysfunction is noted first, and then suppression of the cardiovascular system, respiration, renal and hepatic insufficiency develops due to the formation of hypoxic dystrophies of fatty, granular, vacuolar. More often, a complex of multiple organ failure develops. If hypoxia is not stopped, the process goes into an atonal state.

Diagnostics, in addition to a general clinical examination, should include a study of the acid-base balance of the blood. Undoubtedly, this is possible and necessary to do only in the conditions of the resuscitation and intensive care unit, and the treatment of hypoxia should be carried out by a resuscitation specialist.