Types of hypoxia
Hypoxemia by genesis is divided into 4 types:
- respiratory hypoxia caused by impaired ventilation and gas exchange at the level of the alveolar capillary membrane;
- hemic hypoxia caused by a violation of oxygen transport to tissues due to anemia or hemoglobin binding (CO poisoning, cyanide);
- circulatory hypoxia, caused by blood flow, microcirculation and gas exchange at the blood-tissue level;
- hypoxia of the combined genesis, when all the 3 first components of hypoxemia take place. The rate of development and duration distinguish: fulminant, acute, subacute and chronic hypoxemia.
Respiratory hypoxia may be caused by external factors in connection with: a decrease in the partial pressure of oxygen in the external environment when it is in a discharged atmosphere, for example, at altitude (De Acost syndrome is characterized by shortage of air, rapid breathing, cyanosis, dizziness, headache, hearing, vision, consciousness); with hypercapnic conditions (with an excessive content of carbon dioxide in the atmosphere) in enclosed spaces, mines, etc. With poor ventilation, since hypercapnia itself does not cause gas exchange disorders, on the contrary, improves cerebral blood flow and blood supply of the myocardium, but with a lack of oxygen leads to development of acidosis; with hypocapnic conditions developing during hyperventilation of the lungs due to increased and frequent respiration, as a result of which carbon dioxide is washed out of the blood, with the development of alkalosis, while the respiratory center is depressed. Internal factors can be caused by: alveolar hypoventilation in asphyxia, inflammatory processes, bronchospasm, foreign bodies; a decrease in the respiratory surface of the lungs upon destruction of the alveolar surfactant, pneumothorax, pneumonia; the pathology of breathing mechanics in case of disturbance of the thoracic cage, damage to the diaphragm, spastic conditions of the respiratory musculature; violations of central regulation when the respiratory center is damaged due to trauma or brain disease or oppression by chemical means.
Circulatory hypoxia is formed with cardiovascular failure, when blood flow is reduced in all organs and tissues, or with local decrease in blood flow caused by angiospasm, erythrocyte stasis, thrombosis, arteriovenous shunting, etc.
Hemic hypoxemia is determined by the decrease in circulating hemoglobin due to anemia or blockade of hemoglobin by toxic substances, for example, carbon monoxide, cyanides, lewisite, etc.
In a separate form, hypoxemia is extremely rare, because they are all connected by a pathogenetic chain, just one of the species is trigger, causing attachment and others. As an example, acute blood loss can serve: the hemic component causes disturbance and 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, when poisoned with cyanides, do not give clinical manifestations of hypoxic syndrome, since death occurs instantaneously, moreover, when carbon monoxide and cyanide poisonings are involved, the bound hemoglobin gives the skin a pink "healthy" color.
In 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, first of all, respiration, cardiac activity and brain, since the brain tissues are most sensitive to hypoxia.
In subacute (up to several days or weeks) and chronic, continuing months and years, a pronounced clinical picture of hypoxic syndrome is formed. In this case, also the brain suffers first. A variety of neurological and psychiatric changes develop, with general cerebral symptoms prevailing, a diffuse disorder of the functions of the central nervous system.
Initially, the active internal inhibition is disrupted: excitation, euphoria develops, the critical evaluation of one's condition decreases, and motor anxiety arises. Then, and sometimes initially, there are symptoms of depression of the cerebral cortex: lethargy, drowsiness, tinnitus, headache, dizziness, general retardation, up to the disturbance of consciousness. There may be convulsions, involuntary urination and defecation. Sometimes the consciousness becomes enlightened, but the inhibition remains. Gradually, violations of the cerebral and peripheral innervation increase, focal symptomatology is formed.
With prolonged hypoxia of the brain, mental disorders develop gradually: delirium, Korsak's syndrome, dementia, and others.
The convulsive syndrome and hyperkinesia are diverse in hypoxia. Usually convulsions occur under the influence of an external stimulus, often occur in the form of myoclonias: begin with the face, hands, then involve other muscles of the extremities, abdomen. Sometimes, with hypertension of extensors, opisthotonus is formed. Seizures, like in tetanus, are tonic and clonic in nature, but, in contrast, small muscles are involved (tetanus and brush are free in tetanus and brush), there is always a disturbance of consciousness (in tetanus it is preserved).
On the part of other organs and systems, dysfunction is first noted, followed by inhibition of the cardiovascular system, respiration, renal and hepatic insufficiency develops due to the formation of hypoxic dystrophies of fatty, granular, vacuolar. The complex of polyorganic insufficiency develops more often. If hypoxia does not stop, the process goes into an atonal state.
Diagnosis, in addition to general clinical examination, should include the study of the acid-base state of the blood. Undoubtedly, this is possible and it is necessary to do it only in the conditions of the intensive care unit and intensive treatment of hypoxia should be carried out by a resuscitation specialist.