Hypoxia (Greek – “little oxygen”) is the state of oxygen starvation of the whole organism and individual organs and tissues caused by various external and internal factors.
Causes of hypoxia
- Hypoxic (exogenous) – a decrease in the oxygen content in the inhaled air (stuffy unventilated rooms, high altitude conditions, high-altitude flight without oxygen equipment);
- Respiratory – a complete or partial violation of the air movement in the lungs (example: strangulation, drowning, swelling of the bronchial mucosa, bronchospasm, pulmonary edema, pneumonia, etc.);
- Hemic (blood) – a decrease in the oxygen capacity of the blood, i.e. when blood loses its ability to attach oxygen to hemoglobin of red blood cells (the main carrier of oxygen). It most often occurs with carbon monoxide poisoning, with hemolysis of red blood cells, with anemia;
- Circulatory – cardiovascular insufficiency, when the movement of blood enriched with oxygen to tissues and organs is difficult or impossible (example: myocardial infarction, heart defects, vasculitis, vascular damage in diabetes, etc.);
- Histotoxic (tissue) – a violation of oxygen absorption by body tissues (example: some poisons and salts of heavy metals are able to block enzymes involved in “tissue respiration”);
- Reloading – excessive functional load on the organ or tissue (example: excessive load on the muscles during hard work, when the demand for oxygen is higher than its actual influx into the tissue);
- Mixed – a combination of several of the above options.
Signs and symptoms of hypoxia, mechanisms for protecting the body from hypoxia
The signs of hypoxia are very diverse and almost always depend on the severity of its severity, duration of exposure and cause of occurrence. We will give the most basic symptoms and explain their causes of development.
Hypoxia is acute (develops after a few minutes, hours) from the onset of exposure to a causative factor or may be chronic (develops slowly over several months or years).
Acute hypoxia has a more pronounced clinical picture and severe rapidly developing consequences for the body, which may be irreversible. Chronic hypoxia develops slowly, allows the patient’s body to adapt to it, so patients with severe respiratory failure amid chronic pulmonary diseases live for a long time without dramatic symptoms. At the same time, chronic hypoxia also leads to irreversible consequences.
Main mechanisms of body protection against hypoxia
- Increased respiratory rate – to enhance the flow of oxygen to the lungs and its further transport of blood. At first, breathing is frequent and deep, however, as the respiratory center is depleted, it becomes rare and superficial;
- Increased heart rate, increased blood pressure and increased cardiac output. Thus, an organism experiencing oxygen hunger is trying to “distribute” as much as possible and faster oxygen in the tissue;
- The release of deposited blood into the bloodstream and increased red blood cell formation – to increase the number of oxygen carriers;
- Slowing down the functioning of certain tissues, organs and systems – in order to reduce oxygen consumption;
- The transition to “alternative sources of energy.” Since oxygen cannot fully satisfy the energy needs of the body, alternative sources of energy are launched to provide almost all the processes that take place in the body. This defense mechanism is called anaerobic glycolysis, that is, the breakdown of carbohydrates (the main source of energy that is released during their breakdown) without oxygen. However, the reverse side of this process is the accumulation of undesirable products such as lactic acid, as well as the shift of the acid-base balance to the acid side (acidosis). In conditions of acidosis, hypoxia aggravates. Microcirculation in the tissues is disturbed, respiration and blood circulation become ineffective, and ultimately, there follows complete depletion of reserves and respiratory and blood circulation stop, i.e. death.
The above mechanisms in acute hypoxia short-term quickly depleted, which leads to the death of the patient. In chronic hypoxia, they are able to function for a long time, compensating for oxygen hunger but bring constant suffering to the patient.
The central nervous system is primarily affected. The brain always receives 20% of all body oxygen, this is the so-called “oxygen duty” of the body, which is explained by the enormous oxygen demand of the brain. Mild disorders of brain hypoxia include headaches, drowsiness, lethargy, fatigue, impaired concentration. Severe signs of hypoxia: disorientation in space, impaired consciousness up to a coma, cerebral edema. Patients suffering from chronic hypoxia acquire severe personality disorders associated with the so-called hypoxic encephalopathy.
The low oxygen content in the tissues is manifested by their staining in a bluish color (cyanosis). There is acrocyanosis – the bluish color of the fingers and nail plates and there may be cyanosis of the nasolabial triangle.
Changing the shape of nails and distal phalanges of the fingers. In chronic hypoxia, the nails thicken and acquire a rounded shape resembling a “watch glass”. The distal (nail) phalanges of the fingers thicken, giving the fingers the appearance of “drum sticks”.
Diagnosis of hypoxia
In addition to the characteristic symptom complex described above, there are laboratory-instrumental research methods used to diagnose hypoxia.
- Pulse oximetry is the easiest way to determine hypoxia. It is enough to put a pulse oximeter on the finger and the saturation of the blood with oxygen will be determined in a few seconds. Normally, this indicator is not lower than 95%;
- Study of gas composition and acid-base balance of arterial and venous blood. This type allows a quantitative assessment of the main indicators of the body’s homeostasis: the partial pressure of oxygen, carbon dioxide, blood pH, the state of carbonate and bicarbonate buffers, etc.;
- Examination of exhaled gases. For example, capnography, etc.
Therapeutic measures should be aimed at eliminating the causes of hypoxia, combating the lack of oxygen and correcting changes in the homeostasis system.
Sometimes, to combat hypoxia, it is enough to ventilate the room or walk in the fresh air. In cases of hypoxia, which was the result of diseases of the lungs, heart, blood, or poisoning, more serious measures are required:
- Hypoxic (exogenous) – the use of oxygen equipment (oxygen masks, oxygen masks, oxygen pads, etc.);
- Respiratory – the use of bronchodilator drugs, respiratory analeptics, etc., the use of oxygen concentrators or centralized oxygen supply up to mechanical ventilation. In chronic respiratory hypoxia, oxygen treatment becomes one of the main components;
- Hemic (blood) – blood transfusion, stimulation of blood formation, oxygen treatment;
- Circulatory – corrective surgery on the heart and (or) blood vessels, cardiac glycosides and other drugs with a cardiotropic effect. Anticoagulants, antiplatelet agents to improve microcirculation. In some cases, oxygen therapy is used;
- Histoxic (tissue) – antidotes for poisoning, mechanical ventilation, drugs that improve tissue oxygen utilization, hyperbaric oxygenation.
In addition, to combat hypoxia, doctors prescribe drugs to restore the acid-base balance in the blood, neuro and cardioprotectors.