Cyanosis (Greek kyanos - dark blue) is a bluish tinge of the skin and mucous membranes, caused by an increase in the amount of reduced (deprived oxygen) hemoglobin or its derivatives in small vessels of various parts of the body. Usually cyanosis is most noticeable on the lips, nail beds, ear lobes, gums.
Cyanosis occurs in two situations: with a decrease in the saturation of capillary blood with oxygen and with the accumulation of venous blood in the skin due to the expansion of the venous section of the microcirculatory bed.
The presence of cyanosis directly depends on the total hemoglobin in the blood: when it changes, the content of reduced hemoglobin also changes.
- With anemia, the content of both total hemoglobin and reduced hemoglobin is reduced, therefore, in cases with severe anemia, even with severe hypoxia, cyanosis is usually absent.
- In polycithemia, the content of both total and reduced hemoglobin is increased, therefore patients with severe polycythemia are usually cyanotic. By the same mechanism there is a cyanosis of this or that part of the body with a local stagnation of blood in it, which is often accompanied by edema.
Cyanosis can be central and peripheral.
Central cyanosis is characterized by a bluish tinge of both the skin and mucous membranes, arises when the arterial blood is not saturated with oxygen or when hemoglobin forms in the blood. Central cyanosis increases during physical activity, as the muscle needs for oxygen increase, and oxygen saturation for various reasons is disrupted.
Disturbance of arterial blood oxygen saturation arises in the following situations.
- Decrease in atmospheric pressure (high altitude above sea level).
- Dysfunctions of the lungs, leading to a decrease in alveolar ventilation, perfusion of unventilated areas of the lungs, a decrease in the perfusion of adequately ventilated areas, as well as a violation of the diffusive capacity of the lungs.
- Shunting of blood in the presence of anatomical abnormalities, i.e. "Dropping" blood from the venous bed into the arterial channel, bypassing the microcirculatory bed of the alveoli, thus the oxygenated blood is "diluted" with blood that has already given up oxygen at the periphery. This mechanism of cyanosis is characteristic for some congenital heart defects (for example, tetralogy of Fallot - discharge of blood from right to left through the defect of the interventricular septum (DMF) against the background of pulmonary artery stenosis). A similar situation is also possible in the presence of arteriovenous pulmonary fistulas or small intrapulmonary shunts.
Among the changes in hemoglobin itself is methemoglobinemia and sulfgemoglobinemia, which can be assumed after excluding all other possible causes of cyanosis.
Peripheral cyanosis is the result of slowing blood flow in a particular area of the body. At the same time saturation of arterial blood with oxygen is not violated, but due to the stagnation of blood, more oxygen is "extracted" from it, i.e. The local content of reduced hemoglobin increases. This type of cyanosis occurs with vasoconstriction and a decrease in peripheral blood flow.
The causes of peripheral cyanosis are listed below.
- Reduction of cardiac output, for example, with congestive heart failure, leads to a narrowing of the small arteries and arterioles of the skin, acting as a compensatory mechanism aimed at centralizing blood circulation to provide blood for vital organs - the central nervous system, the heart and lungs. It is for this situation that the term "acrocyanosis" is used - cyanotic color of the distal parts of the body due to venous congestion, most often against the background of blood stagnation over a large range of blood circulation.
- Peripheral cyanosis is characteristic of venous hypertension. It occurs when the veins of the extremities are obstructed (against the background of varicose veins, thrombophlebitis), which leads to edema and cyanosis.
- Peripheral cyanosis when exposed to cold is the result of a physiological reaction of the organism.
- Obstruction of the arteries of the extremities, for example, with embolism. In this case, paleness and cold snap are more characteristic, however, a slight cyanosis is possible.
In many cases, the clinician faces the issue of differential diagnosis of central and peripheral cyanosis.
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