Blood loss

Blood loss always leads to hypovolemia, which is characterized by a decrease in the absolute or relative volume of blood circulating in the body. Among the potentially reversible causes of circulatory arrest, hypovolemia is in second place, and this is quite natural. It can develop with acute blood loss, diseases with concomitant vomiting, diarrhea, deposition of fluid in the third space, etc. Strictly speaking, hypovolemia is present in any critical condition, regardless of its genesis. Reducing the volume of circulating blood and reducing venous return leads to the development of a syndrome of small cardiac output. And the faster the decrease in the volume of circulating blood occurs, the faster and more pronounced these changes.

Most often, the cause of rapid development of an emergency condition with acute blood loss is blood loss.

[1], [2],

Blood loss: pathophysiological changes

The human body effectively compensates for acute blood loss. The blood loss to 10% of the volume of circulating blood is successfully covered by the body due to an increase in the tone of the venous bed. The main indices of central hemodynamics do not suffer at the same time. With a greater volume of blood loss, the flow of blood from the periphery to the small circle decreases. Due to the decrease in venous return, the shock volume decreases. Cardiac output is compensated for by increasing the heart rate.

Further rapid decrease in the volume of circulating blood (continued blood loss, deposition and sequestration of blood) leads to the depletion of compensatory mechanisms, which is manifested by a decrease in venous return by 20-30% of the norm, a decrease in the shock volume below the critical value and development of the low-emission syndrome.

To a certain extent, the body is able to compensate for the small ejection syndrome with tachycardia and redistribution of blood flow in favor of vital organs. The phenomenon of blood circulation centralization (maintenance of blood flow in the heart, brain, liver, kidneys due to the reduction of perfusion of other organs and systems develops).

However, if the blood loss continues, the acid-base and water-electrolyte balance disorders (acidosis, water and electrolyte transfer to interstitium) develop rapidly, blood viscosity increases, stasis and coagulopathy occur. Endotoxicosis develops due to the accumulation of "ischemic toxins", arteriovenous anastomosis is revealed, transcapillary and transmembrane exchange is disturbed. There is a disturbance in the regulation of the tone of peripheral vessels.

In addition, endotoxins can have a direct damaging effect on the heart, lungs, brain, liver, other organs and systems, cause reactions like anaphylactic.

There are violations of the absorption of oxygen by the cells of the body due to the destruction of proteins and cell lipids, blockade of synthetic and oxidative processes, which leads to the development of histotoxic hypoxia. In the future, hypovolemic (hemorrhagic) shock develops and, if adequate therapy is not provided in time, a fatal outcome occurs.

With the same deficiency of circulating blood volume during hemorrhagic shock, in contrast to true hypovolemic shock, hypoxic changes in organs and tissues are more pronounced. This is due to a decrease in the oxygen capacity of the blood and the release of the factor. Depressing myocardium (MDF).

[3], [4], [5], [6], [7], [8], [9], [10]

Determination of blood loss

[11], [12], [13]

Mild blood loss

With blood loss of up to 15% of the total volume of circulating blood, the patient's condition does not practically suffer.

Moderate blood loss

It is characterized by functional changes in cardiovascular activity, which compensate for hypovolemia. The blood loss is 15-25% of the volume of circulating blood. Consciousness of the patient is preserved. The skin is pale, cold. Pulse of weak filling, moderate tachycardia. Arterial and central venous pressure is moderately reduced. Develops a moderate oliguria.

Severe hemorrhage

It is characterized by an increase in circulatory disorders. There is a failure of compensatory mechanisms, in which a reduced cardiac output. It is not compensated by an increase in the tone of peripheral vessels and tachycardia, which leads to the development of severe arterial hypotension and impaired organ circulation. The blood loss is 25-45% of the volume of circulating blood. There is acrocyanosis, the extremities are cold. Dyspnea, tachycardia is increased to 120-140 beats per minute. Systolic blood pressure is below 100 mm Hg. Art. The viscosity of blood sharply increases due to the formation of aggregates of erythrocytes in capillaries, an increase in the content of large-molecule proteins in the plasma, an increase in hematocrit and a proportional increase in the total peripheral resistance. Due to the fact that the blood is not a Newtonian fluid with a characteristic structural viscosity, a decrease in blood pressure increases the viscosity of the blood, and vice versa. Patients with oliguria (less than 20 ml / h).

Extremely heavy blood loss

It occurs if the decompensation of the blood circulation persists for a long time (6-12 hours or more). The patient's condition is extremely difficult. Against the background of the pallor of the skin is a patchy pattern. Pulsation is determined only on large vessels, a sharp tachycardia (up to 140-160 per minute). The systolic pressure is below 60 mm Hg. Art.

The rapid diagnosis of the severity of shock uses the concept of shock index (SHI) - the ratio of the heart rate to the value of systolic blood pressure. Normally its value is 0.5 (60/120). At a shock of I degree SHI = 1 (100/100), shock of II degree - 1,5 (120/80), shock of III degree - 2 (140/70).

Massive blood loss is a decrease in blood volume, approximately equal to 7% of ideal body weight in adults and 8-9% in children, within 24 hours. For the rate of hemorrhage, massive loss of blood is defined as a loss of 50% of the blood volume within 3 hours, or when the loss rate is 150 ml / min or more. The degree of severity of blood loss can be determined with sufficient accuracy from clinical and laboratory data.

Deficiency of the volume of circulating blood can be determined from the value of central venous pressure (norm 6-12 mm of water column).

[14], [15], [16]