Hypovolemia is the decrease in the volume of blood circulating in the human body (BCC). With hypovolemia, the level of blood volume decreases significantly below the normative indices. In men, normal parameters are 70 ml / kg of total circulating blood and 40 ml / kg plasma. In women, 66 ml / kg BCC and 41 ml / kg of circulating plasma.
The volume of circulating blood is a constituent element of extracellular fluid and therefore practically all causes of the appearance of dehydration give rise to hypovolemia. A special role in its development is also played by the redistribution of intravascular fluid into the interstitial space.
Hypovolemia of the cause
The causes of improper distribution of extracellular fluid are: a decrease in oncotic pressure in the blood plasma, increased permeability of the walls of blood vessels, an increase in the arterioles of hydrostatic pressure, an increase in arterial and venous pressure.
Oncotic pressure can be reduced primarily in cases of renal impairment. Receiving diuretics, like other conditions, lead to loss of water and sodium salts through the kidneys. In particular, diuretics increase the excretion of sodium. Also, the reabsorption of sodium salts can be impaired due to increased filtration of such substances that cause osmotic diuresis (urea and glucose). This condition can be with diabetes mellitus in a decompensated form or when feeding people with high protein content.
Increased secretion of water by the kidneys leads to hypovolemia, but at the same time the level of intracellular fluid decreases (2/3 of all losses) and therefore the hypomotion in this process is moderate. This condition can be observed with diabetes insipidus and with nephrogenic diabetes. These conditions are caused by a violation of ADH secretion and a decrease in the sensitivity of kidney work.
Loss of fluid not through the kidneys involves loss through the gastrointestinal tract, lungs, skin and penetration of fluid into the foreign space (burns, peritonitis, acute pancreatitis ). With burns or allergic reactions, as a rule, there is an increased permeability of the walls of the vessels.
Within 24 hours in the gastrointestinal tract, about 7.5 liters of fluid are secreted, and about two liters are supplied with food. Approximately 98% of this fluid is absorbed, which means that the loss of water with a caloric mass when emptying the bowels is about 200 ml / day. Therefore, hypovolemia can result in increased secretion of the gastrointestinal tract and reduced reabsorption of the liquid in it. Such conditions include diarrhea and vomiting.
It is also known that when breathing occurs, the elimination of the liquid and sweating through the skin. Such water losses are called hidden. They are about half a liter per day. With fever, physical activity and in hot weather conditions, sweating is greatly enhanced. The concentration of sodium salts in the perspiration liquid is about 30-50 mmol / l, and on this basis the hypotonic liquid is lost during sweating, which leads to thirst and water loss are replenished. But with profuse sweating hypovolemia may begin, because with this condition, a pronounced and prolonged excretion of sodium occurs.
Loss of fluid through the chest increases with artificial ventilation. The escape of fluid into another space is observed for a number of states. Such a space can not exchange a liquid with either an intracellular space or an extracellular space. Since liquid from the extracellular fluid is discharged into another space, then pronounced hypovolemia develops. Other spaces include: subcutaneous fat with pronounced burns, intestinal lumen with its obstruction, space behind the peritoneum with an attack of acute pancreatitis, the peritoneum area with the development of peritonitis.
In some cases, hypovolemia of the thyroid gland can be observed, in which the level of not only the fluid and hormones produced by it is significantly lowered. But this condition is extremely rare. As a rule, it is preceded by pronounced hypovolemia, which is observed with prolonged blood loss.
Lowering the volume of fluid inside the cells is manifested by lowering blood pressure and decreasing the volume of circulating plasma. Hypotension develops due to preload of the venous apparatus and slowing of cardiac output. This leads to reduced impulses from the 6-receptors of the carotid sinuses and to a decreased impulse of the a-type a-receptor b-receptors. Because of this, the increased excitability of the sympathetic nervous and renin-angiotensin systems begins to develop. Such reactions are adaptive in nature, maintain blood pressure and preserve the perfusion of the heart and brain. Adaptation reactions from the renal system are aimed at replenishing the plasma volume.
The most typical complaints for hypovolemia are: thirst, high fatigue, muscle spasms, dizziness when the body changes from vertical to horizontal position and vice versa. Such symptoms are nonspecific and are caused by secondary impairments of tissue perfusion and electrolyte balance. There is also a decrease in diuresis, pallor of the mucous membranes and skin, a decrease in body temperature, an increase in the heart rate and a decrease in pulse filling.
Expressed hypovolemia is accompanied by a violation of the perfusion of the abdominal cavity and chest. It manifests itself in pain in the abdomen, chest, comparison, deafness, cyanosis, oliguria. And also hypovolemic shock can occur with loss of a large amount of fluid.
In a physical examination, there is a decrease in veins in the neck, as well as tachycardia and orthostatic hypotension. Lowering the turgor of the skin, as well as dryness of the mucous membranes are not considered to be particularly reliable criteria for determining the degree of hypovolemia.
For the diagnosis of hypovolemia, it is enough to collect anamnesis and physical examination. Laboratory diagnosis is used to confirm the diagnosis.
The level of sodium in blood plasma with hypovolemia can vary from normal to high or low. It all depends on the amount of fluid lost and how quickly it is replenished with water intake.
With loss of potassium through the gastrointestinal tract or kidney, hypovolemia can be combined with hypokalemia, and with hyperkalemia - with renal failure, disorders in the adrenal gland and some types of acidosis .
Treatment of hypovolemia is aimed at eliminating its cause, as well as on replenishment of the volume of extra- and intracellular fluid. Solutions fluid to be replenished should be similar in composition to the lost. The severity of hypovolemia is determined on the basis of clinical symptoms. The same criteria is used to evaluate the effectiveness of therapy for hypovolaemia.
With moderate hypovolemia prescribe fluid intake inside, with severe - intravenously. If hypovolemia is accompanied by a slightly reduced level of sodium in the plasma, then a solution of sodium chlorine with a concentration of 145 mmol / l is used. It is also prescribed for shock and hypotension. If sodium is reduced in the plasma to a critical level, sodium chlorine is used at a concentration of 515 mmol / l.
With severe bleeding, anemia, it is advisable to transfuse erythrocyte mass, as well as intravenous administration of Albumin and Dextran.
When hypovolemia of the thyroid gland appoint a hormonal drug in combination with iodine. In the future, it is necessary to measure the level of hormones such as TTG, T3 and T4 quarterly.