hypovolemic shock - this critical condition of the body resulting from the sharp decrease in effective circulating blood volume.The name of the term "shock" is derived from the French or the English consonant word that literally means shock, bump, push.In fact, the concept of a shock denotes extremely dangerous cascade of changes occurring in the body.
The major pathogenetic components of hypovolemic shock include low cardiac output, peripheral vasoconstriction (vasoconstriction), violation of microcirculation, and there is a further respiratory failure.
reasons for the critical reduction in blood volume can serve as acute blood loss (external or internal bleeding), and dehydration that occurs when severe infections of the intestinal group (eg, cholera), and deposit, the redistribution of blood in the microcapillary of the bloodstream (caseat a painful or traumatic shock).
sharp decrease in effective blood volume causes a range of pathological changes in the usual work
reasons hypovolemic shock
The causes hypovolemic shock can serve a number of factors - one-stage profuse blood loss, dehydration, or a sudden redistribution of blood to the periphery, in the microcapillary channel.
Pathogenesis of hypovolemic shock involves a cascade of changes that are, at first, compensatory, and then indicate the exhaustion of compensatory mechanisms.
trigger for further changes in cardiac output becomes small, which results in a critical reduction in blood flow in the tissues.
There is a sequence of changes, which is directly related to the phase of the process.The first change, which serve as the beginning of all the cascade - nonspecific hormonal shifts.
first hypoperfusion and low pressure stimulates the release of ACTH, ADH and aldosterone.The release of the above-mentioned hormones in the bloodstream affects the kidneys and the whole excretory system.This leads to sodium and chloride together with ions and water in the body.Simultaneously excretion of potassium ions accelerated and generally decreased urine output.Further, in the pathogenesis of hypovolemic shock include adrenaline and noradrenaline, which contribute to peripheral vasoconstriction.
In launching a pathological cascade of changes is not so much the volume of blood loss, as the time in which it occurred.
Chronic hypovolemia, although it hurts the body but does not cause such critical changes in it.
All these changes are compensatory in nature.While working endocrine compensatory mechanisms, central venous pressure is normal.These mechanisms fails while providing a constant venous return and maintain the general circulation to the extent necessary for the proper functioning of all systems.But when the blood loss reaches 5-10% of the total volume, the compensatory mechanisms, become insufficient to maintain the venous return, and this leads to a further reduction and central venous pressure.
human body in any way seek to maintain homeostasis, and begins to drive the successor arrangements for the compensation - begins tachycardia.Because of this, some time able to maintain the same level cardiac output.Only when the exhaustion and this compensatory mechanism, which usually occurs in case of a decrease in venous return to figures 25-30%, there is a further drop in cardiac output, which eventually promotes low cardiac output syndrome.
entire series of compensatory and adaptive mechanisms pursue the same goal - to ensure the functioning of vital organs.Proper blood supply should be provided primarily the brain, heart muscle, and filtration, detoxification system - the liver and kidneys.When
stop working above adaptive mechanisms, comprising the steps included in the pathogenesis of hypovolemic shock - peripheral vasoconstriction.
peripheral vasoconstriction allows you to redistribute blood to the vital organs and maintain blood pressure at a level slightly above the critical though.In this mechanism directly involved catecholamines.According to some of their blood levels of this phase can be increased 10-30 times in excess of the usual rules.
centralization of blood flow, on the one hand helps to provide at least minimal functioning of life support systems, and on the other - is profound hypoxia peripheral tissues, and with it, acidosis.This occurs even despite the fact that tissue oxygen demand is greatly reduced.
Not least in the development of pathological changes takes liquid transition with the ions from the extracellular and vascular space into the cells.This phenomenon is due to the weakening of sodium-potassium pump associated with hypoxia.Changes in water-salt balance in hypovolemic shock associated with the gradual loss of tone of the precapillary sphincters while maintaining a tone postkapilyarnogo sphincter.Thus, over time, increase the concentration of endogenous catecholamines ceases to elicit a response in the precapillary sphincters.
In the future, water with electrolytes continue to leave the bloodstream in response to an increasing hydrostatic pressure and increased permeability of blood vessel walls.The transition of liquid in the interstitial space can further enhance the viscosity of the blood.Thickening of blood leads to intravascular platelet aggregation, and multiple thrombosis throughout the body.
Numerous microscopic blood clots break down all the internal organs.This especially affects the lungs and plays a leading role in the development of respiratory failure accompanying shock.
In addition, intravascular thrombus formation results in a decrease in platelet count, fibrinogen and coagulation other factors that lead to the development of the "syndrome of consumption."This reflects one of the phases of disseminated intravascular coagulation.
Hypercoagulation gradually leads to the depletion of the hemostatic system, and develops the inevitable hypocoagulation, with the development of multiple hemorrhages.
separate an important role in the development of hypovolemic shock, should take proteolytic enzymes, which are beginning to be produced inside the cells in excess.Lysosomal enzymes, destroying cell membranes, enter the bloodstream, and the net effect on the internal organs.One of the effects of enzyme group forms a so-called myocardial depressing factor (MDF).By the effects of this factor is a negative inotropic effect, lower blood pressure, increase vascular permeability, the occurrence of pain.
During development, hypovolemic shock also occurs metabolism abnormality, the essence of which consists in the activation of anaerobic energy production pathways in aerobic conditions, inaccessibility, which leads to aggravation of the general acidosis.
stages of hypovolemic shock
Clinic hypovolemic shock phase is over, and includes three stages.It is important to capture the changes in a timely manner to assist with maximum efficiency.
♦ The first stage of hypovolemic shock - Compensated shock occurs when the blood loss of 15-25% of blood volume, it is an average of about 700-1300 ml.It is important to note that this step is completely reversible.The main pathogenetic link of the first stage of hypovolemic shock syndrome appears small output.Clinically, this syndrome appears moderately developed tachycardia, minor (sometimes absent) hypotension.You can fix the venous hypotension.A modest oliguria.Peripheral vasoconstriction manifested pallor and coldness of extremities.
♦ The second stage of hypovolemic shock, which is also called decompensated (reversible) shock occurs when the loss of 26-45% of circulating blood volume.This is translated into the actual amount of blood loss, an average of 1300-1800 ml.In the second step increases tachycardia, the heart rate increases to 120-140 per minute.Detects low pulse pressure and systolic, in turn, drops below 100 mm.rt.Art.You can also record the venous hypotension.Peripheral vasoconstriction pronounced, there Generalized pallor and cyanosis of the skin of the whole body.Of the other symptoms - the appearance of a cold sweat, shortness of breath, restless behavior.Significantly reduced diuresis - oliguria, less than 20 ml per hour.
♦ The third stage of hypovolemic shock - the stage of irreversible shock.When her blood loss exceeds 50% of the total, which is approximately 2000-2500 ml.At this stage, it marked a critical reduction in blood pressure.Figures may reach a level below 60 mm.rt.Art., and often blood pressure and is not determined.Tachycardia continues to grow and reaches 140 beats per minute or more.The man in the third step, hypovolemic shock is unconscious.The skin has a distinctly pale.The skin is covered with cold sweat.The whole body, especially the extremities become cold to the touch, can be seen hypostasis.The excretory function is missing - developing oligoanuria.
One sign that indicates irreversibility hypovolemic shock - increase the hematocrit and decrease the volume of blood plasma component.
Treatment of hypovolemic shock
Since the clinic hypovolemic shock is directly related to pathogenic changes in the body, treatment is carried out taking into account the peculiarities of pathogenesis.The main directions in the treatment of hypovolemic shock should choose address the factors that are involved in the pathogenetic chain.
first steps should be directed at eliminating the causes of hypovolemic shock, namely, to determine the source of bleeding and its termination.
Also worth as soon as possible to begin oxygen therapy, the use of high concentrations of oxygen.This will help counteract the hypoxic changes in the peripheral tissues and exacerbate acidosis.
necessary measure to combat hypovolemic shock is to restore lost blood volume via transfusion of blood substitutes.Restores volume carried out by introducing a combination of colloid and crystalloid.Often it is necessary to resort to transfusion of blood components.This measure is intended to - maintain hemoglobin level indicator 100 g / l.
also for transfusion can be used frozen plasma.These measures are necessary, including the fight against "wasting syndrome," the syndrome of disseminated intravascular coagulation.
exceptionally if there is the possibility of determining the blood pH, conduct correction of metabolic acidosis.In parallel to the transfusion is appropriate to monitor the performance of the sodium-potassium exchange.In parallel with the infusion therapy can be administered drugs that have the ability to improve vascular tone - glucocorticoids.
When unable to stop blood loss and restore blood volume, appropriate administration of inotropic agents, in order to stimulate the heart muscle.In case you can not restore urine output, even after the replenishment of the lost volume diuretic therapy is conducted.