Burn shock

Burn shock is a pathological process caused by extensive thermal damage to the skin and underlying tissues, leading to severe hemodynamic disorders with a predominant disruption of microcirculation and metabolic processes in the victim's body. The duration of the period is 2-3 days.

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How does burn shock develop?

From the moment of receiving an extensive burn, circulatory disorders acquire special significance, which is facilitated by the loss of plasma from the affected surface. From the first hours, the BCC decreases due to a decrease in the volume of circulating erythrocytes and plasma, which leads to blood thickening (hemoconcentration). Due to a sharp increase in capillary permeability (not only in the burn zone, but also in intact tissues) and the release of a significant amount of protein, water and electrolytes from them, the volume of circulating plasma in the burned person is significantly reduced. Hypoproteinemia occurs, mainly due to hypoalbuminemia. Its development is also facilitated by increased protein breakdown in the tissues of the burned person. A decrease in the volume of circulating erythrocytes occurs due to the destruction of erythrocytes in the burn area at the time of thermal injury and, to a greater extent, as a result of pathological deposition of erythrocytes in the capillary network due to microcirculation disorders. A decrease in the BCC leads to a decrease in the return of blood to the heart and a decrease in cardiac output.

Deterioration of myocardial contractility after severe burns is also considered to be the cause of an early drop in cardiac output. As a result, the amount of blood flowing to various organs and tissues decreases, which, together with the deterioration of the rheological properties of the blood, leads to pronounced microcirculation disorders. At the same time, already in the first hours after receiving a burn, a sharp slowdown in the speed of blood movement is observed, which is fraught with the exclusion of a significant part of the capillaries from active circulation. Aggregates of formed elements appear in small vessels, preventing the normal passage of erythrocytes through the capillaries. Despite such hemodynamic disorders, burn shock is accompanied by normal arterial pressure. This is facilitated by an increase in the total peripheral resistance to blood flow due to vasospasm due to increased activity of the sympathoadrenal system, as well as an increase in blood viscosity due to hemoconcentration and deterioration of the rheological properties of the blood. Circulatory disorders lead to a sharp disruption in oxygen delivery to tissues and to hypoxia. It is aggravated by the suppression of mitochondrial respiratory enzymes, which completely excludes the participation of even delivered oxygen in oxidative reactions. Underoxidized metabolic products, especially lactic acid, cause a shift in the oxygen saturation coefficient towards acidosis. Metabolic acidosis contributes to further disruption of the cardiovascular system.

Burn shock has three degrees: mild, severe and extremely severe.

Mild burn shock develops when the area of deep burns is up to 20% of the body surface. Victims are admitted to the hospital in a clear consciousness, sometimes with short-term agitation, rarely vomiting, chills. Moderate thirst is a concern. Some pallor of the skin may be noted. Blood pressure remains within normal values, slight tachycardia is possible (100-110 per minute). Impaired renal function is uncharacteristic, daily diuresis remains normal, there is no hematuria or azotemia. The body temperature of most victims is normal or subfebrile on the first day, and reaches 38 °C on the second. Hemoconcentration is moderate, hematocrit does not exceed 55-58%, however, these changes are stopped on the second day. An increase in the number of blood leukocytes to 15-18x109 / l, slight hypoproteinemia (the level of total protein is reduced to 55 g / l) are characteristic. Bilirubinemia, electrolyte imbalance and acidosis are usually not detected. Moderate hyperglycemia (up to 9 g/l) is observed only in the first day. Usually, most victims are brought out of the state of mild burn shock by the end of the first - beginning of the second day after the injury. The average duration of the period is 24-36 hours.

Severe burn shock develops in the presence of deep burns on an area of 20-40% of the body surface. In the first hours after the injury, agitation and motor restlessness are characteristic, soon followed by lethargy with preserved consciousness. The victim is bothered by chills, thirst, pain in the area of the burns. Vomiting is observed in a significant number of patients. The skin free from burns and visible mucous membranes are pale, dry, cold. Acrocyanosis is often noted. Tachycardia up to 120 per minute, decreased blood pressure are characteristic. As a rule, kidney function suffers, daily diuresis is reduced to 300-400 ml. Hematuria, albumin, sometimes hemoglobinuria, an increase in residual nitrogen in the blood to 40-60 mmol / l by the second day are observed. Hemoconcentration is significant (hematocrit 70-80%, Hb 180-200 g/l), the blood clotting rate decreases to 1 min. Leukocytosis up to 40x109/l is noted, accompanied by neutrophilia, young forms up to myelocytes, lymphopenia and eosinopenia often appear; the number of leukocytes decreases by the end of the third day. The content of total plasma protein decreases to 50 g/l on the first day and 40 g/l on the second day. The number of platelets is slightly reduced. Combined respiratory-metabolic acidosis develops.

Extremely severe burn shock occurs when there are deep burns on an area of more than 40% of the body surface. The general condition of patients is usually severe, consciousness is confused. Short-term excitement quickly gives way to inhibition and indifference to what is happening. The skin is cold and pale. Characteristic symptoms include intense thirst, chills, nausea, repeated vomiting, tachycardia up to 130-150 per minute, and weak pulse filling. Systolic blood pressure can be reduced to 90 mm Hg from the first hours, and central venous pressure also falls. Dyspnea and cyanosis, high hemoconcentration (Hb 200-240 g/l, hematocrit 70-80%) are noted. Urine output is sharply reduced, up to anuria, daily diuresis does not exceed 200-300 ml. Urine is dark brown, almost black, with a burning smell. Acidosis develops from the first hours after receiving a burn, and intestinal paresis occurs. Body temperature is reduced. The duration of this period is 56-72 hours, the mortality rate reaches 90%.

How is burn shock treated?

Burn shock in children is treated with infusion-transfusion therapy, the volume of which is approximately determined by the Wallace scheme - by the product of the child's triple weight (kg) and the % of the burn. This amount of fluid must be administered to the child in the first 48 hours after the injury. The physiological need of the body for water (from 700 to 2000 ml/day depending on age) is satisfied by additional administration of a 5% glucose solution.

In the first 8-12 hours, 2/3 of the daily amount of fluid is administered, the rest - in the next 12 hours. Mild burn shock requires the administration of a daily dose of infusion media, which is about 3000 ml for adults and up to 1500-2000 ml for children; severe burn shock - 4000-5000 ml and 2500 ml; extremely severe burn shock - 5000-7000 ml and up to 3000 ml, respectively. In elderly and senile people, it is necessary to reduce the infusion rate by approximately 2 times, and reduce the volume to 3000-4000 ml / day. In burn patients with concomitant diseases of the cardiovascular and respiratory systems, the volume of transfusions should also be reduced by 1/4 ~ 1/3 of the daily amount.

The above schemes of infusion-transfusion therapy are approximate. In the future, burn shock is treated under the control of blood pressure, central venous pressure, heart rate, hourly diuresis, hemoglobin level, hematocrit, potassium and sodium concentrations in the blood plasma, acid-base balance, etc. The volume and rate of administration of infusion media should be increased at low CVP figures (less than 70 mm H2O); high figures (more than 150 mm H2O) indicate heart failure and the need to stop the infusion or reduce the volume of administered media. With adequate therapy, hourly diuresis is 40-70 ml/h, the concentration of sodium in the blood plasma is 130-145 mmol/l, potassium - 4-5 mmol/l. Hyponatremia is quickly stopped by administering 50-100 ml of 10% sodium chloride solution, which usually eliminates hyperkalemia as well. In case of hypernatremia, the administration of 250 ml of 25% glucose solution with insulin is indicated.

The adequacy of infusion-transfusion therapy is also judged on the basis of clinical data: thirst and dry skin indicate a water deficit in the body and the development of hypernatremia (oral water intake should be increased, a 5% glucose solution should be administered). Pale and cold skin indicates a disturbance of peripheral circulation [dextran (rheopolyglucin), gelatin (gelatinol), hemodez should be administered]. Severe headache, convulsions, weakening of vision, vomiting, salivation are observed with cellular hyperhydration and water intoxication (the use of osmotic diuretics is indicated). Collapse of the subcutaneous veins, hypotension, decreased skin turgor are characteristic of sodium deficiency (infusion of electrolyte solutions, 10% sodium chloride is necessary). If the victim's condition shows positive dynamics, diuresis is restored and laboratory parameters are normalized, the amount of infusion media administered can be reduced by half for 2-3 days.

When performing infusion-transfusion therapy for burn victims, preference should be given to catheterization of the central veins (subclavian, jugular, femoral), which can also be performed through the affected areas of the skin after their careful treatment. However, such a catheter should not be used for a long time due to the risk of developing purulent-septic complications.

Sometimes, extremely severe burn shock caused by combined thermomechanical trauma complicated by bleeding is treated with infusion therapy, which is carried out simultaneously through two catheterized central veins.

Criteria for a patient to emerge from a state of burn shock:

• persistent stabilization of central hemodynamics;
• restoration of diuresis; elimination of hemoconcentration;
• the onset of fever.