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In this article we will discuss about:- 1. Types of Shock 2. Signs and Symptoms of Shock 3. Stages 4. Events Occurs in Irreversible Stages 5. Treatment.
Shock is defined as lack of tissue perfusion which occurs when there is an imbalance between the volume of blood present in the circulatory system and the capacity of the circulatory system itself.
Types of Shock (Table 3.12):
1. Hypovolemic (hemorrhagic shock) is due to loss of blood or body fluids, the remaining volume of the blood are not sufficient to fill the system and supply oxygen to the tissues (Fig. 3.47).
2. Neurogenic shock is loss of sympathetic tone resulting in vasodilatation. The volume of the cardiovascular system is increased. However, the blood volume remains normal, since the capacity of the cardio vascular system is increased even though the blood volume remains normal it is not sufficient to fill the system completely, therefore, the blood pressure falls.
3. Cardiogenic shock is due to sudden failure of the left ventricle, which is unable to pump the blood into systemic circulation. This occurs usually in myocardial infarction or ventricular fibrillation.
4. Anaphylactic shock is a very severe type shock often occurs during allergic reaction. The antigen antibody reaction brings about release of histamine, which is a very powerful vasodilator substance. This results in vasodilatation of the all the blood vessels, decreased peripheral resistance and, therefore, a profound fall in the blood pressure.
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5. Septic shock is due to the release of the endotoxins from gram-negative bacteria. Endotoxins are very powerful vasodilator substance resulting in fall in blood pressure. This is usually associated with very high body temperature (fever).
Signs and Symptoms of Shock:
In hypovolemic shock, the patient is apprehensive, stuporous, and highly talkative; reticular formation is inhibited due to accumulation of metabolites (lactic acid) or stimulated due to increased catecholamine in the blood.
1. Skin—cold and clammy due to peripheral vasoconstriction and sweating
2. Pulse—rapid and thready
3. Respiration—shallow and hurried
4. Blood pressure is usually decreased or it may remain normal, if compensatory mechanism has already set in.
5. Tongue becomes dry, eyes sunken.
6. There may not be any visible bleeding (bleeding might have occurred within the body).
7. Muscle tone is reduced, feeling of extreme degree of fatigue or weakness.
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8. Patient repeatedly asks for water (thirsty).
9. Urinary output may be markedly decreased (oliguria) or not at all (anuria).
Stages of Shock:
a. Non-progressive or reversible or compensatory shock
b. Progressive or irreversible or non-compensatory shock.
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Compensatory Shock:
Signs and symptoms of shock are seen but given time the compensatory mechanisms come into play and blood pressure returns to normal and the person recovers. Compensatory mechanisms try to restore the blood volume and the blood pressure.
Compensatory mechanisms to restore the blood pressure include:
1. Baroreceptor mechanism
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2. Chemoreceptor mechanism
3. CNS ischemic response
4. Secretion of various hormones, like ADH, renin, angiotensin, aldosterone, adrenaline, noradrenaline, etc.
5. The sympathetic system is very powerfully stimulated. All these mechanisms are geared to restore the blood pressure rather than to restore the cardiac output (this can be made out from the above diagram) (Fig. 3.48).
The blood volume is restored back to normal relatively slowly. Components of the blood (RBCs, WBCs and platelets) are restored within a few weeks. If the volume of blood lost is too much, the compensatory mechanisms fail to restore the blood pressure. Hence the shock becomes progressive and may become irreversible (Fig. 3.49).
In the first three sets of dogs, the fall in blood volume and blood pressure is progressively increased. However, given time all the three sets of animals recover. In the IV, V and VI sets, the fall in the blood volume and blood pressure is comparatively much greater.
The compensatory mechanisms try to restore the blood pressure. In spite of this, due to a much greater fall in blood pressure, tissues deterioration has occurred to such an extent that the animals ultimately die.
Whenever the progressive stage of shock sets in, even if a blood transfusion is done after a time lag (Fig. 3.50), it fails to restore the blood pressure. And, therefore, the animal dies. Hence the dictum is whenever shock is diagnosed; the treatment must be started without any further wastage of time.
Events Occurs in Irreversible Stages of Shock (Fig. 3.51):
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1. When once the blood pressure falls below a critical level the positive feedback mechanisms develop, this in turn decreases the blood pressure further, recovery becomes impossible.
2. Decrease in cardiac output decreases the coronary blood flow. Because of this, oxygen supply to the cardiac muscle suffers. This in turn makes the cardiac contraction weaker decreasing the cardiac output further.
3. Decreased blood pressure decreases the blood flow to the brain resulting in hypoxia of the brain and vasomotor center. Vasomotor center function deteriorates resulting in peripheral vasodilatation giving rise to a further fall in blood pressure. This fall in blood pressure further decreases the blood flow to brain.
4. Nutrition and oxygen supply to the capillary endothelial lining cells is decreased resulting in damage to these cells. Fluid from the capillary leaves to the extravascular compartment, decreasing the blood volume and decreasing the blood pressure.
5. Metabolic waste like lactic acid accumulates in the tissues. This acts on the heart, depressing the myocardial contraction.
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6. Inhibition of sodium-potassium pump leads to altered cell membrane permeability.
7. Endotoxins from the gastrointestinal tract enter the circulation. These are powerful vasodilators and they also are toxic to the myocardium. When once irreversibility sets in, any amount of treatment may be in the form of blood transfusion becomes useless. Therefore, treatment should be commenced at the earliest.
Treatment of Shock:
If the cause is blood loss, blood transfusion is must. If the blood is not available then plasma expanders must be used.
In hypovolemic shock, noradrenaline administration is not beneficial because the sympathetic system is already maximally stimulated releasing lot of noradrenaline. In fact, it may do more harm than good because if the blood vessels remain contracted for long time, nutrition of the endothelial cells becomes defective and they suffer.
Vasoconstriction decreases the renal perfusion pressure leading to decreased formation of urine. Toxic materials will accumulate of which urea is the most important. This substance has deleterious effect on the brain.
Dopamine is more beneficial because it brings about renal vasodilatation; it has a positive inotropic effect on the heart. Oxygen may be useful in some cases.
Raising the foot end of the cot is beneficial. It facilitates the blood flow to the brain.
The following things are not to be done:
1. Trying to keep the patient warm by covering the patient with woolen blankets because this will induce peripheral vasodilatation, increase the blood flow to skin and decrease the blood flow to vital organs.
2. Hanging the patient or hold the patient feet end up trying to improve the blood flow to the brain. The diaphragm will not be in a position to contract properly and this will decrease pulmonary ventilation.