Shock is defined as the widespread hypoperfusion of the tissues due to a reduction of the blood volume or cardiac output or redistribution of the blood resulting in an inadequate effective circulatory volume. It occurs due to the serious assault on the body haemostasis. It may be reversible or irreversible. It is a life-threatening medical condition resulting from insufficient blood flow to the various tissues of the body. Shock is a medical emergency and requires immediate treatment as symptoms can worsen rapidly. The shock itself is not a diagnosis and is a symptom of severing underlying disorder causing hypoperfusion of the vital organs of the body. Hypoperfusion of the tissues results in an inadequate supply of the oxygen as well as the nutrients needed for the tissues to perform its functions. Shifting of the aerobic respiration to anaerobic respiration results in acidosis and metabolic derangements. If the shock persists for a long time, it may result in irreversible cell injury.
Classification and causes of shock
Any factors causing hypoperfusion of tissue results in shock. It can be classified as follows:
- Cardiogenic shock
Failure to pump blood out of the heart due to intrinsic damage of the heart muscles or by the extrinsic pressure or by the obstruction in the blood flow results in cardiogenic shock. Causes of cardiogenic shock are Myocardial infarction, Rupture of heart, arrhythmias, cardiac tamponade, massive pulmonary embolism ( obstructs the outflow from the heart in heart failure which leads to shock).
- Hypovolemic shock
Hypovolemic shock occurs due to inadequate blood or plasma volume resulting in decreased cardiac output, which in turn causes hypoperfusion of the tissues. Causes of hypovolemic shock include haemorrhage, diarrhea, vomiting, trauma, severe burn.
- Septic shock
Infection or other causes of a systemic inflammatory response that produces widespread endothelial damage with the vasodilatation, arteriovenous shunting, microvascular occlusion and tissue edema, resulting in the organ failure. Causes of the septic shock are an overwhelming bacterial infection due to gram-negative septicemia or in few cases gram-positive septicaemia or rarely fungal infections.
- Neurogenic shock
It is caused by spinal cord injury or anesthetic accident producing disruption of the brain stem and neurogenic vasomotor control.
- Anaphylactic shock
It is mediated by the type I hypersensitivity reaction in response to an allergen causing inappropriate vasodilation.
Stages of shock
Shock is a progressive disorder and unless the insult to the tissues is massive and fatal it progresses in three stages.
The three stages of shock are
- Non-progressive stage
- Progressive stage
- Irreversible stage
In conditions such as mild trauma and mild haemorrhage, the perfusion of the vital organs is maintained by the reflex compensatory mechanism. A variety of neurohormonal mechanisms such as
- Baroreceptor mechanism
- Activation of Renin-Angiotensin mechanism
- Release of catecholamine and ADH
- Generalized sympathetic stimulation, etc. helps in maintaining cardiac output and blood pressure.
Clinical Features in the non-progressive stage of shock are cooling and pallor of the skin in the hypovolemic shock and cardiac shock.
In this stage, vasoconstriction occurs in less vital organs of the body and spares vital organs such as brain and heart.
If a shock is not corrected at this stage, it will become progressive.
In progressive shock perfusion to the vital organs are not preserved and there is an imbalance of circulatory and metabolic mechanism. The sequence of progressive shock is as follows:
Less perfusion of the vital organs leading to less oxygen and nutrient supply to the tissues which in turn shifts aerobic glycolysis to anaerobic glycolysis. Shifting of aerobic glycolysis to anaerobic glycolysis results in the increased lactic acid formation and lactic acidosis. PH decreases and removes the sympathetic stimulation, which causes vasodilation and pooling of the blood in the periphery. Since the blood accumulates in the periphery, reduction of the central blood volume and decreased cardiac output occurs, which will produce more hypoxia and the injury to endothelium occurs. Endothelial injury progresses to disseminated intravascular coagulation and patient develops confusion and oliguria (impairment of renal function).
After the body has already incurred cellular and tissue injury the irreversible stage starts. Here the cells and tissue are so severely injured that even if the patient’s haemodynamic effects are corrected, survival is impossible. Irreversible stage has following features
- Lysosomal enzymes leak into the blood, causing widespread cell injury.
- Increased nitric oxide synthesis leads to myocardial dysfunction.
- Entry of the intestinal flora causes endotoxic shock.
Renal tubular necrosis resulting in the renal shutdown.
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GENERAL FEATURES OF SHOCK
Features of shock differ according to the cause of shock. In general, these following features mentioned below can be found:
- Rapid, shallow respirations
- Cold and clammy skin
- Tachycardia ( heart rate more than 100 beats per minute )
- Hypotension ( Systolic blood pressure less than 100 mm of Hg )
- Drowsiness, Confusion, irritability
- Urine output less than 30 ml per hour (oliguria)
- Multi-organ failure
MORPHOLOGY OF SHOCK
Cellular and tissue injury caused by shock, are essentially those of hypoxia injury.
It is associated with the failure of multiple organs and can be seen in any tissues of the body. Some of the organs damaged by shock are mentioned below:
- Brain: ischaemic encephalopathy
- Heart: subendocardial damage, contraction band necrosis
- Lung: diffuse alveolar damage
- Kidney: acute tubular necrosis
- Haemorrhagic enteropathy occurs in the gastrointestinal system
- In the adrenal gland, depletion of fat due to excessive synthesis of catecholamine and necrosis occurs in the cortical region.
Management of shock
- Assessment of the patient
- Blood pressure measurement
- Pulse (rate, rhythm, volume) monitoring
- Respiratory rate monitoring
- Measurement of central venous pressure or pulmonary capillary wedge pressure
- Urine output
- Blood gases and electrolyte measurement
Treatment of shock
- Maintenance of respiration by endotracheal intubation or laryngeal mask airway.
- Maintenance of circulation
- Prevention of renal failure by keeping urinary output above 50ml per hour.
- Correction of acidosis by sodium bicarbonate solutions
- Treatment of underlying cause while resuscitation is underway
- Continuous measurement of vital signs.
PREVENTION OF SHOCK
Prevention of shock is easier than its treatment. Lifestyle modifications help in reducing the incidence of shock in many cases.
- Control blood pressure: Light physical exercise for about 30 minutes in most days of the week, management of stress by mediation, limiting salt and alcohol consumption, maintaining proper body weight helps in keeping blood pressure under control. You can also visit your physician, who may prescribe medicines to treat hypertension.
- Don’t smoke: Smoking is one of the risk factors for atherosclerosis. Getting rid of your smoking habit prevents you from an unwanted risk of coronary artery disease and stroke.
- Maintenance of weight: Obesity is linked to diseases such as high blood pressure, cardiovascular disease, and diabetes. These diseases are major risk factors for shock Losing weight around 4 to 4.5 kilograms may lower blood pressure and improve your cholesterol levels.
- Lowering the cholesterol and saturated fat in the diet may reduce your risk of heart disease. Consumption if fatty fish, Salmon containing polyunsaturated fats helps to improve cardiac health. People who cannot control the cholesterol level by dietary changes alone may need cholesterol-lowering drugs such as atorvastatin.
- Exercise regularly: Light physical exercise lowers the risk of suffering from uncontrolled blood pressure, it also increases the level of high-density lipoprotein (HDL) cholesterol, also known as good cholesterol and improve the health of blood vessels and heart. Exercise also helps in controlling body weight, diabetes and stress. Cardiovascular exercise for about 30 minutes in a day such as walking, jogging, swimming or bicycling on most days of weeks helps in prevention of shock.
- To prevent yourself from burning shock, do not smoke indoors, make a fire escape plan, keep a fire extinguisher in the kitchen or places at risk for fire and check the expiry date of the fire extinguisher. You can also teach the children to log and roll if in any case, you may get fire. Maintenance of gas stoves, fireplace and its screening to prevent children helps in preventing burn shock.
- Fluid replacement in people suffering from diarrhea and vomiting helps in prevention of hypovolemic shock. In cases of trauma, bleeding from arteries should be stopped as soon as possible.