What is shock?

Shock is a systemic condition in which blood supply to the body tissues is inadequate for the normal functioning of the cells. This condition is usually life-threatening and needs immediate attention.

During the normal conditions, the cells usually have aerobic respiration. In shock state, the respiration shifts to anaerobic.

Blood flow to the tissues, needs to be restored in time or else the cells will die of hypoxia.

Pathophysiology of shock

Blood is normally the main medium for oxygen transport. In shock, there is low blood supply to the organs meaning that little oxygen is being delivered to the cells and tissues.

They therefore become hypoxic and shift from aerobic to anaerobic respiration. Anaerobic respiration produces minimal energy. There will therefore be an energy deficit in the cell.

Lactic acid is produced and is not sufficiently broken down due to the oxygen deficiency. It accumulates in blood causing a fall in pH. The fall in pH leads to a condition known as metabolic acidosis. This has an effect of causing vasoconstriction on the peripheral blood vessels in an attempt to retain the normal blood flow volume to the major organs such as the heart and the brain in expense of the other organs like the skin and the kidney. This is called shunting of blood. This, however, causes failure of the precapillary sphincters which leads to pooling of blood in the periphery. Blood returning to the heart (venous return) is reduced causing further injury.

Metabolic acidosis also causes cell membrane to dysfunction and the sodium pumps to fail. It corrodes the cell membrane of the lysosomes which then release their stored protyolitc enzymes. This damages the cell membrane rendering it unable to maintain the active transport across it. Sodium pump therefore fails and reverses.

Sodium pump is an active transport mechanism that transports 3 sodium ions out of the cell in exchange for 2 potassium ions. It usually utilizes ATP energy obtained from aerobic respiration. With the case of shock, anaerobic respiration is taking place and hence little energy is being produced. Sodium pump is therefore deprived of energy and further fails. This causes an influx of sodium ions and an efflux of potassium ions from the cell.

Some other toxic substances which are usually contained within the cell are released into the blood because the damaged cell membrane cannot hold these contents anymore. The lysosomal enzymes are still included here. They damage the capillary endothelium. The cells are destroyed, rendered dysfunctional and the die.

Manifestations of shock in different systems of the human body

1. Cardiovascular system

Because of the pooling of blood in the peripheral blood vessels, the venous return is reduced and consequently the cardiac output. Compensatory mechanisms come in place.

The Renin-Angiotensin-Aldosteron system (RAAS) is usually the first to respond. It produces Angiotensins and Aldosteron. The angiotensins stimulate the sympathetic nervous system and cause direct vasoconstriction of the peripheral blood vessels hence increasing blood flow to the heart. Aldosteron increases sodium ion reabsorption from the renal tubules which in turn cause more water retention in the blood. This increases the blood volume.

All these have an effect of increasing the venous return to the heart. Because of the increased venous return, ventricular muscles are stretched more to accommodate the increased blood volume. Consequently, the rate and force of their contractility also increases. This is the reason why people who have shock have an increased heart rate.

People with shock also experience increased sweating, a condition known as diaphoresis. This happens because the sympathetic nervous system also innnervate the sweat glands. When activated by the angiotensins, they too activate the sweat glands hence more sweating.

The increased contractility of the cardiac muscles causes an increase in the cardiac output. The circulatory volume is improved, the blood pressure rises and consequently the mean arterial pressure. Tissue perfusion is thus improved.

2. Respiratory system

The lack of oxygen by the cells of the tissues causes them to shift to aerobic respiration. Lactic acid is produced which causes acidosis in the cells. The body tries to correct this by increasing the respiratory rate so that the rate of elimination of carbon dioxide is increased. This may happen to an extent that the level of carbon dioxide in the body drops below normal hence respiratory alkalosis.

3. Renal system

During the state of shock, blood is usually shunted away from the integumentary system (skin), splanchnic circulation (gastrointestinal system) and the kidneys to the major priority organs such as the liver, the heart and the brain.

Kidneys therefore receive low blood supply, little filtration takes place and the urine output is less. This the reason why people in shock may have oliguria or anuria.

4. Endocrine system

In the endocrine system, there is hormone production particularly the angiotensins and aldosterone by the RAA system. Other hormones produced include cortisol and antidiuretic hormone. ADH increases water reabsorption from the renal tubules back to the blood.

N/B: Reactive oxygen species (ROS) and acidosis are usually injurious to the cell. If a person in shock is resuscitated, the ROS is distributed to the other parts of the circulatory system. Instead of the patients improving, they tend to deteriorate.