Shock Causes

When things go wrong

If cells are deprived of oxygen, instead of aerobic (with oxygen) metabolism, the cells use the anaerobic (without oxygen) pathway to produce energy. Unfortunately, lactic acid is formed as the by product of anaerobic metabolism. This acid changes the acid-base balance in the blood and leads to a downward spiral where cells start to leak toxic chemicals into the bloodstream, cause blood vessel walls to become damaged, and this process ultimately leads to the death of the cell. If enough cells die, then organs start to fail, and the body dies.

Think of the cardiovascular system of the body as similar to the oil pump in your car. For efficient functioning, the electrical pump needs to work to pump the oil, there needs to be enough oil, and the oil lines need to be intact. If any of these components fail, oil pressure falls and the engine may be damaged. In the body, if the heart, blood vessels, or bloodstream (circulation) fail, then the body fails.

Where things go wrong

The oxygen delivery system to the body's cells can fail in a variety of ways.

• The amount of oxygen in the air that is inhaled can be decreased.
  
  
• Examples include breathing at high altitude or carbon monoxide poisoning.

The lung may be injured and not be able to transfer oxygen to the blood stream. Causes of this may include, among others:

• pneumonia (an infection of the lung),
  
  
• congestive heart failure where the lung fills with fluid, or
  
  
• trauma with collapse or bruising of the lung.

The heart may not be able to adequately pump the blood to the tissues of the body. Cases of this may include, among others:

• In the case of a heart attack, where muscle tissue is lost, or by a rhythm disturbance of the heart, when the heart can't beat in a coordinated way.
  
  
• It may also occur because of heart inflammation due to infection or other causes, again where the effective beating capabilities of the heart are lost.

There may not be enough red blood cells in the blood. If there aren't enough red blood cells (anemia), then not enough oxygen can be delivered to the tissues with each heart beat. Causes may include:

• acute or chronic bleeding,
  
  
• inability of the bone marrow to make red blood cells, or
  
  
• the increased destruction of red blood cells by the body (an example includes sickle cell disease).

There may not be enough other fluids in the blood vessels. The blood stream contains the blood cells (red, white, and platelets), plasma (which is more than 90% water), and many important proteins and chemicals. Loss of body water or dehydration can cause shock.

The blood vessels may not be able to maintain enough pressure within their walls to allow blood to be pumped to the rest of the body. Normally, blood vessel walls have tension on them to allow blood to be pumped against gravity to areas above the level of the heart. This tension is under the control of the unconscious central nervous system, balanced between the action of two chemicals, adrenaline (epinephrine) and acetylcholine. If the adrenaline system fails, then the blood vessel walls dilate and blood pools in the parts of the body closest to the ground and may have a difficult time returning to heart to be pumped around the body.

Since one of the steps in the cascade of events causing shock is damage to blood vessel walls, this loss of integrity can cause blood vessels to leak fluid, leading to dehydration which initiates a vicious circle of worsening shock.