Circulatory Shock

Circulatory shock, is a serious, life-threatening medical condition defined as an inadequate blood flow to the body to the extent that body tissues are damaged. As the blood carries oxygen and nutrients around the body, reduced flow hinders the delivery of these components to the tissue cells. [1]

Basically a shock results in decreased cardiac output, which is insufficient to meet body needs. Just as a heart attack (myocardial infarction) causes death of cardiac tissues. A shock is similar to this but it covers whole body including vital organ such as kidneys and liver.

 

 

TYPES

·                    Hypovolemic Shock

·                    Septic Shock

·                    Anaphylactic Shock

·                    Neurogenic Shock

·                    Cardiogenic Shock

 

1.  HYPOVOLEMIC SHOCK:

Hypovolemia means diminished blood volume, Its primary cause is loss of fluid from the circulation. Hemorrhage is most common cause of hypovolemic shock.

Low blood volume is accompanied by lowering of blood pressure and decrease in cardiac output. In response to these changes, activation of sympathoadrenal system takes place. As a result tachycardia is produced, vasoconstriction occurs in skin, digestive tract, and kidneys.

Decreased blood flow to kidneys activates rennin-angiotensin-aldosterone system. AngiotensinII is powerful vasoconstrictor of arterioles throughout the body. AngiotensinII, ADH and aldosterone increase Na and water reabsorption in order to maintain blood volume.

Since constriction of coronary and cerebral blood vessels do not take place, blood is diverted to brain and heart at expense of other organs.

A patient suffering from hypovolemic shock has low blood pressure, cold-sweaty skin, increased heart rate and decreased urine output.

 

2.   SEPTIC SHOCK

It is a condition of dangerously low blood pressure which results from infection. It takes place due to bacterial endotoxins. Endotoxins activate the immune response of the body. An enzyme called nitric oxide synthase is activated within macrophages. It produces nitric oxide which is vasodilator. It decreases total peripheral resistance which ultimately results in decreased cardiac output

 

3. ANAPHYLACTIC SHOCK

It is a rapid fall in blood pressure caused by severe allergic reaction (allergens, antigens, drugs). This results in widespread release of histamine, which causes vasodilation and decrease in total peripheral resistance leading to decreased venus return and ultimately decreased cardiac output.

 

 

4. NEUROGENIC SHOCK

It is caused by injury to the vasomotor center in brain or spinal cord injury resulting in the sudden loss of autonomic reflexes below the injury level. Without stimulation by sympathetic nervous system the vessel walls relax uncontrollably, resulting in a sudden decrease in total peripheral resistance, leading to hypotension and decreased cardiac output.

 

5.CARDIOGENIC SHOCK

This type of shock is caused by the failure of the heart to pump effectively resulting in decreased cardiac output. This can be due to damage to the heart muscle from a large myocardial infarction. Other causes of cardiogenic shock include arrhythmias, congestive heart failure or cardiac valve problems.

 

STAGES OF SHOCK

1- Non progressive stage

In this stage normal circulatory compensatory mechanisms eventually cause full recovery of shock without help from outside therapy.

2- Progressive stage

At this point without therapy the shock becomes steadily worse until death.

3- Irreversible stage

In this stage the shock has progressed to such an extent that all forms of known therapy are inadequate to save the person’s life.

 

 

TREATMENT

Re-establishing circulation to the organs is the primary goal in the treatment. Therefore urgent treatment (stopping of bleeding, rapid restoration of circulating blood volume and respiratory support) is essential.

In all types of shock patient should be given intravenous fluids immediately i.e. 1 liter blood, plasma or normal saline(depending on circumstances) over 10 minutes.

Oxygen therapy should be initiated immediately. In case of respiratory insufficiency, mechanical ventilation should given.[2]

In case of septic shock in addition to steps mentioned above drugs which inhibit nitric oxide production should be administered in this shock.[3]

In anaphylactic shock antihistamines are administered.[4]

 

REFERENCE

[1]Text Book of  Medical Physiology: Guyton and Hall

[2]http://en.wikipedia.org/wiki/Shock_(circulatory)

[3]Human Physiology: Straut Fox

[4]http://en.wikipedia.org/wiki/Anaphylaxis#Management