PathophysiologyPathophysiology of of

Shock Shock

Definition…Shock is an ACUTE

CIRCULATORY CRISIS marked by low blood pressure

(hypotension) and inadequate peripheral blood flow.

Common causes of shock

1. A drop in cardiac output after hemorrhaging or other fluid losses (like in diarrhea and vomiting).

2. Damage to the heart (As in Myocardial Infarction).

3. External pressure on the heart.4. Extensive peripheral vasodilatation.

SYMPTOMS of circulatory shockAppear after fluid losses of about 30 percent

of thetotal blood volume. six basic symptoms:1. Hypotension.2. A rise in heart rate and a rapid, weak

pulse.3. Pale, cool, and moist (“clammy”) skin. 4. confusion and disorientation5. A cessation of urination 6. A drop in blood pH (acidosis)

Note thatIn mild forms of circulatory shock,

homeostatic ad justments can cope with the situation.

When blood volume declines by more than 35 percent, homeostatic mechanisms are no longer able to cope with the situation.

A vicious cycle begins when the low cardiac output damages the myocardium. This damage leads to a further reduction in cardiac output and subsequent reductions in blood pressure and venous return.

In mild forms of circulatory shock, homeostatic adjustments can cope with the situation.

When blood volume declines by more than 35 percent, homeostatic mechanisms are no longer able to cope with the situation.

A vicious cycle begins when the low cardiac output damages the myocardium. This damage leads to a further reduction in cardiac output and subsequent reductions in blood pressure and venous return. As the blood flow to the brain decreases, the individual becomes disoriented, and confused.

Treatment must concentrate on (1) preventing further fluid losses and (2) giving a transfusion of whole blood,

plasma expanders, or blood substitutes. Irreversible shock begins when

conditions in the tissues become so abnormal that the arteriolar smooth muscles and pre-capillary sphincters become unable to contract, despite the commands of the vasomotor centers.

The result is a widespread peripheral vasodilatation and an immediate and fatal decline in blood pressure. This event is called circulatory collapse.