Hypovolemic Shock

 Shock:

It is a situation in which a general disorder of blood flow exists where in tissue perfusion and oxygen delivery are reduced to a level below those required to meet metabolic demands despite the operation of various compensatory mechanism.
Shock is also the term given to the clinical condition in which the patient is pale, cold and sweaty, the pulse is rapid, of low volume and the arterial BP is relatively low, often less than 80 mmHg.

Role of Kidneys in Hypovolemic Shock:
 

Fall in MAP perfusing the kidneys and stimulation of sympathetic nerves, stimulate JGA leading to release of renin.

Renin converts Angiotensinogen to Angiotensin –I which is converted to Angiotensin- II.

Angiotensin- II causes

  i)    constriction of arterioles leading to increase ­ in TPR.

  ii)   release of aldosterone from adrenal cortex which helps in reabsorption of Na+ in the kidneys

  iii)  causes release of ADH which helps in the

            reabsorption of water from the kidney

  iv)  stimulates thirst center in the hypothalamus

           which increases water intake

     Overall effect is increase­ TPR, ­ increase BV, increase ­SV leading to an increase in BP

 

ØDecrease in MAP leads to ­ sympathetic discharge to kidneys which causes

   a) decrease in Renal blood flow (normal blood flow is 20-25% of CO)- diverting blood to increase circulating BV.

  b) decrease in GFR leading to decreased urine output

  c)  Stimulates JGA causing ­ secretion of

          renin.

Ø Increased release of erythropoietin

Overall effect is an­ increase in BV, ­increase in BP, increase in ­ RBC production.

 

 

Stages of Shock:

Stage I  - Stage of compensated, reversible hypotensive shock. This shock occurs when there is decrease in circulating blood volume by 10% or less.

Stage II  -  Stage of decompensated hypotension but potentially reversible shock. This stage of shock results when there is decrease in blood volume of not more than 35-40% and arterial BP does not fall below 50 mmHg.

Stage III  -  Irreversible stage of shock due to microcirculatory failure leading to cellular injury and death. In this stage arterial BP continues to fall to a critical level- usually about 45mmHg or below; at which vital organ perfusion is reduced and a vicious circle of deterioration of functions ensues i.e. shock it self causes shock.

 

Management Principles for Shock
“VIP” 

Ventilation:  To ensure adequate pulmonary exchange of oxygen and carbon dioxide.      Supplement oxygen , some may need mechanical ventilator.

Infusion:  To ensure adequate intravascular volume -  intravenous fluids, blood.

Pump:  To ensure cardiovascular competence:

      give Inotropes and vasopressors

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