SHADES OF SHOCK

4. Shock Syndromes

The events of shock may result from:

4.1 Oligemic (Hypo-volemic) shock due to decrease in circulating
blood volume resulting from :
i) Hemorrhage (internal or external)
ii) Loss of fluid as in burns,trauma(Third space) or
dehydration
iii) Decreased extra-cellular fluid because of hypo-natreamia
as in Addison's disease

Hypovolemic shock occurs most often following trauma resulting
in blood loss.
It also occurs following GI bleeds, or a leak from an aneurysm.
Plasma volume losses can occur in trauma, burns, intestinal obstruction, diarrhea and heat stoke.
*Hypovolemic shock
Hypovolemic shock is the most common cause of shock. It may occur as a result of one of two events:
1. hemorrhage, representing intravascular volume decrease through the loss of whole blood or
2. loss of plasma volume through extra-vascular fluid loss or fluid loss from gastrointestinal, urinary tracts, and insensible loss.
-Hemorrhage is the form of volume loss that is common in practice can be measured and studied and thus is the better understood form of shock.
-Extra-vascular internal fluid leak, also referred to as “third space” fluid losses, is frequently unnoticed as a cause of shock.
-Third space fluid losses are the principal cause of volume loss in the early postoperative period and in local inflammatory processes, such as pancreatitis, in which local changes in capillary permeability result in fluid extravasations from the intravascular space into the interstitial space.
-Fluid leak is the principal cause of shock in patients with small bowel obstruction.
In this case, volume loss results from fluid loss into the interstitial space, bowel lumen, and exudation of fluid into the peritoneal cavity.
-The clinical manifestations of nonhemorrhagic forms of hypovolemic shock are the same as with hemorrhage, although they can be more slow in onset.
-The physiological responses of the body to hypovolemic shock are aimed at maintenance of cerebral and coronary perfusion and improving the circulating blood volume. The major compenstory mechanisms include
- An increase in sympathetic activity
- Release of stress hormones and
- Volume improvement through restoration of interstitial fluid, mobilization of intracellular fluid, saving of fluids and electrolytes by the kidney.
The clinical picture reflects this intense adreno-sympathetic response and renal conservation of fluid.
-Micro-vascular low perfusion of some vascular beds of organs results from a combination of low intravascular blood volume, diminished cardiac output resulting from a reduction in venous return and preload, and compensatory vaso-constriction.*
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