INTESTINAL OBSTRUCTION

INTESTINAL OBSTRUCTION

CLASSIFICATION
Intestinal obstruction may be classified into two types:

? Dynamic, in which peristalsis is working against a mechanical
obstruction.
? Adynamic, in which peristalsis may be absent (e.g. paralytic
ileus) or it may be present in a non-propulsive form (e.g.mesenteric vascular occlusion or pseudo-obstruction) * In both types a mechanical element is absent .
Causes of Intestinal Obstruction

? --------------------------------------Dynamic
-Intraluminal.
? Impaction
? Foreign bodies
? Bezoars
? Gallstones
-Intramural .
? Stricture
? Malignancy
-Extramural .
? Bands/adhesions
? Hernia
? Volvulus
? Intussusception
? --------------------------------------Adynamic

-Paralytic ileus. -Mesenteric vascular occlusion. -Pseudo-obstruct.


Mechanisms of Obstruction
? Volvulus
? Incarceration
? Obstruction
? Intussusception
Summary box 66

PATHOPHYSIOLOGY

Irrespective of aetiology or acuteness of onset, in dynamic (mechanical) obstruction the proximal bowel dilates and develops an altered motility. Below the obstruction the bowel exhibits normal peristalsis and absorption until it becomes empty, at which point it contracts and becomes immobile. Initially, proximal peristalsis is increased to overcome the obstruction, in direct
proportion to the distance of the obstruction. If the obstruction is not relieved, the bowel begins to dilate, causing a reduction in peristaltic strength, ultimately resulting in flaccidity and paralysis.

This is a protective phenomenon to prevent vascular damage secondary
to increased intraluminal pressure.

? The distension proximal to an obstruction is produced by two
factors:
? Gas:
there is a significant overgrowth of both aerobic and
anaerobic organisms, resulting in considerable gas production.
Following the reabsorption of oxygen and carbon dioxide, the
majority is made up of nitrogen (90%) and hydrogen sulphide.
? Fluid :
this is made up of the various digestive juices. Following
obstruction, fluid accumulates within the bowel wall and any
excess is secreted into the lumen, whilst absorption from the
gut is retarded.

? Dehydration and electrolyte loss are therefore due to:
1– reduced oral intake;
2– defective intestinal absorption;
3– losses as a result of vomiting;
4– sequestration in the bowel lumen.