Intestinal obstruction 1

Intestinal obstruction

Introduction:
Intestinal obstruction may be classified into:
-Dynamic: where peristalsis is working against mechanical obstruction

-Adynamic: this may occur in two forms. 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)
Causes:
Dynamic:
-Extramural: - Adhesions & bands
-External or internal hernia
-Volvulus
-Intususception
-Intramural:-Neoplasm
-Strictures
-Intraluminal:-impaction, foreign bodies, bezoar, gallstones
Adynamic: - Paralytic ileus
-Mesenteric vascular occlusion
-Pseudo-obstruction


Dynamic obstruction
The diagnosis of intestinal obstruction is based on pain, Distension, Vomiting & Absolute constipation
-Obstruction may be classified clinically into:
-small bowel obstruction: (high or low).
-Large bowel obstruction.
*In high small bowel obstruction, vomiting occurs early & is profuse with rapid dehydration. Distension is minimal with little evidence of fluid levels on abdominal radiography
*In low small bowel obstruction, pain is predominant with central distension, vomiting is delayed; multiple central fluid levels are seen on an abdominal radiography.
*In large bowel obstruction, the distension is early & pronounced, pain is mild, vomiting & dehydration are late. The proximal colon & caecum are distended on radiography.

-The nature of presentation may be influenced by whether the presentation

-acute: usually occurs in Small bowel obstruction with sudden sever colicky
Central abdominal pain, distension with early vomiting & constipation.

-chronic: usually seen in large bowel obstruction with lower abdominal colic & absolute constipation followed by distension.

-Acute on chronic: when there is short history of distension & vomiting against background of pain & constipation.

-Subacute: it implies an incomplete obstruction

-Presentation will be further influenced by whether the obstruction is:


-Simple: where the blood supply is intact
-Strangulated: where there is direct interference to blood flow, usually by hernia ring or intraperitoneal adhesions & bands.

*Pathophysiology

Generally the proximal bowel dilates &develops an altered motility. Beyond the obstruction, the bowel exhibits normal peristalsis &absorption until it becomes empty when it contracts &becomes immobile

-Initially, proximally the peristalsis increased to overcome the obstruction. If the obstruction not relieved, the bowel begins to dilates, causing reduction in peristaltic strength. Finally flaccidity & paralysis. This is a protective phenomenon to prevent vascular damage secondary to increased intralumenar pressure

-The distension proximal to an obstruction produced by:

-gas: there is significant overgrowth of both aerobic & anaerobic Organisms resulting in considerable gas production which is mainly made up of nitrogen & hydrogen sulphate

-fluids: this is made up of the various digestive juices.

Strangulation:
When strangulation occurs, the viability of the bowel is threatened secondary to a compromised blood supply. The venous return is compromised before the arterial supply, this results in increase in capillary pressure leads to local mural distension with loss of intravascular fluids & RBCs intramurally & intra- & extraluminally. Once the arterial supply is impaired, hemorrhagic infarction occurs. As the viability of the bowel wall is compromised there is translocation of aerobic & anaerobic organisms with their toxin &there will be systemic manifestations.

The causes of strangulation are:

External: hernia, adhesions, bands
Interrupted blood flow: volvulus, Intussusceptions
Increased intraluminal pressure: closed loop obstruction
Primary: mesenteric infarction


Closed-loop obstruction:
This occurs when the bowel is obstructed at both the proximal &distal points. When gangrene of the strangulated segment is imminent, retrograde thrombosis of the mesenteric veins results in distension on both sides of the strangulated segment

A classic form of closed loop obstruction is seen in carcinomatous stricture of right colon with a competent ileocaecal valve (33% of individuals).the inability of distended colon to decompress itself result in increase intraluminal pressure with subsequent impairment of blood supply &eventually necrosis & perforation.

Acute intestinal obstruction

Clinical features vary according to the location of the obstruction, the age of the obstruction, underlying pathology &presence or absence of intestinal ischemia.

Cardinal features of intestinal obstruction:

Pain:
It is the first symptom, it occurs suddenly &usually sever, colicky in nature &usually around the umbilicus (small bowel) or lower abdomen (large bowel).pain coincide with increase peristaltic activity. With increasing distension, the colicky pain is replaced by a mild constant diffuse pain. The development of severe pain is indicative of the presence of strangulation. Pain may not be a significant feature in post operative simple mechanical obstruction and does not usually occur in paralytic ileus.

Vomiting:

The more distal the obstruction, the larger the interval between the onset of symptoms &the appearance of nausea & vomiting. As the obstruction progress, the character of vomitus changes from digested food to feculent material, due to the presence of enteric bacterial overgrowth.

Distension:

In small bowel the more distal site of obstruction the greater the distension. It's delayed in colonic obstruction &minimal or absent in mesenteric vascular occlusion.

Constipation;

*either absolute (i.e. Neither faeces nor flatus is passed) or relative (when flatus only is passed).absolute constipation is a feature of complete I.O.


Other manifestations:

Dehydration: mainly in small bowel obstruction due to vomiting &fluid sequestration, this results in dry skin and tongue, poor venous filling and sunken eyes with oliguria. The blood urea & hematocrit rise.

Hypokalemia: may be present

Pyrexia: may indicate ischemia, perforation or inflammation within the obstruction. Hypothermia indicates septisemic shock.

Clinical features of strangulation:

It's vital to distinguish strangulating from non-strangulating I.O.as the former is a surgical emergency
In addition to the features of non-strangulated intestinal obstruction, the following should be noted:
-the presence of shock indicates underlying ischemia.
-in impending strangulation, pain is never completely absent.
-the symptoms usually commence suddenly& recur regularly.
-the presence& character of any local tenderness are of great significance& however mild, tenderness requires frequent reassessment.

In non-strangulated obstruction, there may be an area of localised tenderness at the site of the obstruction, in strangulation there is always localized tenderness associated with rigidity/rebound tenderness

Therefore:

-generalised tenderness & rigidity are indicative of the need of early surgery
-in I.O. if the pain persists despite conservative treatment: strangulation should be diagnosed
-when strangulation occurs in an external hernia, the lump is tense, tender irreducible &there is no expansile cough impulse& it has recently increased in size



Radiological diagnosis
Supine abdominal radiography
-the obstructed small bowel is characterized by straight segment that are generally central & lie transversely. No gas is seen in colon

-the jejunum is characterized by valvulae conniventes which completely pass across the width of the bowel &are regularly spaced

-ileum is featureless

-caecum; rounded gas shadow in the RIF

-Large bowel except caecum; hausral folds which is spaced irregularly &the indentation not placed opposite one another

-when sigmoid colon is obstructed, there will be grossly dilated loop with or without haustra which arise from the pelvis &extends obliquely across the spine to the upper abdomen

Erect abdominal radiography
-In I.O. fluid levels appear later than gas shadow

-In infant less than 2 years of age, a few fluid level in the small bowel may be physiological

-In adult 2 inconstant fluid level, one at the duodenal cap &the other in the terminal ileum may be regarded as normal


In small bowel obstruction the number of fluid level is directly proportional to the degree of obstruction &to its site, the number increasing the more distal the lesion
The low colonic obstruction doesnt commonly give rise to small bowel fluid levels unless advanced, while high colonic obstruction may do so in the presence of an incompetent ileocaecal valve
-water soluble enema should be undertaken to differentiate LBO from pseudo-obstruction. Barium follow through is contraindicated in acute obstruction
-Impacted F.B. may be seen, gall stones may be seen in RIF in case of gall stone ileus
-Gas-fluid level may also be seen in;
-established paralytic ileus& pseudo-obstruction
-in non obstructing conditions like inflammatory bowel disease, acute pancreatitis &intra-abdominal sepsis.








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