‫ ليث نايف‬.‫د‬
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.
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-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.
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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.
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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.
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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
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-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 doesn’t 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 pseudoobstruction. 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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