Acute intestinal
obstruction
Clinical features
There are four cardinal
features:
pain;
vomiting;
distension;
constipation.
These features vary
according to:
the location of the obstruction;
the age of the obstruction;
the underlying pathology;
the presence or absence of intestinal ischaemia.
Late
manifestations which may be encountered include dehydration, oliguria,
hypovolaemic shock, pyrexia, septicaemia, respiratory embarrassment and
peritonism. In all cases of suspected intestinal obstruction, all hernial
orifices must be examined.
Pain
Pain is the first symptom, it occurs suddenly and is usually severe. It
is colicky in nature and is usually centred around the umbilicus (small bowel)
or lower abdomen (large bowel). The pain coincides with increased peristaltic
activity. With increasing distension, the colicky pain is replace 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
postoperative simple mechanical obstruction and does not occur in paralytic
ileus.
Vomiting
The more distal the obstruction, the longer the interval between the
onset of symptoms and the appearance of nausea and vomiting. As obstruction
progresses the character of the vomitus alters from digested food to faeculent
material due to the presence of enteric bacterial overgrowth.
Distension
In the small bowel the degree of distension is dependent on the site of
the obstruction and is greater the more distal the lesion. Visible peristalsis
may be present (Fig. 58.4). It is delayed in colonic obstruction and may be
minimal or absent in the presence of mesenteric vascular occlusion.
Constipation
This may be classified as absolute (i.e. neither faeces nor flatus is
passed) or relative (where flatus only is passed). Absolute constipation is a
cardinal feature of complete intestinal obstruction. Some patients may pass
flatus or faeces after the onset of obstruction owing to the evacuation of
distal bowel contents.
The
rule that constipation is present in intestinal obstruction does not apply in:
Richters hernia;
gallstone obturation;
mesenteric vascular occlusion;
obstruction associated with a pelvic abscess;
partial obstruction (faecal impaction/colonic neoplasm) where
diarrhoea may often occur.
Other
manifestations
Dehydration
This is seen most commonly in small bowel obstruction due to repeated
vomiting and fluid sequestration. This results in dry skin and tongue, poor
venous filling and sunken eyes with oliguria. The blood urea level and
haematocrit rise giving a secondary polycythaemia.
Hypokalaemia
This is not a common feature in simple mechanical obstruction. An increase in serum potassium, amylase or lactate dehydrogenase may be associated with the presence of strangulation, as may leucocytosis or leucopenia.
Pyrexia in the presence of obstruction may indicate:
the onset of ischaemia;
intestinal perforation;
inflammation associated with the obstructing disease.
Abdominal
tenderness
Localized tenderness indicates pending or established ischaemia. The
development of peritonism or peritonitis indicates overt infarction and/or
perforation.
Clinical
features of strangulation
It is vital to distinguish strangulating from nonstrangulating
intestinal obstruction, as the former is a surgical emergency. The diagnosis is
entirely clinical. In addition to the features outlined above, the following
should be noted:
the presence of shock indicates underlying ischaemia;
in impending strangulation, pain is never completely absent;
symptoms usually commence suddenly and recur regularly;
the presence and character of any local tenderness are of great
significance and, however mild, tenderness requires frequent reassessment.
In nonstrangulated
obstruction there may be an area of localized tenderness at the site of the
obstruction; in strangulation there is always localized tenderness associated
with rigidity/rebound tenderness.
Generalized tenderness and the presence of rigidity are indicative of the
need for early laparotomy.
In cases of intestinal obstruction where pain persists despite
conservative management, even in the absence of the above signs, strangulation
should be diagnosed.
When strangulation occurs in an external hernia the lump is tense,
tender, irreducible, there is no expansile cough impulse and it has recently
increased in size.
Radiological
diagnosis
Erect abdominal films
are no longer routinely provided and the radiological diagnosis is based on a
supine abdominal film (Fig. 58.5).
When distended with gas the jejunum, ileum, caecum and remaining colon
have a characteristic appearance that allows them to be distinguished
radiologically. The diameter of the distended viscus is not diagnostic.
The obstructed small bowel is characterized by straight segments that are
generally central and lie transversely. No gas is seen in the colon.
The jejunum is characterized by its valvulae conniventes that completely pass across the width of the bowel and are regularly spaced giving a concertina or ladder effect.
Ileum the distal ileum has been piquantly described by
Wangensteen as featureless.
Caecum a distended caecum is shown by a rounded gas shadow in the
right iliac fossa.
Large bowel except for the caecum shows haustral folds which,
unlike valvulae conniventes, are spaced irregularly and the indentations are not
placed opposite one another.
Volvulus
of the sigmoid colon has a characteristic radiological appearance with a
grossly dilated loop of colon, with or without visible haustrae which arises
from the pelvis and extends obliquely across the spine to the upper abdomen.
In
intestinal obstruction fluid levels appear later than gas shadows as it takes
time for gas and fluid to separate (Fig. 58.6). In infants less than 2 years of
age, a few fluid levels in the small bowel may be physiological. In adults, two
inconstant fluid levels may be regarded as normal one at the duodenal cap
and the other in the terminal ileum.
During
the obstructive process, fluid levels become more conspicuous and more numerous
when paralysis has occurred. When fluid levels are pronounced the obstruction is
advanced. In the small bowel, the number of fluid levels is directly
proportional to the degree of obstruction and to its site; the number increasing
the more distal the lesion.
In
contrast, low colonic obstruction does not commonly give rise to small bowel
fluid levels unless advanced, whilst high colonic obstruction may do in the
presence of an incompetent ileocaecal valve. Colonic obstruction is usually
associated with a large amount of gas in the caecum. A limited water-soluble
enema may be undertaken to differentiate large bowel obstruction from pseudo-obstruction. A barium
follow-through is contraindicated in the presence of acute obstruction and may
be life threatening.
Impacted
foreign bodies may be seen on abdominal radiographs. In gallstone ileus, gas may
be seen in the biliary tree with the stone visible, usually in the right iliac
fossa, in 25 per cent of cases.
It
is noteworthy that gas-filled loops and fluid levels in the small and large
bowel can also be seen in established paralytic ileus and pseudo-obstruction.
The former can, however, normally be distinguished on clinical grounds whilst
the latter can be confirmed radiologically. Fluid levels may also be seen in non
obstructing conditions such as inflammatory bowel disease, acute pancreatitis
and intra-abdominal sepsis.