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:

• Richter’s 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.

  Hypothermia indicates septicaemic shock.

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.