There are four types of abdominal pain:
- Visceral. Gut organs are insensitive to stimuli such as burning and cutting but are sensitive to distension, contraction, twisting and stretching. Pain from unpaired structures is usually but not always felt in the midline.
- Parietal. The parietal peritoneum is innervated by somatic nerves, and its involvement by inflammation, infection or neoplasia causes sharp, well-localised and lateralised pain.
- Referred pain. (For example, gallbladder pain is referred to the back or shoulder tip.)
- Psychogenic. Cultural, emotional and psychosocial factors influence everyone’s experience of pain. In some patients, no organic cause can be found despite investigation, and psychogenic causes (depression or somatisation disorder)
The acute abdomen
This accounts for approximately 50% of all urgent admissions to general surgical units. The acute abdomen is a consequence of one or more pathological processes
- Inflammation. Pain develops gradually, usually over several hours. It is initially rather diffuse until the parietal peritoneum is involved, when it becomes localised. Movement exacerbates the pain; abdominal rigidity and guarding occur.
- Perforation. When a viscus perforates, pain starts abruptly; it is severe and leads to generalised peritonitis.
- Obstruction. Pain is colicky, with spasms which cause the patient to writhe around and double up. Colicky pain which does not disappear between spasms suggests complicating inflammation.
Causes of acute abdominal pain
- Pelvic inflammatory disease
- Intra-abdominal abscess
- Peptic ulcer
- Diverticular disease
- Ovarian cyst
- Aortic aneurysm
- Intestinal obstruction
- Biliary colic
- Ureteric colic
Initial clinical assessment
If there are signs of peritonitis (guarding and rebound tenderness with rigidity), the patient should be resuscitated with oxygen, intravenous fluids and antibiotics. In other circumstances, further investigations are required
Patients should have a full blood count, urea and electrolytes, and amylase taken to look for evidence of dehydration, leucocytosis and pancreatitis. An erect chest X-ray may show air under the diaphragm, suggestive of perforation, and a plain abdominal film may show evidence of obstruction or ileus. An abdominal ultrasound may help if gallstones or renal stones are suspected. Ultrasonography is also useful in the detection of free fluid and any possible intra-abdominal abscess. Contrast studies, by either mouth or anus, are useful in the further evaluation of intestinal obstruction, and essential in the differentiation of pseudoobstruction from mechanical large-bowel obstruction. Other investigations commonly used include CT (seeking evidence of pancreatitis, retroperitoneal collections or masses, including an aortic aneurysm) and angiography (mesenteric ischaemia). Diagnostic laparotomy should be considered when the diagnosis has not been revealed by other investigations.
All patients must be carefully and regularly re-assessed (every 2–4 hours) so that any change in condition that might alter both the suspected diagnosis and clinical decision can be observed and acted upon early.
The general approach is to close perforations, treat inflammatory conditions with antibiotics or resection, and relieve obstructions. The speed of intervention and the necessity for surgery depend on the organ that is involved and on a number of other factors, of which the presence or absence of peritonitis is the most important.