The abdominal cavity contains the organs that digest food, filter blood and enable reproduction, any of which may give rise to abdominal pain. As with chest pain, patients presenting with a ‘textbook’ collection of symptoms are the exception rather than the rule.
A focused history should be taken, concentrating on the nature and timing of the pain and its associations. Most abdominal space relates to food processing, therefore the relationship of pain to food intake/excretion is important, e.g. pain related to large or fatty meals suggests gallstones. Date of last menstrual period (LMP) is essential information to obtain from any woman of childbearing age.
Nature of the pain
There are three common sorts of abdominal pain.
• Colicky pain: pain that comes and goes in spasms, and is usually the result of peristalsis failing to move a solid mass, e.g. the ureter attempting to move a stone to the bladder. The patient may move about, seeking a comfortable position.
• Peritonism: the sharp, well-localised pain resulting from inflammation of the parietal (outer) peritoneal surface – peritonitis. The patient lies still to avoid moving the inflamed surfaces.
• Distension pain results from an organ or bowel being stretched. The pain is poorly localised and may be felt as central abdominal pain. When the bowel is distended by gas, it may be tympanic: the abdomen sounds ‘hollow’ when percussed.
Less common types of pain are:
• Mucosal pain: burning pain due to inflammation of the mucosa, e.g. reflux of gastric acid into the oesophagus, urinary tract infection (UTI), sexually transmitted infection (STI).
• Ischaemic pain: poorly localised gnawing/cramping pain caused by inflammation progressing to ischaemic necrosis, e.g. menstruation, ischaemic bowel.
• Referred pain: pain occurring in a different area, e.g. cardiac ischaemia may be perceived as abdominal pain. Conversely, pain from within the abdomen may be perceived elsewhere, e.g. shoulder tip pain from diaphragmatic irritation, penile pain from renal colic, and back pain from retroperitoneal structures.
To make things more complicated, a single pathophysiological process may cause different types of pain simultaneously.
From the end of the bed: is the patient well/ill/critically ill? Immunosuppressed patients may appear deceptively well despite significant disease. Also beware patients with neuropathy, e.g. diabetics who may not experience ‘normal’ pain. Patients who cannot get comfortable or who are constantly moving are likely to have colicky pain. Patients who lie very still are likely to have peritonitis.
Palpation, percussion and auscultation
Poorly localised general pain is usually felt around the umbilicus, but specific point tenderness suggests peritonitis. Increased bowel sounds are caused by obstruction; absent bowel sounds indicate peritonitis. Rectal examination is an important part of the exami- nation, and stool should be tested for blood.
• Blood glucose.
• Urine dipstick.
• Urinary βhCG in any woman of childbearing age.
• Ultrasound is used by emergency physicians to rule out abdominal aortic aneurysm or to look for intra abdominal fluid. If the expertise is available, it may be useful in patients with other diseases, e.g. gallstones.
• FBC, U+E, LFTs and amylase/lipase in all patients.
• Arterial blood gases including lactate in sick patients.
• Group and save/cross-match blood if patient likely to go to theatre.
• An erect chest X-ray detects free air from a perforated bowel.
• A supine abdominal X-ray (60 CXR) will demonstrate obstruction but is otherwise unlikely to be helpful.
• Ultrasound is good for biliary, urinary and gynaecological causes of pain.
• CT (300 CXR) is very good at demonstrating most abdominal pathology but is a high dose of radiation.
• MRI is good for imaging abdominal organs, but is not widely available.
• Resuscitation and urgent surgical opinion if clinically unwell. Oxygen for all unwell patients together with observation and monitoring in a suitable clinical area.
• Intravenous fluids are an important part of resuscitation, but also replace ongoing fluid losses (Chapter 3). A nasogastric tube keeps the stomach empty, e.g. if there is bowel obstruction.
• Analgesia: intravenous morphine with anti-emetic is humane, safe and does not impede diagnosis. Intravenous or rectal NSAID, e.g. ketorolac, is good for peritoneal pain and relaxes smooth muscle so is good for colicky pain, although should be avoided in the elderly.
Disposal: who can go home?
Any patient who has abdominal pain requiring ongoing morphine needs to be admitted. Patients who appear well, in whom serious pathology has been excluded, and whose pain has not recurred after analgesia has worn off, are usually safe to discharge. Other patients should be reviewed by the relevant surgical team.