The Acute Abdomen

Acute abdomen is defined as any episode of abdominal symptoms, usually abdominal pain, presenting acutely, potentially as a surgical emergency, with no history of trauma.

Acute abdominal pain is a common presentation. There are multiple causes of severe abdominal pain. These may be differentiated by the nature of the pain, and the area the pain typically presents in. It is important to take a clear history and do a thorough examination with patients with acute abdominal pain.

Are there signs of shock/organ rupture requiring urgent surgery?
A rupture of an organ such as the spleen, aorta or an ectopic pregnancy may cause massive blood loss requiring resuscitation and surgery to repair the ruptured part or to stop the bleeding. In additional to abdominal pain, a patient with shock may have altered vital signs such as tachycardia, tachypnoea, or dropping blood pressure. In addition, they may show signs of reduced end-organ perfusion. The skin, kidneys and the brain are usually the most perfused organs, hypovolaemic shock may therefore present as cold shut down peripheries, with a prolonged capillary refill, reduced urine output, and confusion and reduced consciousness on the glasgow coma score. Falling blood pressure tends to occur late.

Parameter	Class I	Class II	Class III	Class IV
Blood loss	-750mls	750-1500	1500-2000 ml	+2000ml
%	-15%	15-30%	30-40%	+40%
Pulse	-100bpm	+100bpm	+120bpm	+140bpm
Blood pressure	Normal	Normal	Reduced	Reduced
Respiratory rate	14-20	20-30	30-40	+35
Urine output	+30ml/h	20-30ml/h	5-15ml/h	Negligible
Mental state	Slightly anxious	More anxious	Confused	Lethralgic +

Is the pain peritonitic?
Peritonitis is caused by irritation of the peritoneum, which is innervated by somatic nerves, causing a localised sharp pain. It may be generalised over the whole abdomen, or localised.

Generalised peritonitis tends to be caused by perforation of an abdominal organ, such as with doudenal perforation, or perforation of the appendix or diverticulum. Peritonitis tends to be worse on movement, so the patient may lie still and take shallow breaths. The patient may also present with a tender abdomen, with guarding and rigidity of the whole abdomen, and absent bowel sounds. Generalised peritonitis may also be associated to signs of shock.

Localised peritonitis tends to be caused inflammed organs irritating the parietal peritoneum. For example, it may occur with appendicitis, diverticulitis or cholecystitis. Again the patient tends to lie still, as movement worsens the pain. In localised peritonitis, the pain is located in one region, and there may be gaurding in that region, and precussion tenderness. Gaurding may be voluntary where the patient tenses when anticipating pain, or a reflex. To differentiate voluntary gaurding from true gaurding palpate both sides of the abdomen simultaneously whilst talking to the patient, if only one side of the abdomen is rigid, gaurding is unlikely to be voluntary.

Colicky pain occurs when muscles contract in a hollow viscus. This pain tends to come and go, and occurs where there is an obstruction, for example with intestinal obstruction, or uteric colic. A patient with colic tends to be unable to get comfortable and be quite restless. The viscera is innervated by autonomic nerves, and are more dull in nature and may be referred to either the epigastric, umbilical, or suprapubic regions depending on the region the organ developed from embryonically.

Where is the pain?
The position of the pain may help differentiate the cause. Some causes of abdominal pain in each region is outlined below:

Epigastric pain

Pancreatitis

Myocardial infarction

Acute cholecystitis / biliary colic

cholangitis

Peptic ulcer

Perforated oesophagus

Right upper quadrant pain

Liver pain - hepatitis, liver capsule pain from heart failure

Acute cholecystitis

Duodenal ulcer

R pneumonia

Right Iliac fossa pain

Appendicitis - central dull pain radiating to the RIF

Merkel's diverticulum

Mesenteric adenitis

Crohn's disease

Gynaecological causes: 

Ectopic pregnancy

Ovarian cysts - torsion or rupture

Pelvic inflammatory disease

Endometriosis 

Mittleschmerz - mid cycle pain, may be severe, in groin or L or R iliac fossa lasting for hours -days. 

Inguinal/femoral hernia

Left upper quadrant

Ruptured spleen/splenic disease

Gastric ulcer

L Pneumonia

Pancreatitis

Left iliac fossa

Diverticulitis

ulcerative colitis

Crohn's disease

Gynaecological causes as with RIF pain

Inguinal/femoral hernias

Central abdominal pain 

Ruptured aortic aneurysm

Acute pancreatitis

Mesenteric thrombosis

Diverticulitis

Bowel obstruction (large and small bowel) - associated with vomiting, constipation, distension and colicky pain. In small bowel obstruction, vomiting occurs earlier, distension is less and pain is higher. There may not be absolute constipation in higher obstructions. In lower large bowel obstructions, pain is more constant ,and the patient may not have passed faeces or air. 

Mechanical ileus (bowel obstruction due to lack of bowel function) tends to cause no pain and absent bowel sounds. 

Ischaemic bowel

Loin pain 

Renal pain - Renal colic, UTI/pyelonephritis

Other causes

Adhesions

Acute urine retention

Testicular torsion

Myocardial infarction

Pneumonia/Tuberculosis/Pleurisy - tends to be worse on inspiration/pleuritic

Neurological causes

Diabetic ketoacidosis

Porphyria/syphilis

Sickle cell crisis

thyroid storm

Gastroenteritis

Herpes zoster

Tropical diseases - eg. Cholera, typhoid fever, malaria, 

Management
Management of acute abdominal pain depends on its presentation and cause. It may include initial resuscitation, analgesia, and further medical treatment or observation or surgical treatment. Initial investigations may include urine dipstick, pregnancy tests, bloods including FBC, Liver function tests, Urea and electrolytes, Amylase, Inflammatory markers, cross match or group and save and blood cultures. Imaging including erect chest x ray where patient is peritonitic, abdominal xray and abdominal ultrasound.

Goldberg A, Stansby G, Surgical Talk- Surgery for Finals, Imperial College Press, London, 1999
Longmore M, Wilkinson IB, Davidson EH, Foulkes A, Mafi AR, Oxford Handbook of Clinical Medicine, 8th ed. Oxford University Press, Oxford, 2010.

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