An acute abdomen refers to a recent, rapid onset of urgent abdominal or pelvic pathology, usually presenting with abdominal pain. This is a common presentation and has a wide variety of causes.
Differential Diagnoses of Acute Abdominal Pain
It may be helpful to think of the causes as being related to pathology in the organs located in the area of the pain. Bear in mind the pain may not always be localised in the typical area, so keep an open mind for other possible differentials. This list is not exhaustive, and always keep your mind open to other possible differentials.
Generalised abdominal pain:
- Peritonitis
- Ruptured abdominal aortic aneurysm
- Intestinal obstruction
- Ischaemic colitis
Right upper quadrant pain:
- Biliary colic
- Acute cholecystitis
- Acute cholangitis
Epigastric pain:
- Acute gastritis
- Peptic ulcer disease
- Pancreatitis
- Ruptured abdominal aortic aneurysm
Central abdominal pain:
- Ruptured abdominal aortic aneurysm
- Intestinal obstruction
- Ischaemic colitis
- Early stages of appendicitis
Right iliac fossa pain:
- Acute appendicitis
- Ectopic pregnancy
- Ruptured ovarian cyst
- Ovarian torsion
- Meckel’s diverticulitis
Left iliac fossa pain:
- Diverticulitis
- Ectopic pregnancy
- Ruptured ovarian cyst
- Ovarian torsion
Suprapubic pain:
- Lower urinary tract infection
- Acute urinary retention
- Pelvic inflammatory disease
- Prostatitis
Loin to groin pain:
- Renal colic (kidney stones)
- Ruptured abdominal aortic aneurysm
- Pyelonephritis
Testicular pain:
- Testicular torsion
- Epididymo-orchitis
Peritonitis
Peritonitis refers to inflammation of the peritoneum, the lining of the abdomen. The signs of peritonitis are:
- Guarding – involuntary tensing of the abdominal wall muscles when palpated to protect the painful area below
- Rigidity – involuntary persistent tightness / tensing of the abdominal wall muscles
- Rebound tenderness – rapidly releasing pressure on the abdomen creates worse pain than the pressure itself
- Coughing test – asking the patient to cough to see if it results in pain in the abdomen
- Percussion tenderness – pain and tenderness when percussing the abdomen
Localised peritonitis is caused by underlying organ inflammation, for example, appendicitis or cholecystitis.
Generalised peritonitis may be caused by perforation of an abdominal organ (e.g., perforated duodenal ulcer or ruptured appendix) releasing the contents into the peritoneal cavity and causing generalised inflammation of the peritoneum.
Spontaneous bacterial peritonitis is associated with spontaneous infection of ascites in patients with liver disease. This is treated with broad-spectrum antibiotics and carries a poor prognosis.
Initial Assessment
Initial assessment of an acutely unwell patient is with an ABCDE approach, assessing and treating:
- A – Airway: Ensure the patient’s airway is patent and secure.
- B – Breathing: Assess the breathing, respiratory rate and oxygen saturations. Listen to the lungs. Provide oxygen if required.
- C – Circulation: Assess the blood pressure, heart rate, heart sounds and perfusion (e.g., capillary refill time). Gain IV access (wide-bore cannulae are better), take bloods and provide an IV bolus of fluid if required.
- D – Disability: Assess the consciousness level using AVPU or GCS scoring systems. Check the blood glucose level.
- E – Exposure: Finish the full assessment, including examination of the abdomen.
TOM TIP: When asked “how would you manage this acute presentation?” in an exam or teaching session, the obvious and easy answer to start with is “I would start with an ABCDE approach”. This is a good answer because it shows you are considering the immediate assessment and stabilisation of the unwell patient ahead of jumping to more definitive management that would come after the initial assessment (such as “I would perform an immediate right hemicolectomy”). It is not such a good answer for patients that are not acutely unwell, so don’t use it in these scenarios, for example, if a GP supervisor asked how you would manage a patient presenting with a patch of psoriasis.
Investigations
The following investigations are useful for obtaining a diagnosis and preparing the patient for theatre.
Full blood count (FBC) gives an indication of bleeding (drop in Hb) and infection / inflammation (raised WBC).
Urea and electrolytes (U&Es) give an indication of electrolyte imbalance and kidney function (useful prior to CT scans, as they require a contrast injection that can damage kidneys).
Liver function tests (LFTs) give an indication of the state of the biliary and hepatic system.
C-reative protein (CRP) gives an indication of inflammation and infection.
Amylase gives an indication of inflammation of the pancreas in acute pancreatitis.
International normalised ratio (INR) gives an indication of the synthetic function of the liver and is essential in establishing their coagulation prior to procedures.
Serum calcium is required to score acute pancreatitis and for other reasons (e.g., clotting and cardiac function).
Serum human chorionic gonadotropin (hCG) or urine pregnancy test is essential in females of child bearing age.
Arterial blood gas (ABG) analysis will show the lactate (an indication of tissue ischaemia) and pO2 (used for scoring in acute pancreatitis).
Serum lactate gives an indication of tissue ischaemia. It is a product of anaerobic respiration and can also be raised in dehydration or hypoxia. Lactate is also available on an ABG result as mentioned above.
Group and save is essential prior to theatre in case the patient requires a blood transfusion.
Blood cultures if infection is suspected.
Abdominal x-ray can provide evidence of bowel obstruction by showing dilated bowel loops.
Erect chest x-ray can demonstrate air under the diaphragm when there is an intra-abdominal perforation. This is caused by air within the peritoneal cavity (pneumoperitoneum).
Abdominal ultrasound can be useful in checking for gallstones, biliary duct dilatation and gynaecological pathology.
CT scans are often required to identify the cause of an acute abdomen and determine correct management.
Management
Initial management involves:
- ABCDE assessment
- Alert seniors of unwell patients: escalating to the registrar, consultant and critical care as required
- Nil by mouth if surgery may be required or they have features of bowel obstruction
- NG tube in cases of bowel obstruction
- IV fluids if required for resuscitation or maintenance
- IV antibiotics if infection is suspected
- Analgesia as required for pain management
- Arranging investigations as required (e.g., bloods, group and save and scans)
- Venous thromboembolism risk assessment and prescription if indicated
- Prescribing regular medication on the drug chart if they are being admitted (some may need to be withheld)
Patients being admitted to an acute surgical unit will usually be seen by a junior doctor, then reviewed by the surgical registrar if required. A consultant will then review that patient on the post-take ward round, creating a management plan that is then carried out by the junior doctors. This may involve further investigations, preparations for surgery or discharge depending on the presentation.
Further management steps if the patient requires surgery:
- Taking consent for surgery (by someone suitably qualified)
- Review by an anaesthetist
- Putting on the theatre list
- Crossmatch units of blood if required
Last updated May 2021