Clinical Review - Acute abdomen

Contributed by Miss Sophie-Anne Welchman, specialist registrar, Derriford Hospital, Devon.

Abdominal wall hernia (red): palpate the hernial orifices
Abdominal wall hernia (red): palpate the hernial orifices

Section 1: Epidemiology and aetiology
The 'acute abdomen' is a term commonly heard in referral conversations between primary and secondary care. Unfortunately it is often misinterpreted and can lead to confusion.

Abdominal pain
Most doctors use the term to refer to the sudden onset of abdominal pain. A more accu-rate definition is the sudden onset of abdominal symptoms within the last 24 hours, presenting as a single episode.

The key point is that although pain is the most common complaint, it is not the only symptom of an acute abdomen.

We often use this term to describe a patient presenting with severe symptoms and to show our concern that this represents an intra-abdominal catastrophe in patients where the exact aetiology is not immediately obvious.

Patients with an acute abdomen present a significant problem - the proximity of intra- abdominal organs, complicated embryological origins and referred pain characteristics make diagnosis difficult.

In general practice, the key is to identify patients with severe and acute intra-abdominal pathology and choose the most appropriate admitting team.

The focus of this review will be on the presentation, differential diagnosis and management of this group of patients.

Clinical picture
Acute abdominal pain is estimated to be the third most common presenting complaint in the emergency department, with many patients having been seen in the first instance in general practice.

How many of these patients have an acute abdomen is difficult to assess, however this symptom complex creates significant workload in primary and secondary care.

Much of doctors' concerns about the acute abdomen arises from the variety in severity of symptoms and pathology resulting in a similar clinical picture.

In primary care, the first decision is about the need for admission and the second is to which specialty the patient is directed. As such, it is useful to divide causes by system.

A more traditional way to classify this variety of conditions is by the site of maximal pain or clinical signs - with a cautionary note that in more advanced presentations of obstructive, inflammatory or infective processes this technique loses its sensitivity. Medical causes of the acute abdomen are hard to diagnose using this approach as the pain is often vague or migratory.

The most common medical causes that present in this way are inferior MI, lower lobe pneumonia, pulmonary embolus, pyelonephritis, hepatic failure and diabetic complications.

Less common, but important in some demographic groups, are sickle cell anaemia, spontaneous bacterial peritonitis, HIV seroconversion illness, acute porphyrias and poisoning with toxins including heavy metals.

Section 2: Making the diagnosis
The safest approach in the earliest stage of managing the acute abdomen is to begin by considering the most life-threatening causes and directing the clinical assessment to exclude these.

Emergency transfer
The detail of the history taken depends on the severity of the patient's illness.

For patients who are clinically unstable and obviously need emergency transfer to a hospital it is clearly inappropriate to spend time asking questions that will no doubt be revisited on arrival in hospital (at least until basic resuscitation steps have been taken and transfer arrangements made).

History of symptoms
A detailed past medical and surgical history often holds the key to diagnosis.

Explore the risk of a pathology such as glandular fever or splenic rupture or a complication of an existing condition (small bowel obstruction secondary to known hernia) or its treatment (steroids and peptic ulcer disease).

In female patients, a gynaecological and sexual history is crucial, including sexual activity and contraceptive methods used - with particular attention to possibility of pregnancy and the use of intrauterine devices.

Details of onset of pain, site, change in location since onset and nature are useful in narrowing the differential diagnosis.

  • Pathologies with sudden onset are usually caused by a vascular accident (dissection, bleeding or infarction) or perforation of a viscus.
  • The migration of pain from the periumbilical region to the right iliac fossa is classically used to describe the movement of pain in acute appendicitis. This process occurs in many other intra-abdominal conditions as the overlying peritoneum is involved. Pain also moves when obstructing or inflammatory conditions result in perforation - at the point of perforation pain may initially ease and then become more generalised as air, fluid or pus spread through the abdominal cavity.
  • It is often difficult for patients to describe the nature of their pain. Colicky abdominal pain (coming and going in waves lasting only seconds to minutes) arises in hollow organs due to peristalsis. Waves of pain lasting 10-20 minutes are more commonly caused by obstruction of the biliary tree.
  • The radiation of pain is a relatively blunt diagnostic question. Pain arising from the pancreas or abdominal aorta commonly radiates to the back but this should not be used as a rule.

Assessment
Details of symptoms associated with the pain and their temporal relationship to the pain is very useful.

This is a way of distinguishing between a process that has been developing over a number of days, weeks or years or one that has arisen unexpectedly.

Some associated symptoms reflect local processes (haematemesis, dysuria, faeculent vomit, absolute constipation), while others are markers of systemic upset (anorexia and weight loss over the preceding six to 12 months is useful when considering acute presentations of neoplastic disease).

Vomiting is a symptom that can reflect both local and systemic upset as it can be due to local pathology but is also a common response to severe pain, anxiety or analgesia.

Associated symptoms are a useful means of highlighting medical causes of abdominal pain, for example rashes, neurological or respiratory symptoms are most often caused by systemic conditions that are best directed to the care of physicians.

Any history of syncope should raise suspicion of ruptured aortic aneurysm.

Causes of acute abdomen: A system-based approach
Extra-abdominal cause
Cardiac
  • MI
  • Arrhythmia
  • Congestive cardiac failure

Respiratory

  • Pulmonary embolus
  • Pneumonia

Others

  • Shingles
  • Sickle cell crisis
  • Rectus sheath haematoma
  • Diabetic complications
  • Spontaneous bacterial peritonitis
  • Prophyria
  • Toxins eg heavy metal poisoning

Oesophago-gastric causes

  • Peptic ulcer disease and its complications
  • Gastritis
  • Perforated oesophagus

Hepato-biliary causes

  • Hepatitis
  • Cholecystitis
  • Acute pancreatitis
  • Cholangitis

Bowel causes

  • Appendicitis
  • Mesenteric adenitis
  • Meckel's diverticulitis
  • Sigmoid/caecal diverticulitis
  • Intestinal obstruction
  • Hernial obstruction/strangulation
  • Inflammatory bowel disease

Vascular causes

  • Ruptured abdominal aortic aneurysm
  • Mesenteric ischaemia
  • Aortic dissection
  • Haemorrhage from solid organs eg spleen

Genito-urinary causes
Male

  • Testicular torsion
  • Renal colic

Female

  • Acute urinary retention
  • Ovarian cyst accident
  • Ectopic pregnancy
  • Pelvic inflammatory disease (salpingitis, tubo-ovarian abscess)
  • UTI/pyelonephritis
  • Mittelsmertz pain
  • Renal colic

Section 3: Clinical examination
As with all presentations the clinical examination should begin by looking at the patient. Do they look ill? Are they moving with difficulty, lying still (peritonitic) or are they rolling around the bed (renal colic)?

Respiratory rate is a sensitive marker of systemic upset, equally useful in this group of patients is their breathing pattern. Patients with generalised peritonitis or subphrenic pathology take shallow breaths due to pain.

Abdominal distension
Any signs of chronic ill-health, including cachexia or anaemia, may suggest an acute-on-chronic presentation. Abdominal distension is the most common abdominal finding in patients with an acute abdomen.

This may be due to large or small bowel obstruction, a large mass lesion or ascites. It is rare to detect Cullen's or Grey-Turner's sign in primary care as these indicate advanced necrotising pancreatitis.

Gentle palpation can help to localise the site of maximal tenderness in patients who present with generalised pain. Rebound in the early stages of disease, and later, guarding suggest peritoneal involvement.

If a mass is detected, the relationship of the lesion to nearby organs should be considered. Specific examination of the abdominal aorta for both size and tenderness is important when considering rupture of the abdominal aorta.

It is vital to palpate the hernial orifices as part of the abdominal examination as occult hernias are a common cause of bowel obstruction or severe pain when strangulated. It is also important to examine the testicles in male patients as testicular torsion may present as acute abdominal pain and vomiting in a proportion of patients.

For patients with upper abdominal pain, both cardiac and respiratory conditions should be considered and examined. Bedside assessment of respiratory rate, heart rate, BP and temperature are useful in the assessment of severity.

Urine test
The first and most important investigation in females of child bearing age is a urine pregnancy test. Ectopic pregnancy is a life-threatening emergency that commonly presents as an acute abdomen.

Making this diagnosis at the earliest stage possible allows immediate contact with the gynaecological team.

Urine tests are also useful to detect UTI, pyelonephritis or renal tract calculi, which can easily mimic catastropic intra-abdominal injury.

However, it must be kept in mind that a urine dip which is positive for leukocytes can represent all manner of inflammatory processes that involve or abut the ureter or bladder, and that the presence of UTI may be a concommitant problem.

Urine tests may also be useful in detecting diabetic complications that may be the cause of the acute abdomen or a complication of it, such as ketoacidosis in type-1 diabetics and hyperosmolar non-ketotic hyperglycaemic states in type-2 patients.

Analgesia
It has been traditional practice to withhold analgesia from patients with abdominal pain until they have been reviewed by a senior surgeon.

A Cochrane review of this issue supported the use of analgesia before assessment as opiate analgesia has no impact on the diagnostic accuracy of any later assessment.

Section 4: Management
The list of causes of the acute abdomen is so extensive it is not possible to discuss specific management plans or guidelines. The prognosis is also heavily dependent on the aetiology and patient group.

The presentation of the acute abdomen often represents an intra-abdominal catastrophe, which carries significant morbidity and mortality.

Elongated appendix: appendicitis is a cause to consider

Additional difficulties
The elderly, children and women in the third trimester of pregnancy present additional difficulties in diagnosis.

This can be due to communication issues, differences in sensory perception of pain, incidence of disease and altered anatomy. These groups should be approached with extra caution and early referral to secondary care considered.

The details of additional considerations in the paediatric population have not been addressed in this review (see resources).

Conclusion
The acute abdomen is a broad term that describes a plethora of pathologies that present with a narrow spectrum of symptoms.

As such, the assessment of these patients depends on careful history taking and examination and clinical experience.

By forming a list of differential diagnoses, the decision to admit these patients or manage them in the community or the outpatient setting can be made after consideration of the severity of the clinical picture and potential for deterioration.

Mistakes in the assessment of the acute abdomen include underestimation of the severity, late referral to specialist care or the failure to consider extra-abdominal causes.

Resources

Reference

1. Manterolac C, Astudillo P, Losado H et al. Analgesia in patients with acute abdominal pain. Cochrane Database Syst Reveiew 2007; 3: CD005660.

Further reading

  • Cartwright SL, Knudson MP. Evaluation of acute abdominal pain in adults. Am Fam Physician 2008; 77(7): 971-8.
  • Klein MD. Clinical approach to a child with abdominal pain who might have appendicitis. Pediatr Radiol 2007; 37(1): 11-4.
  • Bundy DG, Byerley JS, Liles EA, Perrin EM, Katznelson J, Rice HE. Does this child have appendicitis? JAMA 2007; 298(4): 438-51.

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