The Acute Abdomen

Introduction

The acute abdomen refers to the rapid onset of severe symptoms of abdominal pathology, which may require surgical intervention.¹

Typically, patients present with abdominal pain. Prompt assessment, taking account of the broad differential diagnoses, is required to identify those patients with immediately life-threatening causes.

Aetiology

The differential diagnoses of an acute abdomen are broad and can be classified according to organ system or anatomical location in the abdomen.

Surgical causes

Table 1. Surgical differential diagnoses of an acute abdomen.²

Medical causes

There are also numerous medical differentials of an acute abdomen, including:

• Myocardial infarction
• Spontaneous bacterial peritonitis
• Colitis (inflammatory or infective)
• Diabetic ketoacidosis
• Pyelonephritis
• Acute urinary retention
• Constipation
• Gastroenteritis

Clinical features

Patients with an acute abdomen may be clinically unstable.

In this case, a focused history and clinical examination should be performed concurrently with initial resuscitation. Comprehensive history taking may have to wait until the patient is more stable.

History

Typical symptoms of an acute abdomen include:

• Severe abdominal pain: often sudden onset, may be localised or diffuse
• Nausea and vomiting
• Change to bowel habit: diarrhoea or constipation/obstipation

Other important areas to cover in the history include:

• Urinary and gynaecological symptoms: dysuria, haematuria, vaginal bleeding or discharge
• Type and time of last meal
• Past medical and surgical history
• Last menstrual period: in women of reproductive age
• Medication use: anticoagulants, corticosteroids, regular non-steroidal anti-inflammatory drugs, immunosuppressants
• Social history: alcohol, smoking
• Family history

Maintain a high index of suspicion for serious pathology in older or immunocompromised patients. These patients are more likely to present with vague or non-specific signs and symptoms despite serious disease.³

Clinical examination

Clinical findings on abdominal examination may include:

• Abdominal tenderness: localised or diffuse
• Peritoneal signs: guarding or rigidity, percussion tenderness, pain on coughing, patient lying very still
• Abdominal distension
• Altered bowel sounds: hyperactive (early bowel obstruction), reduced or absent (late bowel obstruction, bowel perforation)
• Irreducible hernia
• Surgical scars: possible adhesions

Other relevant clinical examinations may include:

• PR examination: blood (fresh or black tar-like (melaena)), faecal impaction, tumour
• Testicular examination: swollen, tender, high-riding testicle in testicular torsion, which may present as lower abdominal pain
• Pelvic examination: performed if gynaecological pathology is suspected

Investigations

Bedside investigations

Relevant bedside investigations include:

• Basic observations (vital signs)
• Urinalysis: to identify urinary tract infection or isolated haematuria suggestive of a kidney stone
• Urine β-hCG: to identify undiagnosed intrauterine or ectopic pregnancy
• ECG: to identify myocardial infarction in patients with epigastric pain or atrial fibrillation as a risk factor for mesenteric ischaemia

Laboratory investigations

Relevant laboratory investigations include:

• Full blood count: raised white cell count in infection, low haemoglobin suggestive of blood loss
• Urea & electrolytes: acute kidney injury with vomiting and dehydration or obstructive urinary pathology (e.g. ureteric stone); deranged electrolytes with vomiting and dehydration
• CRP: a non-specific marker of inflammation
• Liver function tests: obstructive picture with obstructing gallstone or cholangitis
• Amylase: significantly raised in pancreatitis (more than three times the upper limit of normal), moderately raised in other acute pathology such as ectopic pregnancy, bowel obstruction or perforation
• Coagulation studies: may be deranged in liver pathology, pre-operative
• Group & save: pre-operative

Imaging

The choice of initial imaging modality is guided by clinical status and the working diagnosis based on history, examination and bedside/laboratory investigations. Rarely, patients may be taken to surgery without definitive imaging if there is a high clinical suspicion of intra-abdominal catastrophe.

CT of the abdomen & pelvis with IV contrast is the imaging of choice in patients who are critically unwell and can diagnose most causes of the acute abdomen.

In stable patients, certain diagnoses are best investigated with alternative imaging modalities.

Table 2. Preferred imaging modality according to suspected diagnosis.

In pregnant women with acute abdominal pain, ultrasound and/or MRI abdomen & pelvis are the preferred first-line imaging modalities to avoid foetal radiation exposure. 

Plain X-rays are less useful in diagnosing acute surgical pathology but may be performed as screening tools:

• Erect chest X-ray: free air under diaphragm suggestive of bowel perforation
• Abdominal X-ray: dilated bowel loops suggestive of obstruction

Management

Initial management

In critically unwell patients, initial management and evaluation should occur concurrently and assessing doctors should have a low threshold for involving HDU/ICU.

Rapidly identifying patients with a true acute abdomen or other surgical emergencies (e.g. testicular torsion) is essential to facilitate early referral to the appropriate team.

Initial management consists of:

• ABCDE approach
• Nil-by-mouth (NBM): pre-operative or bowel rest in obstruction
• Intravenous fluids: replace losses associated with vomiting and sepsis
• Broad-spectrum antibiotics: according to local guidelines
• Analgesia
• Anti-emetics
• Nasogastric tube (NGT): if significant vomiting
• Urinary catheter: in acute urinary retention and/or to monitor fluid balance

Definitive management

Definitive treatment (surgery or otherwise) depends on the underlying diagnosis and patient comorbidities.

Where surgery is required, there should be shared decision-making between the patient (if they are able), next-of-kin, surgical team and intensive care. This ensures care is in line with the patient’s wishes and/or best interests and establishes an appropriate ceiling of care and resuscitation status, particularly in elderly patients or those with multiple comorbidities.

 If a patient declines or is not suitable for surgery, management is with palliation and effective symptom control.

Reviewer

Mr Oddai Alkhazaaleh

Consultant General and Upper GI Surgeon

Editor

Dr Chris Jefferies

References 

1. BMJ Best Practice. Assessment of acute abdomen. Published in 2023. Available from: [LINK]
2. Oxford Textbook of Medicine. Chapter 15.4.1 The acute abdomen. Published in 2020. Available from: [LINK]
3. Patient Info. Acute Abdomen. Published in 2019. Available from: [LINK]