Abdomen Distension

Abdominal Distension in the ICU

DEFINITION

Abdominal distension refers to an abnormal increase in abdominal girth or tension, either:

• Visible (inspection)
• Palpable (tense abdomen)
• Measured (serial abdominal girth or rising intra-abdominal pressure)

It may be:

• Acute or chronic
• Localized or generalized
• Painful or painless
• Associated with organ dysfunction

Key ICU Principle

Any new or progressive abdominal distension in a critically ill patient must be assumed pathological until proven otherwise.

PATHOPHYSIOLOGICAL BASIS

From a critical care standpoint, abdominal distension results from one or more of the following fundamental mechanisms:

1. Intraluminal Accumulation

• Gas
• Fluid
• Feces

2. Extraluminal Fluid Accumulation

• Ascites
• Hemoperitoneum
• Pus (peritonitis)

3. Visceral Edema

• Bowel wall edema
• Mesenteric congestion

4. Mass Effect

• Tumors
• Organomegaly
• Cysts

5. Raised Intra-abdominal Pressure (IAP)

• Leading to abdominal compartment syndrome

ICU-SPECIFIC ETIOLOGICAL CLASSIFICATION

A. Gastrointestinal Causes

1. Paralytic (Adynamic) Ileus

• Most common cause in ICU
• Functional inhibition of peristalsis

Common ICU Triggers

• Sepsis and septic shock
• Electrolyte disturbances (↓ K⁺, ↓ Mg²⁺)
• Opioids, sedatives, anticholinergics
• Postoperative state
• Severe trauma
• Mechanical ventilation with high PEEP

Clinical Clues

• Uniform abdominal distension
• Absent or hypoactive bowel sounds
• Minimal pain
• No transition point on imaging

2. Mechanical Intestinal Obstruction

• Small bowel obstruction (SBO)
• Large bowel obstruction (LBO)

Etiologies

• Adhesions
• Hernia
• Volvulus (sigmoid, cecal)
• Malignancy
• Fecal impaction

Key Differentiation from Ileus 

3. Acute Colonic Pseudo-obstruction (Ogilvie’s Syndrome)

• Functional colonic dilation without mechanical blockage
• Common in:
  • ICU patients
  • Trauma
  • Post-operative states
  • Severe sepsis

Critical Risk

• Cecal diameter > 12 cm → perforation risk

4. Toxic Megacolon

• Fulminant colitis with systemic toxicity

Causes

• Clostridioides difficile infection
• Ulcerative colitis
• Ischemic colitis

Diagnostic Criteria (Harrison-Style)

• Colonic dilation > 6 cm plus
• Fever, tachycardia, leukocytosis, anemia, hypotension, AMS

B. Hepatology & Portal Hypertension

Massive Ascites

• Cirrhosis (most common)
• Acute liver failure
• Budd–Chiari syndrome
• Malignancy

ICU Relevance

• Respiratory compromise
• Reduced venous return
• Risk of spontaneous bacterial peritonitis (SBP)
• Precipitation of abdominal compartment syndrome

C. Vascular & Ischemic Causes

Acute Mesenteric Ischemia

• SMA embolism or thrombosis
• Non-occlusive mesenteric ischemia (NOMI)

Hallmark

Severe abdominal distension and pain disproportionate to physical findings

Often missed in ICU due to sedation.

D. Infectious Causes

• Secondary peritonitis
• Intra-abdominal abscess
• Tubercular peritonitis (important in India)
• Severe pancreatitis with third-spacing

E. Metabolic & Systemic Causes

• Severe hypoalbuminemia
• Capillary leak syndrome
• Massive fluid resuscitation
• Renal failure with volume overload

F. Iatrogenic & ICU-Related Causes

• Enteral feeding intolerance
• Aerophagia during NIV
• Excessive fluid resuscitation
• High PEEP ventilation
• Post-surgical bowel edema

ABDOMINAL COMPARTMENT SYNDROME (ACS)

Definition

• Sustained IAP ≥ 20 mmHg with new organ dysfunction

Causes

• Massive ascites
• Bowel edema
• Hemoperitoneum
• Retroperitoneal hematoma
• Severe pancreatitis

Physiological Consequences

• ↓ Venous return → ↓ Cardiac output
• ↑ Airway pressures → Hypoxemia
• ↓ Renal perfusion → Oliguria
• ↑ ICP via reduced venous drainage

CLINICAL ASSESSMENT IN ICU

1. Inspection

• Symmetry
• Tense or shiny abdomen
• Dilated veins
• Surgical scars

2. Palpation

• Tenderness (localized vs diffuse)
• Guarding / rigidity
• Organomegaly
• Ascitic thrill

3. Percussion

• Tympany → gas
• Shifting dullness → ascites

4. Auscultation

• Absent sounds → ileus
• High-pitched → obstruction

MONITORING & INVESTIGATIONS

Laboratory

• Electrolytes (K⁺, Mg²⁺)
• Lactate (ischemia)
• LFTs
• ABG (metabolic acidosis)
• Inflammatory markers

Radiology

Bedside Ultrasound

• Ascites
• Dilated bowel loops
• Free fluid
• Bladder volume

X-ray Abdomen

• Air-fluid levels
• Colonic dilation
• Coffee-bean sign (volvulus)

CT Abdomen (Gold Standard)

• Transition point
• Ischemia
• Pneumatosis intestinalis
• Portal venous gas
• Perforation

Intra-abdominal Pressure Monitoring

• Via bladder pressure
• Essential in:
  • Severe distension
  • Oliguria
  • Rising ventilatory pressures

MANAGEMENT PRINCIPLES (ICU-ORIENTED)

1. Immediate Stabilization

• ABC approach
• Nasogastric decompression
• Nil per oral (NPO)
• Correct electrolytes

2. Treat the Underlying Cause

3. Ventilatory Adjustments

• Reduce PEEP if possible
• Monitor plateau pressures
• Consider abdominal decompression before escalating ventilation

4. Nutrition Strategy

• Hold feeds in severe distension
• Prefer post-pyloric feeding
• Avoid overfeeding

PROGNOSTIC IMPLICATIONS

• Persistent distension → ↑ mortality
• Associated with:
  • Longer ICU stay
  • Ventilator dependence
  • Renal failure
  • Sepsis