I. Clinical Assessment

Early bedside evaluation differentiates functional from mechanical obstruction and identifies patients at risk for ischemia or perforation.

A. Abdominal Distension

• Serial girth measurements at umbilicus with tape measure.
• Radiographic cecal diameter ≥10 cm confirms Acute Intestinal Pseudo-obstruction (AIPO); >12 cm signals high risk of ischemia/perforation.

B. Pain Characteristics

• Diffuse, mild-to-moderate discomfort in ileus/AIPO vs severe colicky pain in mechanical obstruction.
• Absence of rebound or guarding is reassuring; peritoneal signs require urgent surgical evaluation.

C. Gastrointestinal Symptoms

• Nausea, vomiting common—especially with small-bowel involvement.
• Feeding intolerance (high gastric residuals) is an early red flag.

D. Bowel Sounds

• Hypoactive or absent in adynamic ileus/AIPO.
• High-pitched tinkling suggests mechanical obstruction.

E. Systemic Signs

• Fever, tachycardia, hypotension indicate possible ischemia, sepsis, or perforation.

II. Laboratory Evaluation

Labs identify reversible metabolic drivers of ileus and detect complications such as ischemia.

III. Imaging Modalities

Radiographic studies confirm diagnosis, distinguish functional vs mechanical causes, and assess for complications.

A. Plain Abdominal Radiography

• Diffuse gas in small and large bowel; multiple air–fluid levels.
• No clear transition point in ileus/AIPO.
• Limitation: low sensitivity for partial or early obstruction.

B. Computed Tomography (CT)

• Gold standard: identifies dilation patterns, transition zones, and etiology.
• Signs of ischemia: pneumatosis intestinalis, mesenteric fat stranding, portomesenteric gas.
• IV contrast essential for vascular assessment; beware in renal impairment.

C. Contrast Studies and Endoscopic Assessment

• Water-soluble contrast enema:
  • Excludes distal mechanical obstruction in AIPO.
  • May provoke colonic motility (therapeutic effect).
• Diagnostic endoscopy:
  • Reserved when imaging is equivocal or for therapeutic decompression.
  • Risk of perforation in massively dilated or ischemic bowel.

IV. Differential Diagnosis vs Mechanical Obstruction

Key clinical and radiographic features guide differentiation and trigger surgical consultation.

A. Clinical Red Flags for Mechanical Obstruction

• Localized tenderness, peritoneal signs, severe colicky pain.

B. Radiographic Clues for Mechanical Obstruction

• Abrupt transition point or closed-loop obstruction on CT/X-ray.

C. Indications for Early Surgical Consultation

• Peritonitis, free air, signs of ischemia.
• Cecal diameter >12 cm, persistent pain/distension despite 24–72 h of conservative care.

V. Risk Stratification and Severity Classification

Stratify patients by colonic diameter, symptom duration, and comorbidities to guide monitoring and urgency.

A. Ogilvie’s Syndrome Classification

• Cecal diameter ≥10 cm diagnostic.
• Cecal diameter >12 cm or duration >6 days warrants urgent intervention.

B. Risk Factors for Poor Outcome

• Advanced age.
• Cardiac/pulmonary comorbidities.
• Electrolyte derangements.
• Lactate elevation.

C. Monitoring and Escalation

• High-risk patients: Hourly vital signs and girth measurements, labs every 6–12 hours, consider early promotility or decompression.

VI. Initial Management Pathway

A stepwise algorithm balances conservative measures with timely escalation to pharmacologic or endoscopic therapy.

VII. Pearls, Pitfalls, and Practice Considerations

A. General Pearls & Pitfalls

• Avoid overreliance on auscultation; integrate physical exam findings with imaging and laboratory results.
• Minimize delays in obtaining CT imaging for deteriorating patients or when the diagnosis is uncertain.

B. Role of the Pharmacist

• Identify and recommend discontinuation or modification of medications that impair gastrointestinal motility (e.g., opioids, anticholinergics, calcium channel blockers).
• Guide electrolyte repletion protocols to ensure adequate correction of potassium and magnesium.
• Advise on appropriate dosing and administration of promotility agents like neostigmine, including necessary precautions (e.g., atropine availability).
• Facilitate interprofessional communication regarding medication management and contribute to rapid escalation of care discussions.

C. Practice Considerations

• Develop and implement standardized order-set bundles for electrolyte repletion in patients with ileus or AIPO.
• Embed criteria for neostigmine administration (including contraindications and monitoring parameters) into ICU and relevant ward pathways or protocols.
• Conduct regular audits of time-to-imaging and time-to-decompression interventions to identify areas for quality improvement.