Obstruction syndrome – Ileus: definition, causes, diagnosis, classification, complications and treatment. Paralytic and spastic ileus
DEFINITION AND CLASSIFICATION
Ileus is failure of intestinal contents to pass normally through the bowel. Mechanical obstruction results from a physical barrier; functional (adynamic) ileus results from impaired motility without a fixed obstructing lesion. Mechanical obstruction may be small- or large-bowel, partial or complete, simple or strangulated, and acute or chronic. Functional ileus is commonly paralytic; spastic ileus is uncommon and results from sustained segmental contraction.
AETIOLOGY
Small-bowel mechanical causes include postoperative adhesions (a leading cause), external hernias, Crohn-related strictures, tumours, intussusception, volvulus and gallstone ileus. Large-bowel causes include colorectal carcinoma, diverticular stricture, volvulus and faecal impaction. Paralytic ileus follows abdominal surgery, peritonitis, sepsis, trauma, retroperitoneal disease, pancreatitis, electrolyte disturbance (especially hypokalaemia), opioids and anticholinergic drugs. Spastic ileus may occur with lead poisoning, porphyria or severe intestinal irritation.
PATHOPHYSIOLOGY
Proximal to a mechanical blockage, swallowed air and intestinal secretions accumulate, causing distension, vomiting and fluid sequestration. Increased intraluminal pressure first impairs venous and lymphatic drainage, then arterial perfusion, leading to oedema, ischaemia, bacterial translocation, necrosis and perforation. A closed-loop obstruction traps a bowel segment at two points and carries a particularly high strangulation risk. In paralytic ileus, absent coordinated peristalsis causes diffuse dilatation; fluid and gas accumulate without a transition point.
CLINICAL FEATURES AND EXAMINATION
Mechanical obstruction classically causes colicky abdominal pain, vomiting, distension and absolute constipation/obstipation. Vomiting tends to occur earlier in proximal obstruction; distension and constipation are more prominent in distal obstruction. High-pitched rushes or tinkling sounds may occur early, while late obstruction or ischaemia may produce quiet bowel sounds. Paralytic ileus causes diffuse distension, nausea, vomiting and reduced or absent bowel sounds, often after surgery. Fever, tachycardia, continuous pain, guarding, rebound, shock or metabolic acidosis suggest strangulation, ischaemia or perforation. Examine all hernial orifices and perform rectal examination when indicated.
INVESTIGATIONS AND DIFFERENTIAL
Assess FBC, electrolytes, urea/creatinine, CRP, venous blood gas and lactate; crossmatch if surgery is likely. Plain abdominal radiographs may show dilated small-bowel loops with valvulae conniventes, multiple air-fluid levels, or colonic dilatation. Contrast-enhanced CT abdomen/pelvis is the preferred investigation in most adults: it identifies the transition point, cause, closed loop, free fluid, pneumatosis, reduced enhancement and perforation. Consider constipation, gastroenteritis, mesenteric ischaemia, pseudo-obstruction, pancreatitis and metabolic causes.