What are the causes of paralytic ileus?

Causes of Paralytic Ileus

Paralytic ileus results from impaired intestinal motility due to postoperative status, opioid medications, electrolyte disturbances, neurological disorders, infections, and metabolic derangements, with postoperative ileus and opioid use being the two most common and clinically significant causes. 1

Postoperative Causes

Abdominal surgery is the leading cause of paralytic ileus, with severity directly correlating to the extent of intestinal manipulation during the procedure. 1, 2 The condition follows essentially any operation, though it is most extensive after colonic surgery. 2, 3

• Laparoscopic approaches produce less severe ileus compared to open surgical procedures, making surgical technique a modifiable risk factor. 1
• Fluid overload during perioperative management significantly worsens and prolongs postoperative ileus through intestinal edema formation. 1, 4
• Right colon surgery carries higher risk (odds ratio 2.180) compared to other intestinal locations. 5
• Postoperative ileus typically resolves spontaneously within 2-3 days, while paralytic ileus lasting more than 3 days represents a more severe form requiring intervention. 2, 3

Pharmacological Causes

Opioid medications are major contributors to paralytic ileus through direct inhibitory effects on intestinal motility via mu-opioid receptors in the enteric nervous system. 1, 4, 2

• Anticholinergic medications cause severe dysmotility and should be avoided in at-risk patients. 1, 6
• Other specific medications associated with paralytic ileus include clozapine, baclofen, buserelin, clonidine, fludarabine, phenytoin, verapamil, and vincristine. 1
• Pre-operative antithrombotic drugs increase risk (odds ratio 2.210). 5
• Pre-operative chemotherapy increases risk (odds ratio 2.530). 5

Neurological and Endocrine Causes

Disorders affecting parasympathetic or sympathetic innervation of the gut directly impair coordinated bowel motility. 1

• Diabetes mellitus is the most common endocrine cause through autonomic neuropathy affecting gut innervation. 1
• Brainstem lesions, spinal cord injury, multiple sclerosis, Parkinson's disease, myotonic dystrophy, and porphyria all disrupt neural control of intestinal motility. 1
• Inhibitory alpha-2 adrenergic reflexes with peptidergic afferents contribute to the pathophysiology. 3

Infectious and Inflammatory Causes

Sepsis and severe systemic inflammatory response trigger paralytic ileus through inflammatory mediator release. 1

• Peritonitis from any cause leads to paralytic ileus through local and systemic inflammatory effects. 1
• Specific infections include strongyloidiasis hyperinfection syndrome, herpes viruses, polyoma viruses, Chagas' disease, Lyme disease, and botulism. 1
• Clostridioides difficile infection can present with unexplained paralytic ileus, particularly in severe cases, and stool specimens may be tested via rectal swabs in this context. 7

Metabolic and Electrolyte Causes

Electrolyte abnormalities, particularly hypokalemia and hypomagnesemia, directly impair smooth muscle contractility and neural transmission. 1, 4

• Hypothyroidism leads to intestinal dysmotility through reduced metabolic activity affecting gut function. 1
• Correction of electrolyte imbalances is essential in both prevention and treatment. 2

Trauma and Mechanical Factors

Traumatic injury, particularly spinal trauma, commonly causes paralytic ileus in orthopedic patients. 8

• Lower extremity joint reconstruction carries risk, though the mechanism is less direct than abdominal surgery. 8
• Even minor orthopedic procedures can precipitate ileus in susceptible patients. 8

Critical Clinical Pitfalls

Severe postoperative complications of Clavien-Dindo grade ≥3 dramatically increase ileus risk (odds ratio 12.90), including infectious complications, pneumonia, intra-abdominal abscess, anastomotic leakage, and postoperative bleeding. 5 These complications create a vicious cycle where ileus worsens outcomes and complications worsen ileus, emphasizing the importance of preventing both the initial insult and secondary complications.