Paralytic ileus (also called functional bowel obstruction) is the interruption of the normal passage of bowel contents due to reduced peristalsis in the absence of a mechanical obstruction. It is often transient. Postoperative ileus is one of the most common causes of paralytic ileus. Other etiologies include inflammation of abdominal, pelvic, or retroperitoneal viscera, metabolic disturbances, certain medications, and mesenteric ischemia. Paralytic ileus typically manifests with nausea, vomiting, abdominal pain, abdominal distention, and constipation; bowel sounds are often absent on auscultation. Bowel distention, if present, leads to third-space volume loss, resulting in dehydration and electrolyte abnormalities. Ileus is generally a clinical diagnosis. Imaging may be required to evaluate for the underlying diagnosis and to rule out and complications. The characteristic imaging feature of paralytic ileus is diffuse dilatation of bowel loops with no transition point. Laboratory studies can be useful to identify the underlying cause and/or to assess for complications. Apart from treating the underlying cause, there are few specific treatment measures for paralytic ileus. Management is mainly supportive, involving IV fluid resuscitation, electrolyte repletion, and bowel rest. Surgical intervention is only indicated if necessary for the underlying cause (e.g., acute complicated appendicitis) or if complications arise. Complications such as intestinal ischemia and perforation are rare in paralytic ileus.
Acute colonic pseudoobstruction, also known as Ogilvie syndrome, is a distinct clinical entity that typically affects critically ill or postoperative patients. Like paralytic ileus, there is no mechanical obstruction to the passage of bowel contents. However, the risk of severe colonic dilation with potential perforation and ischemia is significant. For management of this condition, see “Ogilvie syndrome.”
- Intraabdominal; or retroperitoneal surgery (e.g. spinal or pelvic surgery) 
- Inflammation of intraabdominal; , pelvic, or retroperitoneal organs (e.g., appendicitis, cholecystitis, pancreatitis, severe gastroenteritis); with or without peritonitis
- Abdominal; or retroperitoneal trauma (e.g., retroperitoneal hemorrhage)
- Medications (e.g., anticholinergics, opioids, tricyclic antidepressants, vincristine) 
- Endocrine or metabolic abnormalities (e.g., hypothyroidism; , hyperparathyroidism, porphyria, uremia, severe hyperglycemia) 
- Electrolyte disturbances (e.g., hypokalemia, hypomagnesemia, hyponatremia)
- Neuropathy (e.g., diabetes mellitus, spinal injury)
- Vascular diseases (e.g., mesenteric ischemia)
- Irritation of the bowel (e.g., intraoperative manipulation) and/or inflammation (e.g., peritonitis) causing:
- Decreased/arrested peristalsis; leads to the stasis of luminal contents and gas and bowel wall distention.
- In some cases, the pathophysiological consequences of this are similar to those of mechanical bowel obstruction (see “Pathophysiology” in “”).
- Examination findings
- Paralytic ileus, including postoperative ileus, is primarily a clinical diagnosis based on patient history, symptoms, and physical examination.
- Abdominal imaging is often necessary to rule out differential diagnoses (see “ ”).
- Imaging and laboratory studies can help identify the underlying cause and/or complications.
- For a comprehensive overview of the diagnostic modalities, see “ .”
Paralytic ileus must be differentiated from diagnoses that require surgical intervention.
Diagnostic studies are not generally required for early postoperative ileus. However, the possibility of early postoperative obstruction or abdominal infection should always be considered. 
- Imaging is not routinely required to confirm paralytic ileus, especially when the underlying cause is known (e.g., early postoperative ileus).
- Consider imaging in the following instances.
Abdominal ultrasound 
- Indication: commonly performed as an initial test in patients with abdominal pain 
X-ray abdomen 
- Indication: commonly performed as the initial imaging modality in patients with abdominal pain and/or suspected ileus 
- Findings 
CT abdomen and pelvis with or without IV contrast 
- Gold standard for the evaluation of suspected bowel obstruction 
- To diagnose the underlying pathology (e.g., suspected intraabdominal infection)
Laboratory studies 
Laboratory studies are primarily indicated to investigate the underlying cause of paralytic ileus and assess for dehydration and metabolic imbalances secondary to diffuse bowel distension and third-spacing.
Routine workup 
- Blood lactate level: Elevation may indicate ischemia or sepsis.
- Blood gas analysis
- (see “”)
- Other nonobstructive bowel disorders, e.g.:
The differential diagnoses listed here are not exhaustive.
General principles 
- Evidence-based recommendations for the management of paralytic ileus are scarce.
- Management is mainly conservative and includes symptomatic treatment, IV fluids, and bowel rest.
- Surgery is typically not indicated unless the underlying cause necessitates surgical intervention (e.g., appendicitis, gallstone pancreatitis).
- The underlying cause should be evaluated for and managed appropriately.
- For postoperative ileus, preventative measures are paramount.
Conservative management 
Initial measures for all patients 
- Initial bowel rest () 
- Symptomatic treatment
- , if tolerated, or , ideally nonopioids
- Oral antiemetics, if tolerated, or parenteral
- Stop or decrease causative medications, if possible (e.g., opioids, iron, antidiarrheal medication).
- Nutritional management
- Nasogastric tube insertion 
- Serial abdominal examinations
- Fluid balance (input and output chart) including nasogastric tube output
- Bowel movements (i.e., the passage of flatus and feces and auscultation of bowel sounds)
- Obtain surgical consult for nonresolution of ileus, worsening of symptoms, or development of signs of peritonitis
- Additional pharmacological options (not routinely recommended; consider only after mechanical bowel obstruction has been definitively ruled out) 
Treatment of opioid-induced ileus 
- Consider the addition of peripherally-acting μ-opioid receptor antagonists.
- See “ ” for drug recommendations and dosages.
Improvement of symptoms and tolerance of enteral feeding are better predictors of the normalization of gastrointestinal motility than successful bowel movements. 
- Indications: not routinely indicated, except in the following situations
- Treatment of the underlying cause, e.g.,
- Treatment of complications, e.g., ileus) or perforation (rare in paralytic
Acute management checklist
- Consider nasogastric tube insertion (e.g., in patients with recurrent vomiting).
- Initiate IV fluid resuscitation.
- Administer supportive care as needed (e.g., analgesics, antiemetics).
- Consider imaging to identify the underlying etiology or rule out mechanical bowel obstruction and Ogilvie syndrome.
- Urgent surgical consult if there is a concern for mechanical obstruction, complications, or an underlying condition that may necessitate urgent surgery.
- Evaluate for and treat the underlying cause.
- Serial abdominal examinations.
- Postoperative ileus (physiologic): : impaired gastrointestinal motility that occurs following abdominal or pelvic surgery and typically resolves spontaneously within 72 hours; one of the most common causes of paralytic ileus
- Prolonged postoperative ileus: a form of paralytic ileus associated with prolonged impaired gastrointestinal motility for > 72 hours after surgery 
Risk factors for postoperative ileus 
- Open abdominal or pelvic surgery
- Long duration of surgery
- Excessive bowel handling during intraabdominal surgery
- Excessive IV fluids during surgery
- Presence of other independent causative factors, e.g., hypokalemia; , use of opiates, or inflammation of intrabdominal organs
- Prolonged postoperative immobilization
- Similar to paralytic ileus secondary to other etiologies (i.e., nausea, vomiting, abdominal distension, failure to pass flatus, absent/decreased bowel sounds).
- Abdominal tenderness is difficult to assess in the immediate/early postoperative period.
Prevention of postoperative ileus
Prolonged postoperative ileus causes considerable discomfort to the patient and leads to longer hospital stays. The following perioperative measures can decrease the risk in patients undergoing abdominal and other high-risk surgery.
- Minimally invasive surgery, whenever feasible 
- Multimodal analgesic regimens 
- Early initiation of enteral feeding and regular diet 
- Sham feeding with chewing gum 
- Restricted use of IV fluids perioperatively 
- Selective use of nasogastric tubes 
- Early mobilization is generally believed to be beneficial. 
- Consider preoperative initiation of a peripherally-acting μ-opioid antagonist (e.g., alvimopan ) in patients undergoing open colorectal surgeries or other major abdominal surgeries.