Postoperative Ileus

Etiology

Ileus is a common consequence of intra-abdominal surgical procedures. There is little consensus on when the gastrointestinal tract resumes motility postoperatively. However, colonic motility, which is the last to return, is typically restored within 72hrs. Thus, postoperative ileus lasting longer than this duration is often considered pathologic. While operative manipulation is traditionally blamed for inciting ileus, the exact mechanisms which lead to a prolonged ileus are poorly understood. Therefore, it is difficult to predict who will develop prolonged postoperative ileus. However, these underlying mechanisms can be broken into three broad categories: neurogenic, inflammatory, and pharmacologic.[6]

Causes of postoperative ileus were studied extensively in efforts to prevent or treat the condition adequately. Multiple factors contribute to the development of the condition, but no direct causation relationship was confirmed with any of the factors. High correlation with ileus was identified with the following conditions:

1. Interruption of the GI continuity (in cases of resection) or manipulation of the bowel
2. Anesthetic and analgesic medications
3. Immobility
4. Electrolytes imbalance especially hypokalemia
5. Intra-abdominal hematoma
6. Intra-abdominal severe infection or sepsis
7. Chronic medical conditions like diabetes mellitus (DM)
8. Local or generalized abdominal inflammation like pancreatitis
9. Severe pain
10. Cardiopulmonary failure

Epidemiology

Some degree of postoperative ileus is nearly universal after abdominal surgery. Up to 25% of patients will develop postoperative ileus after elective abdominal surgery.[7] Prolonged ileus, while less common, is still frequently seen after intra-abdominal operations. The prevalence of prolonged postoperative ileus after colorectal surgery is anywhere from 5% to 30%.[8] Theoretically, increased intestinal manipulation or large incisions are associated with a higher risk of postoperative ileus than laparoscopic approaches or abdominal surgeries with minimal intestinal manipulation, such as cholecystectomy.[9][10][11]

Pathophysiology

The exact mechanism and causes of postoperative ileus are incompletely understood. However, the pathophysiology of postoperative ileus can be attributed to the following three categories of mechanisms: neurogenic, inflammatory, and pharmacologic. The autonomic nervous system plays a major role in gastrointestinal motility. The parasympathetic system stimulates motility while the sympathetic system inhibits motility. Increased sympathetic stimulation plays a role in the inhibition of gastrointestinal motility after surgery. Hormones and neurotransmitters, such as nitric oxide, calcitonin-gene-related peptide, and corticotropin-releasing factor, may induce the development of postoperative ileus. Postoperative ileus is more likely to develop after prolonged major surgical procedures and general anesthesia with excessive gastrointestinal manipulation or interruption. Postoperative pain medication, particularly opioids, promotes the development or worsening of postoperative ileus due to their known inhibitory effect on gut motility.[6]

History and Physical

Delayed bowel movement or passage of flatus is the hallmark of postoperative ileus. Common symptoms include abdominal distension, bloating, diffuse, persistent pain, nausea, vomiting, inability to pass flatus, and intolerance to an oral diet. Physical exam findings are also typically non-specific, but often patients can have distended, tympanic abdomens on exam associated with absent or sluggish bowel sounds. Tenderness or rebound tenderness should be further investigated for other more serious causes.

Evaluation

The diagnosis of postoperative ileus is clinical. Postoperative ileus causes delayed bowel movement or flatus with abdominal distention and possible nausea or vomiting. It is crucial to differentiate ileus from other causes of the above clinical picture, especially mechanical bowel obstruction. There are some differences that can assist clinicians in distinguishing between the two entities. Postoperative ileus is more insidious in nature. In mechanical obstruction, symptoms are usually more acute and severe. Radiologically (X-rays and computed tomography scans), ileus shows diffuse air-fluid levels and bowel distention, while mechanical bowel obstruction demonstrates a transition point with dilated proximal and collapsed distal small bowel.

The evaluation of ileus focuses on looking for other treatable similar conditions and identifying the predisposing factors. Some factors, like peritonitis or intra-abdominal bleeding, necessitate urgent active treatment of the primary causes. In addition to the clinical assessment, biochemical profile assessment, medications review, pain and analgesics review, patient's ambulation assessment, and co-existing constipation should be considered.

Treatment / Management

Management of postoperative ileus revolves around supportive care. After excluding serious or treatable conditions, supportive treatment and optimizing care almost always resolve the ileus. These measures include intravenous fluid replacement, electrolyte replacement, early ambulation, and often nasogastric tube placement. Some of these interventions are aimed at reducing symptoms, such as nasogastric suction, but have little evidence supporting their overall usefulness otherwise.[12] 

A careful balance between postoperative pain control and analgesics, especially opiates use, is crucial to prevent or treat the ileus. Non-opiate analgesics are encouraged. Optimizing electrolytes and other metabolites are important. Encouraging ambulation very early in the postoperative period is a simple but very important prevention and treatment measure. Regular and serial clinical assessments should be exerted with open eyes and mind for worsening complications or a missed diagnosis. Multiple studies have assessed a few treatment measures to overcome ileus but with no clinically significant outcomes. Studies on gum-chewing showed some improvement in the ileus. Therefore, this is occasionally but not widely used in clinical practice.

Differential Diagnosis

Postoperative ileus carries a nonspecific presentation. While not a surgical or medical emergency, many other diagnoses that share symptoms with postoperative ileus can be emergent. Distinguishing between ileus and mechanical obstruction both at onset and throughout the clinical course, is key. Further, several other intra-abdominal issues can yield similar symptoms to ileus and should be ruled out. This includes ischemia, abscess, surgical complication, or inflammation of the intra-abdominal organs, such as cholecystitis or pancreatitis.

Prognosis

Prognosis is generally good as postoperative ileus typically resolves within one to three days after diagnosis with supportive care. Should ileus remain for several days or symptoms continue to worsen despite management, further investigation and imaging is warranted.

Complications

Complications of postoperative ileus include prolonged hospital stay and increased healthcare costs. Postoperative ileus typically resolves within a few days, although continued ileus introduces complications associated with lack of enteral intake, electrolyte derangements, malnutrition, and poor patient satisfaction.