Ileus, also known as paralytic ileus or functional ileus, occurs when there is a non-mechanical decrease or stoppage of the flow of intestinal contents. Bowel obstruction is a mechanical blockage of intestinal contents by a mass, adhesion, hernia, or some other physical blockage. These two diseases may present similarly, but treatment can be very different depending on the underlying pathology.
Ileus is an often-unavoidable consequence to abdominal or retroperitoneal surgery, but can also be found in severely ill patients with septic shock or mechanical ventilation. Due to the delayed refeeding syndrome seen after an ileus, postoperative ileus has a large economic impact in the United States alone. An ileus usually manifests itself from the third to the fifth day after surgery and usually lasts 2 to 3 days with the small bowel being the quickest to return to function (0 to 24 hours), followed by the stomach (24 to 48 hours), and lastly the colon (48 to 72 hours). A prolonged ileus is diagnosed if the ileus exceeds 2 to 3 days with the continued absence of obstruction signs.
The cause of ileus has yet to be clearly defined. There are, however, several risk factors that have been shown to increase the likelihood and endurance of an ileus.
The risk for an ileus is influenced by a variety of factors, each affecting a small part of the complex neuroimmune system. These factors include pharmacological agents such as opioids, antihypertensives, and antiemetics, as well as medical conditions including pneumonia, stroke, and electrolyte abnormalities.
The incidence of ileus varies greatly, often dependent upon the type of surgery, the amount of bowel manipulation, and preoperative comorbidities. Lower abdominal surgery, especially with large open incisions and increased intestinal manipulation, is associated with a higher risk of ileus. On the contrary, laparoscopic surgery with minimal bowel manipulation, such as in a cholecystectomy, confers a lower risk. The literature shows about a 10-20% chance of ileus occurring depending on the procedure.
The exact mechanism and cause of ileus are incompletely understood due to the complexity and numerous systems and factors involved. Ileus is a neuroimmune interaction that consists of two phases: the early neurogenic phase and the inflammatory phase. This interaction is governed by the bidirectional communication between the autonomic nervous system (including afferents, efferents, and the enteric nervous system) and the immune system both outside and within the GI tract (mast cells, macrophages).
Macrophages residing in the tunica muscularis external of the bowel wall release cytokines that induce the activation of further pro-inflammatory cells, other antiperistaltic cytokines (including interleukin-6 and TNF-alpha), along with neuropeptides and nitric oxide. Overall this interaction is initiated by manipulation of the bowel. The stress of surgery and manipulation of the bowel leads to activation of a local molecular inflammatory response, the release of hormones, and neurotransmitters that result in a sustained inhibitory sympathetic activity and suppression of the neuromuscular apparatus.
The patient will present with abdominal distension and bloating that is often a slow onset as opposed to the sudden onset usually seen with mechanical bowel obstruction. Pain is usually diffuse, persistent without peritoneal signs. Other common signs and symptoms include nausea and vomiting, as well as delayed or inability to pass flatus, and inability to tolerate oral diet. The patient is often distended and tympanic on physical exam with mild diffuse tenderness. Bowel sounds are usually sparse or absent as opposed to a mechanical obstruction where they are intensified in the early phase, although they may be absent in the late phase.
Plain abdominal films are usually the first diagnostic imaging obtained. Eliciting the difference between an ileus and a mechanical obstruction, especially if it is only a partial obstruction, can be difficult but is an important distinction to make. Supine and upright films may reveal dilated small bowel loops but should also show air in the colon and rectum without a transition point. If the plain film is vague, a computed tomography(CT) scan of the abdomen should be obtained. The abdominopelvic CT scan is most useful using oral and intravenous contrast not only to help delineate a potential transition point but also to rule out other intra-abdominal pathology, including a tumor or an abscess.
Laboratory evaluation should be ordered to help identify any potentially reversible causes of an ileus, such as hypokalemia or signs of infection. A complete blood count should look for anemia to rule out bleeding or an elevated white count, as may be seen with an abscess, infection, or intestinal ischemia. The electrolyte panel should look for electrolyte abnormalities and replaced as needed.
Treatment of an ileus requires time and supportive management. Bowel rest, intravenous (IV) fluid therapy, and, if warranted, NG decompression are important steps. Historically these treatments were thought to lower complications and improve outcomes, but a recent review of the evidence shows otherwise. Chewing gum has been studied and seems to be a cheap, well-tolerated way to potentially help with ileus as it stimulates the cephalocaudal reflex, which promotes peristalsis and inhibits inflammation. Unfortunately, these are the only options we currently have as pharmacologic agents have been ineffective. Many have been studied in the past with inconsistent outcomes, including erythromycin, sympathetic inhibitors (guanethidine), parasympathetic stimulators (neostigmine), hormonal agents (cholecystokinin, motilin).
Treatment of the underlying condition is paramount. Treating the infection, electrolyte abnormalities, decreasing opiate use, can all potentially decrease the durability of an ileus. These can be difficult to treat in the case of prolonged illness with mechanical ventilation, and septic shock that leads to lengthy bed-bound periods. Total parenteral nutrition (TPN) is recommended if the patient is unable to tolerate adequate oral intake after seven days. Decreasing opiate use and transitioning to a multimodal pain regimen has benefits, as does early ambulation. In the setting of postoperative ileus, the best treatment is prevention. Enhanced recovery protocols, regional anesthesia, opioid-sparing analgesics, and laparoscopy have all shown improvement in the number of postoperative ileus cases.
The evaluation of an ileus needs to exclude other more concerning diagnoses such as small bowel obstruction, intra-abdominal abscess, or perforation. Some of these may require some type of intervention, and it is important to distinguish them. The most important diagnosis to distinguish from an ileus is an obstruction. Patients with a postoperative obstruction often have an initial return of bowel function and oral intake with subsequent nausea, vomiting, abdominal distention, and pain, whereas an ileus patient usually has no return of bowel function or oral intake. Intense pain, feculent emesis, or rapid onset/progression of pain/distension are usually a sign of obstruction and not of an ileus. The use of small bowel follow-through with gastrografin or water-soluble contrast is becoming increasingly useful for small bowel obstructions and can help to further distinguish obstruction from an ileus. Gastrografin has been noted to therapeutically treat adhesive small bowel obstructions. Its use to treat a postoperative ileus has not been proven; it may improve some of the symptoms, but the duration of the ileus and the length of stay are not reduced.
The overall prognosis from an ileus is good with patients eventually recovering, but the exact number of days until the return of bowel function is uncertain. Having an ileus is only harmful in terms of the length of stay and decreased nutrition. Longer hospital stays increase the risk of nosocomial infections, and a prolonged ileus may lead to the need for TPN, which has its own risks and benefits.
From a surgical perspective, it is paramount to encourage and educate patients on the benefits and risks of surgery, including the possibility of an ileus. Prevention of ileus is the responsibility of both the patient and healthcare providers, including doctors, nurses, pharmacologists, and physical/occupational therapists. Encouraging ambulation, enhanced recovery after surgery (ERAS) protocols, and educating the patient on their importance and benefits should improve patient understanding and compliance.
Ileus needs to be distinguished from other causes of abdominal pain, distension, and nausea/vomiting. Once diagnosed, treatment is supportive (IV fluids, NG decompression) with the management of precipitating factors (opiates, sepsis). Postoperative ileus is common, but steps can be taken to help prevent it, especially in an outpatient/elective setting (ERAS protocols, ambulation, laparoscopy).
The mainstay management of ileus is prevention, followed by appropriate diagnosis, and conservative/expectant management. At times this can be difficult and often requires all aspects of the healthcare system to participate in its prevention. Encouraging ambulation, multimodal pain regimens, ERAS protocols, and monitoring oral intake all are difficult for any person/team to monitor.
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