Ileus and Obstruction


Small Bowel Obstruction

  1. Definition of Terms
    1. Complete Obstruction
      • bowel lumen is completely obstructed
      • no distal passage of stool or air

    2. Partial Obstruction
      • lumen is narrowed
      • some distal passage of bowel contents

    3. Open-Loop Obstruction
      • lumen only obstructed in one place, allowing proximal decompression

    4. Closed-Loop Obstruction
      • lumen is obstructed in 2 places, precluding decompression

    5. Simple Obstruction
      • bowel blood flow is not compromised

    6. Strangulation Obstruction
      • blood flow is compromised, leading to bowel necrosis

  2. Etiology
    1. Intraluminal Causes
      • intussusception, bezoars, gallstone ileus, foreign bodies

      Intraluminal Obstruction: Foreign body and Gallstone Ileus
    2. Intramural Causes
      • primary neoplasm, Crohn’s disease, radiation stricture

      Intramural Obstruction: Carcinoid Tumor and Crohn's Stricture
    3. Extrinsic Causes
      • adhesions, hernias, abscesses, metastatic cancer

      Extrinsic Obstruction: Adhesions and Incarcerated Femoral Hernia
  3. Most Common Etiologies
    1. Adhesions
      • account for 60% of cases
      • pelvic procedures account for the majority of adhesive obstructions (TAH-BSO, LAR, APR, appendectomy)
      • greater mobility of the distal small bowel may account for this

    2. Malignant Tumors
      • account for 20% of cases
      • most are metastatic lesions that obstruct by peritoneal implants (ovarian cancer)
      • cecal cancer may obstruct the ileocecal valve
      • large intraabdominal tumors may obstruct by extrinsic compression
      • primary small bowel tumors (adenocarcinomas, GISTs, carcinoids) are rare causes

    3. Hernias
      • account for 10% of small bowel obstructions
      • incarcerated inguinal or incisional hernias are most common, but incarcerated femoral hernias occur in elderly women

    4. Crohn’s Disease
      • accounts for 5% of cases
      • acute obstructions result from inflammation and edema, and often resolve after treatment of the acute flare up
      • chronic strictures may require strictureplasty or resection

  4. Pathophysiology
    1. Bowel Motility
      • early on, peristaltic activity increases in an effort to overcome the obstruction
      • these contractions occur above and below the point of obstruction, often resulting in diarrhea
      • later on, the intestine fatigues and dilates, with contractions becoming less frequent and less intense

    2. Fluid Sequestration
      • water and electrolytes accumulate in the bowel lumen and bowel wall
      • resulting third space losses can be massive and result in hypovolemia and shock
      • proximal obstructions may result in profound electrolyte loss from vomiting: hypokalemia, hypochloremia, metabolic alkalosis
      • dilated, fluid-filled bowel may result in increased intra-abdominal pressure, decreased venous return, and an elevated diaphragm, resulting in impaired ventilation and decreased cardiac output (abdominal compartment syndrome)

    3. Decreased Mucosal Blood Flow
      • as intraluminal pressure increases, mucosal blood flow decreases
      • untreated, ischemia may progress to necrosis and perforation
      • closed loop obstructions are particularly dangerous, because higher intraluminal pressures are reached

    4. Changes in Intestinal Flora
      • with obstruction, the usually sterile jejunum and proximal ileum take on the flora and bacterial counts of the colon
      • bacterial translocation may occur, resulting in sepsis and multiorgan failure

  5. Clinical Manifestations
    1. History
      • classic symptoms include colicky abdominal pain, nausea, vomiting, abdominal distention, obstipation
      • proximal obstructions are associated with more nausea and vomiting and less distention
      • distal obstructions are associated with more distention and less emesis
      • early on, diarrhea can occur from increased peristalsis
      • obstipation is a late finding
      • feculent vomiting indicates a late and established obstruction
      • closed loop obstructions progress more rapidly than open loop obstructions
      • complete obstructions have more acute findings than partial obstructions

    2. Physical Exam
      • tachycardia, oliguria, hypotension reflect dehydration
      • fever suggests strangulation
      • amount of distention present reflects the level of obstruction
      • in thin patients, visible peristaltic waves may be present
      • early on, hyperactive bowel sounds are present; later on, the abdomen is quiet
      • localized tenderness, guarding, rebound suggest strangulation
      • previous surgical scars should be noted
      • all hernia orifices must be examined
      • blood on rectal exam suggests malignancy, intussusception, or infarction

    3. Lab Studies
      • electrolyte abnormalities must be monitored and corrected
      • BUN/Cr show degree of dehydration and adequacy of fluid resuscitation
      • elevated WBC is concerning for strangulation
      • lactate level correlates with degree of shock
      • lab studies cannot reliably diagnose or exclude bowel ischemia and strangulation

  6. Radiologic Diagnosis
    1. Plain Films
      • standard views include an upright and supine abdominal film and an upright chest x-ray
      • supine films show dilated loops of small bowel with minimal colonic gas
      • upright films will show multiple air-fluid levels
      • upright chest film is necessary to rule out free air and perforation
      • diagnostic accuracy of abdominal films is ~ 60%

      SBO on Upright and Flat Abdominal X-rays
    2. CT Scan with Oral and IV Contrast
      • more sensitive and specific than plain films for obstruction
      • useful for diagnosing the location and cause of the obstruction
      • findings can suggest strangulation: bowel wall thickening, poor contrast enhancement of the bowel wall, pneumatosis intestinalis
      • because of azotemia, many patients cannot have IV contrast administered

      CT Scan: Incarcerated Umbilical Hernia
      Red arrows: collapsed distal bowel.  Yellow arrows: distended proximal bowel

    3. Contrast Studies
      • most useful for distinguishing between ileus and obstruction
      • retained barium from the study may delay CT scan
      • should not be used if perforation or strangulation is suspected

  7. Treatment
    1. Initial Resuscitation
      • most patients require aggressive fluid replacement with an isotonic fluid
      • urine output should be monitored with a Foley catheter
      • electrolyte abnormalities must be corrected
      • there is no convincing evidence for the use of antibiotics in nontoxic patients

    2. NG Tube Decompression
      • decompresses the stomach, minimizing the risk of aspiration
      • decreases further distention from swallowed air
      • provides symptomatic relief of nausea and vomiting
      • NG tubes do not decompress the small bowel nor facilitate resolution of the obstruction

    3. Nonoperative Management
      • appropriate for cases of partial obstruction, post-operative obstruction, obstruction from Crohn’s, carcinomatosis, and patients with multiple recurrent obstructions
      • clinical deterioration or worsening x-rays warrant operation
      • contrast studies predict success of nonoperative management: if contrast reaches the colon within 24 hrs, 99% of patients did not require surgery; if contrast does not reach the colon, 90% of patients required surgery

    4. Operative Management
      • 25% of patients with SBO require surgery
      • patients with complete obstructions or evidence of strangulation should be quickly resuscitated and then operated on
      • laparoscopy can be considered in patients with minimal distention
      • operative approach is dictated by the cause of the obstruction

      1. Adhesions
        • must avoid serosal injuries and enterotomies
        • avoid unnecessary dissection – it is not necessary to lyse every adhesion

      2. Hernias
        • reduce the herniated segment of bowel
        • hernia defects can be closed with synthetic mesh if the bowel is viable
        • biologic mesh or primary repair are safer options if nonviable bowel must be resected

      3. Malignancy
        • in cases of widespread peritoneal implants, bypass may be a safer option than resection/anastomosis
        • primary tumors should undergo an oncologic resection, if possible

      4. Crohn’s Disease
        • strictures require resection or strictureplasty

      5. Radiation Strictures
        • bypass of the affected area is safer than resection/anastomosis because of poor healing

      6. Intra-abdominal Abscesses
        • post-operative abscesses or a perforated appendix may present as an SBO
        • CT-guided drainage will sometimes fix the obstruction

    5. Prevention of Adhesions
      • laparoscopy reduces adhesion formation
      • many intraperitoneal agents have been tried without much success: steroids, cytotoxic drugs, anticoagulants, fibrinolytic agents
      • bioresorbable membranes such as Seprafilm decrease adhesion formation, but there is no evidence to suggest that they reduce the rate of SBO or the need for operation

Ileus

  1. Definition
    • absence of bowel motility without a mechanical obstruction

  2. Causes
    • post laparotomy
    • electrolyte abnormalities (hypokalemia, hyponatremia, hypomagnesemia)
    • metabolic abnormities (uremia, diabetic coma)
    • drugs (opioids, psychotropic drugs, anticholinergic drugs)
    • intra-abdominal inflammation (abscesses)
    • retroperitoneal hemorrhage or inflammation (pancreatitis)
    • systemic sepsis

  3. Presentation
    • similar to SBO
    • distention without colicky pain is typical
    • may continue to pass flatus and have watery bowel movements

  4. Diagnosis
    • plain films often show distended small bowel loops as well as large bowel loops

    Abdominal X-ray Showing a Diffuse Ileus
  5. Management
    • supportive with IV fluids and NG decompression
    • correct hypokalemia and hypomagnesemia
    • minimize narcotics
    • treat sepsis, drain intra-abdominal abscesses
    • TPN may be required until oral intake is tolerated
    • promotility agents are not effective

Postoperative Ileus

  1. Physiologic Versus Pathologic Ileus
    • some degree of ileus is an expected response to abdominal surgery
    • gastric and small bowel motility generally return within 48 hours; colonic motility returns within 72 hours
    • there is no clear consensus on the definition of a prolonged postoperative ileus or what the endpoint should be to asses gut recovery
    • most surgeons would agree that failure to pass gas or stool by postoperative day 6 is abnormal

  2. Mechanisms of Postoperative Ileus
    1. Inflammation
      • intestinal manipulation and trauma results in WBC infiltration into the intestinal muscular layer
      • the inflammatory response and cytokine release decreases intestinal contractility

    2. Inhibitory Neural Reflexes
      • noxious (pain) spinal afferent signals increase inhibitory sympathetic activity in the gut
      • blockade of these spinal afferents (epidural anesthesia or TAP block) can improve postop ileus

    3. Opioids
      • have significant inhibitory effects on the GI tract
      • act via μ-opioid receptors located at the level of the enteric nervous system

  3. Risk Factors
    • prolonged abdominal or pelvic surgery
    • colon surgery
    • open surgery
    • peritonitis
    • intraabdominal abscess
    • intraoperative or postoperative bleeding
    • bowel wall edema from fluid resuscitation
    • nasogastric tubes
    • delayed enteral nutrition

  4. Prevention of Prolonged Postoperative Ileus
    1. Epidural Anesthesia
      • blocks nociceptive spinal afferents and inhibits sympathetic efferents
      • catheter should be placed at the midthoracic level and left in place for 48 – 72 hours
      • although effective, epidurals are not used much because they are associated with many complications: bleeding, infection, urinary retention, delayed ambulation
      • not included in most of the enhanced recovery after surgery (ERAS) protocols

    2. Transversus Abdominis Plane (TAP) Block
      • involves injecting local anesthetic into the plane between the internal oblique and transversus abdominis muscles, which is where the nerves to the anterior abdominal wall lie
      • generally done under ultrasound guidance
      • liposomal bupivacaine provides up to 72 hours of analgesia

    3. Minimally Invasive Surgery
      • decreases the length of postoperative ileus compared with open surgery
      • however, ERAS protocols applied to open surgery patients may minimize these differences

    4. μ-Opioid Receptor Antagonists
      • block the peripheral μ-receptors located in the gut
      • do not lessen the analgesic effect of opioids
      • seem to be more effective after open colon surgery than laparoscopic colon surgery
      • associated with increased cardiovascular and neoplastic complications

    5. Multimodal Analgesia
      • involves several agents, each acting at a different site of the pain pathway
      • local anesthetics (lidocaine, bupivacaine), NSAIDS, tylenol may all decrease postoperative narcotic use

    6. Surgical Technique
      • increased blood loss results in increased ileus
      • rough and excessive handling of the intestines increases ileus
      • over-resuscitation can lead to increased bowel wall edema and prolonged ileus

Acute Postoperative Obstruction

  1. Diagnosis
    • can be difficult to diagnose because its signs and symptoms overlap with post-operative ileus
    • many patients with a post-op SBO will have an initial return of bowel function and oral intake, and then develop nausea, vomiting, distention, intolerance of oral intake
    • intense cramping pain, feculent vomiting, rapidly progressing pain and distention are most consistent with SBO rather than ileus
    • plain films cannot reliably distinguish between post-op SBO and ileus
    • CT scan with oral contrast can reliably distinguish ileus from a complete SBO, but not a partial SBO
    • CT scan can identify abscesses, hematomas, sites of herniation (stomas, incision, port sites)
    • contrast studies can help distinguish an ileus from a partial SBO
    • SBO after laparoscopic surgery is worrisome for an internal hernia or port site hernia

  2. Management
    • most postoperative SBOs are partial and resolve spontaneously
    • SBOs that don’t resolve require surgery
    • patients who clinically worsen require surgery







References

  1. Sabiston, 20th ed., pgs 1247 – 1254
  2. Cameron, 11th ed., pgs 109 – 113
  3. UpToDate. Postoperative Ileus. Kalff MD, Jorg. July 02, 2019. Pgs 1 – 33
  4. UpToDate. Measures to Prevent Prolonged Postoperative Ileus. Kalff MD, Jorg. Oct 10, 2018. Pgs 1 – 29