WHAT YOU NEED TO KNOW ABOUT INTESTINAL OBSTRUCTION

Large bowel obstruction (LBO) is a critical clinical entity requiring prompt diagnosis and management. It represents a mechanical blockage preventing the normal passage of intestinal contents through the colon. Untreated, it can lead to serious complications including ischemia, perforation, peritonitis, and sepsis. This guide outlines the approach to evaluating and managing a patient with presumed LBO, detailing signs, symptoms, diagnostic aids, common causes and their specific management strategies, and the potential complications of inadequate treatment.

Signs and Symptoms of Large Bowel Obstruction

The clinical presentation of LBO is often distinct but can vary depending on the location and completeness of the obstruction, the presence of a competent ileocecal valve, and the underlying cause. A high index of suspicion is crucial. Key signs and symptoms include:

1. Abdominal Distension: This is a cardinal sign, typically more prominent and symmetrical in LBO compared to SBO, particularly if the obstruction is distal. The abdomen can become markedly tympanitic.
2. Abdominal Pain: Usually described as colicky or crampy, though it can become constant and severe if complications like ischemia or perforation develop. Pain may localize near the obstruction site.
3. Constipation or Absolute Constipation: Progressive difficulty passing stool and flatus is a hallmark. Absolute constipation (failure to pass both stool and flatus) indicates complete obstruction. A history of recent changes in bowel habits may also be reported, preceding the acute obstruction.
4. Vomiting: Typically occurs later in the course of LBO compared to SBO. Vomitus is initially bilious or feculent due to stagnation and bacterial overgrowth proximal to the obstruction. It may not be severe or frequent, especially with distal obstructions or a decompressed colon.
5. Change in Bowel Habits: A preceding history of alternating constipation and diarrhea, tenesmus, or decreased stool caliber may suggest a chronic or partially obstructing process, such as a tumor.

Other potential findings on physical examination include visible peristalsis (rare), palpable abdominal mass (suggesting tumor or fecaloma), and signs of dehydration or fluid loss. A rectal examination may reveal an empty vault or, conversely, a large fecal impaction.

Initial Evaluation and Diagnostic Aids

Once LBO is suspected based on the clinical presentation, a focused evaluation using diagnostic aids is necessary to confirm the diagnosis, locate the obstruction, assess its severity, identify potential complications, and begin to determine the underlying cause.

1. History and Physical Examination: A detailed history focusing on the onset and nature of symptoms, previous abdominal surgeries, medical comorbidities, and medication use (e.g., opioids causing constipation) is vital. The physical examination should include a thorough abdominal assessment (inspection, auscultation for bowel sounds which may be hyperactive early, then absent; percussion for tympany; palpation for tenderness, distension, masses) and a digital rectal examination. Assessment of vital signs is critical to identify signs of dehydration, infection (fever), or shock.
2. Laboratory Studies:
   • Complete Blood Count (CBC): May show leukocytosis if there is inflammation, ischemia, or perforation. Anemia may suggest chronic blood loss from a tumor.
   • Serum Electrolytes, Blood Urea Nitrogen (BUN), and Creatinine: Evaluate hydration status and detect electrolyte abnormalities (e.g., hypokalemia from vomiting or fluid shifts).
   • Lactate: Elevated levels may suggest bowel ischemia or sepsis.
   • Coagulation Studies: Important for surgical planning.
   • Type and Screen/Crossmatch: Essential if operative intervention is anticipated.
3. Imaging Studies: Imaging is paramount in confirming LBO and guiding management.
   • Plain Radiographs (Abdominal X-rays): An initial step, typically including supine and upright views (or lateral decubitus if patient cannot stand). Findings suggestive of LBO include:
     • Markedly dilated colon proximal to the obstruction (often greater than 6-8 cm in diameter).
     • Collapsed colon loops distal to the obstruction.
     • Presence of haustral markings (incomplete rings of the colon).
     • Air-fluid levels within the dilated colon loops.
     • Free air under the diaphragm or in the abdomen, indicating perforation (surgical emergency). While readily available, plain films may be non-diagnostic in up to 20% of cases and provide limited information about the cause or complications.
   • Computed Tomography (CT) Scan: The imaging modality of choice in suspected LBO. A CT scan of the abdomen and pelvis, usually with intravenous contrast (oral contrast is often withheld in suspected obstruction), provides detailed cross-sectional images that can:
     • Confirm the presence and level of obstruction.
     • Identify the likely cause (tumor, stricture, volvulus, etc.).
     • Assess for complications (bowel wall thickening/enhancement suggesting ischemia, extraluminal air/fluid suggesting perforation, surrounding inflammation).
     • Evaluate other intra-abdominal organs and assess for metastatic disease if malignancy is suspected.
   • Contrast Enema: Less commonly used now due to the superiority of CT, but can sometimes clarify the site and nature of a distal obstruction (e.g., stricture, extrinsic compression). Water-soluble contrast is preferred if perforation is suspected. Should be used cautiously in the setting of acute obstruction.
   • Endoscopy (Sigmoidoscopy or Colonoscopy): Can be diagnostic (visualize lumen, obtain biopsy) and potentially therapeutic (decompression, stent placement). Requires careful consideration in acute obstruction due to the risk of perforation in a dilated bowel.

Common Causes of Large Bowel Obstruction in Adults

Once LBO is confirmed, identifying the underlying cause is essential for appropriate management. Several etiologies exist, with varying frequencies:

1. Malignancy: By far the most common cause of LBO in the adult, accounting for approximately 60-70% of cases. Colorectal carcinoma, particularly in the left colon (descending, sigmoid), is the primary culprit. The slow growth of tumors often allows gradual compensation until the lumen is critically narrowed.
2. Volvulus: Accounts for about 10-20% of LBO cases. This involves twisting of a loop of bowel around its mesenteric axis, leading to both obstruction and potential vascular compromise. Sigmoid volvulus is the most common type (especially in elderly, debilitated, or institutionalized patients with chronic constipation), followed by cecal volvulus.
3. Diverticular Disease: Complicated diverticular disease can cause obstruction, accounting for about 5-10% of cases. Chronic inflammation in diverticulitis can lead to stricture formation in the colonic wall, commonly in the sigmoid colon. Acute diverticular inflammation or abscess can also cause extrinsic compression.
4. Fecal Impaction: Accounts for approximately 5-10% of LBO cases, particularly in the elderly, immobile, or those with neurological conditions or opioid use. Large, hardened stool mass obstructs the lumen, often in the rectum or sigmoid colon.
5. Other less frequent causes include adhesions (more common in SBO but can affect the colon after extensive pelvic/abdominal surgery), extrinsic compression from other tumors (e.g., ovarian cancer), ischemic strictures, inflammatory strictures (e.g., Crohn’s disease), and incarcerated hernias. Adult intussusception is uncommon but, when it occurs, is usually caused by a definable lead point, often a polyp or tumor.

General Principles of Management and Cause-Specific Plans

Management of LBO involves initial supportive care followed by definitive treatment tailored to the underlying cause and the patient’s clinical status.

General Management Principles:

• Resuscitation: Initiate intravenous fluid resuscitation to correct dehydration and electrolyte imbalances. Monitor urine output and vital signs.
• Bowel Decompression: Nasogastric tube insertion may help with vomiting and upper GI distension, although it does not decompress the colon directly. A rectal tube may provide some decompression for very distal obstructions or sigmoid volvulus.
• NPO Status: The patient should be kept nil per os (nothing by mouth).
• Pain Control: Provide adequate analgesia.
• Antibiotics: Prophylactic antibiotics are often administered, especially if surgery is anticipated or if there is suspicion of ischemia or perforation.
• Surgical Consultation: Immediate consultation with a surgical team is mandatory, as most cases of mechanical LBO require surgical intervention.

Cause-Specific Diagnostic, Preoperative, and Treatment Plans:

Specific management strategies differ based on the etiology:

• Volvulus (Sigmoid and Cecal):
  • Diagnostic Studies: Plain films may show characteristic findings (“coffee bean” sign for sigmoid, dilated cecum shifted ectopically for cecal). CT confirms the diagnosis and assesses for vascular compromise.
  • Preoperative Management: Resuscitation, NPO, ABX. For sigmoid volvulus, flexible sigmoidoscopy should be attempted as an initial management step if there are no signs of ischemia/perforation. Endoscopic detorsion can decompress the colon, converting an emergency into an elective procedure.
  • Treatment:
    • Sigmoid Volvulus: If endoscopic detorsion is successful and there are no signs of complications, elective sigmoid colectomy is recommended at a later date due to high recurrence rates. If endoscopic detorsion fails, or if there are signs of peritonitis/ischemia, emergent surgery is required. This typically involves sigmoidectomy (removal of the twisted segment). Primary anastomosis may be possible in stable patients with viable bowel, but a Hartmann’s procedure (leaving a rectal stump and forming a colostomy) is often necessary in emergent settings or unwell patients.
    • Cecal Volvulus: Endoscopic decompression is rarely successful and generally not attempted. Surgical intervention is almost always required. Options include right hemicolectomy (especially if ischemia is present) or cecopexy (fixation of the cecum to the abdominal wall, if the bowel is viable and patient is low risk/less able to tolerate resection).
• Adult Intussusception:
  • Diagnostic Studies: CT scan is highly accurate, showing the classic “target sign.”
  • Preoperative Management: Resuscitation, NPO, ABX. Unlike pediatric intussusception, non-operative reduction (e.g., with air or contrast enema) is generally not attempted in adults because intussusception is almost always caused by an identifiable lead point (often malignant).
  • Treatment: Surgical resection of the involved segment is the standard of care. The segment proximal and distal to the lead point is removed, typically followed by primary anastomosis. Manual reduction at surgery is discouraged if a lead point is identified or ischemia is present due to the risk of disseminating malignant cells or perforating fragile bowel.
• Fecal Impaction:
  • Diagnostic Studies: Digital rectal examination is diagnostic. Plain films or CT confirm copious retained stool.
  • Preoperative Management: Resuscitation if dehydrated. Analgesia/sedation may be required for disimpaction.
  • Treatment: Primarily non-surgical. Digital disimpaction is the first step, often followed by enemas and suppositories. Addressing underlying causes (hydration, diet, mobility, laxative regimen) is crucial to prevent recurrence. Surgery is rarely needed unless complications like stercoral perforation occur.
• Obstructing Colon Cancer:
  • Diagnostic Studies: CT confirms the obstruction and identifies the mass. Colonoscopy or sigmoidoscopy (often performed after initial decompression or as part of a staged approach) allows for biopsy to confirm malignancy.
  • Preoperative Management: Resuscitation, NPO, ABX. Optimization of the patient’s medical status is important. Assessment of resectability and staging is initiated.
  • Treatment: Management depends on the patient’s overall health, the location of the tumor, and the presence of metastasis. Options include:
    • Emergency Surgery: Resection of the tumor-bearing segment. For left-sided or rectal tumors, this often involves a Hartmann’s procedure (resection with end colostomy and rectal stump), as primary anastomosis carries a high leak risk in an unprepared and obstructed colon. For right-sided tumors, primary anastomosis is often feasible after right hemicolectomy.
    • Staged Procedure: Creating a diverting colostomy or ileostomy proximal to the obstruction to decompress the bowel, followed by definitive tumor resection and restoration of bowel continuity in later, elective procedures.
    • Endoscopic Stenting: Placement of a self-expanding metallic stent across the obstruction to restore luminal patency. This can serve as a “bridge to surgery” (allowing time for bowel prep and optimization) or as palliative treatment in patients who are not surgical candidates.

Potential Complications of Inadequate Treatment for Mechanical Large or Small Bowel Obstruction

Regardless of the specific cause, failure to promptly and adequately treat mechanical bowel obstruction (both large and small bowel) carries significant risks of serious complications. These complications drastically increase morbidity and mortality.

1. Bowel Ischemia and Necrosis: Prolonged distension of the bowel wall increases intraluminal pressure, which can exceed capillary perfusion pressure, compromising blood flow to the bowel wall. This leads to ischemia (reduced blood flow) and, if persistent, necrosis (tissue death). Ischemic bowel becomes gangrenous and non-viable.
2. Bowel Perforation: Ischemic or excessively distended bowel wall becomes thin and fragile and can rupture. Perforation allows the release of intestinal contents (feces, bacteria, digestive enzymes) into the sterile peritoneal cavity.
3. Peritonitis: The presence of intestinal contents in the peritoneum causes severe inflammation and infection, known as peritonitis. This is a surgical emergency and manifests with generalized, severe abdominal pain, rigidity, fever, and signs of sepsis.
4. Sepsis and Septic Shock: The bacterial load from contaminated peritoneum can overwhelm the body’s defenses, leading to a systemic inflammatory response (sepsis). Severe sepsis can progress to septic shock, characterized by dangerously low blood pressure and organ dysfunction, which can be rapidly fatal.
5. Electrolyte Imbalances and Dehydration: Continued vomiting and sequestration of large volumes of fluid into the dilated bowel lumen and peritoneal cavity can lead to severe dehydration, hypovolemia, and profound electrolyte abnormalities (e.g., hypokalemia, hyponatremia), further destabilizing the patient.
6. Pulmonary Complications: Patients with bowel obstruction are at high risk for aspiration pneumonia, especially with vomiting and altered mental status due to sepsis or pain medication.
7. Increased Morbidity and Mortality: Delayed diagnosis or inadequate treatment significantly increases the likelihood of these complications, leading to prolonged hospital stays, need for complex surgical procedures (often with stomas), and a substantially higher risk of death.

In conclusion, the evaluation and management of large bowel obstruction require a systematic approach, starting with prompt recognition of clinical signs, utilizing appropriate diagnostic imaging to confirm the diagnosis and identify the cause, initiating supportive care, and implementing cause-specific definitive treatment, most often surgical. Awareness of the potential for rapid clinical deterioration and life-threatening complications underscores the urgency of this clinical situation.