What are the signs and symptoms of large bowel obstruction?

Signs and Symptoms of Large Bowel Obstruction

Large bowel obstruction presents most commonly with absence of flatus (90%), absence of bowel movements (80.6%), and abdominal distension (65.3%), along with colicky abdominal pain that worsens with attempts to overcome the obstruction. 1

Cardinal Clinical Features

Primary Symptoms

• Absence of flatus occurs in 90% of patients and is one of the most reliable indicators 1
• Absence of bowel movements is present in 80.6% of cases 1
• Abdominal distension occurs in 65.3% of patients and has a positive likelihood ratio of 16.8, making it a strong predictive sign 2
• Colicky abdominal pain that worsens with attempts to overcome the obstruction is characteristic 2
• Abdominal bloating is commonly reported 2

Gastrointestinal Symptoms

• Nausea and vomiting occur but are less prominent and develop later compared to small bowel obstruction 2
• Feculent vomiting can occur specifically in distal large bowel obstruction 2
• Recurrent left lower quadrant abdominal pain may be present 1, 2

Physical Examination Findings

• Abdominal tenderness is a common finding on palpation 1, 2
• Hyperactive or absent bowel sounds depending on the stage of obstruction 1, 2
• Visible peristalsis may be observed in thin patients 2
• Digital rectal examination may reveal blood or a palpable rectal mass, particularly in cases of colorectal cancer 2

Warning Signs of Complications

Signs of Strangulation/Ischemia

These findings indicate urgent surgical intervention is needed:

• Fever, tachypnea, tachycardia, and confusion suggest bowel ischemia 2
• Intense pain unresponsive to analgesics is an ominous sign 2
• Diffuse abdominal tenderness, guarding, or rebound tenderness indicate peritoneal involvement 2
• Absent bowel sounds suggest advanced ischemia 2

Signs of Perforation/Shock

• Hypotension, cool extremities, mottled skin, and oliguria indicate shock 2
• Diffuse peritonitis with guarding and rebound tenderness 3
• When perforation occurs at the tumor site, peritoneal contamination is usually localized; when perforation is proximal to the tumor, fecal spread results in diffuse peritonitis and septic shock 1

Laboratory Abnormalities Suggesting Complications

• Leukocytosis and neutrophilia suggest perforation or necrosis 1, 2
• Elevated lactic acid levels indicate intestinal ischemia 2
• Low serum bicarbonate and arterial blood pH suggest metabolic acidosis 2
• Elevated amylase levels may indicate complications 1, 2
• Elevated urea nitrogen occurs as a consequence of vomiting and dehydration 1
• Metabolic alkalosis may develop from prolonged vomiting 1

Key Distinguishing Features from Small Bowel Obstruction

Understanding these differences helps localize the obstruction:

• Vomiting is less frequent in large bowel obstruction compared to small bowel obstruction 2
• Symptoms develop more gradually in large bowel obstruction 2
• Previous complaint of bloody stools or passage of blood per rectum despite absence of bowel movement can be associated with colon cancer 1, 2
• Cancer is the most common cause (60% of cases) in large bowel obstruction, whereas adhesions cause 55-75% of small bowel obstructions 2

Critical Clinical Pitfalls to Avoid

• Do not mistake incomplete obstruction with watery diarrhea for gastroenteritis, as this leads to delayed diagnosis 2
• Do not overlook bowel obstruction in elderly patients where pain may be less prominent or minimal signs may be present despite severe disease 2, 3
• Be aware that 5% of patients with intestinal perforation may remain asymptomatic, requiring high clinical suspicion 3
• Delay in diagnosis beyond 24 hours increases the likelihood of requiring more invasive treatments and is associated with higher mortality, particularly if perforation occurs 3, 4

Essential Diagnostic Workup

History and Physical Examination

• Inquire about previous diverticulitis episodes, chronic constipation, rectal bleeding, or unexplained weight loss 2
• Examine all hernia orifices and previous surgical incision sites 2
• Complete history focusing on previous abdominal surgeries has 85% sensitivity for adhesive obstruction 2

Laboratory Tests

• Complete blood count to assess for leukocytosis 2
• Electrolyte panel to identify imbalances from vomiting and dehydration 1, 2
• Renal function tests to evaluate dehydration 2
• Lactate levels to assess for intestinal ischemia 2

Imaging Studies

• CT scan is the most accurate diagnostic tool with 93-96% sensitivity and 93-100% specificity, and provides optimal information regarding complications 1, 2
• CT scan identifies the site of obstruction in 95% of cases and the cause in 66-87% of cases 1
• Abdominal ultrasound can be used as an alternative with 88% sensitivity and 76% specificity for confirmation 1
• Plain abdominal X-rays have limited value with only 74-84% sensitivity for confirmation and cannot identify the cause in most cases 1
• Water-soluble contrast enema is a valid alternative when CT is not available, with 96% sensitivity and 98% specificity 1