What are the signs of bowel obstruction?

Signs of Bowel Obstruction

Bowel obstruction presents with a classic tetrad: colicky abdominal pain, vomiting, absence of flatus passage (90% of cases), and abdominal distension (65.3% of cases), with the pattern and timing of symptoms helping distinguish small from large bowel obstruction. 1, 2

Cardinal Clinical Features

Primary Symptoms

• Colicky abdominal pain that worsens as the bowel attempts to overcome the obstruction 1
• Absence of flatus passage occurs in 90% of cases and is one of the most reliable indicators 1, 2
• Absence of bowel movements occurs in 80.6% of cases 1, 2
• Nausea and vomiting are universal symptoms, though timing and character vary by location 1
• Abdominal bloating and distension occur in 65.3% of cases, with distension having a positive likelihood ratio of 16.8 1, 2

Physical Examination Findings

• Abdominal distension is the most common physical finding (65.3% of cases) and strongly predictive 1, 2
• Abdominal tenderness on palpation, with location varying by obstruction site 1
• Hyperactive bowel sounds early in obstruction, progressing to absent bowel sounds in late or complicated cases 1
• Visible peristalsis may be observed in thin patients as the bowel attempts to overcome the obstruction 1
• Digital rectal examination may reveal blood or a rectal mass in colorectal cancer cases 1

Critical Warning Signs of Complications

These signs indicate strangulation, ischemia, or perforation requiring urgent surgical intervention:

Systemic Signs

• Fever, tachypnea, tachycardia, and confusion suggest bowel ischemia or strangulation 1
• Hypotension, cool extremities, mottled skin, and oliguria indicate shock 1
• Intense pain unresponsive to analgesics is a red flag for strangulation 1, 3

Abdominal Examination

• Diffuse abdominal tenderness with guarding or rebound tenderness suggests peritonitis from perforation or ischemia 1, 3
• Absent bowel sounds in the setting of obstruction indicate advanced disease 1

Laboratory Abnormalities

• Leukocytosis and neutrophilia suggest complications 1
• Elevated lactic acid levels indicate bowel ischemia 1
• Low serum bicarbonate and arterial pH reflect metabolic acidosis from ischemia 1
• Elevated amylase may occur with complications 1
• Abnormal renal function tests indicate dehydration 1

Distinguishing Small vs. Large Bowel Obstruction

Small Bowel Obstruction Characteristics

• More frequent and earlier vomiting is the hallmark 1
• Green/yellow vomit suggests proximal small bowel obstruction 4, 1
• Pain tends to be more severe and colicky 3
• Most commonly caused by adhesions (55-75% of cases), followed by hernias (15-25%) 4, 1
• History of previous abdominal surgery has 85% sensitivity for adhesive obstruction 1

Large Bowel Obstruction Characteristics

• Less frequent vomiting that occurs later in the course 1
• Feculent vomiting indicates distal obstruction 4, 1
• More gradual symptom development compared to small bowel 1
• Recurrent left lower quadrant pain may precede acute presentation 1
• Most commonly caused by cancer (60% of cases), followed by volvulus (15-20%) and diverticular disease (10%) 4, 1
• History of rectal bleeding or unexplained weight loss suggests malignancy 1

Key Diagnostic Approach Elements

Essential History Points

• Previous abdominal surgeries (85% sensitivity for adhesive obstruction) 1
• Previous diverticulitis episodes suggest diverticular stenosis 1
• Chronic constipation history may indicate volvulus 1
• Rectal bleeding and weight loss point toward colorectal cancer 1
• Timing of last bowel movement and flatus passage 4

Physical Examination Priorities

• Examine all hernia orifices and previous surgical incision sites for incarcerated hernias 1
• Assess for visible peristalsis in thin patients 1
• Perform digital rectal examination to check for masses, blood, or the "gush sign" 1, 5

Laboratory and Imaging

• Complete blood count to assess for leukocytosis 1
• Electrolyte panel to identify imbalances from vomiting and dehydration 1
• Lactate levels to assess for intestinal ischemia 1
• CT scan is the most accurate diagnostic tool with approximately 90% accuracy 1, 3
• Abdominal ultrasound has 90% sensitivity and 96% specificity as an alternative 1
• Plain abdominal X-rays have limited value (sensitivity only 50-60%) and cannot exclude the diagnosis 1, 3

Common Diagnostic Pitfalls

• Mistaking incomplete obstruction with watery diarrhea for gastroenteritis can lead to dangerous delays in diagnosis 1
• Overlooking bowel obstruction in elderly patients where pain may be less prominent can have severe consequences 1
• Failing to recognize opioid-induced bowel dysfunction which can mimic mechanical obstruction 4
• Missing localized adhesive obstruction when imaging is performed after the obstruction has temporarily resolved 4