What are the signs and symptoms of Small Bowel Obstruction (SBO)?

Signs and Symptoms of Small Bowel Obstruction

The classic presentation of small bowel obstruction includes intermittent crampy central abdominal pain, abdominal distension, nausea, vomiting, and either absent or high-pitched bowel sounds on examination. 1

Core Clinical Features

Primary Symptoms

• Intermittent crampy central abdominal pain that worsens as the bowel attempts to overcome the obstruction 1, 2
• Nausea and vomiting occur early and prominently in SBO, particularly in proximal obstructions where vomit may be green/yellow in color 1, 2
• Abdominal distension is present in approximately 65% of cases and serves as a strong predictive sign with a positive likelihood ratio of 16.8 2
• Constipation to obstipation with absence of flatus in 90% of cases and absence of bowel movements in 80.6% of cases 2, 3

Physical Examination Findings

• Abdominal distension with visible peristalsis potentially seen in thin patients 2
• Either absent or high-pitched bowel sounds depending on the stage and severity of obstruction 1, 2
• Abdominal tenderness on palpation 2
• Signs of dehydration including dry mucous membranes, tachycardia, and hypotension/orthostasis 3

Critical Warning Signs of Complications

Physical examination and laboratory tests alone are neither sufficiently sensitive nor specific to detect bowel strangulation or ischemia (sensitivity only 48%), making early imaging critical since mortality can reach 25% with ischemia. 1

Signs Suggesting Strangulation/Ischemia

• Severe abdominal pain that is intense and unresponsive to analgesics 2
• Fever, tachypnea, tachycardia, and confusion 2
• Diffuse abdominal tenderness, involuntary guarding, abdominal rigidity, or rebound tenderness suggesting peritonitis 2, 3
• Absent bowel sounds (as opposed to high-pitched sounds in uncomplicated obstruction) 2
• Signs of shock including hypotension, cool extremities, mottled skin, and oliguria 2

Laboratory Abnormalities Suggesting Complications

• Elevated white blood cell count (>10,000/mm³), leukocytosis, neutrophilia, or bandemia 1, 2, 3
• Elevated lactic acid levels indicating tissue ischemia 1, 2
• Elevated serum amylase 1, 2
• Low serum bicarbonate and arterial blood pH suggesting metabolic acidosis 2, 3
• Abnormal renal function tests indicating dehydration and potential acute kidney injury 2

Common Diagnostic Pitfalls

Atypical Presentations to Recognize

• Watery diarrhea may be present in incomplete/partial obstruction, which can mistakenly be diagnosed as gastroenteritis 1, 2
• Stools may still be present in patients with relatively high obstruction who present early after symptom onset 1
• Pain is often less prominent in elderly patients, leading to delayed diagnosis 1, 2
• Not all classic symptoms may be present simultaneously, particularly in older populations 1

Key Historical Elements

• Prior abdominal surgery has 85% sensitivity for adhesive SBO, as adhesions account for 55-75% of all SBO cases 2, 4
• History of hernias (second most common cause at 10% of cases) 3
• Previous episodes of diverticulitis, chronic constipation, rectal bleeding, or unexplained weight loss should raise suspicion for alternative etiologies 2

Distinguishing High-Grade from Low-Grade Obstruction

Patients with high-grade SBO present with more severe abdominal pain and carry higher risk of bowel ischemia and perforation, requiring urgent imaging and potential surgical intervention. 1

High-Grade SBO Features

• More severe, continuous abdominal pain rather than intermittent cramping 1
• Complete absence of flatus and stool 2
• Rapid progression of symptoms 1
• Early development of systemic signs including fever and tachycardia 1

Low-Grade/Partial SBO Features

• Intermittent crampy pain that may wax and wane 1
• Possible passage of some flatus or watery stool 1, 2
• Less severe distension 1
• Better tolerance of symptoms allowing for trial of conservative management 1

Essential Physical Examination Components

Examine all hernia orifices and previous surgical incision sites, as these are critical to identifying the etiology and are frequently overlooked. 2

• Digital rectal examination may reveal blood or a rectal mass in cases of colorectal cancer 2
• Inspection of all potential hernia sites including inguinal, femoral, umbilical, and incisional hernias 2
• Assessment for signs of peritonitis through gentle palpation for guarding and rebound tenderness 1, 2
• Evaluation of hydration status through skin turgor, mucous membrane moisture, and vital signs 3