Small Bowel Obstruction Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: This is one of the most common general surgical emergencies you will clerk from the ED. Mastering the initial assessment and management is non-negotiable.
High-Yield Definition: Small bowel obstruction is a mechanical or functional blockage of the small intestine, preventing the normal transit of intestinal contents.
Clinical One-Liner: The gut is blocked, so everything proximal backs up. The patient is vomiting yesterday's dinner, their belly is bloated, and they haven't passed wind or stool.
II. Etiology & Risk Factors
Etiology: Think in terms of what is happening to the bowel wall.
Extraluminal (Most Common): Adhesions (post-operative) are responsible for >70% of cases in our setting. Think previous laparotomy, appendicectomy, or C-section. The second most common cause is incarcerated hernias (inguinal, femoral, incisional).
Intraluminal: Foreign bodies, gallstone ileus (rare).
Mural (from the wall itself): Malignancy (primary small bowel tumours or metastases), strictures (Crohn's disease, TB, radiation).
Risk Factors:
Non-Modifiable: Previous abdominal or pelvic surgery, history of malignancy, personal or family history of Crohn's disease.
Modifiable: None, really. The key is identifying the risk from the patient's history.
III. Quick Pathophysiology
It's simple fluid dynamics. A blockage occurs. Proximally, the bowel dilates with swallowed air and GI secretions. This leads to:
Vomiting & Distension: The bowel tries to decompress itself upwards.
Third Spacing: Fluid moves from the intravascular space into the bowel lumen and peritoneal cavity, causing dehydration and electrolyte imbalance (especially hypokalaemia).
Ischemia & Perforation: If the pressure gets too high or if it's a closed-loop obstruction (blocked at two points, like in a hernia), venous outflow is compromised first, then arterial inflow. This leads to bowel wall ischemia, necrosis, and eventually perforation. This is what kills the patient.
IV. Clinical Assessment
Red Flags & Immediate Actions: If you see any of these, you call your senior immediately. This patient might be heading to the operating theatre.
Peritonism (rebound tenderness, guarding, rigidity): Indicates ischemia or perforation. → Action: Alert Surgical MO/Registrar, get urgent GXM, keep NBM, ensure IV access is secure.
Fever (>38°C) or Hypotension (SBP <100 mmHg): Suggests sepsis or ischemia. → Action: Alert senior, start fluid resuscitation, draw blood cultures, consider starting broad-spectrum IV antibiotics as per local protocol after discussion.
Rising serum lactate: Objective evidence of bowel ischemia. → Action: Inform senior immediately.
History: Focus on the four cardinal symptoms.
Common (>50%):
Colicky, central abdominal pain: Comes in waves.
Vomiting: Early on it's bilious. Later, it becomes faeculent (brown, foul-smelling) as bacterial overgrowth occurs. This is a classic sign.
Abdominal Distension.
Absolute Constipation: No flatus, no feces. Ask specifically "When was the last time you passed wind?"
Pertinent Negatives: Ask about previous surgeries (laparotomy is key), history of hernias, and any constitutional symptoms to suggest malignancy.
Physical Examination:
General: Look for signs of dehydration (dry tongue, reduced skin turgor).
Abdomen:
Inspection: Look for distension, surgical scars, and obvious hernias.
Palpation: Check for tenderness. Is it localised or generalised? Any signs of peritonism?
Percussion: May be tympanitic due to gas-filled loops.
Auscultation: Early on, you might hear high-pitched "tinkling" bowel sounds. Later, the bowel becomes tired and silent.
MUST DO: Check all hernia orifices – inguinal, femoral, and any incisional scars.
Clinical Pearl: Don't be fooled by a patient who has passed a small amount of stool. This could just be the distal bowel emptying. The key is the cessation of passing flatus.
V. Diagnostic Workflow
Differential Diagnosis:
Large Bowel Obstruction (LBO):
Points For: Slower onset, more significant distension, less vomiting (initially).
Points Against: Pain is less colicky.
How to Differentiate: Abdominal X-ray will show peripheral dilated loops of colon with haustra.
Paralytic Ileus:
Points For: Silent abdomen, distension. Often seen post-operatively.
Points Against: Pain is usually absent or minimal, not colicky.
How to Differentiate: History is key. On AXR, both small and large bowel are dilated.
Acute Pancreatitis:
Points For: Severe epigastric pain, vomiting.
Points Against: Pain is constant and radiates to the back.
How to Differentiate: Serum amylase/lipase will be significantly elevated.
Investigations Plan:
Bedside / Initial (First 15 Mins):
Vital signs: Tachycardia and hypotension are ominous.
Abdominal X-ray (Supine & Erect): This is your first-line imaging. Look for the classic triad:
Dilated central small bowel loops (>3 cm).
Multiple air-fluid levels on the erect film.
Paucity of air in the colon.
First-Line Labs & Imaging:
Renal Profile: To check for AKI from dehydration and electrolyte imbalances (K+, Na+).
Full Blood Count: Look for haemoconcentration (high haematocrit) from dehydration or a high WCC suggesting inflammation/ischemia.
Group & Screen/Hold (GSH) or GXM: If surgery is likely.
Arterial Blood Gas (ABG): To check for metabolic acidosis and lactate levels.
Confirmatory / Gold Standard:
CT Abdomen & Pelvis with IV Contrast: This is the gold standard. It confirms the diagnosis, identifies the level and cause of obstruction (the "transition point"), and can show signs of strangulation (bowel wall thickening, poor contrast enhancement, mesenteric stranding).
VI. Staging & Severity Assessment
The main stratification is between uncomplicated and complicated SBO. Your entire management plan hinges on this.
Uncomplicated SBO: Mechanical obstruction without signs of compromised blood supply or peritonism.
Findings: Stable vitals, soft abdomen (may be tender but no guarding), normal lactate.
Impact: Can be managed conservatively initially.
Complicated SBO (Strangulated): Obstruction with vascular compromise leading to ischemia. This is a surgical emergency.
Findings: Any of the red flags (fever, tachycardia, peritonism), localised tenderness, raised WCC, metabolic acidosis, or elevated lactate. CT may show signs of ischemia.
Impact: Requires immediate surgical intervention.
VII. Management Plan
Immediate Stabilisation (The ABCDE / "Drip and Suck" Plan): This is the initial management for ALL patients with suspected SBO. You should be able to start this yourself while waiting for your senior.
N - Nil by mouth (NBM).
I - IV fluids. Start resuscitation with crystalloids (e.g., Hartmann's solution or 0.9% NaCl). Correct electrolyte abnormalities, especially potassium.
L - Ryles tube (Nasogastric tube) insertion on free drainage or low-pressure suction. This decompresses the stomach and reduces vomiting.
C - Catheterise (urinary catheter) to accurately monitor urine output as a guide for resuscitation adequacy (aim for >0.5 ml/kg/hr).
C - Charting of fluid balance and vital signs is mandatory.
Definitive Treatment (The Ward Round Plan):
Conservative Management:
Indication: Uncomplicated adhesive SBO.
Plan: Continue "drip and suck". Monitor clinical status, abdominal girth, and NGT output. A trial of conservative management usually lasts 24-48 hours. If the patient starts passing flatus or stool and the distension resolves, it's working.
Surgical Management (Laparotomy):
Indications:
Any signs of complicated SBO (strangulation/ischemia).
Obstruction due to an incarcerated hernia.
"Virgin" abdomen (no previous surgery, raising suspicion of another cause).
Failure of conservative management.
Procedure: The aim is to relieve the obstruction (e.g., adhesiolysis for adhesions) and resect any non-viable bowel.
Long-Term & Discharge Plan:
Post-operatively, monitor for return of bowel function.
Educate patient on symptoms of recurrence.
TCA (Tunjuk Cara dan Ajar) in the surgical clinic.
VIII. Complications
Immediate (Intra-operative/First 24 hrs):
Bowel Perforation: Management: Resect the perforated segment and perform lavage.
Sepsis/Septic shock: Management: Fluid resuscitation, antibiotics, and source control (surgery).
Short-Term (Days to weeks):
Anastomotic Leak: Management: May require re-operation.
Prolonged Ileus: Management: Continue supportive care with NBM and IV fluids.
Wound infection.
Long-Term (Months to years):
Recurrence of adhesive SBO.
Short Gut Syndrome (if extensive resection was needed).
IX. Prognosis
Uncomplicated SBO: Mortality is low (<5%) with appropriate management.
Complicated (Strangulated) SBO: Mortality can be as high as 20-30% if diagnosis and surgery are delayed.
Top Prognostic Factors:
Presence of bowel ischemia/necrosis.
Patient's age and comorbidities.
Timeliness of intervention.
X. How to Present to Your Senior
Use the SBAR format (Situation, Background, Assessment, Recommendation).
"Dr, for review please.
(S) This is Mr. Tan in ED Zone Merah, a 65-year-old gentleman who presented with central colicky abdominal pain and faeculent vomiting for one day. He is tachycardic at 110 but his BP is stable.
(B) He had an open appendicectomy 10 years ago. He has no other medical issues.
(A) On examination, his abdomen is distended and tender centrally but soft, with no peritonism. His AXR shows dilated small bowel loops. My provisional diagnosis is uncomplicated adhesive small bowel obstruction.
(R) I have already started the 'drip and suck' protocol with IV Hartmann's and inserted a Ryles tube which has drained 500mls of faeculent fluid. I have sent off his bloods including a GXM. Can I request a CT scan to confirm and rule out complications?"
XI. Summary & Further Reading
Top 3 Takeaways:
Adhesions from previous surgery are the number one cause. Always ask about scars.
Initial management is always resuscitation and decompression: "NBM, IVD, NGT, Catheter, Charting".
Your main job is to identify the red flags of strangulation (fever, peritonism, tachycardia, high lactate) which mandate immediate surgical consultation.
Key Resources:
UpToDate: Search for "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults".
Review Article: A good overview is the Bologna Guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO). PMID: 28938933
Amboss: Search "Small Bowel Obstruction". It has an excellent workflow summary.
