Large Bowel Obstruction Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: Large Bowel Obstruction (LBO) is a common general surgical emergency, particularly in our elderly population. A delayed diagnosis leads to bowel perforation, faecal peritonitis, and high mortality. You will see this frequently, both in the emergency department and on the wards.
High-Yield Definition: LBO is the mechanical interruption to the caudal flow of intestinal contents in the colon. This blockage leads to accumulation of gas and fluid proximal to the obstruction, causing progressive bowel distension.
Clinical One-Liner: Basically, the colon is blocked. Nothing can get past. Your job is to resuscitate the patient, find out where and why it's blocked, and urgently determine if the bowel is about to perforate.
II. Etiology & Risk Factors
Etiology: In the adult Malaysian population, the causes are predictable.
Malignancy (approx. 60%): Colorectal adenocarcinoma is the most common cause. The sigmoid colon is the most frequent site.
Volvulus (approx. 15%): Twisting of the colon on its mesentery. Sigmoid volvulus is far more common than caecal volvulus, especially in elderly, institutionalised patients.
Diverticular Disease (approx. 10%): Usually due to stricturing from recurrent episodes of diverticulitis.
Others (Rare): Adhesions (more common in SBO), hernias (e.g., inguinal), inflammatory bowel disease strictures, or faecal impaction.
Risk Factors:
Non-Modifiable:
Age > 60 years
Personal or family history of colorectal cancer or polyps
History of Inflammatory Bowel Disease (IBD)
Modifiable/Other:
History of previous abdominal or pelvic surgery (risk for adhesions)
Chronic constipation, immobility, neuropsychiatric conditions (risk factors for sigmoid volvulus)
III. Quick Pathophysiology
The mechanism depends on the ileocaecal valve.
Competent Ileocaecal Valve (~85% of people): This creates a closed-loop obstruction. The colon is blocked distally by the tumour/volvulus and proximally by the valve. Gas and fluid are trapped, leading to rapid and massive distension. According to the Law of Laplace (T=P×R), the caecum, having the largest diameter, experiences the highest wall tension and is the most common site for perforation.
Incompetent Ileocaecal Valve: The pressure can decompress backwards into the small bowel. This results in less colonic distension but more prominent vomiting, and the clinical picture may mimic a small bowel obstruction.
In both scenarios, rising intraluminal pressure compresses mucosal veins, leading to bowel wall oedema, which then impairs arterial inflow, causing ischemia, necrosis, and eventual perforation.
IV. Clinical Assessment
Red Flags & Immediate Actions:
Peritonism (rebound tenderness, guarding): Indicates perforation or ischemia. -> Action: Alert senior/surgical registrar immediately, keep NBM, secure two large-bore IV cannulas, start fluid resuscitation, and prepare patient for emergency laparotomy.
Systemic Toxicity (Fever >38°C, Tachycardia >100, Hypotension SBP <90 mmHg): Suggests sepsis from perforation or bacterial translocation. -> Action: Same as above, plus take blood cultures and start IV broad-spectrum antibiotics as per your hospital's sepsis protocol (e.g., IV Ceftriaxone 2g OD + IV Metronidazole 500mg TDS).
History:
Common (>50%):
Absolute Constipation: Inability to pass faeces and flatus. This is the cardinal symptom.
Abdominal Distension: Progressive and often massive bloating.
Colicky Abdominal Pain: Typically infra-umbilical. Pain becoming constant is an ominous sign of ischemia.
Less Common (10-50%):
Vomiting: A late feature, especially with a competent ileocaecal valve. Faeculent vomiting is a very late sign.
Pertinent Negatives & Associated Symptoms:
Ask about preceding symptoms suggestive of malignancy: change in bowel habits, rectal bleeding (PR bleeding), loss of weight, loss of appetite.
Physical Examination:
General: Check hydration status (dry mucous membranes, reduced skin turgor) and vital signs for tachycardia/hypotension.
Abdomen:
Inspection: Markedly distended abdomen.
Palpation: Generalised tenderness. Look for signs of peritonism. Try to palpate for any masses.
Percussion: Tympanitic (drum-like) due to trapped gas.
Auscultation: Bowel sounds are often high-pitched ("tinkling") in the early stages, becoming silent later on, which is a worrying sign.
Digital Rectal Examination (DRE): This is mandatory. The rectum is typically empty in mechanical LBO. You may also feel a rectal tumour.
Clinical Pearl: The combination of a massively distended, tympanitic abdomen and an empty rectum on DRE is highly suggestive of a mechanical LBO until proven otherwise.
V. Diagnostic Workflow
Differential Diagnosis:
Colonic Pseudo-obstruction (Ogilvie's Syndrome):
Points For: Massive colonic dilation, often in medically unwell or post-operative patients.
Points Against: No mechanical obstruction or transition point.
How to Differentiate: CT scan shows diffuse dilation of the colon, often to the rectum, without a discrete transition point.
Small Bowel Obstruction (SBO):
Points For: Abdominal distension, vomiting, constipation.
Points Against: Vomiting is earlier and more profuse than in LBO. Pain is usually central/epigastric. AXR shows central loops with valvulae conniventes.
How to Differentiate: CT scan will locate the transition point within the small bowel.
Severe Constipation / Faecal Impaction:
Points For: Obstipation, distension, may have spurious diarrhoea (overflow).
Points Against: Usually a long history of chronic constipation.
How to Differentiate: DRE reveals a rectum packed with hard stool. AXR shows extensive faecal loading throughout the colon.
Investigations Plan:
Bedside / Initial (First 15 Mins):
Venous Blood Gas (VBG): Check lactate levels. A rising lactate is a strong indicator of bowel ischemia.
ECG: Essential baseline for any elderly patient who may require surgery.
First-Line Labs & Imaging:
Bloods:
Full Blood Count (FBC): Leucocytosis may indicate inflammation or perforation.
Renal Profile, Electrolytes: Assess for dehydration and electrolyte disturbances from third-spacing and poor intake.
Group & Cross Match (GXM): Mandatory preparation for potential surgery.
Imaging:
Erect Chest X-ray (CXR): The primary purpose is to look for pneumoperitoneum (free air under the diaphragm), which confirms perforation.
Supine Abdominal X-ray (AXR): Look for peripherally located, dilated large bowel loops (>6 cm in diameter, caecum >9 cm is alarming) with visible haustral markings. The distal colon and rectum will have no air.
Confirmatory / Gold Standard:
CT Scan of Abdomen and Pelvis with IV Contrast: This is the definitive investigation. It will:
Confirm the diagnosis of obstruction.
Identify the precise location and cause (the "transition point").
Detect signs of complications (ischemia, perforation, closed-loop).
VI. Staging & Severity Assessment
Clinically, LBO is staged based on the presence of complications. This dictates the urgency of management.
Simple (Uncomplicated) LBO: Mechanical blockage is present, but the bowel wall is still viable and intact. The patient is haemodynamically stable with no signs of peritonism.
Complicated LBO: The obstruction is associated with:
Ischemia: Compromised blood supply to the bowel. Suggested by constant severe pain, high lactate, and CT findings like bowel wall thickening or pneumatosis intestinalis (air in the bowel wall).
Perforation: A hole in the bowel wall. Confirmed by free air on CXR or CT.
Closed-Loop Obstruction: High risk of rapid progression to ischemia and perforation.
Management Impact: Simple LBO allows for a brief period of resuscitation and planning. Complicated LBO is a surgical emergency requiring immediate intervention.
VII. Management Plan
Immediate Stabilisation (The "Drip and Suck" Plan):
A: Airway - ensure patent.
B: Breathing - give high-flow oxygen via a non-rebreather mask.
C: Circulation - IV access with two large-bore cannulas. Start aggressive fluid resuscitation with warmed crystalloids (e.g., Hartmann's solution or Normal Saline).
"Drip": IV fluids are crucial. These patients are severely dehydrated due to third-space losses.
"Suck":
Nil By Mouth (NBM): Rest the bowel.
Nasogastric (NG) Tube: Insert an NG tube and set to free drainage to decompress the stomach, especially if the patient is vomiting.
Monitoring: Insert a urinary catheter to accurately monitor urine output as a guide for adequacy of resuscitation (aim for >0.5 mL/kg/hour).
Medications: Provide IV analgesia. Start empiric broad-spectrum antibiotics if sepsis or perforation is suspected.
Definitive Treatment (The Ward Round / Surgical Plan): This is decided by the surgical team based on the cause, patient stability, and CT findings.
Non-Operative / Endoscopic:
Sigmoid Volvulus: Can often be decompressed with a flexible sigmoidoscopy and insertion of a flatus tube. This is usually followed by elective surgery later to prevent recurrence.
Malignant Obstruction: In selected cases (e.g., palliative setting or as a "bridge-to-surgery"), a self-expanding metal stent (SEMS) can be placed endoscopically across the tumour to relieve the obstruction.
Emergency Surgery: The mainstay of treatment for most cases. The choice of operation depends on the findings:
Hartmann's Procedure: Resection of the diseased segment of colon, creation of an end colostomy, and oversewing the rectal stump. This is a safe "damage control" option for unstable patients with perforation.
Resection and Primary Anastomosis: Resection of the obstruction and re-joining the bowel. May be done with or without a covering loop ileostomy to protect the join.
Diverting Loop Colostomy/Ileostomy: A stoma is created proximal to an irremovable obstruction to bypass it.
VIII. Complications
Immediate (Pre-operative):
Bowel Perforation: Management: Emergency laparotomy, peritoneal lavage, and resection (usually Hartmann's).
Sepsis & Septic Shock: Management: Aggressive fluid resuscitation, IV antibiotics, and urgent source control (surgery).
Short-Term (Post-operative):
Anastomotic Leak: Management: May require antibiotics, percutaneous drainage, or return to theatre.
Surgical Site Infection, Paralytic Ileus, Stoma-related issues.
Long-Term:
Incisional Hernia.
Adhesional Small Bowel Obstruction.
Recurrence of malignancy.
IX. Prognosis
The outcome is highly dependent on three factors:
Cause: Obstruction from benign causes like volvulus (if treated early) has a better prognosis than that from advanced malignancy.
Presence of Complications: Mortality for uncomplicated LBO is around 5-10%, but this rises sharply to >30% if perforation and faecal peritonitis are present.
Patient's Premorbid Status: Frailty and significant comorbidities increase surgical risk and mortality.
X. How to Present to Your Senior
Use the SBAR (Situation, Background, Assessment, Recommendation) format.
"Dr, for review please.
(S)ituation: This is Mr. Tan in Red Zone, Bed 3. He is a 70-year-old gentleman who presented with a 3-day history of absolute constipation and abdominal distension.
(B)ackground: He has no significant past medical history and is not on any regular medications.
(A)ssessment: On examination, he is tachycardic at 110, but his blood pressure is stable. His abdomen is markedly distended and tympanitic, but currently soft with no signs of peritonism. A DRE reveals an empty rectum. My main differential is a large bowel obstruction, likely secondary to a sigmoid malignancy.
(R)ecommendation: I have kept him NBM, started IV Hartmann's, and sent off bloods including a GXM. The erect CXR shows no free air. I would like to request an urgent CT scan of the abdomen and pelvis to confirm the diagnosis and identify the cause. I have also informed the surgical team on-call."
XI. Summary & Further Reading
Top 3 Takeaways:
Think of LBO in any elderly patient with abdominal distension and absolute constipation.
The immediate management is resuscitation ("drip and suck") while urgently investigating with a CT scan.
Your primary role is to identify the red flags of complication (peritonism, sepsis) which mandate immediate escalation for emergency surgery.
Key Resources:
UpToDate: Search for "Large bowel obstruction". An excellent, evidence-based overview.
StatPearls: Large Bowel Obstruction - A good high-yield summary.
BMJ Best Practice: Large bowel obstruction - Provides a clear, structured approach to management.
