Bowel Obstruction
SBO (#1 cause: adhesions) vs LBO (#1 cause: colorectal cancer). Know when to manage conservatively vs when strangulation signs mandate the OR. Sigmoid volvulus = scope first. Cecal volvulus = surgery.
Overview
SBO vs LBO
| Feature | SBO | LBO |
|---|---|---|
| #1 Cause | Adhesions | Colorectal cancer |
| Other | Hernias, malignancy, Crohn | Volvulus (sigmoid > cecal) |
| Conservative | NGT, NPO, IVF ×48–72h | Depends on cause |
| Surgery | Complete, strangulation, failure to resolve | Cancer → resection. Cecal volvulus → surgery |
Volvulus
| Type | First-Line | Definitive |
|---|---|---|
| Sigmoid | Endoscopic decompression | Interval resection |
| Cecal | Surgery (scope does NOT work) | Right hemicolectomy |
Strangulation signs = SURGICAL EMERGENCY: fever, peritoneal signs, free air, leukocytosis, lactate elevation, non-reducible hernia.
CT Imaging Findings
| Finding | Significance |
|---|---|
| Transition point | Dilated proximal bowel → decompressed distal bowel. Identifies the site of obstruction. Distinguishes SBO from ileus (no transition point in ileus). |
| Air-fluid levels | Multiple, differential levels on upright film. Stepladder pattern classic for SBO. |
| Small bowel feces sign | Particulate matter in dilated SB near transition point. Suggests prolonged obstruction with bacterial overgrowth. |
| Closed-loop obstruction | U-shaped or C-shaped dilated loop with 2 transition points converging. HIGH risk of strangulation → surgical emergency. |
| Pneumatosis intestinalis | Air within bowel wall = ischemia/necrosis. Requires urgent surgery. |
| Portal venous gas | Air in portal system = bowel necrosis. Extremely ominous sign. Emergency laparotomy. |
| Mesenteric haziness / stranding | Suggests venous congestion or early ischemia. Correlate with lactate. |
| Whirl sign | Swirling of mesentery and bowel around a point = volvulus or internal hernia. |
Signs of Strangulation on CT (GO TO OR): Closed-loop obstruction, pneumatosis intestinalis, portal venous gas, mesenteric haziness with non-enhancing bowel wall, free fluid, and whirl sign. Any of these = do NOT attempt conservative management.
Conservative vs Operative Management
| Criteria | Conservative (Trial of Non-Op) | Operative (Go to OR) |
|---|---|---|
| Obstruction type | Partial SBO (contrast passes on CT) | Complete SBO, any LBO with obstruction |
| Etiology | Adhesive SBO (no virgin abdomen) | Hernia, closed-loop, volvulus, tumor |
| Clinical status | Stable, no peritonitis, tolerating NGT | Peritonitis, sepsis, hemodynamic instability |
| Labs | Normal lactate, normal WBC | Elevated lactate, leukocytosis, acidosis |
| Imaging | No closed-loop, no pneumatosis, no portal gas | Any sign of strangulation or ischemia |
| Time frame | Resolution expected within 48–72h | Failure to improve after 48–72h of conservative Rx |
Workup
Workup
- CT abdomen/pelvis with IV contrast, gold standard. Look for transition point, closed-loop, pneumatosis, portal venous gas
- CBC, BMP, lactate, lipase, type and screen
- Upright CXR if free air suspected (perforation)
- AXR: stepladder air-fluid levels (SBO), dilated colon >6 cm or cecum >9–12 cm (LBO)
Management
Conservative (Partial SBO)
- NGT decompression, NPO, IVF, serial exams q4–8h
- Gastrografin (diagnostic + therapeutic: reaches colon on 24h film = resolving)
Surgery Indications
- Complete obstruction, strangulation, closed-loop, failure to resolve 48–72h, incarcerated hernia
🔄 Updated Practice: Old teaching: mandatory nasogastric tube (NGT) decompression for all small bowel obstruction. Current practice: NGT is indicated for patients with significant vomiting, distension, or complete obstruction. Mild partial SBO with minimal symptoms can be managed with bowel rest, IV fluids, and observation without NGT. Water-soluble contrast (Gastrografin) challenge at 24-48h can be both diagnostic and therapeutic, appearance of contrast in the colon predicts resolution without surgery.
Gastrografin Challenge Protocol
| Step | Action | Details |
|---|---|---|
| 1 | Confirm appropriateness | Partial adhesive SBO, no signs of strangulation, no complete obstruction, no peritonitis |
| 2 | Administer Gastrografin | 100 mL water-soluble contrast via NGT (or PO if no NGT). Clamp NGT ×2h after administration |
| 3 | Abdominal X-ray at 8–24h | Check if contrast has reached the colon/cecum |
| 4a | Contrast in colon = RESOLVING | Advance diet. High negative predictive value for need of surgery (~98%). Defined by Defined, Abbas et al. meta-analysis, 2014 |
| 4b | Contrast NOT in colon by 24–48h | Likely requires operative intervention. Surgical consult if not already involved |
Why Gastrografin works therapeutically: Hyperosmolar contrast draws fluid into bowel lumen → reduces bowel wall edema → promotes peristalsis past partial obstruction. Do NOT use barium (if perforation occurs, barium peritonitis is fatal; Gastrografin is water-soluble and absorbed).
LBO-Specific Management
| Etiology | Acute Management | Definitive Treatment |
|---|---|---|
| Colorectal cancer | Colonic stent (bridge to surgery) or diverting colostomy | Oncologic resection with primary anastomosis or Hartmann procedure |
| Sigmoid volvulus | Endoscopic decompression + rectal tube | Interval sigmoid resection (recurrence rate >50% without surgery) |
| Cecal volvulus | Surgery (endoscopy does NOT work) | Right hemicolectomy (cecopexy has high recurrence) |
| Pseudo-obstruction (Ogilvie) | Neostigmine 2 mg IV (monitor for bradycardia). Colonoscopic decompression if fails | Correct underlying cause (post-op, electrolytes, medications) |
Cecal diameter >12 cm = perforation risk. If cecum >9–12 cm on imaging in LBO or Ogilvie syndrome, urgent decompression is needed regardless of etiology.
Medications
Medications
| Drug | Role |
|---|---|
| NS / LR | Aggressive volume resuscitation |
| Gastrografin | 100mL via NGT (diagnostic + therapeutic) |
| Ondansetron | Antiemetic 4mg IV q6h |
| Pip-tazo / Cefepime + Metro | If strangulation/perforation suspected |
On Rounds
SBO vs ileus?
SBO = mechanical (transition point on CT, dilated proximal, decompressed distal). Ileus = functional (diffuse dilation, no transition point). Ileus: post-op, opioids, hypoK, peritonitis.
Why does scope work for sigmoid but not cecal volvulus?
Sigmoid twists at accessible location → sigmoidoscopy can pass tube past twist. Cecal volvulus = cecum twists on mesentery, too proximal for scope. Cecal = surgery (cecopexy or right hemicolectomy).
What is a closed-loop obstruction and why is it dangerous?
A closed-loop obstruction occurs when a segment of bowel is obstructed at two points (e.g., adhesive band trapping a loop). The trapped segment cannot decompress proximally or distally → rapidly increasing intraluminal pressure → venous congestion → arterial compromise → ischemia and necrosis. CT shows U-shaped or C-shaped dilated loop with two adjacent transition points.
What does the Gastrografin challenge tell you, and when should you NOT use it?
Gastrografin in colon by 8–24h = SBO is resolving (98% negative predictive value for surgery). Also therapeutic, hyperosmolar contrast reduces bowel wall edema and promotes peristalsis. Do NOT use if: complete obstruction, signs of strangulation, peritonitis, or suspected perforation. Never use barium (barium peritonitis is fatal if perforation occurs). Abbas et al., Ann Surg, 2014
Name 3 CT findings that indicate bowel ischemia/strangulation and mandate surgery.
(1) Pneumatosis intestinalis, air within bowel wall = necrosis. (2) Portal venous gas, air in portal system, extremely ominous. (3) Non-enhancing bowel wall on IV contrast CT, indicates loss of blood supply. Other concerning signs: closed-loop, mesenteric haziness/free fluid, whirl sign.
What is the #1 cause of LBO and how do you manage malignant LBO acutely?
Colorectal cancer is the #1 cause of LBO. Acute management: colonic stent as a bridge to surgery (allows bowel decompression, optimization of nutritional status, and staging before elective resection) or diverting loop colostomy if stent not feasible. Definitive: oncologic resection. Emergent surgery for LBO carries higher morbidity/mortality vs elective resection after stent decompression.
How do you differentiate SBO from Ogilvie syndrome (acute colonic pseudo-obstruction)?
Ogilvie = massive colonic dilation WITHOUT mechanical obstruction. CT shows dilated colon (often >10 cm) with no transition point and no obstructing lesion. Typically post-operative, critically ill, or electrolyte deranged patients. Treatment: correct underlying cause, neostigmine 2 mg IV (monitor for bradycardia, have atropine ready), or colonoscopic decompression. Surgery if cecum >12 cm or perforation. Ponec et al., NEJM, 1999
A patient with adhesive SBO has been managed conservatively for 72 hours with no improvement. What do you do?
Failure to resolve after 48–72 hours of conservative management is an indication for surgery. Prolonged obstruction increases risk of strangulation, bacterial translocation, and aspiration. If Gastrografin was given and has NOT reached the colon by 48h, this further supports operative intervention. Consult surgery early, delayed surgical intervention in SBO is associated with increased morbidity.
Clinical Examples
📋 Case 1, Adhesive SBO Managed Conservatively
Patient: 54F with history of open appendectomy (20 years ago) and prior cesarean section. Presents with 24 hours of crampy abdominal pain, nausea, bilious vomiting ×4, and obstipation. No prior SBO episodes.
Exam: Abdomen distended, tympanitic, diffusely tender without rebound or guarding. High-pitched bowel sounds. No hernias on exam. Temp 37.1, HR 98, BP 110/70.
Labs: WBC 9.2, lactate 1.1, BMP notable for K+ 3.2, Cr 1.3 (baseline 0.8, dehydration).
CT abdomen/pelvis: Dilated small bowel loops up to 4.5 cm with a transition point in the RLQ at a band adhesion. Decompressed distal ileum and colon. No closed-loop, no pneumatosis, no portal venous gas. Small amount of contrast passes the transition point (partial SBO).
Management:
- Conservative: NGT placed (high output, 800 mL in first 4h), NPO, aggressive IVF with LR, K+ repletion
- Gastrografin challenge: 100 mL via NGT at 24h. AXR at 8h shows contrast reaching cecum → resolving
- NGT output declining. Clears by 36h. NGT removed
- Diet advanced: clears → low-residue → regular. Passing flatus and stool by 48h
- Discharged day 3 with dietary counseling and return precautions
Key lesson: Partial adhesive SBO without strangulation signs is the ideal candidate for conservative management. Gastrografin reaching the colon by 8–24h has a 98% negative predictive value for need of surgery.
📋 Case 2, Strangulated SBO Requiring OR
Patient: 68M with history of multiple prior abdominal surgeries (cholecystectomy, ventral hernia repair with mesh). Presents with acute-onset severe periumbilical pain ×8 hours, now constant and worsening. Multiple episodes of non-bilious emesis.
Exam: Distended, rigid abdomen with involuntary guarding and rebound tenderness. Absent bowel sounds. Temp 38.9, HR 122, BP 88/54, lactate 6.8.
Labs: WBC 22,000, lactate 6.8, BMP with K+ 5.1, Cr 2.1, metabolic acidosis (pH 7.28, bicarb 16).
CT abdomen/pelvis: Closed-loop obstruction in mid-abdomen with C-shaped dilated loop, two adjacent transition points, pneumatosis intestinalis in the affected segment, mesenteric haziness, and small-volume free fluid. No portal venous gas.
Management:
- Resuscitation: 2L LR bolus, NGT (feculent output), Foley, broad-spectrum antibiotics (pip-tazo 4.5g IV)
- Emergency surgery: NO conservative trial, closed-loop + pneumatosis = strangulation. Taken to OR within 2 hours of arrival
- Intra-op: Dense adhesive band causing closed-loop. 60 cm of non-viable small bowel (dusky, no peristalsis, no Doppler signal). Small bowel resection with primary anastomosis
- Post-op ICU: continued antibiotics, serial lactate (normalized by 12h), nutrition via NG feeds on POD 3
- Discharged POD 7 tolerating regular diet
Key lesson: Peritonitis + hemodynamic instability + closed-loop + pneumatosis = NO role for conservative management. These patients need immediate operative intervention. Elevated lactate >4 with leukocytosis strongly suggests bowel ischemia.
📋 Case 3, Malignant LBO with Colonic Stent
Patient: 73M with 3-week history of progressive constipation, abdominal distension, and colicky pain. No BM ×5 days. No prior abdominal surgery. 15 lb weight loss over 2 months.
Exam: Markedly distended abdomen, tympanitic. Mild diffuse tenderness, no peritonitis. Empty rectal vault on DRE. Temp 37.2, HR 90, BP 135/80.
Labs: WBC 11, lactate 1.4, Hgb 9.2 (microcytic, iron deficiency), CEA 28 (elevated).
CT abdomen/pelvis: Dilated colon (cecum 10 cm) with transition point at splenic flexure, circumferential mass causing near-complete LBO. No perforation. Multiple hepatic lesions concerning for metastatic disease. Ileocecal valve competent (no decompression into small bowel).
Management:
- Acute decompression: Interventional GI places a self-expanding metal stent (SEMS) across the obstructing lesion via colonoscopy, “bridge to surgery”
- Patient begins passing flatus and stool within 12h. Cecal dilation resolves on repeat AXR
- Staging workup: CT chest (no pulmonary mets), liver MRI confirms 3 bilobar hepatic metastases. Biopsy: moderately differentiated adenocarcinoma. KRAS mutant. Stage IVA
- MDT discussion: Given metastatic disease, neoadjuvant FOLFOX + bevacizumab started. Elective left hemicolectomy planned after 3–4 cycles if response to chemo
- Stent allows nutritional optimization and avoidance of emergent surgery (which carries 15–20% mortality in obstructed CRC vs <5% elective)
Key lesson: Colonic stenting as a bridge to surgery in malignant LBO allows decompression, staging, and optimization before definitive surgery. Emergent surgery for obstructing CRC has significantly higher morbidity and mortality than elective resection. CReST Collaborative, Lancet Oncol, 2022
Monitoring
| Parameter | Frequency |
|---|---|
| Abdominal exam | q4–8h |
| NGT output | q shift |
| CBC, lactate | q8–12h |
Summary
Summary
Start With Small Bowel or Large Bowel
SBO: adhesions are the number one cause (then hernias, malignancy, Crohn disease), and prior abdominal surgery is the history that gives it away. LBO: colorectal cancer is the number one cause, then volvulus, so every new LBO needs a cancer workup once the obstruction is relieved.
Initial Management Is the Same Four Things
NPO, IV fluids, correct electrolytes, and serial abdominal exams. Third-spacing into obstructed bowel is large and underestimated, so these patients are usually far more volume-depleted than they look.
The NG Tube Is No Longer Automatic
Old teaching was an NG tube for every SBO; current practice is selective. Decompress the patient with significant vomiting, distension or complete obstruction. A mild partial obstruction without vomiting does not need one, and the tube itself causes sinusitis and discomfort.
What Sends Them to the Operating Room
Strangulation is a surgical emergency: fever, peritoneal signs, leukocytosis, rising lactate, free air, or a non-reducible hernia. On CT: closed-loop obstruction, pneumatosis intestinalis, portal venous gas, the whirl sign, free fluid, or a non-enhancing bowel wall. Any one of these means do not attempt conservative management, because the bowel is already ischemic.
Conservative Management Has a Clock
Give an uncomplicated partial SBO 48 to 72 h. Failure to resolve in that window is itself an indication to operate: the ones that were going to open up mostly have by then, and waiting longer just delays surgery on progressively sicker bowel.
Gastrografin Is Both Test and Treatment
Give water-soluble contrast and repeat the abdominal film at 8 to 24 h. Contrast reaching the colon predicts resolution and often produces it. The hyperosmolar contrast pulls fluid into the lumen, reduces bowel wall edema and restarts peristalsis past a partial obstruction. Never use barium: if the bowel perforates, barium peritonitis is catastrophic.
Volvulus Splits by Location
Sigmoid volvulus: scope first. Endoscopic decompression works, and it is followed by interval resection because recurrence is high. Cecal volvulus: surgery. Endoscopic decompression does not work here; the operation is a right hemicolectomy.
Watch the Cecum in Any LBO
A cecal diameter above 12 cm is a perforation risk. The cecum has the thinnest wall and the largest radius, so by Laplace's law it blows first. Anything from 9 to 12 cm needs urgent decompression regardless of the cause, including Ogilvie syndrome.
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