Small Bowel Obstruction & Ileus
SBO: mechanical obstruction (adhesions #1, hernias #2). Ileus: functional without mechanical cause. CT with IV contrast is diagnostic. Most partial SBO resolves with NGT + bowel rest. Surgical emergency if strangulation.
🔍 Overview
SBO vs Ileus
| Feature | SBO (Mechanical) | Ileus (Functional) |
|---|---|---|
| Cause | Adhesions (#1, 60–75%), hernias, tumor, volvulus | Post-operative, electrolyte imbalance, opioids, peritonitis |
| Imaging | Dilated proximal bowel + decompressed distal bowel + transition point | Diffuse dilation of small AND large bowel, no transition point |
| Air-fluid levels | Multiple, differential (step-ladder pattern) | Few, similar height |
| Management | NGT, NPO, IVF. Surgery if complete/strangulated. | Treat underlying cause. Bowel rest. Ambulation. |
Signs of strangulation (surgical emergency): Fever, tachycardia, peritonitis, leukocytosis, elevated lactate, non-reducible hernia, pneumatosis on CT. Do NOT delay surgery.
Partial vs Complete SBO
| Feature | Partial SBO | Complete SBO |
|---|---|---|
| Gas in colon | Present | Absent |
| Passage of flatus/stool | May continue initially | Absent (obstipation) |
| CT findings | Transition point with some distal bowel gas | Discrete transition point, no distal gas, "small bowel feces sign" |
| Conservative trial | Resolves in 60-80% without surgery | Higher failure rate, closer surgical monitoring |
| Gastrografin useful? | Yes, both diagnostic and therapeutic | Less therapeutic benefit, more for surgical decision-making |
Risk Factors for Adhesive SBO
- Prior abdominal surgery - single greatest risk factor. Lower GI and pelvic surgeries have highest adhesion rates Menzies & Ellis, Ann Surg 1990
- Number of prior laparotomies - risk increases with each additional surgery
- Type of surgery - open > laparoscopic for adhesion formation Strik et al, Lancet 2016
- Peritonitis/contamination - inflammatory peritoneal environment drives adhesion formation
- Foreign bodies - mesh, drains, retained surgical materials
Key stat: Adhesive SBO accounts for ~$2.3 billion/year in US healthcare costs and 350,000+ hospital admissions annually. It is the most common cause of surgical emergencies in developed countries.
🚨 Management
Conservative Management (Partial SBO)
- NPO -strict bowel rest
- NGT to low intermittent suction -decompression
- IV fluids -aggressive resuscitation (3rd-spacing)
- Electrolyte repletion -K, Mg, PO₄
- Serial abdominal exams q4–8h
- Water-soluble contrast (Gastrografin) -both diagnostic and therapeutic. If contrast reaches colon by 24h → likely to resolve without surgery
Surgical Indications
- Complete SBO with no improvement in 48–72h
- Signs of strangulation/ischemia
- Closed-loop obstruction
- Free air (perforation)
- Incarcerated/strangulated hernia
Gastrografin Challenge Protocol
| Step | Action | Details |
|---|---|---|
| 1 | Confirm partial SBO | CT showing transition point without signs of strangulation or complete obstruction |
| 2 | Administer Gastrografin | 100 mL via NGT (clamp NGT for 2h after) |
| 3 | Abdominal XR at 8h | Early check for contrast progression |
| 4 | Abdominal XR at 24h | Definitive assessment |
| 5a | Contrast in colon at 24h | High likelihood of non-operative resolution. Continue conservative management |
| 5b | No contrast in colon at 24h | Unlikely to resolve. Surgical consultation for operative planning |
Evidence: Defined meta-analysis, Br J Surg 2014 Meta-analysis of 14 RCTs: Gastrografin reduced need for surgery (RR 0.62) and shortened hospital stay by ~1.8 days. Contrast reaching the colon within 24h has a 97% sensitivity for predicting non-operative resolution. Branco et al, World J Surg 2010
Timeline for Conservative Management
- 0-24h: NPO, NGT, IVF, serial exams. Administer Gastrografin if partial SBO
- 24h: Assess Gastrografin follow-through XR. If contrast in colon, continue conservative Rx
- 48-72h: Maximum window for conservative trial in partial SBO without improvement
- 72h+: If no resolution, strongly consider surgical exploration
Bologna Guidelines: Ten Broek et al, World J Emerg Surg 2018 Recommended maximum 72h conservative trial for uncomplicated adhesive SBO. Earlier intervention if clinical deterioration (rising lactate, worsening pain, peritonitis). Delayed surgery associated with higher complication rates and longer hospital stay.
🧪 Workup
- CT abdomen/pelvis with IV contrast -gold standard. Shows transition point, dilated vs decompressed bowel, signs of ischemia
- Abdominal X-ray -dilated small bowel (> 3 cm), air-fluid levels, absent distal gas (complete SBO)
- BMP -dehydration, electrolyte derangements
- CBC -leukocytosis (strangulation)
- Lactate -elevated with ischemia/strangulation
- Lipase -rule out pancreatitis
CT Findings: What to Look For
| Finding | Significance | Action |
|---|---|---|
| Transition point | Location where dilated bowel transitions to decompressed | Confirms mechanical obstruction vs ileus |
| Small bowel feces sign | Particulate matter in dilated small bowel proximal to obstruction | Suggests prolonged/complete obstruction Mayo-Smith et al, AJR 1999 |
| Decreased wall enhancement | Bowel wall ischemia | Urgent surgical consultation |
| Mesenteric haziness/stranding | Venous congestion, early ischemia | Close monitoring, lower threshold for surgery |
| Pneumatosis intestinalis | Gas in bowel wall - necrosis | Surgical emergency |
| Portal venous gas | Severe ischemia/necrosis | Surgical emergency |
| Free fluid | Strangulation until proven otherwise | Surgical consultation |
| Closed-loop sign | U-shaped or C-shaped dilated loop with convergence of mesentery | High risk for strangulation - surgery |
CT accuracy: CT has 94% sensitivity and 96% specificity for SBO diagnosis. For detecting strangulation, sensitivity is 83% and specificity 93%. Defined, Radiology 2009
💊 Medications
| Drug | Dose | Purpose |
|---|---|---|
| IV Normal Saline | Bolus 1–2 L then maintenance | Volume resuscitation -significant 3rd-spacing |
| Ondansetron (Zofran) | 4 mg IV q6h PRN | Anti-emetic |
| Gastrografin | 100 mL via NGT | Water-soluble contrast -diagnostic and therapeutic (osmotic draws fluid into lumen) |
| Piperacillin-Tazobactam (Zosyn) | 3.375 g IV q6h | If strangulation/perforation suspected -broad-spectrum coverage |
| AVOID opioids | - | Worsen ileus. Use non-opioid pain management when possible. |
📋 On Rounds
Pimp Questions
What is the most common cause of SBO in developed countries?
Adhesions from prior abdominal surgery (60–75%). Second most common: hernias (incarcerated inguinal, ventral, internal). Third: malignancy. In patients with NO prior surgery, always examine for hernias carefully -groin, umbilical, incisional sites.
How does Gastrografin help in SBO management?
Dual role: (1) Diagnostic -if contrast reaches the colon on follow-up XR at 24h, the SBO will likely resolve non-operatively (high negative predictive value for need for surgery). (2) Therapeutic -hyperosmolar → draws fluid into bowel lumen → reduces edema at obstruction point → may help resolve partial SBO. Meta-analyses show reduced need for surgery and shorter hospital stay.
What are the signs of strangulated SBO?
Clinical: Fever, tachycardia, localized peritonitis (rebound/guarding), non-reducible hernia. Labs: Leukocytosis, elevated lactate, metabolic acidosis. CT findings: Mesenteric haziness/fluid, bowel wall thickening, decreased/absent wall enhancement, pneumatosis intestinalis (gas in bowel wall). This is a surgical emergency -do not delay for further workup.
What is the role of CT vs plain film in SBO diagnosis?
CT abdomen/pelvis with IV contrast is the gold standard (94% sensitivity, 96% specificity). Plain films are less sensitive (~70%) and cannot identify the cause, level, or complications of obstruction. CT shows transition point, etiology (adhesion vs hernia vs tumor), and signs of strangulation (decreased enhancement, pneumatosis, portal venous gas). Plain film is acceptable for initial screening in ED but CT should follow.
What is the "small bowel feces sign" on CT?
Particulate matter (gas mixed with solid debris) seen in dilated small bowel proximal to the obstruction. Looks like colonic contents in the small bowel. Indicates prolonged or high-grade obstruction - the stagnant small bowel contents have been broken down by bacteria. Associated with 82% specificity for complete or high-grade SBO. Does NOT necessarily mean strangulation, but indicates the obstruction has been present for some time.
When should you NOT attempt conservative management of SBO?
Go directly to surgery for: (1) Strangulation signs - fever, peritonitis, tachycardia, rising lactate, CT showing ischemia. (2) Closed-loop obstruction - high risk of rapid progression to strangulation. (3) Free air on imaging - perforation. (4) Incarcerated hernia that cannot be reduced. (5) Complete SBO with no improvement after 48-72h of conservative trial. Delayed surgery in strangulated SBO increases mortality from ~5% to 25%+.
What is the difference between SBO in a "virgin abdomen" vs post-surgical?
In a virgin abdomen (no prior surgery), adhesions are NOT the cause. Must evaluate for: incarcerated hernia (examine groin, umbilicus, prior incision sites carefully), malignancy (especially colon/ovarian with peritoneal carcinomatosis), Crohn disease (strictures), gallstone ileus (large gallstone erodes through into duodenum and impacts at ileocecal valve - look for pneumobilia on CT), internal hernia, or Meckel diverticulum. These patients more often require surgery.
What electrolyte abnormalities do you expect in SBO with prolonged vomiting?
Hypochloremic hypokalemic metabolic alkalosis - from loss of gastric HCl and K+ in vomitus. Also: hypovolemia from third-spacing and poor oral intake, prerenal AKI, hypomagnesemia, hypophosphatemia. The alkalosis perpetuates hypokalemia (K+ shifts intracellularly in exchange for H+). Correct the volume deficit and Cl- first (with NS), and the kidneys will retain K+ and correct the alkalosis.
What is the recurrence rate of adhesive SBO after conservative management vs surgery?
After conservative management, recurrence rate is 20-40% within 5 years. After surgical adhesiolysis, recurrence is 15-30% - only slightly lower because surgery itself creates new adhesions. The Defined, Surg Endosc 2014 showed laparoscopic adhesiolysis may have lower recurrence than open. Key prevention strategies: minimize peritoneal trauma, use laparoscopic technique when possible, and consider adhesion barriers in high-risk patients.
Clinical Examples
📋 Case 1 - Partial Adhesive SBO Managed Conservatively
Patient: 58M with PMH of appendectomy 20 years ago presents with 1 day of crampy abdominal pain, nausea, vomiting, and decreased flatus.
Exam: Abdomen distended, diffusely tender without peritonitis. Well-healed RLQ scar. BS hyperactive. T 37.1, HR 95, BP 130/78.
Labs: WBC 9.2, lactate 1.1, BMP with Cr 1.4 (baseline 0.9), K 3.2, Cl 94.
CT: Dilated small bowel to 4.2 cm with transition point in mid-ileum. Decompressed distal bowel. Some gas in colon. No signs of ischemia.
Assessment: Partial adhesive SBO. No strangulation.
Management: NPO, NGT to LIWS, NS at 150 mL/hr, K repletion. Gastrografin 100 mL via NGT. AXR at 24h: contrast in colon. Diet advanced on day 2. Discharged day 3.
📋 Case 2 - Complete SBO with Strangulation Requiring Surgery
Patient: 72F with PMH of hysterectomy and two prior laparotomies presents with 3 days of worsening abdominal pain, no flatus or stool for 48h, and bilious vomiting.
Exam: Distended, rigid abdomen with rebound tenderness in periumbilical area. Absent bowel sounds. T 38.9, HR 120, BP 88/52.
Labs: WBC 18.5, lactate 5.2, BMP with metabolic acidosis (HCO3 16), Cr 2.1.
CT: Dilated small bowel loops with transition point. Closed-loop configuration with C-shaped dilated segment. Decreased bowel wall enhancement. Mesenteric haziness and free fluid. No distal gas.
Assessment: Complete SBO with strangulation (closed-loop, elevated lactate, peritonitis, CT ischemic changes).
Management: Emergent surgical exploration (no conservative trial). IVF resuscitation. Piperacillin-tazobactam 4.5g IV. Found 30 cm of non-viable ileum. Small bowel resection with primary anastomosis. ICU post-op.
📋 Case 3 - SBO in Virgin Abdomen: Incarcerated Hernia
Patient: 65M with no surgical history presents with acute-onset periumbilical pain x6h, nausea, and 2 episodes of vomiting.
Exam: Firm, tender, non-reducible mass in right inguinal region. Abdomen distended and tympanic. T 37.5, HR 105.
Labs: WBC 11.2, lactate 2.0. BMP unremarkable.
CT: Right inguinal hernia containing small bowel loop. Proximal small bowel dilated. Bowel wall enhancing normally.
Assessment: SBO from incarcerated inguinal hernia. No strangulation yet (lactate mildly elevated but wall enhancing). Virgin abdomen: always examine for hernias.
Management: Attempted bedside reduction failed. Urgent surgical hernia repair with reduction. Viable bowel confirmed intra-operatively. Mesh repair. Diet advanced day 1. Discharged day 2.
⚡ Summary
SBO or Ileus
SBO is mechanical, with a transition point on CT, high-pitched or absent bowel sounds and colicky pain. Ileus is functional, with no transition point, diffusely dilated bowel including the colon, and quiet bowel sounds. The distinction matters because ileus never needs an operation: it needs the cause treated (electrolytes, opioids, post-operative state, sepsis).
Know the Causes
Adhesions are number one, then hernias, then malignancy and Crohn disease. Adhesive SBO drives over 350,000 admissions a year in the US and is the commonest surgical emergency in developed countries. Ask about prior abdominal surgery, and examine every hernia orifice, since an incarcerated hernia is both the cause and the cure.
Partial or Complete
Partial: continued passage of flatus or stool, some gas visible in the colon on imaging, and a good chance of resolving without surgery. Complete: obstipation with no distal gas, which resolves far less often and has a higher strangulation risk. That difference determines how long a conservative trial is reasonable.
Standard Conservative Management
NPO, IV fluids, correct electrolytes, nasogastric decompression for vomiting or significant distension, and serial abdominal examinations. These patients are markedly volume-depleted from third-spacing into obstructed bowel, so the fluid requirement is usually larger than it looks.
The Trial Has a 72-Hour Ceiling
The Bologna guidelines set a maximum 72-hour conservative trial for uncomplicated adhesive SBO. Failure to resolve within that window is itself an indication to operate, and earlier intervention if there is deterioration: rising lactate, worsening pain or peritonitis. Waiting longer only means operating on sicker bowel.
Gastrografin Predicts and Treats
Give water-soluble contrast and repeat the film; contrast reaching the colon within 24 h is about 97% sensitive for successful non-operative resolution. A meta-analysis of 14 randomized trials showed it reduced the need for surgery (RR 0.62) and shortened stay by about 1.8 days. Never use barium, because barium peritonitis after a perforation is catastrophic.
What Forces the Operation
Strangulation is a surgical emergency: fever, tachycardia, peritonitis, leukocytosis, rising lactate, a non-reducible hernia, or pneumatosis on CT. Also closed-loop obstruction, portal venous gas, free air, and failure of the conservative trial. Do not delay for further imaging once these are present.
Read the CT for More Than the Transition Point
CT is 94% sensitive and 96% specific for SBO, but only 83% sensitive for strangulation, so a scan that does not show ischemia does not exclude it and the clinical picture still wins. Look for the small bowel feces sign near the transition point, which suggests a longer-standing obstruction, and for a closed loop, mesenteric haziness, free fluid and a non-enhancing bowel wall. A first-time obstruction in a patient with no prior surgery is malignancy or hernia until proven otherwise, not adhesions.
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