Gastrointestinal

Large bowel obstruction and volvulus

Clinical Overview and When to Suspect Large Bowel Obstruction

— Colorectal cancer ~60% — most common cause of LBO in the US; left-sided lesions (sigmoid, descending) obstruct earlier due to narrower lumen and formed stool.

— Volvulus ~15% — sigmoid (older, debilitated, institutionalized, chronic constipation, neuropsychiatric meds) > cecal (younger women, prior surgery, pregnancy).

— Diverticular stricture ~10% — chronic inflammation in sigmoid.

— Hernia, intussusception (adult = malignancy until proven otherwise), anastomotic stricture, radiation, IBD strictures, fecal impaction.

— Progressive abdominal distention, obstipation (no flatus or stool >24–48 h), crampy infraumbilical pain, late feculent emesis.

— Elderly nursing-home patient with sudden massive distention → sigmoid volvulus.

— Older adult with weight loss, iron-deficiency anemia, change in stool caliber + obstructive symptoms → obstructing colorectal cancer.

— Closed-loop obstruction when competent (~75%): rapid cecal distention, ischemia, perforation risk when cecum >12 cm.

— Incompetent valve decompresses retrograde into small bowel, mimicking SBO.

Definition: Mechanical blockage of the colon or rectum preventing distal passage of stool/gas, distinct from ileus (functional) and pseudo-obstruction (Ogilvie's).

Epidemiology and etiology spectrum (adults):

When to suspect on the wards or in clinic:

Competence of the ileocecal valve matters:

Step 3 management: Any patient with suspected LBO needs early NPO, IV fluids, NG decompression if vomiting, electrolyte correction, type and screen, and upright/decubitus films or CT before colonoscopic or surgical decisions. Surgical consult should be placed at the time of imaging order, not after results — delays in source control drive mortality.

Board pearl: LBO in an adult >50 is colon cancer until biopsy proves otherwise; intussusception in an adult is malignancy until proven otherwise.

Presentation Patterns and Key History

— Crampy abdominal pain (infraumbilical, lower than SBO).

— Abdominal distention (more prominent than in SBO).

— Obstipation (failure to pass flatus is more specific than no stool).

— Vomiting — late, may become feculent; absence does not exclude LBO.

— Weeks–months of progressive constipation, narrowing stool caliber, hematochezia, weight loss, fatigue → obstructing colon cancer.

— Hours–days of sudden severe distention in an elderly, bed-bound patient on antipsychotics/anticholinergics → sigmoid volvulus.

— Recurrent episodes of self-resolving distention → intermittent volvulus or partial stricture.

— Postoperative patient day 3–5 with distention but passing flatus → think Ogilvie's pseudo-obstruction, not mechanical.

— Prior colonoscopy date and findings (screening adherence).

— Surgical history (adhesions favor SBO over LBO; prior right hemicolectomy raises anastomotic stricture).

— Diverticulitis history, radiation therapy (pelvic), IBD.

— Medications: opioids, anticholinergics, antipsychotics, calcium channel blockers — all promote dysmotility and volvulus.

— Nursing home or institutional residence, neurologic disease (Parkinson, chronic stroke, spinal cord injury) — strongly associated with sigmoid volvulus.

— Family history of CRC, Lynch, FAP.

Classic tetrad of mechanical LBO:

Tempo gives the etiology:

Key historical anchors to elicit:

Red-flag overlay symptoms suggesting ischemia/perforation: fever, tachycardia out of proportion, peritoneal signs, hematochezia with severe pain, sudden relief of pain followed by diffuse tenderness.

Key distinction: SBO patients vomit early and distend less; LBO patients distend dramatically and vomit late. Obstipation (no flatus) is the most reliable distinguishing symptom of complete obstruction at any level.

Board pearl: "Coffee-bean" abdomen visible on inspection in a thin elderly patient = sigmoid volvulus; ask immediately about constipation and psychotropic meds.

Physical Exam Findings and Hemodynamic Assessment

— Tachycardia, hypotension, oliguria suggest third-spacing, sepsis, or ischemia/perforation.

— Fever >38.5°C with peritonitis → assume perforation or strangulation until proven otherwise.

— Orthostasis is common from vomiting and bowel-wall sequestration; correct before any sedation/procedure.

— Inspection: marked distention, often asymmetric tympanitic bulge in LUQ for sigmoid volvulus; visible peristalsis is uncommon in colon.

— Auscultation: early high-pitched tinkling, then silence with prolonged obstruction or ischemia.

— Percussion: diffuse tympany; dullness shifting suggests ascites/perforation with free fluid.

— Palpation: generalized tenderness is acceptable; localized peritonitis, rebound, or guarding mandates emergent surgical evaluation.

— Palpable mass → cecal cancer, intussusception, or massively distended cecum (perforation risk if >12 cm).

— Hernial orifices (inguinal, femoral, umbilical, incisional) must be examined — easily missed cause of LBO/SBO.

— Empty rectum (collapsed ampulla) is classic for complete proximal obstruction.

— Palpable rectal mass → rectal cancer.

— Hard stool bolus → fecal impaction (especially elderly, opioid use).

— Gross blood, melena, or mucus → malignancy, ischemia, intussusception.

— MAP <65, lactate >2, HR >110, or peritoneal signs = ICU-level resuscitation before imaging if unstable, or expedited imaging plus simultaneous resuscitation.

— Calculate fluid deficit: vomiting + third-space losses often 4–6 L by presentation.

General appearance and vitals:

Abdominal exam:

Digital rectal exam — mandatory:

Hemodynamic assessment for triage:

CCS pearl: On a CCS case, order vitals q1h, place 2 large-bore IVs, start LR bolus, NPO, NG tube to low intermittent suction, Foley for UOP monitoring, type and screen, and surgical consult simultaneously — do not sequence them.

Board pearl: Disproportionate pain with a benign abdomen in an obstructed patient = ischemia; act before peritonitis develops.

Diagnostic Workup — Initial Labs and Imaging

— CBC: leukocytosis with left shift suggests ischemia, perforation, or strangulation; anemia (microcytic) supports chronic GI blood loss from CRC.

— BMP: hypokalemia, hypochloremic metabolic alkalosis from vomiting; AKI from volume depletion.

— Lactate: >2 mmol/L raises concern for bowel ischemia; >4 = strong predictor of mortality.

— LFTs, lipase: exclude hepatobiliary/pancreatic mimics.

— Coags, type and screen (cross 2 units if surgery imminent).

— VBG for acid-base, especially in the unstable patient.

— CEA: baseline if CRC suspected — not diagnostic but prognostic and useful for surveillance after resection.

— Dilated colon >6 cm (cecum >9 cm) = obstruction; cecum >12 cm = imminent perforation.

— Haustral markings (partial, not crossing lumen) distinguish colon from valvulae conniventes of small bowel.

— Sigmoid volvulus: "coffee-bean" or "bent inner tube" sign, apex pointing to RUQ, originating in pelvis.

— Cecal volvulus: dilated cecum displaced to LUQ ("kidney-shape"), single air-fluid level.

— Free air under diaphragm → perforation, immediate OR.

Initial labs (order all at presentation):

Plain abdominal films (upright + supine, or left lateral decubitus if unable to stand):

ECG and preop labs if surgical candidate >50 or with cardiac risk factors — Step 3 expects you to address perioperative cardiac risk (RCRI) before non-emergent surgery.

Step 3 management: Plain films are the fastest triage but CT is the confirmatory study of choice when stable. Do not delay CT for a non-diagnostic plain film. If perforation is confirmed on plain film, skip CT and go to OR.

Board pearl: A dilated cecum on KUB with no small-bowel air = closed-loop LBO with competent ileocecal valve — high perforation risk, surgical emergency even before CT.

Key distinction: Air-fluid levels at different heights favor mechanical obstruction; uniform gas throughout small and large bowel without transition favors ileus.

Diagnostic Workup — Advanced and Confirmatory Studies

— Test of choice — sensitivity and specificity >90% for LBO.

— Identifies transition point, etiology (mass, stricture, volvulus, hernia), and complications (pneumatosis, portal venous gas, free air, mesenteric edema, closed-loop).

— Sigmoid volvulus: "whirl sign" of twisted mesentery, "bird-beak" tapering at the torsion point, dilated sigmoid loop.

— Cecal volvulus: whirl sign in RLQ with cecum rotated to LUQ.

— Colon cancer: apple-core lesion, asymmetric wall thickening, shouldered margins, regional lymphadenopathy, liver/lung metastases on same scan.

— Useful when CT equivocal; differentiates mechanical from pseudo-obstruction.

— Bird's-beak at rectosigmoid junction confirms sigmoid volvulus.

— Avoid barium (risk of barium peritonitis if perforation).

— Diagnostic and therapeutic for sigmoid volvulus (detorsion + rectal tube placement, success ~70–80%).

— Biopsy for suspected malignancy; can place self-expanding metal stent (SEMS) as a bridge to elective surgery or palliation.

— Contraindicated if peritonitis, perforation, or ischemic mucosa seen on initial scope.

CT abdomen/pelvis with IV contrast (oral usually not required; rectal contrast helpful for distal lesions):

Water-soluble contrast enema (Gastrografin):

Flexible sigmoidoscopy/colonoscopy:

MRI: Reserved for pregnancy or pelvic lesion characterization.

CEA, CT chest complete staging when CRC is the cause.

Key distinction: Mechanical LBO has a discrete transition point on CT; Ogilvie's shows diffuse colonic dilation without a transition point — do not take Ogilvie's patients to the OR.

CCS pearl: Once CT confirms sigmoid volvulus without ischemia, the next order is flexible sigmoidoscopy with rectal tube placement, not the OR. Document mucosal viability in your note — ischemic mucosa = straight to surgery.

Board pearl: Pneumatosis intestinalis + portal venous gas on CT in an obstructed patient = transmural ischemia; emergent laparotomy regardless of vitals.

Risk Stratification and First-Line Management Logic

— Peritonitis, free air, hemodynamic instability, lactate >4, or pneumatosis → emergent laparotomy after rapid resuscitation. Do not delay for staging or bowel prep.

— Stable, no peritonitis → pursue etiology-directed management.

— NPO, IV crystalloid resuscitation (LR preferred), correct K/Mg.

— NG tube to low intermittent suction if vomiting or proximal dilation.

— Foley catheter, strict I/O.

— Broad-spectrum antibiotics (piperacillin-tazobactam or ceftriaxone + metronidazole) only if ischemia, perforation, or impending surgery — not routine for uncomplicated obstruction.

— DVT prophylaxis (mechanical until bleeding/surgery risk clarified).

— Surgical consultation at time of diagnosis.

— Sigmoid volvulus, viable mucosa: endoscopic detorsion + rectal tube → same-admission elective sigmoidectomy (recurrence 40–60% if not resected).

— Sigmoid volvulus, ischemic/perforated/failed detorsion: emergent Hartmann's procedure (sigmoid resection + end colostomy).

— Cecal volvulus: detorsion rarely successful and high recurrence → right hemicolectomy is standard; cecopexy/cecostomy only for non-operative candidates.

— Obstructing left-sided CRC: options include (a) resection + primary anastomosis ± diverting loop ileostomy, (b) Hartmann's, or (c) SEMS as bridge to elective resection in selected patients — improves stoma rates and morbidity.

— Obstructing right-sided CRC: right hemicolectomy with primary ileocolic anastomosis (well tolerated even in obstruction).

First branch point — stable vs unstable / perforated vs intact:

Universal initial bundle (CCS-style orders):

Etiology-specific first moves:

Step 3 management: SEMS is appropriate for palliation in unresectable disease and as a bridge to surgery in high-risk operative candidates; avoid in potentially curable patients <70 with low operative risk because of concerns about tumor seeding and long-term oncologic outcomes.

Board pearl: Always recheck cecal diameter serially in proximal LBO; ≥12 cm or rapid expansion triggers urgent intervention even without peritonitis.

Pharmacotherapy — Supportive and Adjunctive Regimens

— Lactated Ringer's 1–2 L bolus, then maintenance titrated to UOP 0.5 mL/kg/h and MAP ≥65.

— Avoid normal saline in large volumes (hyperchloremic acidosis worsens AKI).

— Hypokalemia from vomiting — replete to K >4 before any antiarrhythmic or surgical anesthesia.

— Correct Mg and Ca; hypomagnesemia perpetuates refractory hypokalemia.

— Ondansetron 4 mg IV q8h; monitor QTc, especially with electrolyte derangement.

— Avoid metoclopramide and other prokinetics in mechanical obstruction — risk of perforation. They are useful in ileus/Ogilvie's only after mechanical obstruction excluded.

— Acetaminophen IV preferred; use opioids sparingly and short-acting (fentanyl) — opioids worsen dysmotility and mask peritonitis.

— Avoid NSAIDs (AKI risk in volume-depleted patients, anastomotic leak concern perioperatively).

— Suspected ischemia/perforation/sepsis or preoperative: piperacillin-tazobactam 4.5 g IV q8h, or ceftriaxone 2 g + metronidazole 500 mg IV q8h.

— Continue 4–7 days after source control if perforation/peritonitis; shorter (24 h) for uncomplicated surgical prophylaxis.

— After excluding mechanical obstruction with contrast study or CT, and after conservative measures fail with cecal diameter >10–12 cm:

— Neostigmine 2 mg IV over 3–5 min with continuous cardiac monitoring and atropine at bedside.

— Contraindications: mechanical obstruction, bradycardia, bronchospasm, recent MI, pregnancy, severe renal impairment.

Fluid resuscitation:

Electrolyte correction:

Antiemetics:

Analgesia:

Antibiotics (only when indicated):

Ogilvie's pseudo-obstruction (key drug — testable):

VTE prophylaxis: Enoxaparin 40 mg SC daily once bleeding risk and impending surgery clarified.

Bowel rest and TPN: TPN only if expected NPO >7 days or malnourished surgical candidate.

Key distinction: Prokinetics and neostigmine are harmful in mechanical LBO but therapeutic in Ogilvie's — never give them until imaging excludes a mechanical transition point.

Board pearl: Always have atropine at the bedside when administering neostigmine; symptomatic bradycardia is the rate-limiting adverse effect.

Procedures and Invasive Management

— Flexible sigmoidoscopy, gentle insufflation, advance past torsion → audible gush of gas/stool = success.

— Leave rectal decompression tube 24–72 h.

— Inspect mucosa — dusky/black mucosa = ischemia, abort and go to OR.

— Definitive sigmoid resection on same admission because recurrence risk without surgery is 40–60% at 1 year; elective resection has lower morbidity than emergent.

— Indications: (1) palliation of incurable obstructing CRC, (2) bridge to elective resection in poor surgical candidates or to convert emergent to elective single-stage surgery.

— Best for left-sided obstructing lesions; not for very low rectal (<5 cm from anal verge, tenesmus) or right-sided (technically difficult, hemicolectomy tolerates obstruction well).

— Complications: perforation (~5%), migration, re-obstruction; relative contraindication in patients on bevacizumab (perforation risk).

— Right hemicolectomy with primary ileocolic anastomosis — standard for right-sided obstructing CRC and cecal volvulus.

— Sigmoidectomy with primary anastomosis ± diverting loop ileostomy — for left-sided obstruction in stable patient with clean field.

— Hartmann's procedure (sigmoid resection + end colostomy + rectal stump) — unstable patient, perforation, fecal contamination; reversal possible 3–6 months later.

— Subtotal colectomy with ileorectal anastomosis — synchronous lesions or ischemic proximal colon.

— Cecopexy or cecostomy — only in cecal volvulus patients too frail for resection; high recurrence.

Endoscopic detorsion (sigmoid volvulus, no ischemia):

Self-expanding metal stents (SEMS):

Surgical options:

Decompressive colonoscopy ± cecostomy tube: option for refractory Ogilvie's.

CCS pearl: After successful endoscopic detorsion, the order set is: admit, NPO, IV fluids, surgical consult for same-admission elective sigmoidectomy, mechanical bowel prep, and consent for laparoscopic vs open.

Board pearl: Failed endoscopic detorsion, ischemic mucosa, or recurrent volvulus = immediate surgery; do not attempt repeat scope.

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher prevalence of sigmoid volvulus (chronic constipation, institutionalization, neurodegenerative disease, psychotropic medications).

— Higher prevalence of obstructing CRC — many present obstructed because of poor screening adherence.

— Atypical presentations: minimal pain, delirium as the chief complaint, low-grade fever masking sepsis.

— Frailty assessment (Clinical Frailty Scale, ECOG) drives decision between resection vs stent vs palliation.

— Perioperative optimization: cardiac risk stratification (RCRI), pulmonary toilet, nutrition (albumin <3 g/dL doubles anastomotic leak risk), delirium prevention bundle.

— Aggressive fluid resuscitation still required but watch for volume overload — central monitoring or POCUS if CKD/HF coexist.

— Avoid NSAIDs, nephrotoxic antibiotics (aminoglycosides), and contrast if eGFR <30 unless essential — pre-hydrate and use iso-osmolar contrast if needed.

— Dose-adjust pip-tazo, cefepime, and LMWH; avoid metformin perioperatively.

— Neostigmine for Ogilvie's: caution with CrCl <30 — reduce dose.

— Coagulopathy, thrombocytopenia, ascites complicate surgery; Child-Pugh and MELD predict mortality (Child C / MELD >15 = prohibitive risk for emergent colectomy).

— Avoid hepatotoxic agents; lactulose may worsen distention — hold during acute obstruction.

— Consider SEMS as palliation/bridge in decompensated cirrhotic with obstructing CRC.

— Hold anticholinergics, opioids, antipsychotics, calcium channel blockers, and iron supplements that drive constipation and volvulus.

— Reconcile medications at discharge to prevent recurrence.

Elderly (the dominant LBO demographic):

Renal impairment:

Hepatic impairment / cirrhosis:

Polypharmacy in elderly:

Step 3 management: In a frail nursing-home patient with sigmoid volvulus, endoscopic detorsion + rectal tube is appropriate first line, but do not omit elective sigmoidectomy unless prohibitive surgical risk — recurrence rate is high and emergent reoperation carries worse mortality.

Board pearl: Albumin <3.0 and unintentional weight loss >10% predict anastomotic leak — preoperative nutritional optimization (5–7 days enteral when feasible) is high-yield Step 3 reasoning.

Special Populations — Pregnancy, Pediatrics, and Other Subgroups

— Cecal volvulus is the most common volvulus in pregnancy (gravid uterus displaces cecum); sigmoid volvulus also occurs in third trimester.

— Presentation overlap with labor, hyperemesis, and constipation delays diagnosis.

— Imaging: ultrasound first; MRI without gadolinium is preferred confirmatory study; low-dose CT acceptable if MRI unavailable and benefit outweighs risk — never withhold needed imaging because of pregnancy.

— Management mirrors non-pregnant — endoscopic detorsion for sigmoid if no ischemia; surgery if cecal volvulus or ischemic sigmoid. Multidisciplinary involvement with OB.

— Avoid neostigmine (uterine contraction risk).

— LBO in children is rare; etiologies differ — Hirschsprung disease (delayed meconium >48 h, chronic constipation, explosive stool on rectal exam), intussusception (ileocolic, ages 6 months–3 years, currant-jelly stool, sausage-shaped mass — treat with air/contrast enema), anorectal malformations, meconium ileus (CF).

— Adolescent volvulus is rare and usually associated with malrotation or megacolon.

— High baseline risk of sigmoid volvulus and stercoral colitis.

— Bowel regimen (scheduled laxatives, fiber, prokinetics when appropriate) is secondary prevention.

— Atypical presentation; involve caregivers in history; obtain surrogate consent appropriately.

— Anastomotic stricture as cause of LBO; endoscopic dilation often first-line.

— Megacolon predisposes to sigmoid volvulus — ask about origin and serology.

Pregnancy:

Pediatrics:

Patients with chronic neurologic disease / spinal cord injury:

Institutionalized adults with intellectual disability:

Post–bariatric surgery / prior colon resection:

Patients with Chagas disease (immigrants from endemic regions):

Key distinction: In pediatric LBO, think Hirschsprung, intussusception, malrotation; in adult LBO, think cancer, volvulus, diverticular stricture.

Board pearl: Currant-jelly stool + RUQ sausage mass in a toddler = ileocolic intussusception → air contrast enema is both diagnostic and therapeutic; surgery if reduction fails or peritonitis present.

Complications and Adverse Outcomes

— Closed-loop obstruction with competent ileocecal valve → cecal pressure necrosis (Laplace's law — largest diameter highest wall tension); perforation risk rises sharply at cecum >12 cm.

— Sigmoid volvulus → mesenteric torsion → venous congestion → arterial compromise → transmural infarction within hours.

— Signs: pneumatosis intestinalis, portal venous gas, free air, peritonitis, lactic acidosis, septic shock.

— Bacterial translocation across compromised mucosa; gram-negative and anaerobic bacteremia common; manage with early antibiotics, source control, hemodynamic support per Surviving Sepsis.

— Anastomotic leak (3–10%) — fever, tachycardia, leukocytosis, ileus on POD 3–7; CT with rectal contrast confirms; reoperation or drainage.

— Surgical site infection, wound dehiscence, fascial breakdown.

— Stoma complications (retraction, necrosis, parastomal hernia, prolapse, high output → dehydration).

— Postoperative ileus (universal to some degree; opioid-sparing strategy and early ambulation reduce duration).

— Short bowel syndrome (rare in LBO unless extensive resection).

— Adhesive small-bowel obstruction post-laparotomy.

— Recurrence of volvulus if no resection (40–60% sigmoid, very high cecal).

Bowel ischemia and perforation:

Stercoral perforation: From impacted stool above an obstructing lesion; high mortality.

Sepsis and septic shock:

Aspiration pneumonitis: From feculent vomiting; lower threshold for airway protection in altered or sedated patients.

Acute kidney injury: Pre-renal from third-spacing and vomiting; intrinsic from sepsis/contrast.

Electrolyte derangements: Hypokalemic hypochloremic metabolic alkalosis; refeeding syndrome after prolonged NPO + nutritional support.

Surgical complications:

Long-term sequelae:

Step 3 management: New tachycardia + fever + abdominal pain on POD 4–6 after colon resection = assume anastomotic leak; order CT with rectal contrast, NPO, broad-spectrum antibiotics, surgical reassessment — do not wait for "classic" peritonitis.

Board pearl: Postoperative ileus >5 days warrants imaging to exclude leak or mechanical obstruction, not just continued bowel rest.

When to Escalate Care — ICU, Consult, and Inpatient Triage

— Hemodynamic instability (MAP <65 despite 30 mL/kg crystalloid).

— Lactate >4, signs of bowel ischemia, sepsis, or septic shock.

— Respiratory failure from aspiration or massive distention compromising ventilation.

— Need for vasopressors, mechanical ventilation, or invasive monitoring.

— Post-emergent laparotomy with intraoperative instability or open abdomen.

— Free air, peritonitis, pneumatosis with portal venous gas.

— Cecum >12 cm with rapid progression.

— Failed endoscopic detorsion or ischemic mucosa on scope.

— Closed-loop obstruction.

— General/colorectal surgery at diagnosis — not after CT — for all suspected LBO.

— Interventional GI for SEMS placement or endoscopic detorsion.

— Interventional radiology for percutaneous cecostomy in non-operative candidates.

— Oncology once CRC tissue confirmed for staging and neoadjuvant/adjuvant planning.

— Anesthesia/perioperative medicine for high-risk surgical candidates.

— Palliative care early for unresectable disease or frail patients to align goals of care.

— Stable obstruction without ischemia, normal lactate, awaiting elective intervention → surgical floor with q4h vitals, serial abdominal exams, NG output monitoring.

— Borderline (lactate 2–4, tachycardia, large fluid requirement) → step-down/telemetry.

— Any peritonitis, vasopressor need, or postoperative instability → ICU.

— Critical-access hospital without colorectal surgery, IR, or endoscopy capability → stabilize, decompress, transfer.

— Document and communicate via standardized handoff (SBAR), including pending imaging and antibiotic timing.

Immediate ICU criteria:

OR escalation (regardless of vitals):

Consultation framework:

Floor vs step-down vs ICU triage:

Transfer considerations:

CCS pearl: Move location early — a CCS case where the patient deteriorates on the medical floor while you "wait for surgery" will be penalized; the right answer is to transfer to ICU/OR at the first sign of decompensation.

Board pearl: Surgical consultation timing is a graded item — call surgery when you order the CT, not after you read it.

Key Differentials — Same-Category Causes

— Adhesions (most common in postoperative patients), hernias, Crohn strictures, tumors, intussusception (adult: malignancy).

— Earlier vomiting, less distention, central abdominal pain; KUB shows valvulae conniventes (cross full lumen) and stacked-coin appearance.

— CT shows transition point in small bowel, collapsed colon.

— Postoperative (especially orthopedic, cardiac), critically ill, neurologic disease, electrolyte disturbance, opioid use.

— Massive colonic dilation without mechanical transition point on contrast study or CT.

— Treat with conservative measures, neostigmine, decompressive colonoscopy; cecostomy if refractory.

— IBD (UC > Crohn), C. difficile colitis, ischemic colitis.

— Fever, tachycardia, leukocytosis, anemia, abdominal pain + colonic dilation >6 cm + systemic toxicity.

— Treat underlying disease aggressively; colectomy if no improvement within 48–72 h or perforation.

— Elderly, immobile, opioid users; palpable rectal stool on DRE.

— Manual disimpaction, enemas, then bowel regimen; check for proximal obstructing lesion once cleared.

— Chronic constipation with focal wall thickening and inflammation from impacted stool; risk of stercoral perforation in the sigmoid.

— Recurrent diverticulitis → fibrotic narrowing; presents subacutely with crampy pain and obstipation; CT shows wall thickening without mass (but cannot reliably exclude malignancy → colonoscopy after acute episode).

Small-bowel obstruction (SBO):

Ogilvie's syndrome (acute colonic pseudo-obstruction):

Toxic megacolon:

Fecal impaction:

Stercoral colitis:

Diverticular stricture:

Anastomotic stricture: History of prior colorectal resection; endoscopic dilation usually effective.

Key distinction: Mechanical LBO has a discrete CT transition point; Ogilvie's does not. Get a water-soluble contrast enema or CT before giving neostigmine.

Board pearl: Postoperative orthopedic patient on POD 3 with massive painless abdominal distention and no transition point on CT = Ogilvie's — neostigmine, not laparotomy.

Key Differentials — Other-Category Causes

— Pain out of proportion to exam, AF or vasculopathy, lactic acidosis, minimal early imaging findings; CTA confirms.

— Distinguished by disproportionate pain, embolic source, and gas pattern without true obstruction.

— Elderly male, smoker, sudden tearing back/abdominal pain, hypotension, pulsatile mass; bedside US or CTA. Mimics surgical abdomen of any cause — always check the aorta in elderly abdominal pain.

— Vomiting and abdominal pain with ileus pattern on imaging; check glucose, anion gap, electrolytes.

— Cirrhotic with distention and tenderness; paracentesis distinguishes. No transition point.

— Pelvic origin pain in reproductive-age women; β-hCG and pelvic US mandatory before assuming GI cause.

— Epigastric pain radiating to back, lipase >3× ULN; sentinel-loop ileus on imaging mimics partial obstruction.

— Suprapubic distention in elderly male misread as bowel obstruction; bladder scan and Foley diagnostic.

— Common cause of distention in elderly; KUB shows abundant stool throughout colon without dilation transition; treat with bowel regimen and reassess.

— Can present with referred abdominal pain and ileus, especially in elderly and diabetic patients — order ECG and CXR.

— Rare but classic boards entities for abdominal pain with ileus and no mechanical lesion.

Mesenteric ischemia (acute):

Ruptured AAA:

Diabetic ketoacidosis / adrenal crisis:

Ascites with tense distention / spontaneous bacterial peritonitis:

Ovarian torsion / ectopic pregnancy / tubo-ovarian abscess:

Acute pancreatitis:

Urinary retention with overflow:

Constipation alone:

Pneumonia (lower lobe), MI (inferior):

Heavy-metal poisoning, porphyria, lead colic:

Key distinction: Any abdominal pain in an elderly patient mandates aortic, cardiac, and metabolic workup in parallel with the GI evaluation — anchoring on "obstruction" misses the killer mimics.

Board pearl: Inferior MI presenting as nausea, vomiting, and "indigestion" in a diabetic — get an ECG before committing to a GI diagnosis.

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Same-admission elective sigmoidectomy is the standard because untreated recurrence is 40–60% within a year and emergent reoperation has higher mortality.

— If patient declines or is too frail: aggressive bowel regimen (PEG, scheduled stimulants), minimize anticholinergics/opioids/antipsychotics, treat constipation aggressively, mobility program.

— Adjuvant chemotherapy considered for stage III (FOLFOX) and high-risk stage II — refer to oncology.

— Surveillance (NCCN/ASCO): history, exam, CEA every 3–6 months for 2 years then every 6 months through year 5; CT chest/abdomen/pelvis annually for 3–5 years; colonoscopy at 1 year, then 3 years, then every 5 years if normal.

— If preoperative colonoscopy incomplete due to obstruction, perform clearing colonoscopy within 3–6 months to exclude synchronous lesions (3–5% incidence).

— Bowel regimen: docusate + senna, polyethylene glycol PRN, fiber once anastomosis healed.

— Pain control: scheduled acetaminophen, short-course opioid with concurrent stool softener; transition to non-opioid quickly.

— VTE prophylaxis: extended LMWH (28 days) after colorectal cancer surgery per ACCP.

— Resume cardiovascular medications (statin, antihypertensives); restart anticoagulation per surgeon's timeline.

— Stoma care education before discharge with WOC nurse; supplies and follow-up arranged.

— Hydration, fiber 25–35 g/day, regular physical activity.

— Screening colonoscopy adherence for family members per USPSTF (age 45–75) if CRC diagnosed.

After sigmoid volvulus (endoscopic detorsion only):

After resection for obstructing colorectal cancer:

After resection for diverticular stricture: Outpatient colonoscopy 6–8 weeks after resolution to exclude underlying malignancy if not done preoperatively.

Discharge medications and counseling:

Lifestyle/preventive measures:

Step 3 management: Always close the loop on screening colonoscopy at discharge — obstructed CRC patients often present because they missed screening; document the plan for first-degree relatives.

Board pearl: Extended 28-day LMWH after major abdominopelvic cancer surgery reduces VTE without increasing major bleeding — a frequently tested longitudinal-care point.

Follow-Up, Monitoring, and Counseling

— Wound/staple check and clinical evaluation at 1–2 weeks.

— Comprehensive assessment at 4–6 weeks: bowel function, nutritional status, pain, return to activity, stoma function if applicable.

— Pathology review visit: stage, margins, lymph node yield (≥12 nodes), MMR/MSI status — drives adjuvant therapy and Lynch syndrome workup.

— CEA q3–6 months × 2 years, then q6 months × 3 years.

— CT chest/abdomen/pelvis annually × 3–5 years (more frequent in high-risk).

— Colonoscopy at 1 year, then 3 years, then every 5 years.

— Rising CEA → CT and colonoscopy; if negative, consider PET.

— Post-sigmoidectomy: routine surgical follow-up; reinforce constipation management and medication review.

— If managed non-operatively: educate patient/caregivers on early symptoms of recurrence (distention, obstipation, pain) and emergency return precautions.

— WOC nurse follow-up at 2 and 6 weeks; monitor for high output (>1.5 L/day → dehydration, electrolyte loss — use loperamide, oral rehydration, PPI).

— Reversal planning at 3–6 months after Hartmann's or diverting ileostomy when patient clinically and nutritionally ready.

— Small, frequent meals; protein 1.2–1.5 g/kg/day post-resection; monitor weight and albumin.

— Refer to dietitian, especially after subtotal colectomy.

— Body image and sexual function after stoma — proactively address.

— Cancer survivorship plan: surveillance schedule, late-effect monitoring, return-to-work guidance.

— Smoking cessation, alcohol moderation, weight management — reduce recurrence and second primary cancer risk.

Postoperative follow-up cadence:

CRC surveillance milestones (high-yield):

Volvulus follow-up:

Stoma management:

Nutritional rehab:

Psychosocial and rehabilitative counseling:

Genetic counseling referral: Patients <50 with CRC, multiple primaries, MSI-high or MMR-deficient tumors, or strong family history — evaluate for Lynch syndrome, FAP.

Step 3 management: Build a longitudinal surveillance plan that names specific tests and intervals — vague answers like "follow up with oncology" are penalized; specify CEA, imaging, and colonoscopy timing.

Board pearl: Patients <50 with CRC get universal MMR/MSI testing and genetics referral, regardless of family history.

Ethical, Legal, and Patient Safety Considerations

— Discuss specific operative outcomes: stoma possibility (often >50% in emergent left-sided obstruction), risk of leak, mortality, reoperation, and ICU stay.

— Use teach-back; document. If patient lacks capacity due to sepsis/encephalopathy → identify surrogate per state hierarchy; if no surrogate and life-threatening, two-physician emergency consent is generally acceptable, but document carefully.

— Frail elderly with metastatic obstructing CRC: discuss palliative SEMS, diverting stoma, or comfort-focused care vs aggressive surgery. Involve palliative care early — improves outcomes and reduces non-beneficial interventions.

— Honor advance directives and POLST; do not default to maximally invasive care without exploring values.

— Suspected elder abuse or neglect in an institutionalized patient with severe stercoral impaction or untreated obstruction — mandatory reporting to Adult Protective Services in most US jurisdictions.

— Pediatric obstruction with concerning history → child protective services if abuse/neglect suspected.

— High-risk handoffs: ED → floor, OR → ICU, hospital → SNF/home.

— Mandatory elements: medication reconciliation (especially restarting anticoagulation, holding nephrotoxins), pending labs/pathology, follow-up appointments, stoma supplies and teaching, red-flag return precautions.

— Use structured handoff tools (SBAR, I-PASS); document with verbal read-back for high-acuity items.

— Wrong-site surgery (time-out before colectomy with stoma marking by enterostomal nurse preoperatively).

— Retained surgical items — count protocols.

— VTE prophylaxis omission is a publicly reported quality measure.

— Pressure injury and CAUTI prevention in prolonged immobility.

— Anastomotic leak or intraoperative injury must be disclosed per AMA and Joint Commission standards — full, timely, empathic disclosure improves trust and reduces litigation.

Informed consent in the acutely obstructed patient:

Goals-of-care conversations:

Mandatory reporting and safety:

Transition-of-care risk (Step 3 favorite):

Patient safety / never events:

Disclosure of complications:

Step 3 management: When the stem describes a deteriorating LBO patient whose family demands "everything done" despite a documented DNR, the right answer is to clarify scope (DNR ≠ do not treat), align on goals, and pursue indicated surgery if consistent with prior values — not to default to either extreme.

Board pearl: Stoma site marking by a trained nurse before surgery is a safety standard; unmarked emergent stomas have higher complication rates.

High-Yield Associations and Rapid-Fire Clinical Facts

Most common cause of LBO in US adults = colorectal cancer (~60%).

Most common location of obstructing CRC = sigmoid colon (narrow lumen, formed stool).

Right-sided CRC presents with anemia and occult bleeding; left-sided with obstruction and altered stool caliber.

Sigmoid volvulus demographics: elderly, institutionalized, neuropsychiatric meds, chronic constipation, Chagas, high-fiber diet in endemic regions ("volvulus belt" — Africa, Andes, South Asia).

Cecal volvulus demographics: younger women, pregnancy, prior abdominal surgery, congenital cecal mobility.

Cecal diameter >12 cm on imaging → imminent perforation, surgical emergency.

Plain film signs: coffee bean (sigmoid volvulus), kidney bean displaced to LUQ (cecal), apple core (CRC).

CT signs: whirl sign (volvulus mesentery), bird-beak (volvulus transition), pneumatosis + portal venous gas (ischemia).

Treatment of choice for stable sigmoid volvulus without ischemia: endoscopic detorsion + same-admission sigmoidectomy.

Treatment of choice for cecal volvulus: right hemicolectomy.

SEMS best role: palliation or bridge to elective surgery for obstructing left-sided CRC.

Neostigmine is for Ogilvie's, never for mechanical obstruction; have atropine at bedside.

Adult intussusception = malignancy until proven otherwise; resect, don't reduce.

Toddler intussusception = ileocolic, air enema first-line.

Hirschsprung disease: delayed meconium, rectal biopsy diagnostic (absent ganglion cells).

Pseudo-obstruction triggers: opioids, anticholinergics, hypokalemia, hypomagnesemia, hypothyroidism, recent surgery.

CRC surveillance: CEA q3–6 months, CT annually × 3–5 yrs, colonoscopy at 1, 4, 9 yrs.

Lynch syndrome screen: universal MMR/MSI testing on all CRC tumors.

Extended VTE prophylaxis after abdominopelvic cancer surgery: LMWH × 28 days.

Anastomotic leak presents POD 3–7 with fever, tachycardia, abdominal pain ± leukocytosis.

Cecum on the left + dilated, distended air-filled loop = cecal volvulus.

Board pearl: "Coffee bean pointing to RUQ" = sigmoid volvulus; "kidney bean in LUQ" = cecal volvulus — memorize the directionality.

Board Question Stem Patterns

— 78-year-old nursing-home resident with Parkinson's on multiple anticholinergics presents with 2 days of progressive distention, obstipation, mild crampy pain. Massively distended tympanitic abdomen, empty rectal vault. KUB: coffee-bean loop pointing to RUQ. Next best step?

— Answer: Flexible sigmoidoscopy with rectal tube placement (after fluids, NPO, NG, surgical consult). Follow with same-admission elective sigmoidectomy.

— 38-year-old pregnant woman at 32 weeks with sudden severe distention and RLQ pain progressing to diffuse. CT-equivalent imaging shows whirl sign with cecum in LUQ.

— Answer: Right hemicolectomy.

— 67-year-old with 3 months of weight loss, narrowing stool caliber, now obstipated. CT: apple-core sigmoid lesion with proximal dilation, no perforation, no ischemia, no metastases, ASA III.

— Answer (curative intent, fit patient): Emergent or urgent sigmoidectomy with primary anastomosis ± diverting loop ileostomy. SEMS as bridge if frail/high-risk.

— Competent ileocecal valve, cecum 13 cm, mild peritonitis. Next?

— Answer: Emergent laparotomy.

— POD 3 after hip replacement, massive painless distention, no transition point on CT, cecum 11 cm, K 3.0.

— Answer: Correct electrolytes, hold opioids/anticholinergics, NG and rectal tube; if no improvement and cecum >10–12 cm or persists 24–48 h → neostigmine with monitoring. If fails → decompressive colonoscopy.

— Toddler with intermittent inconsolable crying, currant-jelly stool, RUQ sausage mass.

— Answer: Air contrast enema (diagnostic and therapeutic).

— POD 5 after sigmoidectomy, fever 38.8°C, HR 115, abdominal pain, WBC 18.

— Answer: NPO, broad-spectrum antibiotics, CT with rectal contrast, surgical reexploration if leak confirmed.

— 55-year-old with intermittent obstruction, CT shows ileocolic intussusception with lead point mass.

— Answer: Surgical resection (do not attempt reduction — risk of perforation and tumor seeding).

Stem 1 — Sigmoid volvulus, classic:

Stem 2 — Cecal volvulus:

Stem 3 — Obstructing left-sided CRC:

Stem 4 — Closed-loop obstruction:

Stem 5 — Ogilvie's mimic:

Stem 6 — Pediatric:

Stem 7 — Anastomotic leak:

Stem 8 — Adult intussusception:

Step 3 management: When stems describe perioperative or post-discharge scenarios, prioritize surveillance schedules, VTE prophylaxis duration, medication reconciliation, and goals-of-care — these are the differentiating Step 3 distractors.

One-Line Recap

Large bowel obstruction in an adult is colorectal cancer or volvulus until proven otherwise — resuscitate, image with CT to find the transition point, decompress sigmoid volvulus endoscopically (then resect on the same admission), take cecal volvulus to right hemicolectomy, operate emergently for ischemia/perforation/closed-loop, and never give prokinetics or neostigmine until a mechanical cause is excluded.

Diagnostic anchor: Distention + obstipation + late vomiting + crampy infraumbilical pain → KUB then CT with IV contrast; cecum >12 cm or pneumatosis/portal venous gas = surgical emergency.

Etiology-driven management: Sigmoid volvulus → endoscopic detorsion + elective sigmoidectomy; cecal volvulus → right hemicolectomy; obstructing left CRC → resection ± diverting stoma or SEMS as bridge/palliation; obstructing right CRC → right hemicolectomy with primary anastomosis.

Do not confuse with Ogilvie's: No transition point on imaging = pseudo-obstruction → correct electrolytes, withdraw offending meds, then neostigmine with atropine standby; colonoscopic decompression if refractory.

Longitudinal Step 3 layer: Post-CRC surveillance with CEA q3–6 months, CT annually × 3–5 years, colonoscopy at 1/4/9 years; extended 28-day LMWH after cancer surgery; universal MMR/MSI testing; genetics referral if <50 or strong family history; reconcile constipating medications and arrange stoma teaching before discharge to prevent recurrence and rehospitalization.

Safety net: Always document surgical consultation timing, stoma site marking, time-outs, advance directive review, and structured handoffs — these process measures are graded targets on Step 3 vignettes and CCS cases.