Perioperative & Surgical Care

Postoperative ileus and bowel obstruction

Clinical Overview and When to Suspect Postoperative Ileus vs Bowel Obstruction

— Early postop SBO (<30 days): adhesions, anastomotic edema, hematoma, abscess, technical error.

— Late SBO (>30 days): adhesions dominate (~75%), hernia, malignancy.

Key distinction: POI = diffuse, painless distention, no transition point, gas throughout colon and rectum on imaging; mechanical SBO = focal transition point, dilated proximal/decompressed distal bowel, often colicky pain.

Board pearl: Return of flatus (not bowel sounds) is the most reliable bedside sign that POI is resolving — auscultation alone is unreliable and should not drive feeding decisions on ERAS pathways.

Postoperative ileus (POI) = transient impairment of coordinated GI motility after surgery without mechanical obstruction; near-universal physiologic ileus resolves in 0–3 days (small bowel <24h, stomach 24–48h, colon 48–72h).

Prolonged/paralytic POI = failure to pass flatus/stool or tolerate oral diet by postop day 3–5, or recurrence after initial recovery, in absence of mechanical cause.

Postoperative small bowel obstruction (SBO) = mechanical blockage, typically from adhesions (most common cause overall after abdominopelvic surgery), internal hernia, port-site hernia, or intussusception.

Suspect POI when distention + nausea + no flatus develop gradually after open abdominal, colorectal, or emergency surgery, often with electrolyte derangement or opioid use.

Suspect mechanical SBO when symptoms appear after a period of return of bowel function ("ate, then obstructed"), with crampy pain, bilious or feculent emesis, and obstipation.

Risk factors for prolonged POI: open vs laparoscopic approach, opioid burden, prolonged operative time, intraoperative bowel handling, electrolyte abnormalities (↓K, ↓Mg, ↓Na), hypoalbuminemia, peritonitis, retroperitoneal hematoma, advanced age, male sex.

Presentation Patterns and Key History

— Type and date of surgery; laparoscopic vs open; bowel resection with anastomosis?

— Opioid dose (MME/day), anticholinergics, calcium channel blockers.

— Prior abdominal surgeries (adhesion burden), Crohn disease, radiation, malignancy.

— Time of last flatus, last bowel movement, last tolerated PO.

— Character of emesis: bilious (proximal SBO) vs feculent (distal SBO or late) vs nonbilious (gastric outlet).

— Fevers, tachycardia, oliguria → suggest complicated obstruction (strangulation, perforation, anastomotic leak).

Step 3 management: When a postop patient on POD 4 develops new vomiting after previously tolerating diet, do not reflexively label as ileus — order a CT abdomen/pelvis with IV (± oral) contrast to identify mechanical obstruction, anastomotic leak, or intra-abdominal abscess before escalating bowel rest.

Board pearl: "Ate then obstructed" = mechanical SBO until proven otherwise; "never recovered from surgery" = POI more likely.

Classic POI timeline: patient is POD 2–4 from colectomy/hysterectomy/AAA repair, develops nausea, abdominal distention, hiccups, inability to tolerate diet; no crampy pain; minimal flatus; NG output (if tube in place) increases.

Classic early postop SBO: POD 5–14, initial return of bowel function and tolerance of clears, then abrupt onset of cramping periumbilical pain, bilious then feculent vomiting, obstipation, progressive distention.

Ogilvie syndrome (acute colonic pseudo-obstruction): massive colonic distention (especially cecum) in elderly, bedbound, or post-orthopedic/cardiac/spinal surgery patients; mimics mechanical large bowel obstruction but no transition point.

Key history points to elicit:

Closed-loop obstruction red flags: severe constant pain out of proportion, rising lactate, leukocytosis, peritoneal signs — surgical emergency.

Physical Exam Findings and Hemodynamic Assessment

— POI: uniformly distended, tympanitic, soft, mildly tender, hypoactive or absent bowel sounds, no peritoneal signs.

— Mechanical SBO: distended with high-pitched, "tinkling" bowel sounds early; rushes during cramps; later silent if decompensating; localized tenderness over transition point.

— Strangulation/ischemia: focal peritonitis, rebound, guarding, severe tenderness out of proportion — surgical emergency.

— Ogilvie: massive distention, often nontender, tympanitic over cecum; concerning if cecal diameter >12 cm.

Key distinction: Pain out of proportion to exam + lactic acidosis + tachycardia = think bowel ischemia/strangulation or mesenteric event, not POI. Mobilize surgery immediately.

CCS pearl: On CCS, when evaluating a postop patient with distention, order vital signs, abdominal exam, NG tube placement (if vomiting), IV access, CBC, BMP, lactate, lipase, and upright/supine abdominal films or CT in the same action block — do not silo orders.

General: assess volume status — postop patients with vomiting/NG losses are often hypovolemic with tachycardia, orthostasis, dry mucous membranes, low urine output (<0.5 mL/kg/h).

Vitals red flags: HR >110, MAP <65, fever >38.5°C, RR >22, or rising trend suggests complication (sepsis, leak, ischemia) rather than uncomplicated ileus.

Abdominal exam:

Hernia exam is mandatory: palpate inguinal, femoral, umbilical, incisional, and port sites — incarcerated hernia is a surgically correctable cause that is easy to miss in obese patients.

Rectal exam: empty vault supports complete obstruction; gross blood suggests ischemia, intussusception, or malignancy; fecal impaction can mimic distal obstruction in elderly.

Wound/drain inspection: erythema, purulent drainage, or feculent drain output → anastomotic leak.

Diagnostic Workup — Initial Labs and Imaging

— CBC: leukocytosis with left shift → infection, leak, ischemia.

— BMP: hypokalemia, hypomagnesemia, hyponatremia, hypocalcemia all prolong POI; check creatinine for AKI from hypovolemia.

— Lactate: elevated lactate is a red flag for bowel ischemia (low sensitivity early, high specificity late).

— LFTs, lipase: rule out cholecystitis, pancreatitis as mimics.

— CRP trend: rising CRP after POD 3–4 suggests anastomotic leak.

— Coagulation, type & screen if surgery anticipated.

— POI: gas throughout small bowel, colon, AND rectum; uniform dilation; no air-fluid levels with distinct transition.

— Mechanical SBO: dilated small bowel (>3 cm) with air-fluid levels at different heights ("string of pearls"), decompressed distal bowel/colon, paucity of colonic gas.

— Free air under diaphragm = perforation (note: small amount of postop pneumoperitoneum is normal up to 7 days).

— Sigmoid volvulus: "coffee bean"; cecal volvulus: dilated cecum displaced to LUQ.

— Identifies transition point, closed loops, pneumatosis, mesenteric edema, free fluid, abscess, leak.

— Oral contrast may aid but is not required; can be given as water-soluble (Gastrografin) which is both diagnostic and therapeutic in partial SBO.

Step 3 management: In a postop patient with possible SBO who is stable, order water-soluble contrast study (Gastrografin challenge) — passage of contrast to the colon within 24h predicts nonoperative resolution with >90% sensitivity and may shorten LOS.

Board pearl: Gas in the rectum on KUB strongly favors ileus over complete mechanical obstruction.

Labs:

Plain abdominal radiographs (supine + upright/left lateral decubitus):

CT abdomen/pelvis with IV contrast is the test of choice for postop abdominal pain/distention:

Diagnostic Workup — Advanced and Confirmatory Studies

— Closed-loop obstruction: U- or C-shaped fluid-filled loop, mesenteric whirl sign → urgent OR.

— Strangulation: bowel wall thickening, hypoenhancement of wall ("target sign"), pneumatosis intestinalis, portal venous gas, mesenteric haziness/fat stranding → emergent OR.

— Anastomotic leak: extraluminal contrast, free fluid, perianastomotic abscess, ectopic gas.

— Internal hernia (post-bariatric, especially Roux-en-Y): swirled mesentery, mushroom sign, clustered bowel loops.

— Intra-abdominal abscess: rim-enhancing fluid collection — may cause secondary ileus, drainable by IR.

Key distinction: Pneumatosis intestinalis + portal venous gas in a postop patient = transmural bowel ischemia until proven otherwise → emergent surgical exploration, do not order a repeat CT in 12 hours.

CCS pearl: On the CCS interface, advance the clock judiciously — a patient with SBO and stable vitals can be reassessed at 6–12 h intervals; a patient with peritonitis or rising lactate must be taken to OR at the next clock advance, not observed.

CT findings that change management:

Water-soluble contrast challenge (Gastrografin): 50–100 mL via NGT, KUB at 8 and 24 h; contrast in colon by 24h → nonoperative trial likely to succeed; failure → surgery.

CT enterography or MR enterography: for recurrent/chronic adhesive disease workup, not acute postop.

Colonoscopy/sigmoidoscopy: diagnostic and therapeutic in Ogilvie syndrome (decompression) and sigmoid volvulus (detorsion); contraindicated if peritonitis or perforation suspected.

Upper GI series: for suspected gastric outlet obstruction or anastomotic stricture after bariatric/gastric surgery.

Diagnostic laparoscopy/laparotomy: when imaging equivocal but clinical deterioration continues — never delay for repeat imaging if patient is septic with peritonitis.

Risk Stratification and First-Line Management Logic

— Complicated → NPO, NGT, IV fluids, broad-spectrum antibiotics, surgery consult, OR.

— Uncomplicated → nonoperative trial.

— POI: supportive management, address reversible causes.

— Partial SBO: trial of nonoperative management 24–72 h with Gastrografin challenge.

— Complete SBO without resolution at 48–72 h or any clinical deterioration: surgery.

— NPO.

— NG tube for decompression if vomiting or significant distention (not routinely for uncomplicated POI on ERAS).

— IV isotonic fluids; replace electrolytes (K >4, Mg >2, correct Ca, Na).

— Discontinue opioids or minimize; switch to scheduled acetaminophen, NSAIDs (if renal/anastomosis allow), regional/epidural analgesia.

— Stop anticholinergics, calcium channel blockers if possible.

— Early ambulation (level B evidence for return of bowel function).

— Gum chewing (sham feeding) — modest reduction in time to flatus/stool, low cost, recommended.

— Alvimopan (peripheral μ-opioid antagonist) for accelerating GI recovery after bowel resection — limited to 7 days inpatient, REMS program.

Step 3 management: A postop colectomy patient with prolonged ileus on POD 5 — check K/Mg, stop PCA opioids, transition to ketorolac + acetaminophen, ambulate TID, start gum chewing, and obtain CT if no improvement in 24 h to exclude leak or mechanical cause.

Board pearl: Routine NGT placement after elective abdominal surgery delays return of bowel function and increases pulmonary complications — use selectively.

Step 1 — Triage: Is this complicated (ischemia, perforation, leak, closed loop, peritonitis, hemodynamic instability) or uncomplicated?

Step 2 — Distinguish POI vs partial SBO vs complete SBO:

Nonoperative bundle ("drip and suck"):

ERAS protocols reduce POI: minimize opioids, multimodal analgesia, early feeding, early mobilization, goal-directed fluids (avoid both over- and under-resuscitation), minimally invasive surgery when possible.

Pharmacotherapy — First-Line Regimen

— Multimodal: scheduled acetaminophen 1 g IV/PO q6h; ketorolac 15–30 mg IV q6h (max 5 days, avoid in renal impairment, fresh GI anastomosis controversy — many surgeons avoid NSAIDs x 48–72h post-anastomosis).

— Gabapentin 300 mg TID (caution sedation/elderly).

— Lidocaine IV infusion intraop/early postop reduces POI duration.

— Epidural (thoracic) analgesia for open abdominal/thoracic surgery reduces POI vs systemic opioids.

— Opioids: reserve for breakthrough; prefer hydromorphone or oxycodone over morphine; avoid meperidine.

Board pearl: Neostigmine 2 mg IV for Ogilvie syndrome (cecum >12 cm, failed 48–72h conservative care) produces dramatic decompression in ~80–90% within minutes; contraindicated with mechanical obstruction, recent MI, severe asthma, or significant bradyarrhythmia.

Key distinction: Metoclopramide is useful in POI/gastroparesis but contraindicated in mechanical bowel obstruction — exclude it first.

Analgesia (minimize opioid-induced ileus):

Antiemetics: ondansetron 4 mg IV q6h PRN; metoclopramide 10 mg IV q6h (also prokinetic, avoid with bowel obstruction — relative contraindication, EPS risk, QT).

Alvimopan: 12 mg PO 30 min–5 h preop, then 12 mg PO BID up to 7 days, for patients undergoing partial bowel resection with primary anastomosis; contraindicated if opioid use >7 days preop, severe hepatic impairment, end-stage renal disease; black-box warning for MI risk with long-term use (hence 15-dose limit, REMS).

Methylnaltrexone/naloxegol: peripherally acting μ-opioid antagonists for opioid-induced constipation; not standard for acute POI.

Neostigmine (parasympathomimetic): 2–2.5 mg IV over 3–5 min is first-line for Ogilvie syndrome after failed conservative therapy and exclusion of mechanical obstruction. Monitor on telemetry — bradycardia, bronchospasm; have atropine at bedside.

Erythromycin (motilin agonist): useful for gastroparesis/gastric ileus, less effective for colonic POI.

Electrolyte repletion: K, Mg, Ca, PO4 — aggressive, IV when oral not tolerated.

Procedures and Invasive Management

— Sigmoid volvulus: flexible sigmoidoscopy with detorsion + rectal tube placement; elective sigmoidectomy during same admission (recurrence ~60% without resection).

— Ogilvie syndrome refractory to neostigmine: colonoscopic decompression with decompression tube; success ~70–80%.

— Cecal volvulus: surgical (right hemicolectomy or cecopexy) — endoscopic detorsion rarely successful.

— Peritonitis, hemodynamic instability, suspected ischemia/strangulation, closed-loop obstruction, free perforation, failure of nonoperative management at 48–72 h, anastomotic leak with sepsis.

— Approach: laparoscopic if feasible (less adhesion formation, faster recovery); laparotomy for hostile abdomen, dense adhesions, ischemic bowel.

— Lysis of adhesions for adhesive SBO; bowel resection with anastomosis or stoma if nonviable bowel.

— Re-do anastomosis or diversion (ileostomy/colostomy) for leak.

Step 3 management: Postop POD 6 patient with fever, tachycardia, distention, and CT showing 6 cm pelvic abscess after sigmoid colectomy — IR-guided percutaneous drainage + IV piperacillin-tazobactam + bowel rest; surgical reoperation reserved if drainage fails or leak is large/uncontrolled.

CCS pearl: Order "surgery consult" early; on CCS, delaying consultation for a peritonitic abdomen lowers your score even if you eventually take the patient to OR.

Nasogastric tube: 14–18 Fr Salem sump to low intermittent suction; indications — significant vomiting, gastric distention, aspiration risk; confirm placement radiographically; remove early when output <500 mL/24 h and patient passing flatus.

Rectal tube: useful in Ogilvie syndrome or sigmoid volvulus pre-detorsion for decompression.

Endoscopic decompression:

Percutaneous drainage (IR): for postop intra-abdominal abscesses ≥3 cm causing secondary ileus — drainage often resolves ileus and avoids reoperation.

Surgical exploration indications:

Postoperative damage-control: in unstable patients with grossly contaminated abdomen, perform abbreviated laparotomy with temporary abdominal closure (vac dressing) and return for definitive repair after resuscitation.

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher baseline risk for POI, Ogilvie, and adverse drug events.

— Polypharmacy: anticholinergics (diphenhydramine, oxybutynin, TCAs), opioids, calcium channel blockers, iron — all prolong POI; deprescribe when feasible.

— Sensitivity to opioids → use half doses, scheduled acetaminophen, regional anesthesia.

— Higher delirium risk with prolonged hospitalization; ileus + delirium → consider occult infection (UTI, pneumonia, leak).

— Cecal diameter threshold for intervention in Ogilvie is lower (10–12 cm) because of higher perforation risk with thinner, age-related cecal wall.

— Avoid NSAIDs: AKI, GI bleed risk.

— Avoid NSAIDs and ketorolac (worsen AKI).

— Adjust gabapentin (CrCl-based), morphine (active metabolite M6G accumulates — use hydromorphone or fentanyl).

— Alvimopan contraindicated in ESRD.

— Aggressive electrolyte management — hyperkalemia from AKI complicates volume resuscitation; metabolic acidosis worsens ileus.

— Ascites worsens postop ileus and increases hernia/wound complications.

— Avoid sedating drugs that precipitate hepatic encephalopathy; lactulose continued — ironically helps motility.

— Alvimopan contraindicated in Child-Pugh C.

— Coagulopathy increases bleeding/hematoma risk → adhesions, secondary obstruction.

— Hyponatremia common — correct slowly to avoid ODS.

Key distinction: In an elderly hospitalized patient with new massive colonic distention and no transition point on CT, think Ogilvie syndrome, not mechanical obstruction — most are post-orthopedic (hip), cardiac, or neurologic surgery patients on multiple anticholinergics.

Board pearl: Use fentanyl or hydromorphone over morphine in CKD to avoid accumulation of neuroexcitatory metabolites that worsen confusion and ileus.

Elderly (>65):

Chronic kidney disease/AKI:

Hepatic impairment / cirrhosis:

Frailty assessment preoperatively (e.g., Clinical Frailty Scale) predicts prolonged POI and complications; consider prehabilitation.

Special Populations — Pregnancy, Pediatrics, and Bariatric Patients

— SBO in pregnancy is rare but morbid (fetal loss up to 20%, maternal mortality up to 6% if delayed); most common cause = adhesions from prior abdominal/pelvic surgery.

— Presentation often delayed; nausea/vomiting attributed to pregnancy.

— Imaging: ultrasound first; MRI without gadolinium preferred for definitive imaging; CT acceptable if MRI unavailable and benefit outweighs risk (fetal dose <50 mGy generally safe).

— Avoid NSAIDs in 3rd trimester (premature ductal closure); avoid alvimopan (limited data); ondansetron generally safe; metoclopramide safe.

— Decision for surgery should not be delayed for pregnancy concerns — maternal stabilization is fetal stabilization.

— Postop ileus less common; mechanical obstruction often intussusception, adhesions, or anastomotic stricture.

— Post-appendectomy SBO from adhesions or stump abscess.

— Neonates: necrotizing enterocolitis differential; pneumatosis on imaging is ominous.

— Use weight-based fluids (Holliday-Segar) and dosing; avoid metoclopramide <1 year (EPS risk).

— Roux-en-Y gastric bypass: internal hernias (Petersen's space, mesojejunal, mesocolic) cause SBO months to years later; CT may show mesenteric swirl sign — surgical emergency due to closed-loop risk.

— Sleeve gastrectomy: stricture at incisura → gastric outlet obstruction.

— Always have low threshold for diagnostic laparoscopy in post-bariatric patients with persistent vomiting even if imaging equivocal.

Step 3 management: Pregnant patient with prior C-section presenting with bilious emesis, distention, and obstipation — don't anchor on hyperemesis; obtain abdominal US/MRI, place NGT, IVF, surgical consult, and proceed to OR if mechanical SBO confirmed regardless of gestational age.

Board pearl: Persistent postprandial pain + nausea months after Roux-en-Y = internal hernia until proven otherwise — CT swirl sign mandates urgent laparoscopy.

Pregnancy:

Pediatrics:

Bariatric surgery:

Inflammatory bowel disease: postop SBO may reflect anastomotic stricture or recurrent Crohn — endoscopy/MRE may be required.

Complications and Adverse Outcomes

Key distinction: New atrial fibrillation in a postop colorectal patient on POD 5 is an anastomotic leak clue until proven otherwise — workup with CT, not just rate control.

Board pearl: Cecal diameter >12 cm in Ogilvie or LBO predicts imminent perforation — intervene urgently (neostigmine, colonoscopic decompression, or surgery).

Aspiration pneumonitis/pneumonia: from emesis in obtunded or supine patients — elevate HOB, place NGT, consider intubation if depressed consciousness.

Electrolyte derangements: hypokalemia, hypomagnesemia, hypochloremic metabolic alkalosis from prolonged NG suction or vomiting; replace aggressively.

AKI: from hypovolemia (third-spacing, vomiting, NG losses) and nephrotoxins (NSAIDs, contrast).

Bowel ischemia/strangulation: in mechanical SBO, especially closed-loop; mortality rises with each hour of delay; pneumatosis, portal venous gas, lactic acidosis are late signs.

Perforation: free perforation from closed loop, cecal blowout in Ogilvie (cecum >12 cm), or stercoral perforation from impaction — leads to peritonitis, sepsis.

Anastomotic leak: classically POD 5–7 after colorectal surgery; presents as tachycardia, fever, ileus, oliguria, atrial fibrillation; CT with rectal contrast confirms; treatment per leak severity (drainage, diversion, or takedown).

Intra-abdominal abscess: secondary ileus; IR drainage + antibiotics.

Prolonged hospitalization & deconditioning: VTE risk, pressure injuries, hospital-acquired infections, delirium.

Nutritional decline: prolonged NPO → start enteral nutrition when tolerated, parenteral nutrition if expected NPO >7 days or already malnourished.

Recurrent adhesive SBO: lifetime risk after open abdominal surgery ~10–30%; risk reduced by laparoscopy and use of adhesion barriers (e.g., hyaluronate-carboxymethylcellulose film) in selected cases.

Short bowel syndrome: if massive resection (<200 cm remaining small bowel) for ischemia — chronic malabsorption.

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

— Hemodynamic instability requiring vasopressors after fluid resuscitation.

— Sepsis/septic shock from leak, ischemia, or perforation.

— Respiratory failure from aspiration or massive distention.

— Severe metabolic derangement (pH <7.2, lactate >4, K >6 with arrhythmia).

— Postop bowel ischemia/strangulation requiring damage-control surgery and open abdomen.

— Suspected mechanical obstruction with peritonitis, closed loop, ischemia, perforation, hernia incarceration, anastomotic leak, post-bariatric internal hernia.

— Failure of nonoperative management at 48–72 h for partial SBO.

— Volvulus.

— Stable POI, no vomiting, tolerating clears: regular surgical floor.

— Vomiting with NGT, IVF needs, recurrent electrolyte issues: telemetry/step-down.

— Hemodynamic concern, sepsis: ICU.

CCS pearl: On the CCS, the highest-yield actions in a deteriorating ileus/SBO case are simultaneously: NPO, NGT, IVF bolus, broad-spectrum antibiotics, blood cultures × 2, lactate, type & cross, surgery consult, and OR booking — bundle these in one order set rather than sequentially.

Step 3 management: In a hypotensive postop patient with fever and distention, do not wait for CT if peritonitis is present on exam — resuscitate and call surgery while imaging is arranged in parallel.

ICU admission criteria:

Surgery consult (urgent):

Interventional radiology consult: drainable intra-abdominal abscess ≥3 cm without free perforation.

Gastroenterology consult: colonoscopic decompression for Ogilvie refractory to neostigmine, sigmoid volvulus detorsion.

Nutrition consult: prolonged NPO >5–7 d, baseline malnutrition, short gut.

Pain/palliative consult: complex opioid weaning, multimodal regimen optimization.

Floor vs step-down:

Transfer: if facility lacks IR, advanced laparoscopy, or ICU support for complicated cases — initiate transfer early with surgery accepting team.

Key Differentials — Same-Category (GI/Surgical) Causes

Key distinction: Toxic megacolon has fever, systemic toxicity, colonic distention >6 cm with mucosal abnormalities on imaging; Ogilvie lacks systemic toxicity and mucosal disease.

Board pearl: Always palpate for hernias and check old surgical sites — a missed incarcerated femoral hernia is a classic exam pitfall in an elderly woman with "ileus."

Mechanical SBO from adhesions: most common cause overall in post-laparotomy patients; transition point on CT.

Internal hernia (especially post-Roux-en-Y, post-colectomy): mesenteric swirl, closed-loop risk.

Incarcerated/strangulated ventral, inguinal, femoral, port-site, or umbilical hernia: palpable mass, focal pain; femoral hernia high strangulation risk in elderly women.

Anastomotic stricture/edema: early postop, usually self-limited; if late and persistent → endoscopic dilation.

Anastomotic leak: ileus + fever + tachycardia + leukocytosis POD 3–7; CT with contrast confirms.

Intra-abdominal abscess: focal collection causing secondary ileus.

Phytobezoar/foreign body: rare; consider in post-gastric surgery patients with high-fiber intake.

Intussusception: rare in adults; usually lead point (tumor, Meckel's, polyp) — consider in pediatric postop.

Mesenteric ischemia (acute): severe pain out of proportion, AF, post-AAA repair; lactate, CTA mesenteric.

Ogilvie syndrome (acute colonic pseudo-obstruction): massive colonic dilation without mechanical cause; non-abdominal surgery (orthopedic, cardiothoracic, neuro) is classic.

Sigmoid/cecal volvulus: coffee-bean sign; cecal volvulus → right hemicolectomy; sigmoid → endoscopic detorsion + elective sigmoidectomy.

Crohn stricture, malignancy, radiation enteritis: in patients with relevant histories.

C. difficile colitis (toxic megacolon): postop antibiotic exposure → severe colitis, leukocytosis >20k, distention; stool PCR, IV vancomycin + IV metronidazole, surgery if megacolon.

Key Differentials — Other-Category (Non-GI) Causes

— Hypokalemia (most common, classic POI prolonger), hypomagnesemia, hypocalcemia, hyponatremia, hyperglycemia, uremia, hypothyroidism, DKA → all cause secondary ileus.

— Opioids (most common iatrogenic cause), anticholinergics (diphenhydramine, antipsychotics, TCAs, oxybutynin), calcium channel blockers, clonidine, ondansetron (constipation), iron, alpha-agonists.

— Spinal cord injury, retroperitoneal hematoma irritating splanchnic nerves, recent epidural with sympathectomy → paralytic ileus.

— Diabetic autonomic neuropathy → gastroparesis, chronic ileus.

— Sepsis (any source) suppresses GI motility.

— Pneumonia, UTI in elderly — always consider as occult driver of new ileus.

— Pancreatitis: classic cause of ileus (sentinel loop, colon cut-off sign).

— Retroperitoneal pathology: pyelonephritis, ureteral stone, AAA, psoas abscess.

Step 3 management: A postop patient on chronic prednisone with persistent vomiting, hyponatremia, hypotension, and ileus — give stress-dose hydrocortisone 100 mg IV while pursuing other workup; missed adrenal crisis is a sentinel safety event.

Key distinction: Inferior MI with nausea and ileus can masquerade as primary GI postoperative complication — always check ECG and troponin in postop patients with new GI symptoms, especially elderly or diabetics.

Electrolyte/metabolic:

Medications:

Neurogenic:

Endocrine: hypothyroidism (myxedema ileus), pheochromocytoma, hypoparathyroidism.

Infectious/inflammatory:

Cardiac: MI (especially inferior) can present with nausea/ileus; right heart failure with hepatic congestion; mesenteric ischemia from new AF.

Psychiatric/functional: rare in postop period but consider in chronic recurrent cases.

Withdrawal: opioid or alcohol withdrawal can cause autonomic GI dysfunction.

Adrenal insufficiency: postop in patient on chronic steroids — give stress-dose hydrocortisone.

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Confirm tolerating regular diet, passing flatus and stool, ambulating, pain controlled on oral analgesics, no fever.

— Discharge medications: scheduled acetaminophen, short opioid course (3–5 day supply, lowest effective dose), stool softener (docusate) + osmotic laxative (PEG 17 g daily) to counter opioid effect, ondansetron PRN.

— Avoid chronic NSAIDs if fresh anastomosis (typically wait 2–4 weeks; surgeon-specific).

— Bowel regimen anytime opioids are prescribed — Step 3 patient safety point.

— Counsel on high lifetime recurrence; teach early warning signs (cramping pain, vomiting, obstipation).

— Encourage adequate hydration, high-fiber diet once healed, avoidance of constipation.

— Consider laparoscopic vs open approach for any future surgery; adhesion barriers at index operation in selected cases.

Board pearl: When discharging on opioids, always co-prescribe a stimulant or osmotic laxative (senna or PEG) — not just a softener — and document the bowel regimen; this is a National Patient Safety Goal-style item.

Step 3 management: After a successful Gastrografin challenge for partial adhesive SBO, discharge with clear return precautions (recurrent vomiting, no stool/flatus >24 h, fever, severe pain) and surgery follow-up in 2 weeks.

At discharge after resolved POI or nonoperative SBO:

Recurrent adhesive SBO prevention:

Post-volvulus: elective sigmoidectomy during index admission or within weeks for sigmoid volvulus; right hemicolectomy for cecal volvulus.

Post-bariatric internal hernia: closure of mesenteric defects at primary surgery reduces recurrence.

Hernia repair: schedule elective repair of reducible hernias to prevent future incarceration.

Nutrition: oral nutritional supplements if weight loss >5%; outpatient TPN only if true short gut.

Smoking cessation, glycemic control, weight optimization improve future surgical outcomes.

Follow-Up, Monitoring Parameters, and Rehab/Counseling

— I&Os, weights, electrolytes daily (K, Mg, Ca, PO4, Cr).

— Abdominal exam BID; document flatus, BM, distention, tenderness.

— NGT output trend; CRP trend if leak concern.

— Pain scores, opioid MME totals, bowel regimen compliance.

— Daily mobility goals (out of bed POD 0, ambulating POD 1).

— Wound check and surgical follow-up at 1–2 weeks.

— Phone or telehealth check at 48–72 h for high-risk patients to confirm tolerating diet and bowel function.

— Imaging only if symptoms recur.

— Pathology review if resection performed; oncology referral if malignancy found.

— Physical therapy for deconditioning, especially in elderly post-prolonged hospitalization.

— Pulmonary toilet (incentive spirometer) to reduce postop atelectasis/pneumonia.

— Nutritionist follow-up if significant weight loss or new ostomy.

— Ostomy nurse follow-up if stoma created — appliance management, skin care, dehydration prevention (high-output stoma >1.5 L/d risk).

— Recurrence warning signs and when to return to ED.

— Importance of mobility, hydration, bowel regimen.

— Reasonable expectations: bowel function may take weeks to fully normalize after major colorectal surgery.

— Smoking cessation, glycemic optimization for future surgical risk reduction.

CCS pearl: Scheduling 2-week surgical clinic follow-up and counseling on return precautions at discharge is a CCS scoring action — do not omit even if the patient seems stable.

Board pearl: New-onset high-output stoma in the first 2 weeks post-ileostomy is a top cause of readmission — counsel on loperamide, oral rehydration, and daily weights.

Inpatient daily monitoring:

Postdischarge follow-up:

Rehabilitation:

Patient counseling:

Quality metrics: LOS, 30-day readmission for SBO/ileus, surgical site infection rate, ERAS protocol adherence.

Ethical, Legal, and Patient Safety Considerations

— In a peritonitic, septic patient who lacks capacity, proceed under emergency exception (implied consent) if delay risks life/limb; document inability to consent and attempts to reach surrogate.

— For elective re-exploration, full disclosure of risks (mortality, ostomy, reoperation, leak, prolonged ICU, long-term adhesions) is required, including specific risks like need for diverting stoma that may be permanent.

— Use teach-back to confirm understanding, especially when patient is on opioids — document mental status at consent.

— Follow state hierarchy (spouse, adult children, parents, siblings) when patient incapacitated.

— Honor existing advance directives and POLST/MOLST; clarify whether DNR applies to operative setting (many institutions require "required reconsideration" before OR).

— In elderly, frail, or terminal patients with recurrent malignant SBO, palliative care consult for symptom management (octreotide, dexamethasone, scopolamine, venting gastrostomy) may be preferable to surgery. Discuss prognosis honestly.

— Retained foreign body (sponge, instrument) causing postop SBO is a never event → root-cause analysis, disclosure to patient, institutional reporting.

— Wrong-site surgery causing subsequent obstruction similar reporting.

— Discharge with unrecognized partial obstruction → readmission. Use structured handoffs (SBAR), medication reconciliation (especially opioids + bowel regimen), and scheduled follow-up within 1–2 weeks.

— Communicate pending pathology, anticoagulation plan, and stoma teaching to PCP.

Step 3 management: If a sponge count was reported as incorrect in the OR and the patient develops postop SBO, obtain abdominal imaging emergently, disclose findings to the patient/family, file an incident report, and arrange reoperation — disclosure of medical errors is both ethical and legally required in most US states.

Informed consent for emergency laparotomy:

Surrogate decision-making:

Goals of care:

Mandatory reporting & safety events:

Transition of care risks:

Opioid stewardship: prescribe lowest effective dose for shortest duration; check state PDMP; co-prescribe naloxone for high-risk patients.

High-Yield Associations and Rapid-Fire Clinical Facts

Board pearl: Neostigmine 2 mg IV for Ogilvie + alvimopan 12 mg PO for post-resection POI + Gastrografin 100 mL via NGT for partial adhesive SBO — memorize these three pharmacologic levers.

Most common cause of SBO overall (and postop): adhesions.

Most common cause of LBO in adults: colorectal cancer (consider in elderly with new LBO without prior surgery).

Sigmoid volvulus: elderly, institutionalized, chronic constipation; coffee-bean sign; flexible sigmoidoscopy detorsion + elective sigmoidectomy.

Cecal volvulus: younger patients; surgical management (right hemicolectomy).

Ogilvie syndrome: postop (orthopedic, cardiac, neuro), elderly, electrolyte abnormalities, opioids; neostigmine 2 mg IV is first-line after conservative measures fail.

Cecal diameter >12 cm: imminent perforation risk in Ogilvie or LBO.

Alvimopan: peripheral μ-antagonist, accelerates GI recovery post-bowel resection, inpatient only ≤7 d, REMS, MI risk.

Gum chewing (sham feeding): reduces POI duration.

Gastrografin challenge: both diagnostic and therapeutic in partial adhesive SBO; passage to colon in 24 h predicts nonoperative success.

Anastomotic leak: classically POD 5–7; tachycardia, fever, ileus, new AF.

Internal hernia post-RYGB: mesenteric swirl on CT; closed-loop emergency.

ERAS: minimize opioids, early feeding, early ambulation, multimodal analgesia → reduces POI.

Hypokalemia is the most common electrolyte cause of prolonged POI.

Pneumatosis + portal venous gas = bowel ischemia until proven otherwise.

Free air on KUB up to 7 days postop can be physiologic (laparotomy).

Femoral hernia: high strangulation rate; elderly women; always palpate groin.

Right-sided diverticulitis is rare except in Asian populations.

Cecal/right colon LBO in young patient: think Crohn or cecal volvulus.

Postop AF: think anastomotic leak in colorectal patients until ruled out.

High-output ileostomy (>1.5 L/d): dehydration, AKI, hypomagnesemia; treat with loperamide, PPI, ORS.

Board Question Stem Patterns

Step 3 management: Recognize the "ate, then obstructed" stem — it almost always means mechanical SBO requiring CT and Gastrografin challenge or surgery rather than continued ileus management.

Stem 1 — POI vs SBO: POD 5 after open colectomy, distention and vomiting, had been tolerating clears and passing flatus on POD 3. CT shows transition point with proximal dilation, distal collapse. Best next step? → NGT, IVF, NPO, surgical consult; Gastrografin challenge or OR if peritonitis.

Stem 2 — Ogilvie: 78-year-old s/p hip ORIF on POD 3, on hydromorphone PCA and diphenhydramine, develops massive painless distention, cecum 11 cm on KUB, no transition point on CT. Next step? → Conservative (NPO, NGT, decompress rectal tube, stop opioids/anticholinergics, correct K/Mg). If cecum >12 cm or failure at 48–72 h → neostigmine 2 mg IV on telemetry; if fails → colonoscopic decompression.

Stem 3 — Anastomotic leak: POD 6 after low anterior resection, new atrial fibrillation, fever 38.8, tachycardia, ileus. CT with rectal contrast shows extraluminal contrast and pelvic abscess. Best next step? → NPO, IV antibiotics (pip-tazo), IR drainage if contained, OR for diversion/washout if sepsis.

Stem 4 — Internal hernia post-bypass: 35-year-old 2 years post-RYGB, recurrent postprandial cramping, vomiting, CT with mesenteric swirl sign. Next step? → Urgent diagnostic laparoscopy (closed-loop risk).

Stem 5 — Sigmoid volvulus: Nursing-home patient with abdominal distention, coffee-bean sign on KUB. Next step? → Flexible sigmoidoscopy detorsion + rectal tube, then elective sigmoidectomy this admission.

Stem 6 — Opioid-induced ileus prevention: Patient undergoing partial colectomy, asked about pharmacologic adjunct to accelerate GI recovery. Answer: alvimopan 12 mg PO preop and BID postop.

Stem 7 — Electrolyte mimic: Postop ileus persisting despite no opioids; K 2.9, Mg 1.4 → replete K and Mg.

Stem 8 — Adrenal crisis: Chronic prednisone user, postop hypotension and ileus → stress-dose hydrocortisone.

One-Line Recap

Postoperative ileus is a transient, reversible loss of GI motility managed with multimodal analgesia, opioid minimization, electrolyte repletion, early mobilization, and selective use of alvimopan or neostigmine, while postoperative bowel obstruction is a mechanical process — most commonly adhesive — requiring CT identification of a transition point, Gastrografin challenge for partial cases, and prompt surgery for any sign of closed loop, ischemia, peritonitis, anastomotic leak, or failure of nonoperative management at 48–72 hours.

Board pearl: The single highest-yield Step 3 reflex — any postop patient with new vomiting after initially tolerating diet gets a CT abdomen/pelvis with contrast and a surgical re-evaluation, not just more ileus management.

POI vs SBO: "never recovered" (gradual, painless, diffuse gas to rectum) vs "ate then obstructed" (colicky pain, transition point, decompressed distal bowel).

First-line POI bundle: NPO PRN, minimize opioids, multimodal analgesia, correct K/Mg, ambulate, gum chew, alvimopan after bowel resection; reserve NGT for vomiting.

First-line SBO bundle: NPO, NGT, IVF, electrolytes, antibiotics if complicated, Gastrografin challenge for partial adhesive SBO, surgery for peritonitis/closed loop/ischemia/failed nonop trial.

Red flags demanding OR: peritonitis, pneumatosis/portal venous gas, closed loop, hemodynamic instability, lactic acidosis, anastomotic leak with sepsis, new AF + fever post-colorectal surgery, post-RYGB swirl sign.

Special syndromes: Ogilvie (neostigmine 2 mg IV after conservative care), sigmoid volvulus (endoscopic detorsion + elective resection), cecal volvulus (right hemicolectomy), internal hernia post-bariatric (urgent laparoscopy).