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symptom.diarrhea.ed.v1

Acute diarrhea (ED triage — undifferentiated adult)

symptomacuteundifferentiatedadult
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Encounter flow

12/12 authored

Canonical 12-phase frame with authored status for this dossier.

Current phase

Frame

Detailed

Duration (acute <14d / persistent 14-30 / chronic >30), frequency + volume + nocturnal, character (watery / bloody / mucus / steatorrhea) — anchors DDx (Shane IDSA 2017 PMID 29074568)

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pattern characterized

Patient inputs (37)

Age shifts priors: elderly → ischemic colitis / fecal impaction / drug-induced; young adult → IBD / travel parasites / IBS (Shane IDSA 2017 PMID 29074568)

Sex-based — IBS female predominant; microscopic colitis older female predominant; rare anatomic concerns

Recent antibiotic (clindamycin, FQ, cephalosporin, PPI) OR hospitalization within 12 weeks → C diff (Kelly ACG PMID 32198213)

International travel (developing countries) → ETEC, Salmonella, Shigella, parasites; outbreak / cruise → norovirus

Known IBD / celiac → flare workup; medication compliance / triggers; route gi.crohns.core.v1 / gi.ulcerative-colitis.core.v1

HIV / transplant / chemo / biologics → CMV colitis / cryptosporidium / MAC / microsporidium / atypical presentations

PPI / NSAID / SSRI / metformin / acarbose / colchicine / chemo / radiation / ICI → drug-induced or microscopic colitis or ICI colitis (steroids + infliximab if severe)

AFib / CAD / hypercoagulable / atherosclerotic → ischemic colitis (acute LLQ + bloody)

Hypotension + diarrhea → severe volume depletion / sepsis / adrenal crisis (overlap); hypovolemic vs distributive

Tachycardia + diarrhea → volume depletion / sepsis / thyroid storm / hyperthyroid

Tachypnea + diarrhea → metabolic acidosis (NAGMA from HCO3 loss) / sepsis

Hypoxia + diarrhea → severe sepsis / aspiration overlay

Fever + diarrhea → invasive bacterial / IBD / appendicitis; hypothermia → severe sepsis / adrenal crisis

Fever + diarrhea → infectious (especially invasive bacterial) / IBD / appendicitis-mimic; afebrile → viral / functional / drug-induced / microscopic / ischemic

Crampy + relieved by BM → IBS / IBD; severe + out of proportion → ischemic; LLQ + bloody → ischemic colitis; periumbilical migratory → appendicitis; RUQ → cholecystitis with diarrhea overlay

Vomiting + diarrhea → gastroenteritis (route symptom.nausea_vomiting.ed.v1 if vomiting-predominant); food poisoning (S. aureus, B. cereus emetic)

Tenesmus + bloody → invasive bacterial (Shigella, EHEC) OR IBD; rectal involvement

Weight loss + diarrhea → IBD / malabsorption / neuroendocrine / hyperthyroidism / TB / cancer (>5% in 3 months alarm)

Nocturnal diarrhea waking patient → organic (IBD, microscopic, infectious); against functional

Acute <14 days vs persistent 14-30 vs chronic >30 days (Shane PMID 29074568) — anchors DDx; chronic shifts toward IBD/IBS/microscopic/malabsorption/neuroendocrine

Frequency (3+/24 h definition) + volume (low/moderate/high) + nocturnal (organic vs functional)

Bloody → invasive bacterial / EHEC / IBD / ischemic; mucus → IBD / IBS / amoebic; steatorrhea (greasy, floating, foul) → malabsorption (pancreatic insufficiency, celiac, SIBO)

Leukocytosis + left shift → invasive bacterial / C diff; eosinophilia → parasitic; anemia → IBD / chronic blood loss / malabsorption

Na/K/Cl/HCO3 (NAGMA from HCO3 loss), BUN/Cr (volume depletion / AKI), glucose, anion gap; severe hypokalemia → ECG monitoring

Albumin <30 → severe IBD flare (Truelove-Witts); LFT for hepatic / cholangitis overlay

Stool calprotectin / lactoferrin → distinguishes inflammatory (IBD) vs functional (IBS); not for ED acute use but downstream

Acute abdominal series — toxic megacolon (transverse colon >6 cm), thumbprinting (ischemic colitis), free air (perforation)

CT abdomen/pelvis with IV + PO contrast — IBD pattern, ischemic colitis, mesenteric ischemia, complications (abscess, perforation, megacolon)

Flex sig (ED) or colonoscopy (planned) for IBD diagnosis, ischemic colitis, microscopic colitis, CMV colitis, infectious overlap; AVOID in toxic megacolon

Known hyperthyroid / Graves / multinodular toxic → storm trigger (infection, surgery, contrast) → thyroid storm with diarrhea (route endo.thyroid-storm.core.v1)

Chronic constipation + elderly + immobile + nursing home → fecal impaction with overflow (paradoxical diarrhea) — DRE + manual disimpaction

Lactate ≥4 → severe sepsis OR ischemic colitis / mesenteric ischemia → STAT CT angio + vascular surgery

CRP + PCT (panel.inflammation) — PCT supports bacterial; CRP ≥100 + albumin <30 → severe IBD flare

TSH suppressed + T4 elevated → hyperthyroidism / thyroid storm (route endo.thyroid-storm.core.v1)

Stool culture (Salmonella, Shigella, Campylobacter, E coli incl. O157:H7 — STEC), C diff NAAT + GDH + toxin, ova & parasites + Giardia/Crypto antigen, multipathogen GI PCR panel; selective per phenotype (Shane IDSA 2017 PMID 29074568)

Heme-positive stool → bleeding (invasive bacterial / IBD / ischemic colitis / cancer); macroscopic blood obvious

ECG for hypokalemia (U waves), hyperkalemia changes (rare in diarrhea), AFib (ischemic colitis prior), QTc pre-antiemetic

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (14)

14 need judgement
  • informationallife_threateningsevere_volume_depletion_shock
    Diarrhea + hypotension + tachycardia + oliguria + AMS + lactate ≥4 — severe volume depletion / septic shock; aggressive IV NS/LR + sepsis bundle + cause workup
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningfulminant_c_diff
    C diff + hypotension OR ileus OR megacolon OR severe AKI — fulminant C diff; vancomycin 500 mg PO q6h + metronidazole 500 mg IV q8h + surgery consult (Kelly ACG 2021 PMID 32198213)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningehec_with_hus_risk
    Bloody diarrhea + EHEC O157:H7 (Shiga toxin positive) + age <5 or >65 or pregnant — HUS risk; AVOID antibiotics + AVOID loperamide + monitor CBC/platelets/LDH/Cr q12-24h (Tarr Lancet 2005 PMID 21228399)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningtoxic_megacolon
    Transverse colon >6 cm on AXR + systemic toxicity (fever, tachycardia, hypotension, AMS, leukocytosis) — toxic megacolon; STAT surgery + IV vancomycin (C diff) or steroids hold (IBD)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningischemic_colitis_with_gangrene
    Acute LLQ pain + bloody diarrhea + elderly vasculopath + AFib / CAD + CT thumbprinting + transmural changes OR right colon ischemia OR pancolitis OR failure to improve in 24-48 h — gangrenous ischemic colitis; STAT surgery
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningthyroid_storm_with_diarrhea
    Diarrhea + tachycardia + fever + AMS + AFib + BWPS ≥45 + suppressed TSH + elevated T4 — thyroid storm; PTU + propranolol + hydrocortisone + iodine (AFTER PTU) → endo.thyroid-storm.core.v1
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereinvasive_bacterial_dysentery
    Bloody dysentery + fever + tenesmus + stool culture positive (Salmonella, Shigella, Campylobacter) — invasive bacterial; ciprofloxacin 500 mg PO BID × 3-5 d OR azithromycin 1 g (Campylobacter / FQ-resistance); AVOID antibiotics if EHEC (Shane IDSA 2017 PMID 29074568)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseveresevere_ibd_flare
    Bloody diarrhea + ≥6 stools/day + systemic toxicity (HR >90, fever, anemia, ESR/CRP elevation) + known IBD OR concerning presentation — Truelove-Witts severe UC OR severe Crohn; IV methylprednisolone + GI consult; rescue with infliximab or cyclosporine if non-responsive by day 3
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereici_checkpoint_colitis
    Diarrhea + recent ICI (ipilimumab, nivolumab, pembrolizumab) + grade 3-4 (≥7 stools above baseline + colitis symptoms) — ICI colitis; hold ICI + IV methylprednisolone 1-2 mg/kg + infliximab if refractory by 72 h
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereimmunocompromised_opportunistic_diarrhea
    Diarrhea + HIV (CD4 <100) OR transplant OR chemo OR biologic — opportunistic (CMV colitis, cryptosporidium, microsporidium, MAC); flex sig + CMV PCR + targeted therapy
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseveresevere_nagma_with_hypokalemia
    Diarrhea + NAGMA (HCO3 <15, normal anion gap) + K <2.5 — severe bicarbonate + K loss; aggressive LR + K replacement + bicarbonate if pH <7.1
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderateparasitic_traveler_diarrhea
    Persistent diarrhea (>14 d) + international travel + Giardia / Crypto / Entamoeba / Cyclospora — parasitic; tinidazole 2 g (Giardia), nitazoxanide 500 mg BID × 3 d (Crypto), metronidazole + paromomycin (E histolytica)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatefecal_impaction_with_overflow
    Diarrhea (paradoxical) + chronic constipation + elderly + nursing home + DRE confirms impaction — fecal impaction with overflow; manual disimpaction + enemas; AVOID antidiarrheal
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmildmicroscopic_colitis_drug_induced
    Chronic non-bloody diarrhea + PPI / NSAID / SSRI / acarbose / ranitidine + colonoscopy biopsy (lymphocytic / collagenous) — microscopic colitis; discontinue trigger + budesonide 9 mg PO daily × 6-8 weeks
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

ed playbook — drug actions (12)

  1. 1. IV NS or LR (volume resuscitation)
    1-2 L bolus then 100-200 mL/h titrate to vitals + UOP ≥0.5 mL/kg/h • IV • continuous
    trigger: Hypotension OR tachycardia OR oliguria OR severe volume depletion
    Shane IDSA 2017 PMID 29074568 — fluid resuscitation first-line; LR if NAGMA from HCO3 loss; correct K simultaneously
  2. 2. KCl IV / PO (hypokalemia)
    10-20 mEq IV/h via central; PO 40-80 mEq divided • IV/PO • titrate
    trigger: K <3.5 + diarrhea ongoing
    Diarrhea-associated hypokalemia common; replete to 4.0-4.5; ECG monitor if K <3.0
  3. 3. oral rehydration solution (ORS / WHO formula)
    50-100 mL/kg over 4 h then maintenance with ongoing losses • PO • continuous
    trigger: Mild-moderate dehydration tolerating PO
    WHO ORS standard care for non-severe diarrhea; effective in adults + peds
  4. 4. loperamide (non-invasive only)
    4 mg PO first dose then 2 mg PO per loose stool (max 16 mg/d adult) • PO • PRN
    trigger: Non-bloody, afebrile, non-invasive diarrhea only (gastroenteritis-not C diff-not IBD-not EHEC)
    AVOID in invasive/bloody (Salmonella/Shigella/Campylobacter/EHEC) or C diff or IBD; risk of toxic megacolon and prolonged shedding
  5. 5. ciprofloxacin OR azithromycin (traveler / bacterial)
    Ciprofloxacin 500 mg PO BID × 3-5 d OR azithromycin 1 g PO single dose (Campylobacter region, pregnancy, peds) • PO • varies
    trigger: Severe traveler diarrhea OR confirmed invasive bacterial (Salmonella in immunocompromised, Shigella, Campylobacter — NOT EHEC)
    IDSA 2017 PMID 29074568 — azithromycin preferred for Campylobacter region (FQ-resistance); AVOID antibiotics in EHEC (HUS risk per Tarr PMID 21228399); ciprofloxacin or rifaximin for non-Campylobacter traveler
  6. 6. vancomycin PO (C diff first-line)
    125 mg PO q6h × 10 d (non-severe); 500 mg PO q6h ± metronidazole 500 mg IV q8h (fulminant) • PO/PR/IV (severe) • q6h
    trigger: C diff (NAAT/toxin positive OR clinical with concerning features)
    IDSA 2021 / Kelly ACG PMID 32198213 — vancomycin OR fidaxomicin first-line; fidaxomicin reduces recurrence; metronidazole IV added if fulminant or ileus
  7. 7. fidaxomicin PO (C diff alternative / recurrence)
    200 mg PO BID × 10 d (or extended-pulsed for second recurrence) • PO • BID
    trigger: C diff first episode OR recurrence (preferred over vancomycin for recurrence prevention)
    IDSA 2021 — fidaxomicin reduces recurrence; cost-benefit; for recurrence: bezlotoxumab adjunct or FMT
  8. 8. IV methylprednisolone (severe IBD / UC flare)
    40-60 mg IV daily (Truelove-Witts severe UC) × 3-5 d then transition PO prednisone taper • IV • daily
    trigger: Severe IBD flare (Truelove-Witts severe: ≥6 bloody stools + 1 systemic toxicity)
    AGA / ACG — IV steroids first-line; non-response by day 3-5 → rescue with infliximab or cyclosporine; route to gi.crohns.core.v1 / gi.ulcerative-colitis.core.v1
  9. 9. infliximab IV (steroid-refractory severe UC / ICI colitis)
    5 mg/kg IV at 0, 2, 6 weeks (induction); ICI colitis: 5-10 mg/kg single dose if refractory to steroids • IV • single / induction
    trigger: Steroid-refractory severe UC OR steroid-refractory ICI checkpoint colitis (immunotherapy adverse event)
    ACT-1 / ACT-2 — infliximab rescue for steroid-refractory severe UC; ICI colitis grade 3-4 → hold ICI + steroids + infliximab if refractory by 72 h
  10. 10. tinidazole or metronidazole (Giardia / Entamoeba)
    Tinidazole 2 g PO single dose OR metronidazole 250 mg PO TID × 5-7 d (Giardia); metronidazole 750 mg PO TID × 7-10 d + paromomycin 25-35 mg/kg/d for Entamoeba histolytica liver abscess • PO • varies
    trigger: Giardia (Ag positive / O&P trophozoites) OR Entamoeba (symptomatic + serology + bloody)
    CDC / IDSA — tinidazole single dose preferred Giardia (better compliance); metronidazole + paromomycin combination for invasive E histolytica
  11. 11. nitazoxanide (Cryptosporidium / Cyclospora)
    500 mg PO BID × 3 d (adult) • PO • BID
    trigger: Cryptosporidium (Ag positive) in immunocompetent (immunocompromised → ART for HIV + supportive)
    FDA-approved for Crypto; limited efficacy in HIV (depends on CD4 recovery)
  12. 12. beta-blocker + PTU + hydrocortisone + iodine (thyroid storm)
    Propranolol 60-80 mg PO q4h + PTU 200-300 mg PO q4h + hydrocortisone 100 mg IV q8h + saturated KI 5 drops PO q6h (start AFTER PTU/methimazole) • PO/IV • q4-8h
    trigger: Thyroid storm (BWPS ≥45) with diarrhea + tachycardia + fever + AMS
    AACE / ATA — multimodal: block synthesis (PTU/MMI), block release (iodine after PTU), block conversion (steroids), block peripheral effects (beta-blocker); route to endo.thyroid-storm.core.v1

Auto-drafted A&P note

ed

Subjective

- Possible entry pathways: Acute watery diarrhea (3+ loose stools/24 h, <14 days) WITHOUT blood — most often viral (norovirus / rotavirus); supportive only (Shane IDSA 2017 PMID 29074568); Bloody dysentery + fever + tenesmus — invasive bacterial (Salmonella / Shigella / Campylobacter / EHEC O157:H7); STOOL CULTURE + Shiga toxin (AVOID antibiotics for EHEC — HUS risk per Tarr Lancet 2005 PMID 21228399); Diarrhea + recent antibiotic (clindamycin, fluoroquinolone, cephalosporin) OR hospitalized — C difficile NAAT + GDH + toxin → IDSA 2021 fidaxomicin or vancomycin (Kelly ACG PMID 32198213).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Acute diarrhea (ED triage — undifferentiated adult)** (symptom.diarrhea.ed.v1).
Phenotype framing: Acute self-limited (~60-70%): viral (norovirus #1, rotavirus, enteric adeno), bacterial non-invasive (ETEC, Vibrio non-cholera, B cereus, S aureus, C perfringens). Invasive bacterial: Salmonella, Shigella, Campylobacter, EHEC O157:H7 (HUS), C difficile (post-antibiotic / hospital), Yersinia. Parasitic: Giardia, Cryptosporidium, Entamoeba, Cyclospora, Strongyloides. IBD: Crohn / UC flare. Ischemic colitis: elderly vasculopath. Microscopic colitis: drug-induced. Functional: IBS-D, IBS-mixed. Malabsorption: celiac, SIBO, pancreatic insufficiency, lactose intolerance. Hyperthyroid. Neuroendocrine: VIPoma, carcinoid, ZES, mastocytosis. Drug-induced: chemo, radiation, ICI colitis, laxative abuse, PPI/NSAID/SSRI. Fecal impaction. Immunocompromised opportunistic: CMV, MAC, cryptosporidium, microsporidium
Scope: Duration (acute <14d / persistent 14-30 / chronic >30), frequency + volume + nocturnal, character (watery / bloody / mucus / steatorrhea) — anchors DDx (Shane IDSA 2017 PMID 29074568)

No severity triggers fired against current inputs.

Plan

No regimen axis selected (engine has no regimen_axes or could not match).

Setting playbook (ed) — Pattern-anchored triage (acute self-limited vs invasive bacterial vs C diff vs IBD flare vs ischemic colitis vs parasitic traveler vs drug-induced vs hyperthyroid vs ICI colitis vs fecal impaction); rule out severe volume depletion, toxic megacolon, EHEC with HUS risk, fulminant C diff, ischemic colitis with gangrene, thyroid storm, perforation; activate downstream engine (Shane IDSA 2017 PMID 29074568; Kelly ACG C diff PMID 32198213; Tarr Lancet 2005 PMID 21228399 EHEC/HUS)
1. IV NS or LR (volume resuscitation) 1-2 L bolus then 100-200 mL/h titrate to vitals + UOP ≥0.5 mL/kg/h IV continuous — Hypotension OR tachycardia OR oliguria OR severe volume depletion (Shane IDSA 2017 PMID 29074568 — fluid resuscitation first-line; LR if NAGMA from HCO3 loss; correct K simultaneously)
2. KCl IV / PO (hypokalemia) 10-20 mEq IV/h via central; PO 40-80 mEq divided IV/PO titrate — K <3.5 + diarrhea ongoing (Diarrhea-associated hypokalemia common; replete to 4.0-4.5; ECG monitor if K <3.0)
3. oral rehydration solution (ORS / WHO formula) 50-100 mL/kg over 4 h then maintenance with ongoing losses PO continuous — Mild-moderate dehydration tolerating PO (WHO ORS standard care for non-severe diarrhea; effective in adults + peds)
4. loperamide (non-invasive only) 4 mg PO first dose then 2 mg PO per loose stool (max 16 mg/d adult) PO PRN — Non-bloody, afebrile, non-invasive diarrhea only (gastroenteritis-not C diff-not IBD-not EHEC) (AVOID in invasive/bloody (Salmonella/Shigella/Campylobacter/EHEC) or C diff or IBD; risk of toxic megacolon and prolonged shedding)
5. ciprofloxacin OR azithromycin (traveler / bacterial) Ciprofloxacin 500 mg PO BID × 3-5 d OR azithromycin 1 g PO single dose (Campylobacter region, pregnancy, peds) PO varies — Severe traveler diarrhea OR confirmed invasive bacterial (Salmonella in immunocompromised, Shigella, Campylobacter — NOT EHEC) (IDSA 2017 PMID 29074568 — azithromycin preferred for Campylobacter region (FQ-resistance); AVOID antibiotics in EHEC (HUS risk per Tarr PMID 21228399); ciprofloxacin or rifaximin for non-Campylobacter traveler)
6. vancomycin PO (C diff first-line) 125 mg PO q6h × 10 d (non-severe); 500 mg PO q6h ± metronidazole 500 mg IV q8h (fulminant) PO/PR/IV (severe) q6h — C diff (NAAT/toxin positive OR clinical with concerning features) (IDSA 2021 / Kelly ACG PMID 32198213 — vancomycin OR fidaxomicin first-line; fidaxomicin reduces recurrence; metronidazole IV added if fulminant or ileus)
7. fidaxomicin PO (C diff alternative / recurrence) 200 mg PO BID × 10 d (or extended-pulsed for second recurrence) PO BID — C diff first episode OR recurrence (preferred over vancomycin for recurrence prevention) (IDSA 2021 — fidaxomicin reduces recurrence; cost-benefit; for recurrence: bezlotoxumab adjunct or FMT)
8. IV methylprednisolone (severe IBD / UC flare) 40-60 mg IV daily (Truelove-Witts severe UC) × 3-5 d then transition PO prednisone taper IV daily — Severe IBD flare (Truelove-Witts severe: ≥6 bloody stools + 1 systemic toxicity) (AGA / ACG — IV steroids first-line; non-response by day 3-5 → rescue with infliximab or cyclosporine; route to gi.crohns.core.v1 / gi.ulcerative-colitis.core.v1)
9. infliximab IV (steroid-refractory severe UC / ICI colitis) 5 mg/kg IV at 0, 2, 6 weeks (induction); ICI colitis: 5-10 mg/kg single dose if refractory to steroids IV single / induction — Steroid-refractory severe UC OR steroid-refractory ICI checkpoint colitis (immunotherapy adverse event) (ACT-1 / ACT-2 — infliximab rescue for steroid-refractory severe UC; ICI colitis grade 3-4 → hold ICI + steroids + infliximab if refractory by 72 h)
10. tinidazole or metronidazole (Giardia / Entamoeba) Tinidazole 2 g PO single dose OR metronidazole 250 mg PO TID × 5-7 d (Giardia); metronidazole 750 mg PO TID × 7-10 d + paromomycin 25-35 mg/kg/d for Entamoeba histolytica liver abscess PO varies — Giardia (Ag positive / O&P trophozoites) OR Entamoeba (symptomatic + serology + bloody) (CDC / IDSA — tinidazole single dose preferred Giardia (better compliance); metronidazole + paromomycin combination for invasive E histolytica)
11. nitazoxanide (Cryptosporidium / Cyclospora) 500 mg PO BID × 3 d (adult) PO BID — Cryptosporidium (Ag positive) in immunocompetent (immunocompromised → ART for HIV + supportive) (FDA-approved for Crypto; limited efficacy in HIV (depends on CD4 recovery))
12. beta-blocker + PTU + hydrocortisone + iodine (thyroid storm) Propranolol 60-80 mg PO q4h + PTU 200-300 mg PO q4h + hydrocortisone 100 mg IV q8h + saturated KI 5 drops PO q6h (start AFTER PTU/methimazole) PO/IV q4-8h — Thyroid storm (BWPS ≥45) with diarrhea + tachycardia + fever + AMS (AACE / ATA — multimodal: block synthesis (PTU/MMI), block release (iodine after PTU), block conversion (steroids), block peripheral effects (beta-blocker); route to endo.thyroid-storm.core.v1)

Non-pharmacologic actions:
- Two IV access points; central line if vasopressors or hyperK with IV K replacement
- Contact + enteric precautions: C diff (handwash with soap + water; alcohol gel insufficient); norovirus; bacterial dysentery
- NPO if surgical concern; oral rehydration if tolerated otherwise
- Foley if shock / severe volume depletion / I/O tracking
- NG decompression if ileus / megacolon
- GI consult: severe IBD flare, ICI colitis, ischemic colitis, microscopic colitis (outpatient)
- Surgery consult: toxic megacolon, perforation, gangrenous ischemic colitis, severe IBD failing rescue
- ID consult: severe traveler / immunocompromised / unusual pathogen
- Endocrinology if thyroid storm
- Vascular surgery if mesenteric ischemia (CT angio findings)

Monitoring

Setting (ed) monitoring:
- Vitals q1h × 4 then q4h once stable
- I/O hourly until stable; UOP target ≥0.5 mL/kg/h
- BMP q4-6h while diarrhea ongoing (K, Na, HCO3, BUN/Cr)
- Stool frequency + character + volume
- Daily weight
- CRP + albumin trend in IBD flare
- Repeat lactate q4-6h in septic / ischemic colitis
- ECG monitoring if K <3.0
- Renal function q12-24h if HUS risk (EHEC bloody diarrhea + age <5 or >65 + AKI / thrombocytopenia / schistocytes / LDH elevation)
- Abdominal exam q4h in severe phenotype
- CT/colonoscopy follow-up per specialist

Follow-up plan: Outpatient GI for IBD chronic management; PCP for IBS-D; endocrinology for hyperthyroid / neuroendocrine; chronic IBD on biologic/immunomodulator; C diff recurrence protocol; HUS hematology + nephrology; traveler diarrhea preventive education; fecal impaction bowel regimen; ICI immune-related AE clinic; deprescribing offending drugs (PPI/NSAID/SSRI in microscopic colitis)
- Close-out criterion: discharge bundle prescribed + follow-up scheduled

Monitoring phase: Vitals q1-4h, I/O, BMP q4-6h while diarrhea ongoing (K, Na, HCO3, BUN/Cr); stool frequency + character; abdominal exam q4h in severe phenotype; serial lactate in ischemic colitis / sepsis; CRP/albumin trend in IBD flare; ECG monitoring if K <3.0; renal function trend if HUS risk

Disposition

Current setting: ed — Pattern-anchored triage (acute self-limited vs invasive bacterial vs C diff vs IBD flare vs ischemic colitis vs parasitic traveler vs drug-induced vs hyperthyroid vs ICI colitis vs fecal impaction); rule out severe volume depletion, toxic megacolon, EHEC with HUS risk, fulminant C diff, ischemic colitis with gangrene, thyroid storm, perforation; activate downstream engine (Shane IDSA 2017 PMID 29074568; Kelly ACG C diff PMID 32198213; Tarr Lancet 2005 PMID 21228399 EHEC/HUS)

Disposition criteria:
- Discharge: viral gastroenteritis tolerating PO + stable vitals + mild dehydration corrected; uncomplicated traveler diarrhea on oral antibiotics; mild C diff on PO vancomycin/fidaxomicin with reliable follow-up; mild IBD flare on PO steroid taper + GI follow-up
- Observation: moderate dehydration responding to IV fluids; pending stool studies; mild-moderate C diff requiring 24-h monitoring
- Ward: severe volume depletion; C diff non-fulminant; ischemic colitis non-gangrenous on conservative; IBD flare moderate; fecal impaction post-disimpaction
- Telemetry / step-down: severe electrolyte derangement (K <2.5); hyperthyroid storm post-stabilization
- ICU: shock (septic, hypovolemic, adrenal), fulminant C diff (megacolon, ileus, hypotension), severe ischemic colitis, thyroid storm with AMS, severe ICI colitis on infliximab
- OR: toxic megacolon failing medical, perforation, gangrenous ischemic colitis, severe IBD with megacolon failing rescue (subtotal colectomy)

Escalation triggers (move to higher acuity):
- Hypotension (SBP <90) + diarrhea + lactate ≥4 → sepsis bundle + consider adrenal crisis + mesenteric ischemia + EHEC HUS workup
- Toxic megacolon (transverse colon >6 cm + systemic toxicity) → STAT surgery + IV vancomycin + metronidazole + steroids hold if IBD; perforation → emergent laparotomy
- EHEC O157:H7 with bloody diarrhea → AVOID antibiotics + AVOID loperamide + watch for HUS (CBC + smear + LDH + Cr + platelets q12-24h) (Tarr Lancet 2005 PMID 21228399)
- Fulminant C diff (hypotension, ileus, megacolon, severe AKI) → vancomycin 500 mg PO q6h + metronidazole 500 mg IV q8h + surgery consult
- Severe UC flare (Truelove-Witts severe ≥6 bloody stools + 1 systemic) → IV methylprednisolone + GI + non-response by day 3 → infliximab or cyclosporine → gi.ulcerative-colitis.core.v1
- Ischemic colitis with gangrene (right colon / pancolitis / failure of medical management) → STAT surgery
- Thyroid storm with diarrhea + AMS + fever + AFib → multimodal (PTU + beta-blocker + steroids + iodine after PTU) → endo.thyroid-storm.core.v1
- ICI checkpoint colitis grade 3-4 → hold ICI + IV methylprednisolone 1-2 mg/kg + infliximab if refractory 72 h
- Severe NAGMA (HCO3 <10) + hypokalemia → aggressive LR + K replacement + bicarbonate if pH <7.1
- Severe parasitic diarrhea in immunocompromised → ID consult + targeted therapy (CMV PCR + ganciclovir if positive; HIV CD4 if <100)

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Diarrhea + hypotension + tachycardia + oliguria + AMS + lactate ≥4 — severe volume depletion / septic shock; aggressive IV NS/LR + sepsis bundle + cause workup
- [LIFE_THREATENING] C diff + hypotension OR ileus OR megacolon OR severe AKI — fulminant C diff; vancomycin 500 mg PO q6h + metronidazole 500 mg IV q8h + surgery consult (Kelly ACG 2021 PMID 32198213)
- [LIFE_THREATENING] Bloody diarrhea + EHEC O157:H7 (Shiga toxin positive) + age <5 or >65 or pregnant — HUS risk; AVOID antibiotics + AVOID loperamide + monitor CBC/platelets/LDH/Cr q12-24h (Tarr Lancet 2005 PMID 21228399)

Citations

- 2017 IDSA infectious diarrhea (Shane) + 2021 ACG C diff (Kelly) + 2005 Tarr Lancet EHEC/HUS + ACG IBD severity (Truelove-Witts) + Brandt ACG ischemic colitis + ATA/AACE thyroid storm + ASCO/ESMO ICI colitis + WHO ORS + CDC parasitic diarrhea [PMID:35839362](https://pubmed.ncbi.nlm.nih.gov/35839362/)

Last reconciled with current guidelines: 2026-05-30.
References
  • 2017 IDSA infectious diarrhea (Shane) + 2021 ACG C diff (Kelly) + 2005 Tarr Lancet EHEC/HUS + ACG IBD severity (Truelove-Witts) + Brandt ACG ischemic colitis + ATA/AACE thyroid storm + ASCO/ESMO ICI colitis + WHO ORS + CDC parasitic diarrhea — PMID:35839362