12-phase flow (12)

1. 1FRAME
   Duration (acute <14d / persistent 14-30 / chronic >30), frequency + volume + nocturnal, character (watery / bloody / mucus / steatorrhea) — anchors DDx (Shane IDSA 2017 PMID 29074568)
   inputs: diarrhea_duration, diarrhea_frequency_volume, diarrhea_character_bloody_mucus_steatorrhea
   advance: pattern characterized
2. 2ENTRY
   Associated fever, abdominal pain, vomiting, tenesmus, weight loss, nocturnal — DDx-narrowing features
   inputs: associated_fever, associated_abdominal_pain, associated_vomiting, associated_tenesmus_bloody, associated_weight_loss, associated_nocturnal_diarrhea
   advance: phenotype-defining features captured
3. 3CONTEXT
   Age, sex, vitals + temp, recent antibiotic/hospitalization (C diff), travel/food outbreak, known IBD/celiac, immunocompromised, medications (PPI/NSAID/SSRI/chemo/ICI), cardiac/vascular risk (ischemic colitis), thyroid, chronic constipation (fecal impaction) — Shane IDSA 2017 PMID 29074568; Kelly ACG PMID 32198213
   inputs: age, sex, sbp, hr, rr, spo2, temp, recent_antibiotic_or_hospital, recent_travel_food_outbreak, known_ibd_or_celiac, immunocompromised_state, medications_ppi_nsaid_ssri_metformin_chemo, cardiac_vascular_risk_afib_cad
   advance: context complete
4. 4RED_FLAGS
   Severe volume depletion / shock; toxic megacolon (transverse colon >6 cm + systemic toxicity); EHEC with HUS risk (AVOID antibiotics); C diff fulminant (pseudomembranous colitis, shock, megacolon); severe IBD flare (Truelove-Witts severe); ischemic colitis with gangrene; mesenteric ischemia (pain out of proportion + lactate); severe NAGMA + hypokalemia; ICI checkpoint colitis (steroids + infliximab); typhoid with intestinal perforation
   inputs: sbp, temp, associated_tenesmus_bloody, lactate_venous
   advance: no immediate life-threat OR emergent intervention activated
5. 5INITIAL_WORKUP
   CBC, BMP (electrolytes, anion gap, BUN/Cr, glucose), LFT + albumin, lactate (severe), CRP+PCT (selective), TSH (selective), stool studies (selective by phenotype — culture, C diff NAAT+GDH+toxin, O&P, GI PCR panel, Shiga toxin if bloody), fecal occult blood, ECG (electrolyte derangement)
   inputs: cbc_with_diff, bmp_anion_gap_bicarbonate, lactate_venous, crp_pct, lft_albumin, stool_studies, fecal_occult_blood, ecg_12_lead
   actions: panel.cbc, panel.renal, panel.lft, panel.inflammation
   advance: initial workup reviewed + phenotype narrowed
6. 6BRANCHING_WORKUP
   Bacterial dysentery: stool culture + Shiga toxin → IDSA guideline (Shane PMID 29074568); AVOID antibiotics if EHEC suspected (Tarr Lancet 2005 PMID 21228399). C diff: NAAT + GDH + toxin → IDSA 2021 vancomycin/fidaxomicin (Kelly ACG PMID 32198213). IBD flare: CRP, albumin, calprotectin, CT, colonoscopy → gi.crohns.core.v1 / gi.ulcerative-colitis.core.v1. Ischemic colitis: CT with contrast + colonoscopy (non-gangrenous). Parasitic: O&P + Giardia/Crypto antigen + GI PCR panel; tinidazole/metronidazole/nitazoxanide. Microscopic: colonoscopy with biopsies. Hyperthyroid: TSH + T4 → endo.thyroid-storm.core.v1. ICI checkpoint colitis: stop ICI + steroids + infliximab. Fecal impaction: DRE + manual disimpaction. Immunocompromised: flex sig + CMV PCR + crypto/microsporidium
   inputs: abdominal_xray_upright_supine, ct_abdomen_pelvis_iv_contrast, colonoscopy_flexible_sig, stool_inflammation_markers
   advance: definitive pathway selected
7. 7DIFFERENTIAL
   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
   advance: phenotype ranked with pre-test priors
8. 8RISK_STRATIFICATION
   qSOFA / SIRS for septic phenotype; Truelove-Witts severity for UC flare (schema-blocked); Hinchey for diverticulitis overlap; HEART if chest symptoms overlap (rare); volume-depletion severity (clinical) drives fluid bolus + admission
   advance: risk scores documented
9. 9TREATMENT
   Volume + electrolyte resuscitation (IV NS or LR; correct K early — diarrhea hypokalemia common). Empiric antibiotics ONLY for: severe bacterial dysentery (NOT EHEC), C diff (vancomycin 125 mg PO q6h or fidaxomicin 200 mg PO BID per IDSA 2021), traveler diarrhea (ciprofloxacin or azithromycin), severe immunocompromised. AVOID antibiotics for EHEC O157:H7 (HUS risk per Tarr 2005 PMID 21228399); AVOID loperamide in invasive/bloody diarrhea. IBD flare: IV methylprednisolone 40-60 mg/day × 5 d; rescue with infliximab or cyclosporine in steroid-refractory severe UC (route gi.ulcerative-colitis.core.v1 / gi.crohns.core.v1). Hyperthyroid / storm: beta-blocker + PTU/methimazole + hydrocortisone + iodine (route endo.thyroid-storm.core.v1). Parasitic: tinidazole 2 g PO single dose for Giardia; nitazoxanide 500 mg PO BID × 3 d for Crypto. ICI colitis: hold ICI + methylprednisolone 1-2 mg/kg + infliximab if refractory. Microscopic colitis: discontinue offending drug + budesonide. Fecal impaction: manual disimpaction + enemas (NO antidiarrheal). Loperamide: 4 mg then 2 mg per loose stool max 16 mg/d ONLY in non-invasive non-bloody diarrhea with no fever; not in C diff or IBD flare
   inputs: sbp, bmp_anion_gap_bicarbonate
   advance: definitive intervention initiated
10. 10DISPOSITION
    Discharge: viral gastroenteritis tolerating PO + stable vitals + mild dehydration corrected + reliable follow-up; uncomplicated traveler diarrhea on PO antibiotics; mild C diff with PO vancomycin/fidaxomicin and follow-up. Observation: moderate dehydration responding to IV fluids; pending stool studies. Ward: severe dehydration; C diff with concerning features; ischemic colitis non-gangrenous; IBD flare moderate-severe; fecal impaction post-disimpaction; HUS workup. Telemetry: severe electrolyte derangement (K <2.5); hyperthyroid storm. ICU: shock, fulminant C diff (megacolon, hypotension, ileus), perforation, severe ischemic colitis, thyroid storm, severe ICI colitis. OR: toxic megacolon (failed medical), perforation, gangrenous ischemic colitis, severe IBD with megacolon failing rescue
    advance: disposition assigned + downstream handoff complete
11. 11MONITORING
    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
    inputs: sbp, hr, bmp_anion_gap_bicarbonate
    advance: stability achieved or escalation triggered
12. 12FOLLOWUP
    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)
    advance: discharge bundle prescribed + follow-up scheduled