12-phase flow (12)

1. 1FRAME
   Frame the suspected IHPS presentation: age band (< 2 wk atypical-early / 2-3 wk / 3-5 wk / 5-8 wk classic peak 4-6 wk / > 8 wk atypical-late) drives pretest probability + atypical-presentation index. Sex + first-born + family history drive demographic priors (4:1 male predominance, first-born most over-represented). Duration of symptoms drives metabolic-derangement depth + dehydration severity. Macrolide exposure in first 2 wk drives pharmacologic association (erythromycin > azithromycin).
   inputs: age_in_weeks_or_days_at_presentation, sex_at_birth, duration_of_symptoms_in_days, macrolide_exposure_in_first_2_weeks_of_life
   advance: Age + sex + duration + macrolide-exposure tagged; pretest probability + atypical-presentation framing set
2. 2ENTRY
   Recognise via classic clinical features (progressive non-bilious projectile vomiting + hungry-after-vomit + weight loss or poor weight gain + dehydration) OR pathognomonic exam (palpable olive — LR+ ~ 25 when present; visible peristaltic waves — LR+ ~ 5) OR classic lab pattern (hypochloremic hypokalemic metabolic alkalosis) OR imaging signature (pyloric muscle thickness ≥ 3 mm AND channel length ≥ 14-17 mm on US).
   inputs: pattern_of_vomiting_projectile_non_bilious, hunger_after_vomit_vs_lethargy, weight_trend_vs_growth_curve
   advance: IHPS suspected by clinical features, exam, lab pattern, or US signature
3. 3CONTEXT
   Age + sex + weight + gestational age + vitals + duration + vomiting pattern + hunger-after-vomit + weight trend + palpable olive + visible peristalsis + macrolide exposure + family history + first-born status + maternal smoking + feeding pattern + PGE1 exposure (rare CHD-comorbid case).
   inputs: age_in_weeks_or_days_at_presentation, sex_at_birth, weight_kg, gestational_age_at_birth_term_vs_preterm, hr_pediatric, capillary_refill_pediatric, mucous_membranes_and_tear_production, pattern_of_vomiting_projectile_non_bilious, hunger_after_vomit_vs_lethargy, weight_trend_vs_growth_curve, macrolide_exposure_in_first_2_weeks_of_life, family_history_of_ihps, first_born_status
   advance: Demographic + risk-factor + clinical context + hydration status documented
4. 4RED_FLAGS
   Severe metabolic alkalosis (Cl < 100, K+ < 3.5, HCO3 > 30) → defer OR until corrected; severe dehydration (> 10%, hypotension by age, capillary refill > 3 s, mottling) → IVF resus 20 mL/kg NS bolus + reassess; bilious emesis → urgent UGI series for malrotation (NOT classic IHPS); bloody emesis → NEC or allergic enterocolitis differential; jaundice with direct bilirubin > 2 → urgent hepatology workup (biliary atresia < 60 d Kasai window); preterm with comorbidity → lower threshold for ICU/NICU level care.
   inputs: sbp_pediatric, jaundice_with_direct_bilirubin_level
   advance: OR-contraindication red flags evaluated; resuscitation initiated if needed; multidisciplinary consults triggered
5. 5INITIAL_WORKUP
   IV access + NPO; CMP with chloride + potassium + bicarbonate (target Cl > 100, K+ > 3.5, HCO3 < 30 pre-op); CBC + glucose + total/direct bilirubin (if jaundiced); urinalysis with urine Cl + pH (paradoxical aciduria); bedside abdominal US for pyloric muscle thickness ≥ 3 mm AND channel length ≥ 14-17 mm (sensitivity > 97% per Hernanz-Schulman 2003); pediatric surgery consult triggered by positive US.
   inputs: cmp_with_chloride_potassium_bicarbonate, cbc_with_diff_pediatric, glucose_pediatric, abdominal_ultrasound_pyloric_first_line
   actions: panel.cbc, panel.renal
   advance: IV access + NPO + labs returned + US obtained; pediatric surgery consult initiated if US-positive
6. 6BRANCHING_WORKUP
   Source-directed: upper-GI contrast study if US non-diagnostic + persistent vomiting OR malrotation differential (string + shoulder + mushroom signs in IHPS; corkscrew duodenum in malrotation); KUB if free-air concern; total/direct bilirubin + hepatology consult if jaundice + persistent vomiting (biliary atresia < 60 d Kasai window); type-and-screen if surgical management likely (routine pre-op); UGI study repeat in 24-48 h if borderline US measurements + persistent symptoms (pyloric muscle may hypertrophy further).
   inputs: upper_gi_contrast_study_if_us_non_diagnostic_or_malrotation_concern, total_and_direct_bilirubin, type_and_screen_pediatric
   advance: Pre-surgical workup ready if surgical management indicated; alternative diagnoses excluded
7. 7DIFFERENTIAL
   GER (most common differential — non-projectile, infant well-appearing, growing along curve, normal labs, normal pyloric US); malrotation with midgut volvulus (bilious emesis at any age; UGI series with corkscrew duodenum); duodenal atresia (bilious emesis in first 24-48 h of life; double-bubble on KUB); sepsis-related ileus (febrile, lethargic; routes to peds.febrile-infant.core.v1 or id.neonatal-sepsis.early-late.v1); intussusception (different age band 6 mo - 3 y; target sign on US — `peds.intussusception.v1`); eosinophilic gastroenteritis (eosinophilia on CBC + endoscopy with eosinophil infiltration); food protein-induced allergic enterocolitis (bloody stool + atopic family); gastroparesis (rare in infants; gastric emptying study); biliary atresia (direct hyperbilirubinemia > 2 + acholic stool; < 60 d Kasai window); cow milk protein intolerance (bloody emesis; resolves with formula change).
   advance: Mimics excluded by US + UGI series (if obtained) + clinical features; IHPS diagnosis confirmed or alternative pathway entered
8. 8RISK_STRATIFICATION
   Tier 1 (life-threatening — uncorrected alkalosis with severe dehydration): OR DEFERRED until corrected; PICU/NICU/HDU level care; serial labs q4-6h. Tier 2 (severe — moderate-severe alkalosis): pre-op IVF correction 12-48 h targeting Cl > 100, K+ > 3.5, HCO3 < 30; inpatient ward with serial labs q6-8h. Tier 3 (moderate — classic case mild dehydration mild alkalosis): pre-op IVF correction over 12-24 h; serial labs q8-12h. Tier 4 (mild — borderline US + persistent symptoms): repeat US in 24-48 h; consider UGI series for malrotation; pediatric GI consult for GER ddx. Tier 5 (atypical — preterm or > 8 wk presentation): broader ddx; lower imaging threshold; PICU/NICU level care if preterm with comorbidity. Jaundice tier: direct bilirubin > 2 → hepatology urgent.
   inputs: cmp_with_chloride_potassium_bicarbonate, sbp_pediatric, gestational_age_at_birth_term_vs_preterm
   advance: Tier assigned + correction pathway chosen + admit-vs-PICU decision documented
9. 9TREATMENT
   Pre-op IVF correction: NS or LR 20 mL/kg IV bolus over 30-60 min if severe dehydration / shock (max ~ 60 mL/kg cumulative bolus before reassessing for fluid overload); then maintenance D5 1/2NS + 20 mEq/L KCl at 1.5 × maintenance with measured deficit replacement after first void documented. Target Cl > 100, K+ > 3.5, HCO3 < 30 over 12-48 h before OR. Pediatric surgical evaluation + OR scheduling (laparoscopic Ramstedt pyloromyotomy preferred at most centers; open via right upper transverse incision is the historical alternative). Pre-op antibiotic prophylaxis cefazolin 25-30 mg/kg IV single dose at induction (routine pre-op prophylaxis; no prolonged course for uncomplicated). Anesthesia + airway management per pediatric anesthesia society; avoid muscle relaxants requiring full reversal in the infant cohort. Intraoperative perforation rate < 1%; if perforation → expand antibiotics to pip-tazo or meropenem + metronidazole × 5-7 d (Solomkin IDSA peds-adapted PMID 20583865).
   inputs: weight_kg, cmp_with_chloride_potassium_bicarbonate, abdominal_ultrasound_pyloric_first_line
   actions: panel.renal
   advance: Resuscitation complete + metabolic correction complete (Cl > 100, K+ > 3.5, HCO3 < 30); pre-op antibiotics given; pyloromyotomy performed
10. 10DISPOSITION
    Post-laparoscopic pyloromyotomy → inpatient ward 24-48 h LOS for feed advance + monitoring; post-open pyloromyotomy → inpatient ward 48-72 h LOS; PICU/NICU/HDU for severe alkalosis (HCO3 > 35) + severe hypokalemia (K+ < 3) + severe dehydration unresponsive to bolus + preterm with comorbidity; outpatient surgical follow-up at 2-4 weeks for wound check + weight-gain review.
    inputs: sbp_pediatric, cmp_with_chloride_potassium_bicarbonate
    advance: Disposition + level of care set; post-op monitoring plan in place
11. 11MONITORING
    Post-op laparoscopic uncomplicated: vitals q4h × first 24 h then per protocol; serial abdominal exams q4h; feed advance from clear liquids → formula/breastmilk as tolerated within 4-6 h (early feeding well tolerated); first 24-48 h emesis common and typically self-limited (residual edema; rates 50-80% reported); transition to ad-lib feeding by 24 h; wound inspection daily; early ambulation. Post-op perforation case: as above + IV antibiotic course continuation × 5-7 d + serial labs (CBC + CMP) + watch for post-op abscess (rising CRP + persistent fever + worsening exam → CT for evaluation). Discharge planning: family education on feed advance + return precautions (return of projectile vomiting, fever, wound issues → ED) + surgical follow-up at 2-4 weeks.
    inputs: pattern_of_vomiting_projectile_non_bilious, weight_trend_vs_growth_curve
    advance: Recovery progressing; feeds advanced; weight stable; discharge criteria approaching
12. 12FOLLOWUP
    Post-op pediatric surgical follow-up at 2-4 weeks for wound check + scar inspection + weight-gain review; pediatrician follow-up within 1-2 weeks for routine well-baby care including weight-gain trajectory + feeding tolerance + family education on macrolide-avoidance principle in neonates < 6 weeks (CDC + AAP advisory); long-term outcomes excellent (most infants recover completely with no long-term sequelae); recurrence after pyloromyotomy < 1-2% (incomplete myotomy). Atypical / preterm / older infant cases: ongoing pediatric GI follow-up for differential broader workup if persistent symptoms (eosinophilic gastroenteritis, gastroparesis, pyloric dysfunction without classical hypertrophy). Jaundice cases: pediatric hepatology follow-up for biliary atresia workup if applicable (< 60 d Kasai window) OR Gilbert-related management.
    advance: Follow-up scheduled + return precautions delivered + family education on macrolide-avoidance complete + atypical-case ddx workup queued if persistent symptoms