Preterm Infants - Exam-Prep Guide

1. Definitions and Classification

• Low birth weight (LBW): < 2500 g
• Very low birth weight (VLBW): < 1500 g
• Extremely low birth weight (ELBW): < 1000 g

2. Mortality Risk

3. Complications by Organ System

4. Key Complications - Detailed Review

A. Respiratory Distress Syndrome (RDS) / Hyaline Membrane Disease

• Prematurity (incidence: ~80% at 28 weeks, ~90% at 24 weeks)
• Cesarean delivery without labor
• Maternal diabetes
• Perinatal asphyxia
• Male sex, Caucasian race, surfactant protein B deficiency

• Antenatal betamethasone/dexamethasone (24-34 weeks; also now 34-37 weeks for late preterm)
• Exogenous surfactant replacement therapy (postnatal)
• CPAP or mechanical ventilation
• Supplemental O2 to target SpO2 (in <32 weeks, titrate with O2 blender)

B. Bronchopulmonary Dysplasia (BPD)

C. Intraventricular Hemorrhage (IVH)

D. Necrotizing Enterocolitis (NEC)

• Stage I: Suspected NEC
• Stage II: Definite NEC (pneumatosis on imaging)
• Stage III: Advanced NEC (perforation, shock)

E. Retinopathy of Prematurity (ROP)

• Born ≤27 weeks: first exam at 31 weeks postmenstrual age
• Born ≥28 weeks: first exam at 4 weeks chronologic age
• Born <25 weeks: consider earlier exam at 6 weeks chronologic age (to detect aggressive posterior ROP)

F. Apnea of Prematurity

G. Patent Ductus Arteriosus (PDA)

• Pharmacologic closure: Indomethacin (COX inhibitor, reduces PGE2) or ibuprofen; acetaminophen also used
• Surgical ligation if pharmacologic treatment fails
• Conservative/expectant management (many PDAs close spontaneously - evidence has shifted toward less aggressive treatment)

5. Key Prenatal Interventions

6. Postnatal General Management Principles

• Thermoregulation: Plastic wrap/polyethylene bag immediately at delivery; servo-controlled incubator; preterm infants have large body surface area/weight ratio with minimal brown fat.
• Fluid management: Limited IV fluids initially; preterm infants have excess insensible water losses (thin skin, no vernix).
• Nutrition: Early parenteral nutrition (PN) followed by enteral feeds; breast milk preferred (reduces NEC, improves neurodevelopment); human milk fortification improves protein/caloric density for VLBW infants.
• Infection control: VLBW infants are profoundly immunocompromised; strict hand hygiene, aseptic line care.
• Neurodevelopmental follow-up: Standard for all infants <32 weeks or <1500 g.

7. Late Preterm Infants (34-36+6 weeks) - High-Yield Points

• 3x higher infant mortality rate than those born at 40 weeks
• At 35 weeks, brain volume is approximately half that of a term infant
• Increased risk of: hypoglycemia, hypothermia, jaundice (hyperbilirubinemia), poor feeding, sepsis, readmission
• Long-term: learning disabilities, attention deficit disorders
• IVH rare after 32 weeks, but white matter myelination is still rapidly occurring through the 3rd trimester

8. Viability and Ethics

• Current threshold of viability: approximately 22-23 weeks GA
• At 22-23 weeks: outcomes are uncertain; shared decision-making with parents is standard
• NRP protocols apply but experienced neonatologist should assess gestational age, weight, and response to resuscitation
• Parents are primary surrogate decision-makers
• Moral distress is common among NICU staff; ethics consultation available when providers and parents conflict

1. RDS - surfactant deficiency, CXR ground glass pattern, treated with antenatal steroids + surfactant replacement
2. BPD - chronic lung disease from ventilation/O2 injury, defined as O2 need >28 days in <32-week infant
3. IVH - germinal matrix bleeding, Papile grades I-IV, screening by cranial U/S, prevented by antenatal steroids + MgSO4
4. NEC - intestinal necrosis, pneumatosis intestinalis on imaging, Bell staging, breast milk is protective
5. ROP - retinal neovascularization from O2 exposure, 5 stages, screened by ophthalmology per strict GA-based protocol, treated with laser or anti-VEGF

Acute Diarrhea Disease - Management Algorithm

Pathophysiology Classification

Step 1 - Initial Assessment: History and Physical

• Acute onset (<14 days)
• Nausea, vomiting, fever
• Epidemiologic clues: recent travel, contaminated food/water, sick contacts, outbreaks (cruise ships, daycare, nursing homes)
• Recent antibiotic use (think C. difficile)

• New medication (hundreds of drugs cause diarrhea)
• Post-surgical bowel changes
• IBD flare, ischemic colitis, partial obstruction
• Radiation exposure → If likely noninfectious: evaluate and treat the underlying cause separately.

Step 2 - Severity Stratification (determines urgency)

Step 3 - Rehydration (Always First)

Oral Rehydration Therapy (ORT)

• Indicated for mild to moderate diarrhea with any dehydration
• Works by Na⁺-glucose co-transport in small bowel (intact even during acute diarrhea)
• WHO ORS formula: ½ tsp salt + 6 tsp sugar + 1 L clean water
• Commercial premixed solutions (e.g., Pedialyte, Ceralyte) are equivalent
• Zinc supplementation (10 mg/day <6 months; 20 mg/day ≥6 months) for children in resource-limited settings - reduces severity, duration, and recurrence

IV Rehydration

• Indicated for severe diarrhea with significant volume depletion, unable to tolerate oral intake, or profoundly dehydrated patients (especially infants and elderly)
• Fluids: Ringer's lactate (preferred) or normal saline
• Transition to ORS as tolerated

Step 4 - Decision: Evaluate or Observe?

Diagnostic Workup (when indicated)

1. First-line: Multiplex PCR stool panel - rapid, sensitive, cost-effective; identifies common bacteria, viruses, parasites simultaneously
2. Stool culture - used when multiplexed tests unavailable, for outbreak investigation, or antibiotic sensitivity needed
3. Fecal leukocytes / calprotectin - elevated = invasive/inflammatory etiology
4. C. difficile toxin EIA or PCR - if recent antibiotics, hospitalization, or prolonged course
5. Ova and parasites (O&P) - if travel history, immunocompromised, or diarrhea lasting >7-10 days
6. Specific cultures - EHEC (O157:H7), Vibrio, Yersinia if clinical clues present

Step 5 - Management Algorithm (Harrison's, Fig. 49-3)

Reading the Algorithm:

Acute Diarrhea
     ↓
History & Physical
     ↙           ↘
Likely Infectious    Likely Noninfectious → Evaluate & Treat
     ↓
Severity: Mild / Moderate / Severe
     ↓
FLUID & ELECTROLYTE REPLACEMENT (all patients)
     ↙                    ↘
Mild: Observe        Fever ≥38.5°C, bloody stools,
     ↓               ↑ fecal WBCs, immunocompromised, elderly
  Resolves?               ↙           ↘
    Yes → done         No            Yes
    No →          Antidiarrheal    Stool Microbiology Studies
             agents                      ↙             ↘
              ↓                   Pathogen         Pathogen
           Resolves?               NOT found        Found
           Yes → done               ↓                 ↓
           No → ↓          Empirical Tx +       Specific Tx
                    Stool microbiology   Further evaluation

Step 6 - Symptomatic (Non-Antibiotic) Treatment

Antimotility Agents

• Loperamide 4 mg initial dose, then 2 mg after each unformed stool (max 16 mg/day)
• Use only in nonfebrile, non-bloody diarrhea (moderate, watery)
• AVOID with:
  • Febrile dysentery (prolongs illness)
  • Bloody/mucoid stools
  • Suspected EHEC O157:H7 or Shigella (may worsen HUS risk)
  • C. difficile

Bismuth Subsalicylate

• 524 mg every 30-60 min as needed, up to 8 doses/day
• Useful for mild diarrhea and viral gastroenteritis; reduces nausea and stool frequency
• Avoid in: immunocompromised, renal impairment (bismuth encephalopathy risk)
• Contains salicylate - avoid in children (Reye syndrome risk)

Probiotics

• Not recommended as treatment for acute diarrhea (Goldman-Cecil, 2024)

Step 7 - Antibiotic Therapy

When to use antibiotics:

• Moderate-severe febrile diarrhea
• Bloody diarrhea (invasive pathogen confirmed or suspected - except EHEC)
• Traveler's diarrhea
• Immunocompromised patients (treat regardless of identified organism)
• Mechanical heart valves, recent vascular grafts, elderly

Empiric Regimens

Pathogen-Specific Antibiotic Choices

Step 8 - When Diarrhea Persists (>7-14 days)

1. Reconsider stool studies: Giardia is the most common cause of persistent diarrhea
2. Rule out C. difficile (especially if antibiotics recently given)
3. Consider Cryptosporidium, Campylobacter, E. histolytica
4. If >30 days (chronic): sigmoidoscopy/colonoscopy with biopsies and upper endoscopy with duodenal aspirates may be needed to exclude celiac disease, Crohn's disease, or microscopic colitis (do NOT scope during or immediately after acute enteritis - false positives)

Special Populations

High-Yield "Avoid" Summary (Exam Favorite)