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Prematurity and Hyaline Membrane Disease (HMD)

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1. Definition of Prematurity

Sub-classifications by gestational age:

Complications of prematurity (due to organ immaturity):

• Pulmonary: Hyaline membrane disease (RDS), apneic spells, bronchopulmonary dysplasia
• Cardiovascular: Patent ductus arteriosus → left-to-right shunt → pulmonary edema / congestive heart failure
• GI: Necrotizing enterocolitis (from hypoxia/ischemic gut)
• CNS: Intraventricular hemorrhage, periventricular leukomalacia
• Metabolic: Hypothermia, hypoglycemia, hypocalcemia, hyperbilirubinemia (immature liver)
• Ocular: Retinopathy of prematurity
• Immunologic: Increased susceptibility to infection, kernicterus

• Morgan & Mikhail's Clinical Anesthesiology, 7e, p. 1711; Medical Physiology, p. 463

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2. Hyaline Membrane Disease (HMD) — Neonatal RDS

Pathophysiology (Summary)

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3. Clinical Features of HMD

Risk Factors

• Preterm birth (strongest association; <28 weeks highest risk)
• Male sex
• Infant of a diabetic mother (insulin counteracts glucocorticoid-induced surfactant synthesis)
• Cesarean section (especially before onset of labour — labour itself stimulates surfactant synthesis)

Onset and Progression

1. At birth: The infant may require resuscitation, but usually establishes rhythmic breathing within a few minutes and appears normal in color initially.
2. Within 30 minutes of birth: Breathing becomes progressively more labored.
3. Within a few hours: Frank cyanosis develops in the untreated infant.

Signs and Symptoms

Chest X-Ray (CXR) Findings

• Uniform minute reticulogranular (ground-glass) densities bilaterally
• Air bronchograms superimposed on the diffuse haziness
• In severe cases: complete "white-out" of lung fields

Gross Pathology

• Lungs are normal in size but solid, airless, and reddish-purple (liver-like in color)
• They sink in water (indicating absence of entrapped air)

Histopathology

• Alveoli are poorly developed and collapsed
• Eosinophilic hyaline membranes line the respiratory bronchioles, alveolar ducts, and alveoli
• Membranes composed of fibrin admixed with necrotic cellular debris
• Hyaline membranes are never seen in stillborn infants (they require a period of breathing)

Natural Course

• If untreated, death may occur within hours to days.
• If the infant survives beyond 3–4 days, recovery is likely.
• In survivors beyond 48 hours, alveolar epithelium proliferates beneath the membranes; macrophages phagocytose the debris.

• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 432–434

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4. Management of HMD — Outline

A. Prevention

B. Supportive Care

C. Specific Therapy — Exogenous Surfactant

• Prophylactic surfactant at birth for extremely premature infants (<28 weeks gestational age) — highly beneficial.
• Rescue surfactant for infants who develop RDS — instilled directly into the trachea via endotracheal tube.
• Types: Natural/animal-derived (poractant alfa, beractant) — preferred over synthetic preparations.
• Results in dramatic improvement in pulmonary function, shortened clinical course, and markedly reduced mortality.

D. Complications to Monitor and Treat

• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 432–434; Robbins & Kumar Basic Pathology, p. 152; Morgan & Mikhail's Clinical Anesthesiology, p. 1711; The Developing Human: Clinically Oriented Embryology, p. 954

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Thyroid Function Tests in the Early Newborn Period

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Background: Fetal Thyroid Development

The hypothalamic–pituitary–thyroid (HPT) axis does not fully mature until 1–2 months after birth.

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The Neonatal TSH Surge — The Key Postnatal Event

Sequence of events immediately after birth:

1. Cold exposure → stimulates hypothalamus → acute TRH surge
2. TRH surge → anterior pituitary → massive TSH surge
   • TSH peaks at 60–80 mIU/L (some sources: up to 70–100 mIU/L) within 30 minutes of birth
3. High TSH → stimulates thyroid gland → T₄ rises moderately; increased peripheral conversion of T₄ → T₃ (3–4-fold rise in T₃)
4. Over the next 3–5 days: Rising T₄ and T₃ exert negative feedback → TSH falls to normal adult levels
5. By 4–6 weeks: T₄ and T₃ concentrations return to stable normal adult levels

Summary of TFT values at key time points:

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Physiological Explanation for High rT₃ at Birth

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TFT Interpretation Pitfalls in the Newborn Period

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Thyroid Function in Premature Neonates

• The physiological TSH surge is dramatically lower or absent in preterm infants
• FT₄ and FT₃ levels are low in the face of normal TSH — a pattern called transient hypothalamic hypothyroidism of prematurity
• It takes 3–8 weeks after birth for FT₄/FT₃ levels to reach term-equivalent values
• Seen in up to 50% of infants born < 28 weeks gestation
• Difficult to distinguish from true central hypothyroidism
• Associated with cognitive and neurological delays, though optimal T₄ target levels are not yet established and there is no universal treatment consensus

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Newborn Screening for Congenital Hypothyroidism

Why it matters:

• Congenital hypothyroidism (CH) occurs in ~1:2,000–4,000 births
• The newborn looks clinically normal at birth (maternal T₄ partially protects)
• Untreated CH causes irreversible intellectual disability (cretinism)
• Early detection and treatment (within 2 weeks) leads to normal neurodevelopment

Screening strategy:

Timing:

• Term infants: ideally at 2–4 days of age (by day 5 of life at latest); avoids false-positive results from the physiological TSH surge
• Preterm infants: within 7 days of birth; may need repeat testing at 2–4 weeks due to the attenuated initial TSH response
• Specimen: dried blood spot on filter paper (Guthrie card), heel-prick capillary blood

Causes detected by screening:

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Special Situations

Infants of Graves' disease mothers:

• Maternal TSH-receptor stimulating antibodies (TSI/TRAb) cross the placenta
• Can cause neonatal Graves' hyperthyroidism — transient but potentially dangerous
• Screen by measuring TRAb/TSI in at-risk mothers (history of Graves' disease) during pregnancy

Maternal hypothyroidism effect:

• Low maternal T₄ in first trimester (before fetal thyroid function begins) → impaired fetal neurodevelopment
• Associated with lower IQ, ADHD in offspring
• Maternal TSH screening is recommended before pregnancy or in the first trimester

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Key Points Summary

1. TSH surges to 60–80 mIU/L within 30 minutes of birth (cold stimulus) — a normal physiological event; do not interpret as pathological
2. T₃ rises 3–4-fold in the first 24–48 hours; rT₃ falls postnatally
3. T₄ and T₃ normalize by 4–6 weeks; the HPT axis matures by 1–2 months
4. Prematurity blunts the TSH surge and causes transient low FT₄/FT₃ with normal TSH
5. Newborn screening for congenital hypothyroidism uses dried blood spot TSH (± T₄) at 2–4 days in term infants
6. TSH-only screening misses central hypothyroidism — combined TSH + FT₄ is more sensitive
7. Neonatal TFT values must always be interpreted using age- and gestational-age-specific reference intervals

• Creasy & Resnik's Maternal-Fetal Medicine, pp. 1497–1499; Tietz Textbook of Laboratory Medicine, 7th ed., pp. 4767–4773

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Delivery Room Care & Neonatal Management — Complete Answer Set

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1. Anticipated Problems in a Preterm Baby & Prevention of Hypothermia

Anticipated Problems in a Preterm Baby

Prevention of Hypothermia in a Newborn

1. Large surface area-to-body mass ratio (especially the head)
2. Inability to shiver — can only generate heat via non-shivering thermogenesis in brown fat
3. Thin subcutaneous fat — poor thermal insulation
4. No behavioral adaptation (cannot change clothing or move away from cold)
5. Wet at birth — evaporation is the primary heat loss mechanism immediately after delivery

Measures to Prevent Hypothermia in the Delivery Room

Normal axillary temperature in newborn: 36.5°C – 37.5°C

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2. Classification of Hypothermia & Management of Severe Hypothermia

Classification of Hypothermia in a Newborn (WHO Classification)

Management of Severe Hypothermia (< 32°C)

Step-by-step Management:

• Check airway, breathing, circulation
• Assess blood glucose immediately (hypoglycemia frequently co-exists)
• Attach cardiac/SpO₂ monitoring

• Place under pre-warmed radiant warmer or in a servo-controlled incubator (set at 35–36°C skin temperature)
• Apply warm blankets; warm the room
• Use warm, humidified oxygen if O₂ therapy needed
• Avoid rapid rewarming with water > 38–40°C (risk of burns and cardiovascular instability)
• Target: raise temperature by 0.5–1°C per hour; aim for normothermia (36.5–37.5°C) within 2–6 hours

• If blood glucose < 40 mg/dL: give IV 10% dextrose (2 mL/kg bolus), then continuous infusion at 80–100 mL/kg/day of D10W
• Monitor glucose every 1–2 hours during rewarming

• Apnea and bradycardia are common in severe hypothermia
• Provide oxygen and PPV/CPAP/ventilation as indicated

• Metabolic acidosis → correct with adequate ventilation; sodium bicarbonate only if ventilation is adequate
• Coagulopathy → fresh frozen plasma/platelets as needed
• Sepsis → broad-spectrum antibiotics (ampicillin + gentamicin) if infection suspected
• Fluid and electrolyte imbalance → careful IV fluid management

• Withhold enteral feeds until temperature is ≥ 36°C and baby is stable
• Start IV nutrition early

• Temperature every 15–30 minutes during rewarming
• Blood glucose, electrolytes, blood gases
• Avoid hyperthermia during rewarming (can cause apnea and worsen hypoxic-ischemic injury)

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3. Apgar Score

Components (Mnemonic: Appearance, Pulse, Grimace, Activity, Respiration)

Scoring and Interpretation

When to Assess

• 1 minute: Reflects intrauterine/intrapartum status and need for immediate intervention
• 5 minutes: Reflects response to resuscitation; most predictive
• If score < 7 at 5 minutes: repeat every 5 minutes up to 20 minutes

Important Points

• Resuscitation must NOT be delayed to calculate the Apgar score
• Score is influenced by: gestational age (preterm infants score lower), maternal medications, infection, trauma, ongoing resuscitation
• A 5-minute score of 0–3 correlates with increased neonatal mortality
• A low score alone cannot diagnose birth asphyxia or predict neurological outcome

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4. Four Basic Needs of a Baby at Birth & How to Provide Them

1. Warmth
2. Clear airway
3. Breathing
4. Prevention of infection

How to Provide These Needs in Routine Care

(a) Warmth

• Warm delivery room (25–28°C)
• Pre-warm radiant warmer/blankets
• Dry immediately after birth; remove wet towels
• Skin-to-skin with mother for vigorous term infants
• Cap on the head; wrap in dry, warm blanket

(b) Clear Airway

• Position: head in neutral position (slight neck extension / "sniffing position")
• Suction mouth first, then nose only if visible secretions or obstruction are present
• Current guidelines: routine suctioning is not recommended for vigorous infants with clear or meconium-stained fluid
• Stimulate breathing by rubbing the back or flicking the soles of the feet (2–3 times)

(c) Breathing

• Assess: breathing? Crying? Good tone? → if yes, routine care
• If not breathing after stimulation: provide positive pressure ventilation (PPV) with bag and mask
• Rate: 40–60 breaths/min; peak inspiratory pressure ~20 cmH₂O
• Start with room air; increase FiO₂ only if SpO₂ targets not met

(d) Prevention of Infection

• Strict aseptic technique at delivery
• Sterile cord clamping and cutting (delayed cord clamping 1–3 min in vigorous infants)
• Eye prophylaxis: 1% tetracycline or 0.5% erythromycin ointment (or 1% silver nitrate drops) — against Neisseria gonorrhoeae and Chlamydia
• Vitamin K₁ 1 mg IM — prevents haemorrhagic disease of the newborn
• Early breastfeeding — provides passive immunity via IgA
• Hepatitis B vaccine + HBIg (if mother HBsAg positive) within 12 hours of birth

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5. Delivery Room Care

(a) Requirements for Normal Newborn Care

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(b) Algorithm for Routine Care of a Normal Newborn

BIRTH
  │
  ▼
Assess: Term gestation? Breathing/crying? Good muscle tone?
  │
  YES → All three YES
  │
  ▼
ROUTINE CARE (with mother)
  • Warm (skin-to-skin with mother or radiant warmer)
  • Dry and stimulate
  • Delayed cord clamping (1–3 minutes, if vigorous)
  • Clear airway ONLY if obstructed (bulb suction, mouth then nose)
  • Ongoing assessment every 30 seconds:
       – Respiratory effort
       – Heart rate
       – Colour/SpO₂
  │
  ▼
After 30 seconds: breathing well, HR >100, good tone, colour improving?
  │
  YES
  │
  ▼
Continue routine care:
  • Eye prophylaxis (erythromycin/tetracycline ointment)
  • Vitamin K₁ 1 mg IM
  • Identification band, weight, head circumference
  • Apgar at 1 and 5 minutes
  • Encourage early breastfeeding within 1 hour
  • Hepatitis B vaccine (within 24 hours)
  • Initiate neonatal screening (metabolic screen, hearing screen)

If any of the three initial questions is NO → move to resuscitation algorithm (see next section)

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(c) Indications for Artificial Ventilation (Positive Pressure Ventilation — PPV)

• Rate: 40–60 breaths/min
• Peak inspiratory pressure: ~20 cmH₂O (up to 30–40 cmH₂O for first breaths)
• Start with room air (21% O₂); titrate FiO₂ upward to meet SpO₂ targets
• Place orogastric tube if BMV required for > 2 minutes (prevents gastric distension)

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(d) Contraindications for Bag and Mask Ventilation

SOPA mnemonic for correcting ineffective BMV before moving to intubation:

• S — re-adjust mask Seal
• O — Open and reposition mouth
• P — reposition head/neck (Positioning)
• A — suction Airway / Alternate airway (ETT)

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(e) Drugs Used via the Intratracheal (Endotracheal) Route

• Sodium bicarbonate — may worsen intracellular acidosis; not routinely recommended in neonatal resuscitation
• Naloxone — no longer recommended even for maternal opiate exposure; contraindicated if maternal narcotic addiction suspected (risk of seizures)
• Atropine — not recommended in neonatal resuscitation
• Calcium — not given via ETT

Important: IV/IO access (umbilical venous catheter is first choice) should always be sought in preference to the intratracheal route for drug delivery, as intratracheal absorption is unpredictable.

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6. Steps of Neonatal Resuscitation (NRP Algorithm)

(a) Steps During the First 30 Seconds

1. Provide warmth — place under pre-warmed radiant warmer
2. Dry — dry the baby thoroughly with a warm towel
3. Stimulate — rub back vigorously 2–3 times; flick soles of feet
4. Position airway — head in neutral/sniffing position (slight neck extension); avoid hyperextension
5. Suction — only if airway is visibly obstructed; mouth first, then nose; use bulb syringe or mechanical suction ≤100 mmHg
6. Remove wet linen
7. Assess at 30 seconds: Is the baby breathing/crying? HR? Tone? Color?

Current NRP guidelines no longer recommend routine suctioning of all newborns, including those born through meconium-stained amniotic fluid who are vigorous.

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(b) Indications for Bag and Mask Ventilation

1. Apnea — not breathing despite stimulation
2. Gasping respirations — agonal breathing
3. Heart rate < 100 beats/min — regardless of respiratory effort
4. Persistent SpO₂ below targets despite supplemental oxygen

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(c) Indications for Initiating Chest Compressions

• Heart rate remains < 60 beats/min

• Ensure ventilation is truly effective (chest rise, bilateral breath sounds)
• Switch to 100% O₂
• Intubation is recommended when chest compressions are initiated

• Location: lower third of sternum (just below nipple line)
• Depth: one-third of the AP diameter of the chest
• Two methods: two-thumb technique (preferred; encircle chest with fingers) or two-finger technique
• Ratio: 3 compressions : 1 ventilation = 90 compressions + 30 breaths per minute
• Stop compressions when HR > 60 beats/min

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(d) Drugs Given Through the Endotracheal Tube

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(e) Volume Expanders in the Delivery Room

• Pallor despite adequate oxygenation
• Weak, rapid pulse
• Poor response to resuscitation (persistent low HR despite adequate ventilation and compressions)

• Avoid rapid bolus in premature infants → risk of intraventricular hemorrhage
• Higher-volume boluses (20 mL/kg) may be used in full-term infants
• Repeat as needed based on clinical response
• D10W (dextrose) is NOT a volume expander — it is used only for hypoglycemia

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7. Low Birth Weight (LBW)

Definition

• Prematurity (< 37 weeks) — most common in developed countries
• Intrauterine growth restriction (IUGR/FGR) — small for gestational age (SGA)
• Both prematurity + IUGR may coexist

Problems in LBW Neonates

Feeding of LBW Babies

Principles

• LBW infants have high metabolic demands but immature GI tract, poor suck-swallow coordination, small gastric capacity, and risk of aspiration

Feeding Methods (by maturity/stability):

Preferred Feeds:

• Breast milk — FIRST CHOICE for all LBW infants
  • Provides IgA, growth factors, reduces NEC risk significantly
  • Fortified breast milk: add human milk fortifier (HMF) for VLBW infants (increases protein, calcium, phosphorus, energy)
• Donor pasteurised human milk — if own mother's milk unavailable (VLBW/ELBW)
• Preterm formula — only if human milk unavailable; higher protein and mineral content than term formula

Feeding Schedule and Volumes:

• Start with trophic/minimal enteral feeds (10–20 mL/kg/day) from day 1–2 to stimulate gut maturation
• Advance by 10–20 mL/kg/day if tolerated
• Full enteral feeds: ~150–180 mL/kg/day
• Feed frequency: every 2–3 hours (8–12 feeds/day)
• Monitor for feed tolerance: gastric residuals, abdominal distension, vomiting, blood in stools (signs of NEC)

Energy Requirements:

• 110–130 kcal/kg/day for VLBW infants
• Protein: 3.5–4.5 g/kg/day (higher than term infants)
• Supplement Vitamin D (400–800 IU/day), Iron (from 2–4 weeks), Folate, Zinc

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Sources: Rosen's Emergency Medicine, pp. 3120–3132; Tintinalli's Emergency Medicine, pp. 3780–3857; Textbook of Family Medicine 9e, pp. 526–528; Medical Physiology, pp. 1698–1699; Barash Clinical Anesthesia, p. 3616