Hyaline Membrane Disease

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Hyaline Membrane Disease

• Vincent Patrick Uy

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Infants First Breath

• Intermittent compression of the thorax
  facilitates removal of lung fluids
• Surfactant DECREASES surface tension to allow low
  pressure to aerate the lungs preventing
  alveolar collapse
• Functional residual capacity (FRC) must be
  established
• Air entry into the alveoli displaces fluid,
  decreases the hydrostatic pressure and increase
  pulmonary blood flow.

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Infants First Birth

• Decline in PaO2
• Decline in pH
• Rise in PaCO2
• Redistribution of the cardiac output
• Decrease body temperature
• Tactile and sensory inputs

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Timeline of Lung Development

• Embryonic Period
• Protrusion from the foregut
• Initial branching

• Saccular Stage
• Gas exchange may be possible
• Septal growth into saccules and into alveoli

• Pseudoglandular
• 15-20 generations of air branching
• Progressive epithelial differentiation

• Canalicular
• Bronchioles and ducts of gas exchange regions are
  formed
• Alveolar Type II cells

16-33 days AOG
7-16th weeks AOG
16th-25th week AOG
gt24 weeks AOG
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Lung Surfactant

• Type II pneumocytes
• Reduces surface tension allowing lesser pressures
  to maintain the alveoli open.

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Lung Surfactant

• 20 weeks start to appear (appearance of
  lamellar bodies)
• 28-32 weeks detectable in amniotic fluid
• 35 weeks Mature levels of surfactant

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Components of Lung Surfactant

• Lipids (70)
• Majority of the lipid component is
  dipalmitoylphosphatidyl choline (DPPC) which is
  the major surface tension reducing substance
• Proteins (30)
• Hydrophobic surfactant proteins (SP) B C
• Hydrophilic SP A D

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Surfactant Proteins

• Hydrophobic

• Hydrophilic

SP B Surface tension lowering capabilities Homozygous deficiency is lethal in term infants. Found in commercially prepared surfactant with SP-C
SP C Surface tension lowering capabilities Deficiency results in interstitial lung disease Works cooperatively with SP-B by spreading the phospholipids over the alveolar surface
SP A Innate host defense protein Phagocytosis SP-A increase with steroid exposure Not found in commercially prepared surfactant
SP D Innate host defense mechanisms Has limited roles in humans
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Lung Surfactant
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Synthesis, Secretion and Adsorption of Surfactant
Tubular Myelin
Lamellar body
Type II pneumocyte
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Law of Laplace
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Factors that Enhance Surfactant Synthesis

• Normal pH
• Normal temperature of the neonate
• Normal perfusion
• Adequate amount of oxygen
• Low insulin levels
• Chronic intrauterine stress (Pregnancy-induced
  hypertension)
• Twin gestations
• Antenatal corticosteroids

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Hyaline Membrane Disease

• Occurs primarily in premature babies inversely
  related to gestational age
• 60-80 of infants lt28 weeks
• 15-30 of infants 32-36 weeks
• Rare in term neonates (consider genetic
  abnormalities in surfactant proteins)
• Incidence increases with
• Maternal DM
• Multiple gestations
• Asphyxia
• Cold stress
• Maternal history of previously affected infants

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Pathophysiology

• Poor Surfactant Quantity and Quality
• Lungs of premature babies have surfactant rich in
  phosphatidylinositol and smaller amounts of
  phosphatidylglycerol (PPG). PPG has the greatest
  surface activity.
• Protein content of surfactant from preterm lung
  is low relative to the amount of phospholipids.
• Inflammation and pulmonary edema ensues

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Pulmonary Edema

• Leads to poor gas exchange
• Results from inflammation and lung injury
• Reduced pulmonary fluid reabsorption
• Low urine output
• Proteinaceous edema and inflammatory cytokines
  increase the conversion rate of surfactant into
  inactive forms.

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Lung Mechanics in Preterms

• Worsening RDS with formation of hyaline membranes
  result in less compliant lungs
• Lower part of the chest is pulled in as the
  diaphragm descends ? intrathoracic pressure is
  more negative ? atelectasis
• Highly compliant chest wall ? less resistant ?
  volume of the lung tends to approach RV ?
  Atelectasis

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Disease Processes
Low surfactant levels
ATELECTASIS
HYPOXEMIA
?Chest Compliance
Small Alveoli
HYPERCAPNIA
Alveolar Ventilation Impaired
Pulmonary Artery Constriction
Shunting
Ischemic Injury to the lungs
Pulmonary Artery Constriction
Proteinaceous effusion into the alveolar space
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Clinical Manifestations

• HISTORY

• PHYSICAL EXAM

• Often preterm
• Had asphyxia in the perinatal period
• Respiratory distress at birth
• Apnea

• Tachypnea
• Grunting
• Nasal flaring
• Retractions
• Cyanosis
• Decreased breath sounds

Classic chest radiograph is also an additional
feature of the disease.
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Diagnostic Tests

• Chest Radiograph
• Blood Gas sampling
• Sepsis Work-up
• Serum glucose levels
• Serum electrolytes and calcium levels
• Echocardiography

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Differentials
Diagnosis Key Points
Transient Tachypnea of the NB Mature infants Milder respiratory distress with quick improvement Rarely will require mechanical ventilation
Bacterial Pneumonia and Sepsis Signs and symptoms overlap with RDS Infants with respiratory distress will need blood cultures
Air Leak Syndromes May result from RDS and treatment of RDS
Congenital Heart Disease If lung function does not improve after support and surfactant therapy, obtain an ECHO.
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Preventive Management

• Avoid unecessary and untimely Cesarean sections.
  
• Antenatal Corticosteroids 24-34 weeks gestation
  is associated with overall reduction in
  neonatal deaths, RDS, IVH, NEC, ICU admissions
  and systemic infections in the first 48 hours of
  life
• Betamethasone Two 12 mg doses IM given 24 hours
  apart
• Dexamethasone is no longer given due to increase
  risk of cystic periventricular leukomalacia among
  preemies

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Surfactant Replacement

• Considered the standard of care in RDS
• Surfactant prophylaxis (within 15 minutes of
  birth) to all infants lt27 weeks.
• Consider prophylaxis if 27-29 weeks if baby was
  intubated or mother did not get antenatal
  steroids
• Repeated doses every 6-12 hours for a total of
  3-4 doses.

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Natural Surfactant

• Obtained from animal lung lavage or by mincing
  lung tissues
• Lipid extraction removes hydrophilic components
  (SP-A and SP-D). The purified lipid derivative
  contains the necessary components to control the
  surface tension
• Choice of natural surfactant is based on
  clinician/hospital preference

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Respiratory Management

• Because of increase risk of BPD, preterm infants
  without signs of respiratory failure can be
  managed with CPAP or NIPPV

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Respiratory Management

• Indications for immediate intubation and
  mechanical ventilation
• Respiratory acidosis (pH lt7.20 and PCO2 gt60 mmHg)
• Hypoxemia
• Severe apnea
• Unresponsive and limp babies with impending
  respiratory distress

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Target Values

• Oxygen Saturation
• Saturations above 95 and below 89 are
  associated with poor outcomes
• O2sat by Pulse ox 90-95 is optimal
• PCO2 levels
• 45-60 mmHg is the optimal level
• If it exceeds 60 mmHg, the pH falls lt7.25 which
  is associated with poor CV function
• Babies initially on CPAP that develop acidosis,
  should be intubated

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Sedation and Pain Relief

• Advantages

• Disadvantages

• Improved ventilatory synchrony and pulmonary
  function
• Neuroendocrine responses are alleviated
• Decreased adverse long term neurologic sequelae

• Side effects
• Morphine hypotension
• Fentanyl rigid chest wall
• Benzos Tolerance and dependence

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Supportive Measures

• Umbilical artery line
• Thermoregulation
• Fluid management
• Treat hypotension with vasopressor support and
  cautious use of saline boluses
• Early nutrition

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Complications

• Survival from HMD is dependent of gestational age
  and birthweight
• Major morbidities such as IVH, BPD and NEC remain
  high in smaller infants
• Endotracheal tube complications
• Air leak syndromes rupture of overdistended
  alveoli
• BPD

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Bronchopulmonary Dysplasia

• Result of lung injury among infants managed with
  mechanical ventilation and supplemental oxygen
• Defined as persistent oxygen dependency up to the
  28 day of life.