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Physiologic Basis for the Management of Acute Respiratory Disorders in the Newborn

Physiologic Basis for the Management of Acute Respiratory Disorders in the Newborn. Marc Collin, MD. 18 November 2003. Developmental Anatomy.

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Physiologic Basis for the Management of Acute Respiratory Disorders in the Newborn

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  1. Physiologic Basis for the Management of Acute Respiratory Disorders in the Newborn Marc Collin, MD 18 November 2003

  2. Developmental Anatomy • Alveoli-developed by 25th week -increase in # until 8 yr. -from 20 to 300 million -surface area: 2.8 m2 @ birth 32 m2 @ 8 yr. 75 m2 @ adulthood -diameter: 150- 300 um(NB-Adult)

  3. Developmental Anatomy • Airways- cartilaginous - relatively weak in infancy - dynamic compression - bronchiolitis (RSV) - RAD - crying!

  4. Developmental Anatomy • airways enlarge in diameter/length • distal airways lag in first 5 yr. • high peripheral resistance in infancy • Resistance = 1/R4

  5. Pulmonary Physiology • Compliance = Change in Volume Change in Pressure

  6. Static Lung Volumes

  7. Mechanics of Infant v. Adult Lung

  8. Pulmonary Physiology • Alveoli at birth • fluid-filled v. air-filled v. air-liquid interface • pressures up to 80 cm H2O @ birth • alveolar rupture

  9. Pressure-Volume Curves after Air v. Liquid Lung Expansion

  10. Pulmonary Physiology  LaPlace relationship: P = 2T/R P= distending pressure T= wall tension R= radius (alveolar)

  11. Pressure-Volume Curves of First 3 Breaths

  12. Developmental Biochemistry of Alveoli • History: Avery & Mead-1959 - RDS secondary to surfactant deficiency - Treatment: CPAP

  13. Surfactant • Phospholipids - phosphatidylcholine - phosphatidylglycerol • Surfactant proteins - A, B, C

  14. Surfactant Components

  15. Surfactant • Type II alveolar epithelial cells -responsible for synthesis, storage, secretion, and reuptake • Lamellar bodies -intracellular storage form of surfactant -secreted via exocytosis -forms tubular myelin in extracellular space

  16. Surfactant and Type II Cells

  17. Surfactant • Inactivation by: - alveolar-capillary leak - pulmonary edema - hemorrhage (hemoglobin) - alveolar cell injury - meconium

  18. Surfactant • Recycling - spent forms taken up/reused by Type II cells. - process facilitated by SP-A, B, and C - half-life = 3.5 days

  19. RDS • US incidence: 30,000/yr. • Inversely related to gestational age • Onset-shortly after birth • Signs-grunting, flaring,retracting • Duration-1 week

  20. RDS

  21. RDS • Progressive atelectasis • V/Q mismatch • Decreased FRC • Impaired ventilation (weak respiratory m’s, compliant chest wall) • Increased PVR due to hypoxia, acidosis

  22. RDS • Right to left shunting leading to further hypoxemia • Left to right shunting leading to pulmonary edema

  23. Exogenous Surfactants • Replacement therapy/Fujiwara, Japan, 1980 • Human (from C/S) • Artificial (Exosurf) • Bovine (Survanta) • Calf (Infasurf) • Pig (Curosurf)

  24. Compliance Before and After Surfactant VOLUME Before surfactant After surfactant PRESSURE

  25. Air Leaks • Pulmonary interstitial emphysema (PIE) • Pneumomediastinum • Pneumothorax • Pneumopericardium • Pneumoperitoneum

  26. Subtle left pneumothorax

  27. Left pneumothorax now more obvious

  28. Left pneumothorax?

  29. pneumothorax

  30. Transillumination of left pneumothorax

  31. pneumomediastinum

  32. Pneumopericardium (note air under heart)

  33. Air Leaks • initiating factor: PIE (alveolar rupture into perivascular and peribronchial spaces) • dissection into mediastinum • further dissection into pleural, pericardial space • rupture from surface blebs • direct lung rupture-VERY rare

  34. Air Leak Risk Factors • RDS: 12-26% • MAS/other aspirations • Spontaneous

  35. Air Leak Management • early recognition (esp. in preterms) • nitrogen wash-out (term/near-term) • needle aspiration v. tube thoracotomy • limit barotrauma • HFOV • positioning • selective ET intubation

  36. Meconium Aspiration Syndrome (MAS) • GI secretions, cellular debris, bile, pancreatic juice, mucus, lanugo hairs, vernix; blood. • incidence: ~15% (30% @ >42 wks) • cause v. result of ‘asphyxia’

  37. MAS • Asphyxia  intestinal ischemia  anal sphincter relaxation  meconium passage

  38. MAS • Asphyxia  fetal gasping  enhanced meconium entry into respiratory tract

  39. MAS-Presentation • Respiratory distress - tachypnea - prolonged expiratory phase - hypoxemia • Increased A-P diameter (‘barrel’ chest) • Pulmonary hypertension

  40. MAS-Radiographic Findings • coarse alveolar infiltrates • consolidation/hyperaeration • pleural effusion (30%) • pneumothorax/pneumomediastinum

  41. Meconium aspiration syndrome

  42. Meconium aspiration syndrome

  43. MAS-Pathophysiology • Acute small airway obstruction -increased expiratory resistance -increased FRC -regional atelectasis -V/Q mismatching

  44. MAS-Pathophysiology • Surfactant inactivation -decreased compliance -hypoxia • Pulmonary hypertension

  45. MAS-Treatment • Intubation/tracheal suction @ delivery • Saline lavage? • Surfactant therapy

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