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10. Lung Physiology And Image


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10. Lung Physiology And Image

  2. 2. Chemoreceptors <ul><li>Medulla Oblongata and Carotid Body </li></ul><ul><li>Respond to changes in pH, CO 2 and O 2 </li></ul><ul><li>Resetting of carotid chemoreceptors occurs at birth in response to oxygenation </li></ul><ul><li>Not essential at initiation of respiration but used for control of breathing </li></ul><ul><li>Responses are weak in the immediate newborn period and in preterm babies </li></ul>
  3. 3. Response to Hypoxia Breathing Efforts + - Time in Minutes Older Infant Fetus Preterm baby Term baby 5 mins
  4. 4. Respiratory Reflexes <ul><li>Hering-Breuer reflexes </li></ul><ul><ul><ul><li>Lung inflation -> inhibition of breathing </li></ul></ul></ul><ul><ul><ul><li>Prolonged inhalation -> expiratory muscle contraction </li></ul></ul></ul><ul><ul><ul><li>Rapid deflation -> prolonged inspiratory response </li></ul></ul></ul><ul><li>Head’s paradoxical reflex </li></ul><ul><ul><ul><li>Rapid inflation -> diaphragmatic contraction (sigh) </li></ul></ul></ul><ul><li>Intercostal phrenic inhibitory reflex </li></ul><ul><ul><ul><li>Chest wall distortion -> shallow inspiratory efforts </li></ul></ul></ul><ul><li>Irritant reflexes </li></ul><ul><li>Upper airway reflexes </li></ul><ul><ul><ul><li>Nasal irritation/ suction -> apnoea </li></ul></ul></ul><ul><ul><ul><li>Liquid in larynx -> apnoea </li></ul></ul></ul>
  5. 5. Lung Mechanics <ul><li>Total lung capacity </li></ul><ul><li>Tidal volume </li></ul><ul><li>Functional residual capacity </li></ul><ul><li>Vital capacity </li></ul><ul><li>Inspiratory & expiratory reserve volumes </li></ul><ul><li>Residual volume </li></ul>
  6. 6. Definitions <ul><li>Tidal volume = volume of gas each breath </li></ul><ul><ul><li>5 - 7 mL/Kg in babies </li></ul></ul><ul><li>Minute volume = vol. of gas each minute </li></ul><ul><ul><li>200 – 400 mL/kg/min </li></ul></ul><ul><li>Minute volume = Tidal volume x resp. rate </li></ul><ul><li>PaCO2 inversely  MV </li></ul><ul><li>PaCO2 ↓ by ↑ tidal volume or ↑ resp. rate </li></ul><ul><li>Dead Space = Vol. of lung not involved in ventilation (eg, airways and ET tubes) </li></ul>
  7. 7. Compliance <ul><li>Compliance is a measure of the distensibility of the lung </li></ul><ul><li>Compliance = Change in Volume (L) </li></ul><ul><li> Change in Pressure (cm H 2 O) </li></ul><ul><li>Lung disease decreases compliance </li></ul><ul><ul><ul><li>RDS (Alveolar collapse) </li></ul></ul></ul><ul><ul><ul><li>TTN (Fluid in insterstitium) </li></ul></ul></ul><ul><ul><ul><li>BPD (Lung fibrosis) </li></ul></ul></ul><ul><ul><ul><li>Pneumothorax (Lung compression) </li></ul></ul></ul><ul><li>Surfactant improves compliance (beware over distension) </li></ul>
  8. 8. Airways Resistance <ul><li>Measure of the pressure gradient needed for gas to flow through a tube </li></ul><ul><li>Airway resistance = Pressure difference </li></ul><ul><li>(R AW ) Gas flow </li></ul><ul><li>Poiseuilles’ equation </li></ul><ul><ul><li>R AW  airway length </li></ul></ul><ul><ul><li>R AW  1/ radius 4 </li></ul></ul><ul><ul><ul><ul><ul><li>Small & long ET tubes </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Subglottic stenosis </li></ul></ul></ul></ul></ul>
  9. 9. Work of Breathing <ul><li>Energy required to produce change in lung volume </li></ul><ul><ul><li>Increases with decreased compliance </li></ul></ul><ul><ul><li>Increases with increased resistance </li></ul></ul><ul><li>If energy required to breath exceeds capacity to supply oxygen to provide that energy then respiratory failure develops requiring mechanical ventilation </li></ul>
  10. 10. Pressure Volume Curves (Lung hysteresis loops) PRESSURE VOLUME INSP EXP
  11. 11. Pressure Volume Curves (Lung hysteresis loops) PRESSURE VOLUME LOW COMPLIANCE HIGH COMPLIANCE
  12. 12. Pressure Volume Curves (Lung hysteresis loops) PRESSURE VOLUME LOWER RESISTANCE HIGHER RESISTANCE
  13. 13. Questions on Anatomy & Physiology ?
  14. 14. Neonatal respiratory disease Aims:- <ul><li>Overview of neonatal respiratory disease </li></ul><ul><li>Pathophysiology </li></ul><ul><li>Clinical presentation </li></ul><ul><li>Aetiology </li></ul><ul><li>X-ray appearances </li></ul><ul><li>Treatments </li></ul>
  15. 15. Hyaline membrane disease Clinical:- <ul><li>Usually preterm </li></ul><ul><li>Tachypnoea > 60 </li></ul><ul><li>Indrawing/ retraction/ recession </li></ul><ul><li>Grunting </li></ul><ul><li>Nasal flaring </li></ul><ul><li>Cyanosis in air </li></ul><ul><li>Presents within a few hours of life </li></ul>
  16. 17. HMD - Aetiology <ul><li>Surfactant deficiency </li></ul><ul><li>Structurally immature lungs </li></ul>
  17. 18. HMD - Treatment <ul><li>Oxygen </li></ul><ul><li>CPAP </li></ul><ul><li>Mechanical ventilation </li></ul><ul><li>Surfactant replacement </li></ul>
  18. 19. TTN Clinical:- <ul><li>Usually close to term </li></ul><ul><li>Tachypnoea 100-120/min </li></ul><ul><li>Overinflated chest </li></ul><ul><li>No grunting/ retraction </li></ul><ul><li>Settles within 24-48 hours </li></ul>
  19. 20. TTN - Aetiology <ul><li>Delayed fetal lung fluid clearance </li></ul><ul><li>Caesarean section - no squeeze of thorax at birth </li></ul><ul><li>Mum not in labour - no catecholamine surge to promote absorption of fetal lung fluid </li></ul>
  20. 22. TTN - treatment <ul><li>Prevention - avoid early elective caesarean sections at term </li></ul><ul><li>Oxygen supplementation and IV fluids until resolution </li></ul>
  21. 23. Airleak Syndromes <ul><li>Pneumothorax </li></ul><ul><li>Pneumomediatinum </li></ul><ul><li>Pneumopericardium </li></ul><ul><li>Pulmonary interstitial emphysema </li></ul>
  22. 24. Pneumothorax Clinical:- <ul><li>May be asymptomatic </li></ul><ul><li>May be life threatening </li></ul><ul><li>Sudden deterioration in gas exchange </li></ul><ul><li>Poor colour </li></ul><ul><li>Hypotension and tachycardia </li></ul><ul><li>Unilateral overexpanded thorax </li></ul>
  23. 26. Pneumothorax - aetiology <ul><li>Uneven alveolar ventilation </li></ul><ul><li>Air trapping and high pressure swings </li></ul><ul><li>Tracking of air from pulmonary interstitial emphysema </li></ul>
  24. 27. Pneumothorax - predisposing factors <ul><li>Spontaneous in 1% of all babies </li></ul><ul><li>Increases with mechanical ventilation </li></ul><ul><li>Increased x 4 with HMD </li></ul><ul><li>Increased x 16 with CPAP </li></ul><ul><li>Increased x 34 with IPPV </li></ul>
  25. 28. Pneumothorax - prevention <ul><li>Early surfactant therapy </li></ul><ul><li>Avoid overdistension </li></ul><ul><ul><ul><li>Volume guarantee </li></ul></ul></ul><ul><ul><ul><li>Low PIP </li></ul></ul></ul><ul><li>Short inspiratory time </li></ul><ul><li>Faster ventilation rates - entrainment </li></ul><ul><li>HFOV </li></ul><ul><li>Trigger ventilation - no proven benefit </li></ul><ul><li>Paralysis - no proven benefit </li></ul>
  26. 29. Pneumothorax - Treatment <ul><li>None if asymptomatic </li></ul><ul><li>Nitrogen washout technique - high FiO2 in term babies only </li></ul><ul><li>Chest drain if tension pneumothorax or on mechanical ventilation </li></ul><ul><li>Emergency needle thoracocentesis </li></ul>
  27. 30. Pulmonary interstitial emphysema <ul><li>Mainly occurs in preterm babies ventilated for HMD </li></ul><ul><li>Gas trapping in perivascular sheaths </li></ul><ul><li>Increased incidence at lower gestations </li></ul>
  28. 32. PIE - Clinical features <ul><li>Severe hypoxaemia and CO2 retention </li></ul><ul><li>Deteriorating clinical condition </li></ul><ul><li>X- Ray </li></ul><ul><li>Overinflation with gross cystic changes </li></ul>
  29. 33. PIE - Treatment <ul><li>Lower PEEP and PIP </li></ul><ul><li>Paralysis </li></ul><ul><li>High rate low pressure ventilation </li></ul><ul><li>? HFOV </li></ul><ul><li>? Selective bronchial intubation </li></ul>
  30. 34. Persistent pulmonary hypertension of the newborn Clinical features <ul><li>Severe hypoxaemia (cyanosed in 100% O2) </li></ul><ul><li>No severe lung disease </li></ul><ul><li>Evidence of R to L shunt (pre vs. postductal) </li></ul><ul><li>Structurally normal heart </li></ul>
  31. 35. PPHN - Aetiology and predisposing factors <ul><li>Failure of NO synthase </li></ul><ul><li>Asphyxia/ acidosis </li></ul><ul><li>Infection </li></ul><ul><li>Diaphragmatic hernia </li></ul><ul><li>Alveolar capillary dysplasia </li></ul><ul><li>Meconium aspiration syndrome </li></ul>
  32. 36. PPHN - treatment <ul><li>Minimal handling </li></ul><ul><li>Inotropic support </li></ul><ul><li>Ventilation - maintain low normal CO2 </li></ul><ul><li>Paralysis </li></ul><ul><li>Hyperventilation - ? Risk of PVL </li></ul><ul><li>HFOV </li></ul><ul><li>Nitric Oxide </li></ul><ul><li>Pulmonary vasodilators </li></ul><ul><ul><ul><li>Tolazoline/ Prostacyclin/ MgSO4 </li></ul></ul></ul>
  33. 37. Meconium aspiration syndrome Clinical: <ul><li>Meconium passage prior to delivery </li></ul><ul><li>Meconium in pharynx and trachea </li></ul><ul><li>Respiratory distress post delivery with typical X-ray changes </li></ul>
  34. 40. MAS - Aetiology <ul><li>Asphyxia and intrauterine stress </li></ul><ul><li>Passage of meconium + gasping movements </li></ul><ul><li>Inhalation usually prior to delivery </li></ul>
  35. 41. MAS - effects of meconium <ul><li>Ball valve effect - air trapping </li></ul><ul><li>Chemical irritation and pneumonitis </li></ul><ul><li>Superinfection with bacteria </li></ul><ul><li>Surfactant inhibition </li></ul>
  36. 42. MAS - Management <ul><li>Prevention in delivery suite </li></ul><ul><li>Minimal handling </li></ul><ul><li>Maintain normoxaemia </li></ul><ul><li>May need ventilation + ? Paralysis </li></ul><ul><li>Surfactant lavage </li></ul><ul><li>Antibiotics </li></ul>
  37. 43. Pulmonary haemorrhage Clinical <ul><li>Sudden deterioration </li></ul><ul><li>Copious bloody secretions from airway </li></ul><ul><li>Hypotension </li></ul><ul><li>Pallor </li></ul><ul><li>Hypoxaemia </li></ul>
  38. 46. Pulmonary haemorrhage -Aetiology <ul><li>Usually preterm </li></ul><ul><li>HMD with PDA </li></ul><ul><li>Post surfactant therapy </li></ul><ul><li>Coagulopathy </li></ul><ul><li>Congestive cardiac failure </li></ul>
  39. 47. Pulmonary haemorrhage - Treatment <ul><li>Ventilation with high PEEP </li></ul><ul><li>Surfactant </li></ul><ul><li>Indomethacin for PDA </li></ul><ul><li>Treat coagulopathy </li></ul>
  40. 48. Chronic lung disease Clinical <ul><li>Protracted respiratory insufficiency and oxygen requirement beyond 28th day or 36th week post conceptional age </li></ul><ul><li>Very preterm with early ventilation for HMD </li></ul>
  41. 49. CLD - Aetiology <ul><li>Ventilation </li></ul><ul><li>Oxygen toxicity </li></ul><ul><li>PROM </li></ul><ul><li>Chorioamnionitis </li></ul><ul><li>Inflammation </li></ul><ul><li>Proteolytic enzymes </li></ul>
  42. 50. CLD - prevention <ul><li>Minimise ventilation and oxygen exposure </li></ul><ul><li>HFOV </li></ul><ul><li>Early surfactant </li></ul><ul><li>Corticosteroids </li></ul><ul><li>Early extubation </li></ul>
  43. 51. CLD treatment <ul><li>Minimise ongoing barotrauma </li></ul><ul><li>Nutrition </li></ul><ul><li>Permissive hypercapnia </li></ul><ul><li>Diuretics </li></ul><ul><li>Bronchodilators </li></ul><ul><li>Corticosteroids - controversial </li></ul><ul><li>Home oxygen therapy </li></ul>
  44. 52. Summary <ul><li>Knowledge of respiratory anatomy </li></ul><ul><li>Physiology of adaptation at birth </li></ul><ul><li>Surfactant </li></ul><ul><li>Gas exchange </li></ul><ul><li>Gas transport </li></ul><ul><li>Lung mechanics </li></ul><ul><li>Application of knowledge to the clinical management of babies with respiratory disease </li></ul>