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10. Lung Physiology And Image
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10. Lung Physiology And Image

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  • 1. Control of Breathing RESPIRATORY CENTRE (Medulla) MEDULLARY & CAROTID CHEMORECEPTORS Higher Control Centres RESPIRATORY REFLEXES DRUG EFFECTS e.g. OPIATES & CAFFEINE CRANIAL & SPINAL MOTOR NEURONES STRETCH & PROPRIOCEPTORS LUNGS & CHEST WALL INSPIRATION
  • 2. Chemoreceptors
    • Medulla Oblongata and Carotid Body
    • Respond to changes in pH, CO 2 and O 2
    • Resetting of carotid chemoreceptors occurs at birth in response to oxygenation
    • Not essential at initiation of respiration but used for control of breathing
    • Responses are weak in the immediate newborn period and in preterm babies
  • 3. Response to Hypoxia Breathing Efforts + - Time in Minutes Older Infant Fetus Preterm baby Term baby 5 mins
  • 4. Respiratory Reflexes
    • Hering-Breuer reflexes
        • Lung inflation -> inhibition of breathing
        • Prolonged inhalation -> expiratory muscle contraction
        • Rapid deflation -> prolonged inspiratory response
    • Head’s paradoxical reflex
        • Rapid inflation -> diaphragmatic contraction (sigh)
    • Intercostal phrenic inhibitory reflex
        • Chest wall distortion -> shallow inspiratory efforts
    • Irritant reflexes
    • Upper airway reflexes
        • Nasal irritation/ suction -> apnoea
        • Liquid in larynx -> apnoea
  • 5. Lung Mechanics
    • Total lung capacity
    • Tidal volume
    • Functional residual capacity
    • Vital capacity
    • Inspiratory & expiratory reserve volumes
    • Residual volume
  • 6. Definitions
    • Tidal volume = volume of gas each breath
      • 5 - 7 mL/Kg in babies
    • Minute volume = vol. of gas each minute
      • 200 – 400 mL/kg/min
    • Minute volume = Tidal volume x resp. rate
    • PaCO2 inversely  MV
    • PaCO2 ↓ by ↑ tidal volume or ↑ resp. rate
    • Dead Space = Vol. of lung not involved in ventilation (eg, airways and ET tubes)
  • 7. Compliance
    • Compliance is a measure of the distensibility of the lung
    • Compliance = Change in Volume (L)
    • Change in Pressure (cm H 2 O)
    • Lung disease decreases compliance
        • RDS (Alveolar collapse)
        • TTN (Fluid in insterstitium)
        • BPD (Lung fibrosis)
        • Pneumothorax (Lung compression)
    • Surfactant improves compliance (beware over distension)
  • 8. Airways Resistance
    • Measure of the pressure gradient needed for gas to flow through a tube
    • Airway resistance = Pressure difference
    • (R AW ) Gas flow
    • Poiseuilles’ equation
      • R AW  airway length
      • R AW  1/ radius 4
            • Small & long ET tubes
            • Subglottic stenosis
  • 9. Work of Breathing
    • Energy required to produce change in lung volume
      • Increases with decreased compliance
      • Increases with increased resistance
    • If energy required to breath exceeds capacity to supply oxygen to provide that energy then respiratory failure develops requiring mechanical ventilation
  • 10. Pressure Volume Curves (Lung hysteresis loops) PRESSURE VOLUME INSP EXP
  • 11. Pressure Volume Curves (Lung hysteresis loops) PRESSURE VOLUME LOW COMPLIANCE HIGH COMPLIANCE
  • 12. Pressure Volume Curves (Lung hysteresis loops) PRESSURE VOLUME LOWER RESISTANCE HIGHER RESISTANCE
  • 13. Questions on Anatomy & Physiology ?
  • 14. Neonatal respiratory disease Aims:-
    • Overview of neonatal respiratory disease
    • Pathophysiology
    • Clinical presentation
    • Aetiology
    • X-ray appearances
    • Treatments
  • 15. Hyaline membrane disease Clinical:-
    • Usually preterm
    • Tachypnoea > 60
    • Indrawing/ retraction/ recession
    • Grunting
    • Nasal flaring
    • Cyanosis in air
    • Presents within a few hours of life
  • 16.  
  • 17. HMD - Aetiology
    • Surfactant deficiency
    • Structurally immature lungs
  • 18. HMD - Treatment
    • Oxygen
    • CPAP
    • Mechanical ventilation
    • Surfactant replacement
  • 19. TTN Clinical:-
    • Usually close to term
    • Tachypnoea 100-120/min
    • Overinflated chest
    • No grunting/ retraction
    • Settles within 24-48 hours
  • 20. TTN - Aetiology
    • Delayed fetal lung fluid clearance
    • Caesarean section - no squeeze of thorax at birth
    • Mum not in labour - no catecholamine surge to promote absorption of fetal lung fluid
  • 21.  
  • 22. TTN - treatment
    • Prevention - avoid early elective caesarean sections at term
    • Oxygen supplementation and IV fluids until resolution
  • 23. Airleak Syndromes
    • Pneumothorax
    • Pneumomediatinum
    • Pneumopericardium
    • Pulmonary interstitial emphysema
  • 24. Pneumothorax Clinical:-
    • May be asymptomatic
    • May be life threatening
    • Sudden deterioration in gas exchange
    • Poor colour
    • Hypotension and tachycardia
    • Unilateral overexpanded thorax
  • 25.  
  • 26. Pneumothorax - aetiology
    • Uneven alveolar ventilation
    • Air trapping and high pressure swings
    • Tracking of air from pulmonary interstitial emphysema
  • 27. Pneumothorax - predisposing factors
    • Spontaneous in 1% of all babies
    • Increases with mechanical ventilation
    • Increased x 4 with HMD
    • Increased x 16 with CPAP
    • Increased x 34 with IPPV
  • 28. Pneumothorax - prevention
    • Early surfactant therapy
    • Avoid overdistension
        • Volume guarantee
        • Low PIP
    • Short inspiratory time
    • Faster ventilation rates - entrainment
    • HFOV
    • Trigger ventilation - no proven benefit
    • Paralysis - no proven benefit
  • 29. Pneumothorax - Treatment
    • None if asymptomatic
    • Nitrogen washout technique - high FiO2 in term babies only
    • Chest drain if tension pneumothorax or on mechanical ventilation
    • Emergency needle thoracocentesis
  • 30. Pulmonary interstitial emphysema
    • Mainly occurs in preterm babies ventilated for HMD
    • Gas trapping in perivascular sheaths
    • Increased incidence at lower gestations
  • 31.  
  • 32. PIE - Clinical features
    • Severe hypoxaemia and CO2 retention
    • Deteriorating clinical condition
    • X- Ray
    • Overinflation with gross cystic changes
  • 33. PIE - Treatment
    • Lower PEEP and PIP
    • Paralysis
    • High rate low pressure ventilation
    • ? HFOV
    • ? Selective bronchial intubation
  • 34. Persistent pulmonary hypertension of the newborn Clinical features
    • Severe hypoxaemia (cyanosed in 100% O2)
    • No severe lung disease
    • Evidence of R to L shunt (pre vs. postductal)
    • Structurally normal heart
  • 35. PPHN - Aetiology and predisposing factors
    • Failure of NO synthase
    • Asphyxia/ acidosis
    • Infection
    • Diaphragmatic hernia
    • Alveolar capillary dysplasia
    • Meconium aspiration syndrome
  • 36. PPHN - treatment
    • Minimal handling
    • Inotropic support
    • Ventilation - maintain low normal CO2
    • Paralysis
    • Hyperventilation - ? Risk of PVL
    • HFOV
    • Nitric Oxide
    • Pulmonary vasodilators
        • Tolazoline/ Prostacyclin/ MgSO4
  • 37. Meconium aspiration syndrome Clinical:
    • Meconium passage prior to delivery
    • Meconium in pharynx and trachea
    • Respiratory distress post delivery with typical X-ray changes
  • 38.  
  • 39.  
  • 40. MAS - Aetiology
    • Asphyxia and intrauterine stress
    • Passage of meconium + gasping movements
    • Inhalation usually prior to delivery
  • 41. MAS - effects of meconium
    • Ball valve effect - air trapping
    • Chemical irritation and pneumonitis
    • Superinfection with bacteria
    • Surfactant inhibition
  • 42. MAS - Management
    • Prevention in delivery suite
    • Minimal handling
    • Maintain normoxaemia
    • May need ventilation + ? Paralysis
    • Surfactant lavage
    • Antibiotics
  • 43. Pulmonary haemorrhage Clinical
    • Sudden deterioration
    • Copious bloody secretions from airway
    • Hypotension
    • Pallor
    • Hypoxaemia
  • 44.  
  • 45.  
  • 46. Pulmonary haemorrhage -Aetiology
    • Usually preterm
    • HMD with PDA
    • Post surfactant therapy
    • Coagulopathy
    • Congestive cardiac failure
  • 47. Pulmonary haemorrhage - Treatment
    • Ventilation with high PEEP
    • Surfactant
    • Indomethacin for PDA
    • Treat coagulopathy
  • 48. Chronic lung disease Clinical
    • Protracted respiratory insufficiency and oxygen requirement beyond 28th day or 36th week post conceptional age
    • Very preterm with early ventilation for HMD
  • 49. CLD - Aetiology
    • Ventilation
    • Oxygen toxicity
    • PROM
    • Chorioamnionitis
    • Inflammation
    • Proteolytic enzymes
  • 50. CLD - prevention
    • Minimise ventilation and oxygen exposure
    • HFOV
    • Early surfactant
    • Corticosteroids
    • Early extubation
  • 51. CLD treatment
    • Minimise ongoing barotrauma
    • Nutrition
    • Permissive hypercapnia
    • Diuretics
    • Bronchodilators
    • Corticosteroids - controversial
    • Home oxygen therapy
  • 52. Summary
    • Knowledge of respiratory anatomy
    • Physiology of adaptation at birth
    • Surfactant
    • Gas exchange
    • Gas transport
    • Lung mechanics
    • Application of knowledge to the clinical management of babies with respiratory disease

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