The document discusses control of breathing and neonatal respiratory diseases. It covers the respiratory center in the medulla, chemoreceptors, respiratory reflexes, lung mechanics, definitions of terms like tidal volume and compliance. It then summarizes several neonatal respiratory diseases like hyaline membrane disease, transient tachypnea of the newborn, pneumothorax, pulmonary interstitial emphysema, persistent pulmonary hypertension of the newborn, meconium aspiration syndrome, and chronic lung disease. For each disease it discusses clinical features, etiology, treatments and methods of prevention.

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

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

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

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

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

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

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