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Control of Breathing
RESPIRATORY
CENTRE (Medulla)
MEDULLARY &
CAROTID
CHEMORECEPTORS
Higher Control
Centres
RESPIRATORYREFLEXES
DRUG EFFECTS e.g.
OPIATES &
CAFFEINE
CRANIAL & SPINAL
MOTOR NEURONES
STRETCH &
PROPRIOCEPTORSLUNGS & CHEST WALL
INSPIRATION
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Chemoreceptors
Medulla Oblongata and Carotid Body
Respond to changes in pH, CO2and O2
Resetting of carotid chemoreceptorsoccurs 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
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Response to Hypoxia
Breathing
Efforts
+
-
Time in Minutes
Older Infant
Fetus
Preterm baby
Term baby
5 mins
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Respiratory Reflexes Herin
g-Breuer reflexes Lung inflation inhibition of breathingProlonged inhalation expiratory muscle contraction
Rapid deflation prolonged inspiratory response
Heads paradoxical reflexRapid inflation diaphragmatic contraction (sigh)
Intercostal phrenic inhibitory reflexChest wall distortion shallow inspiratory efforts
Irritant reflexes Upper airway reflexes
Nasal irritation/ suction apnoea
Liquid in larynx apnoea
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Lung Mechanics
Total lung capacity
Tidal volume
Functional residual
capacity
Vital capacity
Inspiratory & expiratory
reserve volumes
Residual volume
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Definitions
Tidal volume = volume of gas each breath 5 - 7 mL/Kg in babies
Minute volume = vol. of gas each minute
200400 mL/kg/minMinute 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)
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Compliance
Compliance is a measure of the distensibility ofthe lung
Compliance = Change in Volume (L)
Change in Pressure (cm H2
O)
Lung disease decreases compliance RDS (Alveolar collapse)
TTN (Fluid in insterstitium)
BPD (Lung fibrosis)
Pneumothorax (Lung compression)
Surfactant improves compliance
(beware over distension)
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Airways Resistance
Measure of the pressure gradient neededfor gas to flow through a tube
Airway resistance = Pressure difference
(RAW) Gas flow
Poiseuilles equation RAWairway length
RAW1/ radius4 Small & long ET tubes Subglottic stenosis
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Work of Breathing
Energy required to produce change in lungvolume
Increases with decreased compliance
Increases with increased resistance
If energy required to breath exceeds
capacity to supply oxygen to provide thatenergy then respiratory failure develops
requiring mechanical ventilation
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Pressure Volume Curves
(Lung hysteresis loops)
PRESSURE
VOLUME
LOW
COMPLIANCE
HIGH
COMPLIANCE
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Pressure Volume Curves
(Lung hysteresis loops)
PRESSURE
VOLUME
LOWER
RESISTANCE
HIGHER
RESISTANCE
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Questions on Anatomy
& Physiology
?
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Neonatal respiratory disease
Aims:-
Overview of neonatal respiratory disease
Pathophysiology
Clinical presentation
Aetiology
X-ray appearances Treatments
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Hyaline membrane disease
Clinical:- Usually preterm
Tachypnoea > 60
Indrawing/ retraction/ recession Grunting
Nasal flaring
Cyanosis in air Presents within a few hours of life
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HMD - Aetiology
Surfactant deficiency
Structurally immature lungs
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HMD - Treatment
Oxygen
CPAP
Mechanical ventilation Surfactant replacement
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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
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TTN - treatment
Prevention - avoid early elective
caesarean sections at term
Oxygen supplementation and IV fluids until
resolution
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Airleak Syndromes
Pneumothorax
Pneumomediatinum
Pneumopericardium Pulmonary interstitial emphysema
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Pneumothorax
Clinical:- May be asymptomatic
May be life threatening
Sudden deterioration in gas exchange Poor colour
Hypotension and tachycardia
Unilateral overexpanded thorax
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Pneumothorax - aetiology
Uneven alveolar ventilation
Air trapping and high pressure swings
Tracking of air from pulmonary interstitial
emphysema
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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
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Pneumothorax - prevention
Early surfactant therapy
Avoid overdistensionVolume guarantee
Low PIP
Short inspiratory time
Faster ventilation rates - entrainment
HFOV
Trigger ventilation - no proven benefit
Paralysis - no proven benefit
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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
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Pulmonary interstitial
emphysema
Mainly occurs in preterm babies ventilatedfor HMD
Gas trapping in perivascular sheaths
Increased incidence at lower gestations
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PIE - Clinical features
Severe hypoxaemia and CO2 retention
Deteriorating clinical condition
X- Ray
Overinflation with gross cystic changes
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PIE - Treatment
Lower PEEP and PIP
Paralysis
High rate low pressure ventilation ? HFOV
? Selective bronchial intubation
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Persistent pulmonary
hypertension of the newbornClinical features
Severe hypoxaemia (cyanosed in 100% O2)
No severe lung disease
Evidence of R to L shunt (pre vs. postductal)
Structurally normal heart
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PPHN - Aetiology and
predisposing factors
Failure of NO synthase
Asphyxia/ acidosis Infection
Diaphragmatic hernia
Alveolar capillary dysplasia Meconium aspiration syndrome
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PPHN - treatment
Minimal handling Inotropic support
Ventilation - maintain low normal CO2
Paralysis Hyperventilation - ? Risk of PVL
HFOV
Nitric Oxide
Pulmonary vasodilators Tolazoline/ Prostacyclin/ MgSO4
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Meconium aspiration syndrome
Clinical:
Meconium passage prior to delivery
Meconium in pharynx and trachea Respiratory distress post delivery with
typical X-ray changes
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MAS - Aetiology
Asphyxia and intrauterine stress
Passage of meconium + gasping
movements
Inhalation usually prior to delivery
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MAS - effects of meconium
Ball valve effect - air trapping
Chemical irritation and pneumonitis
Superinfection with bacteria Surfactant inhibition
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MAS - Management
Prevention in delivery suite
Minimal handling
Maintain normoxaemia May need ventilation + ? Paralysis
Surfactant lavage
Antibiotics
P l h h
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Pulmonary haemorrhage
Clinical
Sudden deterioration
Copious bloody secretions from airway Hypotension
Pallor
Hypoxaemia
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P l h h
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Pulmonary haemorrhage -
Aetiology
Usually preterm
HMD with PDA
Post surfactant therapy
Coagulopathy
Congestive cardiac failure
P l h h
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Pulmonary haemorrhage -
Treatment
Ventilation with high PEEP
Surfactant Indomethacin for PDA
Treat coagulopathy
Ch i l di
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Chronic lung disease
Clinical
Protracted respiratory insufficiency and
oxygen requirement beyond 28th day or36th week post conceptional age
Very preterm with early ventilation for
HMD
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CLD - Aetiology
Ventilation
Oxygen toxicity
PROM
Chorioamnionitis
Inflammation
Proteolytic enzymes
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CLD - prevention
Minimise ventilation and oxygen exposure
HFOV
Early surfactant
Corticosteroids
Early extubation
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CLD treatment
Minimise ongoing barotrauma
Nutrition
Permissive hypercapnia
Diuretics
Bronchodilators
Corticosteroids - controversial Home oxygen therapy
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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