Lung Physiology and Image

8/13/2019 Lung Physiology and Image

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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

Date post:	04-Jun-2018
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Lung Physiology and Image

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