Normal Cardiopulmonary Development Flashcards
What are the 4 sequential stages of prenatal lung development?
- Embryonic period
- Pseudoglandular period
- Cannicular period
- Terminal sac period: Saccular phase, alveolar phase
How do the lungs develop during the embryonic period?
- First 5 weeks after conception
- Primitive lung buds
- Main & lobar bronchi formed
- Pulmonary arteries follow airways & divide as airways divide
How do the lungs develop during the pseudoglandular phase?
- 5-16 weeks gestation
- Mucous glands are formed, increase in number
- Muscle fibres, elastic tissue & early cartilage formation
- Tracheobronchial tree established
- Diaphragm develops
How do the lungs develop during the cannicular phase?
- 13-25 weeks gestation
- Rapid proliferation of pulmonary capillary bed
- Increase in surface of respiratory epithelium
- Formation of alveolar buds
- Type I & II pneumocytes (type II site of storage & synthesis of surfactant)
- After this phase supported extra uterine life becomes possible
When does supported extra uterine life become possible?
- After cannicular phase
- Approx 32 weeks
- Enough surfactant to inflate lungs fully for first breath
How do the lungs develop during the terminal sac period?
- 24 weeks to birth
- Cilia begin to develop
- Saccular phase: Alveolar buds become saccules, decreased interstitial tissue, cough & gag reflex develop
- Alveolar phase: Adult number of alveoli achieved around 8 years
What is lung development influenced by?
- Hormones
- Growth factors
- Extracellular matrix interactions involved in regulating development (proteins)
- Corticosteroids & thyroid hormone accelerate lung development
- Distension of the lung during the final phase of development is also thought to be important
- Development is not complete until approx 8 years
What is the general overview of cardiac development?
- Precedes other systems
- Mesodermal tissues that become the heart evident from week 3
- Continuous with brain & observable pericardial sac
- As tube increases in size, it becomes central in location & Y shaped
- Chambers form
- Heart beats at day 22-23
- Blood flows at week 4
- Original paired cardiac tubes fuse
- Cardiac tube changes to S shape
What causes the cardiac tube to change to an S shape?
- Ventricles originally located superior to atria
- Ventricles rotate downward, pushing atria upwards
- Followed by septation (conversion of simple tube into 4 chambered heart)
What is involved in foetal cardiac function?
- Oxygenation of foetus via the placenta.
- Blood flows within the foetus through right & left sides of the heart in parallel
- Cardiac output is a function of both ventricles
Where are the two points of cardiac shunting?
- Foramen ovale: Right to left atria (i.e. bypassing lungs)
- Ductus arteriosus: LV & RV
What happens when placental blood flow is interrupted at birth?
- Increased CO2, decreased SaO2
- Infant inspires
- Increase blood flow to the lungs
- Increased blood returns from the lungs into the left atrium
What happens to atrial pressure at birth?
- Pressure increases in left atrium
- Forces flap covering the foramen ovale closed
- Blocks communication between left & right atrium
What happens to the ductus arteriosus at birth?
Closes almost immediately after birth due to muscular contraction
What are some of the cardiac abnormalities that only become apparent at birth?
- Patent Ductus Arteriosus (PDA)
- Coarctation of the aorta
- Atrial septal defect (ASD)
- Ventricular septal defect (VSD)
- Tetrology of Fallot
What are the differences between children and adults in the upper respiratory tract?
- Head larger
- Neck shorter
- Tongue is large
- Lack of hair leads to increased heat loss
- Preferential nose breathers up to 3-4 months of age
- Nostrils are smaller and easily obstructed
- Heart, adenoids & tonsils are large
- Crico-thyroid membrane narrow and vulnerable to open suction & intubation until 7 years of age
What are the differences between children and adults in the lower respiratory tract?
- Lungs less compliant
- Horizontal ribs
- Less space for lung tissue
- Weak intercostals
- Diaphragm fatigues easily
- Bronchial wall structure different
- Smaller diameter airways
- Fewer alveoli (decreased surface area for gas exchange)
- Collateral channels poorly developed until 2-3 years
- Lungs don’t reach edge of rib cage until 8 years
How does the difference in rib structure affect children?
Horizontal ribs
- No bucket handle mechanism
- Unable to increase lung volume when distressed
- Increased RR when distressed
- Develops during first 2 years
What can diaphragm excursion cause in children?
Subcostal retraction rather than rib elevation
What are the consequences of smaller diameter airways in children?
- High airflow resistance
- Muscosal oedema can increase WOB
- Endotracheal tube uncured to minimise airway trauma
What are the physiological differences of the respiratory system between children and adults?
- Increased resting metabolic rate & O2 demand
- Hypoxia causes bradycardia
- Less reliable cough reflex & poorly developed abs to assist force generation
- Closing volume > FRC in small infants especially when asleep
How is oxygen consumption different in infants and young children?
- Higher than adults
- Metabolic cost of respiration is higher & may reach 15% of total O2 consumption
- O2 desaturation occurs quickly
How is ventilation & perfusion different in children?
- In adults, ventilation & perfusion distributed to dependent areas first
- In children, the uppermost areas of the lung are better ventilated & lowermost are better perfused
- Leads to an increased V/Q mismatch compared with adults
What are the signs of respiratory distress in children?
- Nasal flaring
- Tachypnoea
- Cyanosis
- Abnormal breath sounds
- Pallor
- Reluctance to feed
- Stridor
- Irritability/restlessness
- Headache
- Tachycardia/bradycardia
- Hypertension/hypotension
- Neck extension
- Head bobbing
- Altered conscious level
- Expiratory grunting
What are some of the other factors that can contribute to respiratory distress in children?
- Naive immune systems
- Dehydrate quickly
- Immobility
- Poor historians
- Co-operation +/-
- Immature breathing control
What are the consequences of an immature respiratory system?
- Predisposed to more serious lung pathologies from simple causes
- Less protective mechanisms
- Less efficient than adult system
- More likely to have alveolar collapse, V/Q mismatch, diaphragm fatigue, desaturation, retained secretions
What are wheezes, crackles, stridor and pleural rub on auscultation indications of?
- Wheeze: Spasm or secretions
- Crackles: Upper airway secretions, interstitial disease, pulmonary oedema
- Stridor: Laryngeal obstruction, tracheobronchial obstruction, glottic/subglottic anomaly
- Pleural rub: Pleural friction associated with pleurisy
What are the indications for airway clearance in children?
Evidence of retained secretions not removed by coughing, turning or suction alone
What are the indications not to use airway clearance techniques in children?
- High pitch inspiratory wheeze
- Signs of worsening respiratory distress/failure
What are the treatment choices for children?
- Postural drainage and percussion
- Positioning
- Expiratory vibes
- Exercise, walking, breathing games
- PEP therapy
- ACBT/FET
- Humidification/hydration
How is suction used in children?
- Guedels & NP airways not used
- Only suction to pharynx
What are the precautions for treating children?
- Explain assessment outcomes & treatment goals clearly to parents
- Treat before a feed or 1-2 hours after
- Use ventolin or hypertonic saline only after nebuliser or puffer via spacer
- Have short rest periods between treatment to allow quiet breathing
- Stop treatment if baby becomes wheezy or distressed
- Allow for short attention span or refusal of one treatment (have backups)
