Artificial Respiratory Suppport ✅ Flashcards
What can artificial respiratory support be classified into?
- Non-invasive respiratory support
- Invasive respiratory support
How is invasive respiratory support given?
Via a tracheal tube
What are the levels of support that can be given in artificial respiratory support?
- Single level support
- Intermittent positive pressure ventilation
Give 2 examples of single level respiratory support?
- CPAP (continuous positive airway pressure)
- HFNC (high flow nasal cannula)
What does single level respiratory support provide?
A form of distending pressure
Does single level respiratory support provide mechanical breaths?
No
Who is single level respiratory support suitable for?
Babies who are breathing spontaneous and have sufficient central drive
What is required if babies are not breathing spontaneously and show signs of respiratory failure?
Intermittent positive pressure ventilation
How can intermittent positive pressure ventilation be delivered?
Via a tracheal tube or nasal prong
What do the ventilatory needs of a patient depend largely on?
- Mechanical problems of respiratory system
- Type of abnormality in gas exchange
What drives the flow of gases in the lungs?
The pressure gradient between the airway opening and alveoli
What determines the pressure gradient necessary for adequate ventilation?
- Compliance
- Resistance
What does compliance describe?
The elasticity or distensibility of the lungs or respiratory system (lungs + chest wall)
How is compliance calculated?
Volume / pressure
What is the normal compliance of infants lungs?
3-5ml/cmH2O/kg
Give a condition that lowers the compliance of infant lungs
RDS
What is the compliance of an infants lungs in RDS?
0.1-1ml/cmH2O/kg
What does resistance describe?
The ability of the gas-conducting parts of the lungs or respiratory system to resist airflow
How is resistance calculated?
Pressure/flow
What is the resistance in normal infant lungs?
25-50cmH2O/L/second
Is resistance altered in RDS?
Not markedly
What can increase resistance in infants lungs?
Small endotracheal tubes
By how much can small endotracheal tubes increase the resistance in fetal lungs?
To 100cmH2O/L/second or more
What is meant by the time constant?
The time (milliseconds) necessary for the alveolar pressure (or volume) to reach 63% of a change in airway pressure (or volume)
How is the time constant calculated?
Compliance x resistance
What duration of inspiration or expiration is required for inspiration or expiration to be relatively complete?
3-5x the time constant
What is the implication of needing a duration of 3-5x the time constant for relatively complete inspiration or expiration?
The time constant is affected by resistance and compliance, and so the inspiratory and expiratory times are also affected by resistance and compliance
What happens to the time constant if the compliance is decreased?
It will be shorted
What effect does RDS have on inspiratory times?
RDS decreases compliance, so decreases the time constant, so enables shorter inspiratory times to be effective
When will the time constant be higher?
- If compliance is high
- If resistance is high
When might resistance in the lungs be high?
In bronchopulmonary dysplasia
On what basis can ventilators be classified?
- By the variables that are controlled, e.g. pressure or volume
- If they start (or trigger), sustain (or limit), and end (cycle) inspiration
- If they maintain expiratory support (or baseline pressure)
What is the function of a pressure controller ventilator?
Controls airway pressure
What are the types of pressure controller ventilators?
- Positive pressure ventilators
- Negative pressure ventilators
What do positive pressure ventilators do?
Make the airway pressure rise above body surface pressure
What do negative pressure ventilators do?
Make airway pressure fall below the body surface pressure
What do volume controller ventilators to?
Controls and measures the tidal volume generated by the ventilator
What do flow controller ventilators do?
Controls the tidal volume by limiting gas delivery by flow
What does a time controller ventilator do?
Controls the timing of a ventilatory cycle but not the pressure or volume
What kind of ventilators are high frequency ventilators?
Time controllers
What aspects need monitoring in infants on ventilators?
- Underlying lung pathology
- Response to treatment
- Surveillance for associated complications
What are the categories of monitoring used in infants on ventilators?
- Clinical evaluation
- Assessment of gas exchange
- Chest imaging
- Pulmonary function and pulmonary mechanics testing
- Cardiac monitoring with echocardiography and imaging
What does clinical evaluation include when monitoring infants on ventilators?
Observation for general physical condition and complications of mechanical ventilation
Give 2 examples of complications of mechanical ventilation?
- Gas trapping
- Air leaks
What features may suggest air hunger or increased work of breathing?
- Rapid shallow breathing
- Subcostal/intercostal retraction
How can air hunger/increased work of breathing be corrected in a ventilated infant?
Augmentation of ventilator parameters
What might suggest a left-to-right shunt via a PDA in a ventilated infant?
- Hyperactive precordium
- Presence of a cardiac murmur
What might suggest persistent pulmonary hypertension of the newborn (PPHN) in a ventilated infant?
- Cyanosis
- Desaturation on pulse oximetry
How can a pneumothorax be identified quickly in a ventilated infant?
Bedside transillumination with a fibre-optic light source applied to the chest wall
How can gas exchange be assessed in a ventilated infant?
Blood gas assessment
What makes assessment of gas exchange difficult?
- Has to be interpreted in clinical context
- Wide range of normal blood gas values
What factors should be taken into account when assessing blood gases?
- Work of breathing
- Recent trends
- Stage of illness
What does the normal blood gas value depend on?
- Gestational age
- Postnatal age
- Source (arterial, venous, or capillary)
- Disease status
What is oxygenation dependent on?
Ventilation-perfusion matching
What is elimination of CO2 from the blood dependent on?
Alveolar ventilation
How is alveolar ventilation calculated?
Tidal volume x respiratory rate
How is the pH of the arterial blood determined?
Primarily by PaCO2, lactic acid, and buffering capacity
What produces lactic acid?
Anaerobic metabolism
What is particularly important in determining the buffering capacity?
The serum or plasma bicarbonate and plasma haemoglobin concentration
What is the base deficit in a healthy term infant?
3-5 mEq/L
What is the difficulty of interpreting base deficit in a ventilated infant?
Base deficit can vary widely
What is an acceptable base deficit in a baby?
5-10 mEq/L (assuming reasonable perfusion)
What should be done if a ventilated infant has a base deficit of >10mEq/L?
Careful assessment for evidence of hypoperfusion
What is usually the best way of managing metabolic acidosis?
Correcting the cause
What is the use of CXR in NICU?
- Diagnosis
- Monitoring the course of a disease process
What are the problems with CXR?
Poor specificity
What needs to be remembered when considering a CXR?
Needs to be interpreted in context with the clinical information
What is the limitation of the use of CXR for diagnosis?
Findings are mostly suggestive of pathology rather than being diagnostic
How can pulmonary function and pulmonary mechanics testing be done in ventilated infants?
Using pulmonary graphics on the ventilator
What can pulmonary function and mechanics testing be useful in determining in ventilated infants?
- Dynamic compliance
- Airway resistance
- Inspired and expired tidal volumes
What can the use of pulmonary function and mechanics testing facilitate?
The use of gentile ventilation
What is the purpose of gentile ventilation?
Minimising ventilator-induced lung injury
How can cardiac monitoring be carried out in a ventilated infant?
- Echocardiography
- Imaging
What is cardiac monitoring useful for in ventilated infants?
- Confirm diagnosis of PDA and assess ductal shunting
- Identify PPHN and congenital heart disease
