What is assisted ventilation of the newborn?
Assisted ventilation of the newborn is a procedure to help a newborn breathe, if the baby does not spontaneously begin to breathe at birth or has difficulty breathing. A mechanical ventilator provides oxygen to the lungs at the required pressure and frequency, until the baby’s respiratory system works normally.
Respiration is a combination of precise functioning of respiratory muscles and exchange of oxygen for carbon dioxide in the lungs, with the brain regulating the entire activity. Lungs are composed of tiny air sacs known as alveoli which deliver oxygen to the blood and remove the carbon dioxide, which is exhaled.
What are the types of assisted ventilation for the newborn?
Different approaches are used in assisted ventilation depending on the reason for the infant’s respiratory distress or failure. The types of assisted ventilation include:
Continuous positive airway pressure (CPAP)
The continuous positive airway pressure (CPAP) device maintains a continuous flow of air with a stable pressure during inhalation and exhalation. CPAP is delivered through nasal prongs or a mask that fits over the baby’s nose.
CPAP is used in babies who can breathe spontaneously but are in respiratory distress and need support. Early and preventive use of CPAP in preterm babies can reduce the need for mechanical ventilation. CPAP may also be used to wean a baby off mechanical ventilation.
Nasal intermittent positive pressure ventilation (NIPPV) is another positive airway pressure system which can be programmed to provide continuous breaths or synchronized with the baby’s own breath.
Conventional frequency ventilation
Conventional frequency ventilation is administered through a thin tube placed in the baby’s airway. Conventional frequency ventilators can be adjusted to provide airflow at different pressures and time cycles, based on the baby’s specific needs. The ventilatory parameters that can be adjusted include the following:
Peak inspiratory pressure (PIP): Peak inspiratory pressure is the highest level of pressure applied on the lungs during inhalation. The level of PIP is based on the baby’s lung compliance (elasticity) and chest wall motion (the rise and fall of the chest wall during breathing).
Positive end-expiratory pressure (PEEP): Positive end-expiratory pressure is the air pressure that remains in the airway at the end of exhalation. PEEP helps prevent the collapse of alveoli and maintains the lung volume after exhalation.
Respiratory rate: Rate is the number of breaths delivered per minute adjusted based on oxygen/carbon dioxide levels in the blood.
Inspiratory and expiratory times: The inspiratory and expiratory times are adjusted based on the baby’s time constant. “Time constant” is the time taken for an alveolus to fill (inspiratory) or empty (expiratory) at a stable pressure. Inspiratory time is gradually shortened to wean the baby off the ventilator.
Inspiratory-expiratory ratio (I:E ratio): Inspiratory-expiratory ratio refers to the ratio of time taken for inspiration and expiration. A normal newborn has a ratio of 1:1.5 to 1:2.
Fraction of inspired oxygen: Fraction of inspired oxygen is the concentration of oxygen in the airflow, which can be adjusted based on the baby’s oxygen saturation.
Flow rate: Flow rate is the volume of airflow delivered per minute to maintain adequate tidal volume. Tidal volume is the volume of air that flows in or out of the lungs in a respiratory cycle.
What are the strategies used in assisted ventilation of the newborn?
Ventilation strategies are individualized based on a baby’s specific condition and requirement, to provide optimal ventilation support while preventing lung injury.
- Respiratory distress syndrome (RDS): Typical characteristics of respiratory distress syndrome are low lung compliance and functional residual capacity (FRC), which is the volume of air in the lungs after normal exhalation. RDS results in low blood oxygen levels (hypoxemia).
- Bronchopulmonary disease (BPD): Bronchopulmonary disease occurs because of underdeveloped lungs which are highly vulnerable to injury after birth. In babies with BPD, time constant varies in different areas of the lungs and resistance to airflow may increase.
- Persistent pulmonary hypertension: Pulmonary hypertension is high blood pressure in the lung’s arteries. This condition may occur due to underdevelopment of lungs or intrauterine hypoxia, among other reasons.
- In addition to appropriate ventilation, the baby may be administered a surfactant to prevent alveolar collapse. Lung surfactant is a fatty protein that reduces surface tension at the blood-gas barrier in the alveoli. The baby is also usually administered medications to reduce the blood pressure.
Strategies to prevent lung injury
An infant’s lungs are fragile and are highly susceptible to injury from mechanical ventilation. Studies of immature animals indicate that lung injury from ventilation occurs with high air volumes at low pressures (volutrauma), and not with low volumes and high pressures.
Lung injury may also be caused by repeated collapse and inflation of alveoli due to low end-expiratory pressure.
Two strategies followed to prevent lung injury are:
- Permissive hypercapnia: Permissive hypercapnia is to allow an increased level of carbon dioxide in blood that a baby can tolerate, using low volume ventilation. This strategy is adopted to prevent permanent lung injury from high volume ventilation.
- Low tidal volume ventilation: Keeping the tidal volume low prevents overdistension of the lung and associated injury, while maintaining functional residual capacity.
Alternative modes of ventilation
Advancement in technology has led to improved strategies in assisted ventilation. The newer methods of ventilation include:
- Patient-triggered ventilation (PTV): Patient-triggered ventilation allows the babies to take spontaneous breaths when they can, unlike the earlier versions of ventilators which deliver time-based airflow at preset frequency.
- Synchronized intermittent mandatory ventilation (SIMV): SIMV delivers a mandatory number of breaths, while also allowing the baby to breathe spontaneously. SIMV detects inspiratory effort from the baby and waits until exhalation before delivering the next breath.
- Proportional assist ventilation (PAV): Proportional assist ventilation provides ventilation in proportion to the volume of airflow with spontaneous breaths, which can be adjusted according to the baby’s needs.
- Volume-targeted ventilation (VTV): Volume-targeted ventilators self-adjust the flow and maintain preset tidal volume.
- Tracheal gas insufflation (TGS): Tracheal gas insufflation is used as an adjunct to mechanical ventilation. Gas delivered into the trachea clears out the carbon dioxide in the respiratory tract.
- High-frequency ventilation (HFV): High-frequency ventilators deliver low tidal volume at a far higher respiratory rate than normal breathing. Types of high-frequency ventilation include:
- High-frequency jet ventilation (HFJV)
- High-frequency flow interruption (HFFI)
- High-frequency oscillatory ventilation (HFOV)
What are the benefits and risks of assisted ventilation of the newborn?
The benefits and drawbacks of specific ventilation strategies include the following:
Use of CPAP or high PEEP
- Increased volume in the alveoli and functional residual capacity
- Opening up of the alveoli
- Stability of alveoli
- Redistribution of fluid from the lungs
- Improved ventilation/perfusion matching (synchronization of blood flow and air flow in the alveoli) which facilitates gas exchange
- Increased risk of air leak from the alveoli
- Overdistention of alveoli
- Carbon dioxide retention
- Cardiovascular impairment
- Reduced compliance
- Possible increase in resistance in the pulmonary blood vessels
High rate and low tidal volume ventilation
- Reduced risks of
- Air leaks
- Cardiovascular adverse effects
- Pulmonary edema
- Gas trapping (abnormal retention of air in the lungs)
- Alveolar collapse (atelectasis)
- Maldistribution of gas
- Increased resistance
High inspiratory-to-expiratory (I:E) ratio (long inspiratory time)
- Increased oxygenation
- Potentially improved delivery of oxygen to areas of atelectasis
- Gas trapping
- Increased risk of volutrauma and air leaks
- Impaired venous blood return to the heart
- Increased resistance in the pulmonary blood vessels
- Decreased risk of volutrauma and lung injury
- Reduced duration of mechanical ventilation
- Reduced ventilation to the alveoli
- Elimination of hypocapnia (low carbon dioxide level) side effects
- Increased oxygen unloading
- Cerebral vasodilation (dilation of blood vessels in the brain)
- Hypoxemia (low blood oxygen)
- Hyperkalemia (low potassium)
- Reduced oxygen uptake by hemoglobin
- Increased resistance in the pulmonary blood vessels
Ventilation with short inspiratory time
- Faster weaning off from ventilation
- Reduced risk of lung collapse (pneumothorax)
- Possibility for use of higher respiratory rate
- Inadequate tidal volume
- Potential need for high airflow rates
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