Overview of High-Frequency Oscillator in the Neonate
More than 75% of babies born before they are 27 weeks old need some kind of breathing assistance or mechanical ventilation to survive. While we have seen improvement in survival rates for extremely premature babies or those who are very low in weight at birth, we still face a high rate of chronic lung disease due to the damage lungs can get from these breathing machines. That’s why it is critical that these machines properly ventilate the lungs and supply oxygen in a way that prevents chronic lung disease.
The main factors that put a baby at risk for developing chronic lung disease are immature lungs, damage from too much oxygen, and trauma from the breathing machine. The term bronchopulmonary dysplasia, also known as BPD, was first used in 1967 and is still used to describe babies who depend on oxygen for more than 28 days after birth. One of the key factors that causes BPD is the use of invasive breathing machines. Furthermore, BPD is the most common illness in premature babies, which is why a lot of research is focusing on ways to protect the lungs from damage and limit the development of chronic lung disease.
High-frequency oscillatory ventilation, which is a method of helping babies breathe that was developed in the 70s, could be used as a primary method for newborns or for those who can’t be helped by traditional methods. This method works by producing small tidal volumes, basically small amounts of air, provided by an oscillating piston to reduce lung damage. While using these small volumes of air, this high-frequency method also helps prevent atelectasis, which is the collapse or closure of the lung, another primary cause of lung damage from ventilation machines. This method also controls the amount of oxygen supplied by measuring the average airway pressure and inspired oxygen, while the breathing is controlled by the strength and the number of times the device oscillates. Unlike conventional breathing machines, which are more likely to cause damage through tearing forces, high-frequency oscillation maintains air space in the lung and thus prevents this tearing force. So, High-frequency strategies aim to control the volume of air in each breath to prevent lung damage in extremely premature babies.
Why do People Need High-Frequency Oscillator in the Neonate
High-frequency oscillatory ventilation (HFOV), a special kind of machine-assisted breathing, is often used for newborn babies who are having difficulty breathing. This may happen because the baby’s lungs are not working properly, or they need extra help to get oxygen. While some medical centers use HFOV as the initial treatment for very premature babies, it’s usually used as a backup option to traditional forms of assisted breathing if these don’t work or when the settings for traditional machines have to be set very high.
Conditions that may trigger the use of HFOV in newborns include:
* Meconium aspiration syndrome, which happens when a newborn breathes in a mixture of meconium (their first stool) and amniotic fluid around the time of delivery.
* Pulmonary hypoplasia, a condition where the baby’s lungs are not fully developed.
* Persistent pulmonary hypertension of the newborn (PPHN), a condition that causes high blood pressure in the lungs’ blood vessels.
* Respiratory distress syndrome (RDS), a common breathing disorder in premature babies.
* Airleak syndromes, which occur when air accumulates outside the lungs but inside the chest.
For newborns born with a birth defect called congenital diaphragmatic hernia, where the diaphragm doesn’t develop properly, HFOV can be used to help with breathing by making sure the underdeveloped lungs do not over-expand. However, a clinical study has shown that initial treatment with HFOV may lead to less favorable outcomes compared to traditional breathing support.
Finally, HFOV might not be as effective in conditions such as bronchopulmonary dysplasia (BPD), a chronic lung disease usually seen in premature babies, because air can get trapped due to the narrowness of the airways.
How is High-Frequency Oscillator in the Neonate performed
The lungs of premature babies are different from those of full-term babies. These tiny lungs lack a substance called surfactant, which helps the lungs fill with air and keeps them from collapsing. Also, a premature baby’s chest wall is more flexible and the amount of air left in the lungs after a breath can vary, which can increase the risk of lung injuries due to repeated collapse and reinflation.[7] Because of these differences, it’s especially important to use a method of ventilation, called an open lung strategy, which can help prevent these lung problems.
The open lung concept is about finding the best balance between pressure and lung volume to avoid damaging the lungs. Picture it as a zone going from point A, where there is lung collapse (medically termed as atelectasis), to point C, where the lungs are over-expanded. We want to operate in the middle (point B) where the lungs are just right – not too collapsed and not too expanded. The open lung approach helps keep the lungs in this “safe window.”
To help achieve this balance, a technique called High-frequency Oscillatory Ventilation (HFOV) is often used. This method provides many small breaths at a very fast rate (300 to 900 breaths per minute), helping to keep the lungs open and at an optimal volume. Three main factors control how HFOV works: mean airway pressure (MAP), amplitude, and frequency.
MAP and the amount of oxygen (FiO2) helps control how much oxygen your baby gets. In order to maintain the stability of air sacs in the lungs and minimize oxygen toxicity, MAP is usually set slightly higher than the pressure used during conventional ventilation. This can then be adjusted depending on how well your baby’s lungs are inflating or if they need less or more oxygen.[7] Monitoring this through chest X-rays is crucial to avoid over or under inflation of the lungs.
The amplitude, which is linked to the tidal volume (the amount of air moved in and out of the lungs), is adjusted based on the baby’s chest movements. If there is too much or too little carbon dioxide being removed from the body, the amplitude can be adjusted to change the tidal volume.
Finally, the frequency refers to how fast the breaths are given. This can be adjusted based on the specific lung condition and the size of the baby. Generally, those with stiff lungs benefit from faster frequencies and those with flexible lungs do better with slower frequencies.[3] Depending on the disease, the frequency can also be adjusted to control the amount of carbon dioxide being removed from the baby’s body. For example, a lower frequency will increase the amount of air moving in and out with each breath, helping to remove more carbon dioxide.
Unlike other ventilation methods, HFOV actively controls both inhalation and exhalation. It typically operates with 33% of the time spent on inhalation and the rest on exhalation.
HFOV works by two main mechanisms: convection and diffusion. The pressure is applied to the windpipe and dampened by the resistance of the airway.[3] Alveoli, the tiny air sacs in the lungs, that are collapsed have a higher resistance and are thus exposed to higher pressures. Accordingly, these pressures are transmitted to surrounding alveoli helping inflate neighboring alveoli and promote gas exchange. In simpler terms, HFOV helps to distribute the air better in the lungs.[3]
What Else Should I Know About High-Frequency Oscillator in the Neonate?
High Frequency Oscillating Ventilation (HFOV), which is a type of breathing support, is used in neonatal intensive care units (NICUs) for newborns who don’t respond well to standard breathing support. Despite many studies on HFOV, a definitive conclusion on its benefits is yet to be reached.
The first major study comparing HFOV to standard ventilation was conducted in 1989 and it found an increased incidence of severe brain bleeding, however, recent studies don’t show the same finding.
A 2015 review of 19 studies indicated no differences in brain bleeding among newborns treated with HFOV or conventional ventilation. Yet, it suggested that HFOV could potentially reduce the risk of chronic lung disease, a condition characterized by long-term breathing problems.
In addition, a review of 20 studies found that HFOV was associated with lower death rates from respiratory distress syndrome (RDS), a breathing disorder common in preterm babies. Another study found that very-low-birth-weight infants were able to stop using the ventilator sooner and had lower rates of chronic lung disease when treated with HFOV.
In a large trial, 200 newborns with severe oxygen deprivation and a lung condition called persistent pulmonary hypertension showed improvement in oxygenation when treated with HFOV and inhaled nitric oxide compared to standard ventilation. Another study found that most prematurely born babies with severe respiratory distress syndrome showed significant improvement within three days after starting HFOV.
While HFOV can have benefits like reducing lung damage caused by excessive oxygen and pressure from the ventilator, it has some limitations. These include lung collapse caused by suctioning and the need for sedation for comfort, as HFOV feels different from normal breathing.
In conclusion, HFOV is used in NICUs to reduce lung damage by limiting over-inflation and excessive oxygen use. Regardless of various studies showing reduced lung injury with HFOV, there’s no one-size-fits-all guideline for using ventilators as every child’s case is unique and needs an individualized approach.
