Overview of Neurally Adjusted Ventilatory Assist (NAVA)
Mechanical ventilation, a method of aiding a person’s breathing, has been around since the 16th century, but it only became widely used in the 20th century. Over time, strong evidence has shown that it can significantly help patients with respiratory failure.
In this method, machines are used to help a person breathe in two ways: invasive, where a tube is inserted into the windpipe; and noninvasive, where a mask is fitted over the nose or mouth. However, sometimes there can be a mismatch between the patient’s breathing and the ventilator’s rhythm – this is known as patient-ventilator asynchrony. When this happens, the ventilator may miss the patient’s breath or recognize it too late. This can lead to complications, including increased need for sedation, discomfort, and potentially higher risk of complications or death. Also, using invasive mechanical ventilation can cause lung damage.
However, in 1999, Sinderby and his team introduced a new concept: using the patient’s own neural activity to control the ventilator, a method known as Neurally Adjusted Ventilatory Assist (NAVA). By using a special catheter placed in the throat, NAVA machines pick up the electrical activity of the diaphragm, the primary muscle used for breathing. This method may lead to less mismatch between the patient and ventilator, more comfort for the patient, and better control over the breathing process. This way of using a ventilator can be applied in both invasive and noninvasive manners, like in the noninvasive ventilation-NAVA method.
Anatomy and Physiology of Neurally Adjusted Ventilatory Assist (NAVA)
Our brain controls our breathing by sending signals through a nerve called the phrenic nerve. This nerve tells our main breathing muscle, the diaphragm, to contract, which lets air flow into our lungs. After the diaphragm contracts, we take a breath in. This whole process is dependent on the signals from our brain. These signals can vary from breath to breath.
In medical scenarios like hospitals, sometimes people can’t breathe on their own and need the help of machines called mechanical ventilators. These machines help patients breathe by using a few different trigger variables: pressure, flow, and time. Pressure is used to sense a change in the baseline pressure, which indicates the patient is trying to breathe and so the machine starts a new breath. In time-triggered ventilation, the machine simply starts a new breath at set time intervals. Flow-triggered ventilation, on the other hand, initiates a new breath when it notices a drop in the flow of air. But all these mechanisms have a delay because they only start working after a patient has already tried to initiate a breath. This delay can be quite significant for some patients especially newborns, making it harder to detect when a breath needs to be initiated.
Neurally Adjusted Ventilatory Assist (NAVA) is a smarter technique used in ventilation. It works by monitoring the electrical activity in the patient’s diaphragm (our body’s main breathing muscle) using a special tube with electrodes. This electrical activity is a signal from our brain to breathe. In NAVA, not only does the ventilator provide support based on this signal, but it also adjusts the size of each breath according to the patient’s effort and needs. This means that each breath is initiated earlier and more accurately, which feels more comfortable and natural for the patient.
Moreover, with NAVA, the pressure given for each breath is regulated based on the individual patient’s effort measured through the electrical activity of the diaphragm. This means the patient has greater control over both their own breath and the machine’s support, which further increases synchrony and comfort.
The machine calculates the highest pressure needed for each breath using the NAVA level (which measures the electrical activity of the diaphragm) and any additional positive pressure provided by the machine. This ensures that each breath remains as comfortable and supportive as possible for the patient.
Why do People Need Neurally Adjusted Ventilatory Assist (NAVA)
NAVA (Neurally Adjusted Ventilatory Assist) is a type of breathing support that can be used in situations where traditional breathing machines are needed. The need for this support can vary between adults and children.
For adults, NAVA may be utilized when they are suffering from conditions like Acute Respiratory Distress Syndrome, which is a severe lung condition causing shortness of breath, or Acute Hypoxemic Respiratory Failure, which is a situation when your blood doesn’t have enough oxygen.
For newborn babies or children, NAVA can be helpful when dealing with problems like Respiratory Distress Syndrome, which makes it hard for newborns to breathe. It can also assist kids suffering from Primary or Secondary Pulmonary Hypertension, a condition that affects the blood vessels in the lungs, making it harder for the heart to pump blood.
Furthermore, NAVA can be used for children dealing with Bronchopulmonary Dysplasia, a chronic lung disease often affecting premature babies and disrupting normal breathing. Lastly, if a child suffers from Central Hypoventilation Syndrome, a disorder that affects automatic control of breathing, continuous assessment of breathing activity can be provided through NAVA.
When a Person Should Avoid Neurally Adjusted Ventilatory Assist (NAVA)
Sometimes, medical conditions that impact either the central nervous system (such as the brain) or the peripheral system (nerves outside the brain and spinal cord) may prevent a person from using a NAVA. NAVA, or neurally adjusted ventilatory assist, is a type of breathing support. This also applies when there are physical problems with the diaphragm, the major muscle involved in breathing.
To provide some examples:
Issues with the central nervous system might include the use of drugs that cause muscle paralysis or the suppression of the body’s normal urge to breathe due to strong sedative medications or brain injury.
Nervous system problems outside of the brain and spinal cord could involve injury to the phrenic nerve, which controls the diaphragm, or the use of drugs causing paralysis.
Physical abnormalities could include esophageal atresia, a birth defect where the esophagus doesn’t properly form, and a diaphragmatic hernia, which is when there is an abnormal hole in the diaphragm.
Additionally, the NAVA catheter, a tube used in the treatment, is not safe to use with MRI machines. This means that it isn’t an appropriate option for patients who need MRI scans (imaging test that uses magnetic fields to take pictures of the body’s interiors).
Equipment used for Neurally Adjusted Ventilatory Assist (NAVA)
The Servo ventilator is a specific type of machine that helps patients breathe. This machine can only work with a device called the NAVA catheter. The NAVA catheter comes in different sizes, which need to be chosen carefully based on the patient’s size and weight.
Picking the right size for the catheter is very important. If the catheter is too big or too small, it may not be able to properly detect the Edi signal. The Edi signal is a measurement of your diaphragm’s (the muscle that helps you breathe) activity. The accurate detection of this signal is important for the ventilator to help you breathe properly. This miscalculation can happen because of where the electrodes (small sensors that catch electrical activity) are placed and the distance between them.
Who is needed to perform Neurally Adjusted Ventilatory Assist (NAVA)?
A respiratory therapist, who is an expert in helping patients with breathing problems, needs to prepare the medical equipment. A nurse will then put in a special tube called an Edi catheter. After that, the doctor will stay by your side to fix any issues with the tube, make sure it’s in the right place, and choose the best starting settings on the machine. They do all this to ensure your treatment goes as smoothly as possible.
Preparing for Neurally Adjusted Ventilatory Assist (NAVA)
Medical staff are responsible for placing and confirming the correct position of the Edi catheter. It’s also crucial that they ensure that the machine being used is working as it should.
How is Neurally Adjusted Ventilatory Assist (NAVA) performed
In medical procedures sometimes it is necessary to monitor the diaphragm’s electrical activity. The way this is done is through a small gadget with 9 tiny electrodes, which is packaged inside a thin tube known as a catheter. This catheter is placed in your lower esophagus, which is near your diaphragm. The tiny electrodes within the catheter pick up on the electrical activity from your diaphragm and send this information to a breathing machine known as a ventilator.
There are three vital steps doctors follow when placing the catheter. First, is the “Anatomical placement”. Here, doctors typically measure a path from your nose, past your earlobe, and end up at a small point just below your sternum, known as the xiphoid process. This method is known as the NEX method. Lubricants are not advised in this process as they could tamper with the sensitive electrodes. Instead, just dipping the catheter in water should do the trick.
Once in place, the location of the catheter is confirmed, which is the second step, “Verification of the electrode’s position”. This is done by checking the heart rhythm patterns shown in the ‘Edi catheter positioning’ section of the ventilator. If the top electrodes near the heart are displaying certain patterns and the lower ones near the stomach are not, then the position of the catheter could be confirmed good.
The third step is “Verification of the Edi signal”. Here, the doctors look for a strong signal from the diaphragm. A weak signal might indicate issues with your nerves, or even that you’re under heavy sedation or muscle relaxant medication conditions.
When these steps are completed, the catheter must be held in place and the procedure documented.
The ventilator has a set of settings that allow it to interpret the signals from the diaphragm and provide the necessary support for your breathing. They include the amount of support it gives, pressure settings, alarm settings, and the oxygen levels among other things.
As an example, the ventilator is programmed to match the level of support it gives with the work your diaphragm is doing. The goal here is to help you breathe normally with the right amount of effort. The level of aid provided by the ventilator is then adjusted accordingly, based on whether you are putting in too much effort, or too little. The danger of having the support set too high is that your body may become reliant on the ventilator or even lead to pauses in your normal breathing rhythm, especially in newborn babies.
As you can imagine there are a lot of variables to consider during this procedure and so a multitude of factors must be carefully monitored. Things such as oxygen saturation, carbon dioxide levels, and your blood gases are just a few of the things that are tracked. Monitoring the breathing effort over time is extremely important in understanding the patient’s respiratory condition. The ventilator can provide a consistent interpretation of your breathing needs and adjusts itself accordingly, reducing or increasing the support it provides based on your needs.
Possible Complications of Neurally Adjusted Ventilatory Assist (NAVA)
The ventilator mode called NAVA doesn’t have unique problems of its own. But, like other ventilator modes, it can sometimes cause side effects. These can include damage to the lungs or diaphragm from the ventilator, pneumonia linked to ventilator use, or pneumothorax, which is a collapsed lung. However, NAVA may reduce the risk of lung or diaphragmatic damage because it adjusts the pressure to the patient’s efforts. Also, studies have shown a potentially smaller need for a high level of positive pressure in the airway when using NAVA.
What Else Should I Know About Neurally Adjusted Ventilatory Assist (NAVA)?
NAVA, short for neurally adjusted ventilatory assist, is a newer method of helping patients breathe using a mechanical ventilator. It was created to improve the issues that other breathing support systems can have. More research is still being done, but so far, we’ve seen that NAVA has several benefits.
First, NAVA improves the patient’s connection with the ventilator. Normally, there’s a slight delay from when the brain tells the diaphragm, the muscle that helps in breathing, to work and when the ventilator starts providing support. With NAVA, as soon as the brain signals the diaphragm, the ventilator starts working. This seamless connection reduces discomfort and can help improve a patient’s breathing and oxygen levels in the body.
Another challenge in mechanical breathing support systems is air leaks. Whether through a hose inserted directly into the patient’s airway or a breathing mask, some of the air can escape. This is especially an issue with non-invasive ventilators (that use a mask or other means instead of a hose in the airway). NAVA has been found to work effectively even when there are substantial air leaks.
NAVA has also been increasingly used in infants, especially those born prematurely. It has been found that NAVA requires less pressure to assist in breathing than other ventilators, but there is still no conclusive evidence on its overall effectiveness. It is considered safe for use in premature infants, but more research needs to be done.
Lastly, there’s a non-invasive form of NAVA, called NIV-NAVA, that simply uses a mask or nose prongs. Studies have shown that it works effectively, even when there are significant air leaks. Babies who were taken off invasive ventilators and switched to NIV-NAVA stayed off the invasive ones for longer and required less breathing pressure.
Overall, although NAVA is a promising development in ventilation technology, we still need more research to confirm its long-term effectiveness.
