Overview of Pressure Support Ventilation
Pressure support ventilation, often abbreviated as PSV, is a type of breathing support provided by a machine. This machine is used to assist patients who are having trouble breathing on their own. The patient starts every breath, which then gets a boost from the machine.
This method can be used with either a tube that’s passed down the patient’s throat (invasive), or a mask that fits over the patient’s face or nose (non-invasive). This technique is considered the most comfortable for patients and is often used when preparing patients to breathe on their own again (weaning from invasive ventilation) or when providing additional help with breathing (supportive care with non-invasive ventilation).
The machine works by pushing a set amount of air into the lungs. The amount of air given and how fast it enters depends on several factors, including the set pressure, resistance in the airways, the flexibility of the lungs, and the patient’s own effort to breathe. The machine will stop providing the additional push of air once it detects that the patient’s breath is slowing down, typically to around 25% of the maximum flow.
The total volume of air delivered will depend on the flow and how long the breath lasts. The settings that can be adjusted in PSV mode include the pushing pressure, positive end-expiratory pressure (PEEP, which is the pressure in the lungs at the end of a breath), and the percentage of oxygen in the air provided by the machine (FiO2). The total amount of air moved in and out of the lungs per minute (minute ventilation) will depend on the patient’s breath rate, and the amount of air provided with each breath.
Unlike other modes, PSV doesn’t have a setting to guarantee a minimum amount of air will be moved in and out of the lungs, because all breaths are initiated by the patient.
Anatomy and Physiology of Pressure Support Ventilation
Mechanical ventilation involves creating a sealed pathway between a ventilating machine and the patient’s lungs. This pathway involves various parts of the respiratory system, including the nose, mouth, windpipe, smaller airway branches in the lungs, and the tiny air sacs called alveoli.
There are two types of mechanical ventilation methods. The invasive method involves inserting a tube (endotracheal tube) into the windpipe (trachea) and inflating a cuff to make the airway airtight. The non-invasive method uses a mask over the nose and mouth, secured by a cushion and elastic straps around the head.
It’s essential that the tube cuff (in invasive ventilation) or the mask (in non-invasive ventilation) is completely sealed to avoid air escaping, which would compromise the air flow and volume reaching the lungs.
Once the sealed route is established, a set amount of positive pressure (known as PEEP – positive end expiratory pressure) is applied throughout this route. This pressure is higher than the pressure in the surrounding air, which helps prevent the lungs from emptying completely when the person breathes out, and supports the open airways, including the nose, mouth and small air sacks in the lungs.
When the ventilator delivers a breath, the lungs fill with air, and this causes the diaphragm, a muscle that helps you breathe, to move downwards and flatten. If the patient makes an extra effort to breathe, the diaphragm contracts, which increases the airflow. After the breath has been delivered, the patient then breathes out passively and the air returns to the ventilator.
Why do People Need Pressure Support Ventilation
Pressure support ventilation is a technique used to help patients who are struggling with breathing problems. This method is applied in situations where a patient is having difficulty getting enough oxygen (hypoxemic), struggling to remove carbon dioxide from their body (hypercapnic), or experiencing a mix of these two conditions.
This technique is also used in cases where the doctors want to test if a patient, who’s been supported by a machine to breathe, is ready to breathe on their own. This test is known as a spontaneous breathing trial or SBT.
In this process, the machine (also known as a ventilator) uses pressure to deliver a higher flow of air than what the patient could achieve on their own. This increased flow can help in delivering more oxygen to the patient and also in removing more carbon dioxide from their body. Basically, it boosts the overall efficiency of the breathing process.
One part of this ventilation process called PEEP (positive end-expiratory pressure), helps to keep the small airways and tiny air sacs in the lungs (known as alveoli) open even when the patient breathes out. This improves the flow and distribution of air in the lungs, which further helps in oxygen delivery. Further, this method also helps to lower the effort the patient’s body has to put into breathing, thus saving energy.
When a Person Should Avoid Pressure Support Ventilation
The use of pressure support ventilation, a form of breathing support through a machine, might not be suitable for some patients. This includes those who have a weak breathing drive, highly increased oxygen usage, or high resistance in their airways. In pressure support ventilation, the machine doesn’t force the patient to breathe a certain number of times per minute, therefore it cannot guarantee a minimum amount of air intake and output in a minute.
Patients with a brain injury, critical illness-related brain disorders, or those who are given medication to make them sedated or relaxed might breathe too shallowly or too slowly. The effort required to breathe and therefore the oxygen usage can be higher in pressure support ventilation than in other modes where the machine takes over the work of breathing.
Patients with conditions like shock or low heart activity might require more respiratory support. Finally, if patients have lung diseases that obstruct air flow, this can limit the maximum flow and can lead to small breaths.
Equipment used for Pressure Support Ventilation
Blankets or pillows for comfort may also be used. With a mechanical ventilator, which is a machine used to assist or replace spontaneous breathing, and an external supply of oxygen, the doctor can deliver what is known as Pressure Support Ventilation (PSV). This mode of ventilator support simply helps you breathe more easily and can be especially helpful if you’re having trouble breathing on your own.
If this ventilator support is delivered invasively, meaning it is delivered via a tube inserted into your airways, several items will be needed. These include an endotracheal tube (a flexible plastic tube), ventilator tubing (to connect the ventilator machine to the endotracheal tube), a tube holder for the endotracheal tube, and equipment to monitor your heart’s electrical activity, blood pressure, and the level of oxygen in your blood, which is known as oxygen saturation. These tools help the doctor to monitor your vital signs closely while the ventilator is in use.
For non-invasive ventilation, which is a method of ventilator support that does not require the insertion of a tube in your airways, a few different items are needed. This includes Continuous Positive Airway Pressure (CPAP) tubing, which is a flexible tube that connects the ventilator to a mask that you wear over your nose or mouth and nose, and a mask that fits well on your face or just your nose called a nasal mask. The CPAP method helps keep your airways open while you sleep and can be especially beneficial if you have sleep apnea.
How is Pressure Support Ventilation performed
When you are placed on pressure support ventilation (PSV), the settings are usually decided based on the reason you need ventilation. PSV is a type of machine-based breathing support where the machine gives a ‘boost’ to your breaths to make them deeper, giving your lungs more oxygen. If you are breathing at a regular pace, setting a higher pressure will provide bigger and faster breaths. However, your overall breathing volume will depend on your own breath rate and effort. Once PSV starts, your doctor will watch closely to make sure your breathing, oxygen levels, and comfort is okay. They will use tools like a pulse oximeter, which checks oxygen levels in your blood, observe changes to your vital signs, and conduct an arterial blood gas test. This test measures the oxygen and carbon dioxide levels in your blood.
This PSV system could be used in two different scenarios. One is for patients who need help to breathe but don’t have a tube inserted into their windpipe (non-invasive ventilation). This machine will give positive air pressure when you breathe in (IPAP) and when you breathe out (EPAP), making your breaths easier and deeper. It’s important to have the right amount of pressure difference (also known as driving pressure) between the IPAP and the EPAP to take in the right amount of air each breath. The usual initial settings for non-invasive PSV are as follows: IPAP 10-15cmH20, EPAP 5-10cmH20, with the amount of oxygen in the air you breathe set at 100% (FiO2).
The second scenario is for patients who have a tube inserted into their windpipe because their bodies can’t breathe on their own (invasive ventilation). The settings on the PSV machine, like the driving pressure, PEEP (pressure given at the end of the breath to keep the lungs open), and FiO2 are set the same way as your previous breathing support machine. PSV is not the first choice for these patients because they feel drowsy following the injection (sedation) given during the tube placement. Once you’re on PSV, doctors will continue to monitor your condition to ensure your comfort and your body’s acceptance of the PSV system.
One of the advantages of PSV for patients with a tube is that it could improve comfort and the coordination between your breaths and the machine’s breaths since you control more of the breath delivery and breath rate. There could be less discomfort or struggle from the breaths provided by the machine during your breathing in or out. Because you’re more comfortable, the amount of sedation can be reduced, which means you can be more awake to communicate and participate in physical therapy.
The PSV mode is also used to do a spontaneous breathing trial (SBT) to determine if your body is ready to breathe on its own again. Doctors may consider you for an SBT if your condition has improved and you meet certain criteria such as stable body functions, right balance of body fluids, a suitable arterial pH level (a measure of how acidic or basic your blood is), and ability to initiate a breath. Once the SBT starts, doctors will continue to watch closely for any signs of distress or changes in your vital signs and overall breath volume. If you can breathe comfortably on PSV for 30-120 minutes while maintaining good breath volumes, then doctors may think you’re ready to breathe on your own.
Possible Complications of Pressure Support Ventilation
Some people using something known as PSV, which stands for pressure support ventilation (a common method used help people breathe), might experience issues like low breathing (hypoventilation), low-oxygen levels in the blood (hypoxemia), and changes in consciousness or overall health. This is why it’s crucial for a patient on PSV to be properly monitored so these complications can be noticed and the PSV settings can be adjusted quickly or switched to a different breathing support mode. These issues can occur due to changes in the patient’s awareness, blockages in the airways, and changes in the lung’s flexibility.
Mental changes like heavy sedation, sudden airway narrowing known as bronchospasm, as well as fluid build-up in the lungs called pulmonary edema are examples of situations that can further affect breathing and the performance of the PSV. These situations might cause a patient’s breathing rate to lower, decrease the amount of air that the ventilation can provide, or both.
What Else Should I Know About Pressure Support Ventilation?
Pressure support ventilation is a setting often used on machines that help patients breathe, sometimes called ventilators. This can be for both situations where a tube is inserted into the patient’s airway (invasive) and for scenarios where no such tube is used (non-invasive). It’s important for healthcare workers caring for patients using these breathing machines to understand the good and bad sides of pressure support ventilation. They should also know how to check how well it’s working and be aware of any problems that could happen.
