Overview of Positive Pressure Ventilation
Positive pressure ventilation is a type of therapy used to help with breathing. It works by pumping a mix of air and oxygen under pressure into the lungs. As the gas fills the lungs, the pressure in the air sacs of the lungs (called “alveoli”) goes up. The machine senses this change in pressure or flow, or when a set amount of gas has been delivered, and that signals the end of a breath. The patient then breathes out naturally due to the built-up pressure in the lungs.
In the past, a different technique was used which created a vacuum around the patient to draw air into the lungs. This was called negative pressure ventilation, and was used for patients with severe respiratory failure due to polio, often using a machine known as an “iron lung”. However, in the 1950s following a large polio outbreak in Copenhagen, Denmark, the technique of positive pressure ventilation was introduced.
Positive pressure ventilation can be applied in two ways: non-invasive positive pressure ventilation (NIPPV), which uses a tightly-sealed special face mask; and invasive positive pressure ventilation (IPPV), which delivers the pressurized gas via a tube inserted into the windpipe or through a tracheostomy (a hole made in the neck leading to the windpipe). Each method has its own advantages, risks and appropriate uses. NIPPV can be very helpful in situations of severe respiratory failure, especially in conditions like chronic obstructive pulmonary disease (COPD) and acute heart-related lung fluid buildup. However, in certain situations such as cardiac arrest, severe instability of vital signs, when the patient can’t cooperate, or when the airway can’t be kept open and protected by reflex actions, NIPPV is not suitable and the more invasive IPPV may be needed instead.
Anatomy and Physiology of Positive Pressure Ventilation
The upper and lower parts of our breathing system, known as the airway, play a critical role in how we breathe. The upper airway includes the nose, the area behind our nose and mouth, and the path down to our windpipe or trachea. The tissue lining and the structures of the upper airway are essential in the passage and the quality of the air we breathe. They also come into play when a doctor has to perform a procedure known as ‘positive pressure ventilation’. This might be hard to perform on people with certain facial conditions, injuries or in individuals who are obese and have sleep apnea.
The lower part of the airway begins from our vocal cords, goes through the trachea, splits into two main tubes called bronchi. These bronchi further divide into smaller branches which ends in tiny air bags called alveoli, where the actual exchange of gas (oxygen and carbon dioxide) happens.
When a doctor places a breathing tube into the windpipe, known as ‘endotracheal intubation’, it is placed below the vocal cords.
Every time we take a breath using ‘positive pressure ventilation’, it involves changes in pressure, volume and flow. These changes can be defined by a simple mathematical equation that describes how these factors relate to each other. This equation hints at specific aspects of our respiratory system, such as the initial pressure in the alveoli at the start of a breath, the resistance to the flow of air, and volume of air in each individual breath.
Alveolar pressure is the pressure inside the tiny air sacs in our lungs. In a normal breath or in ‘positive pressure ventilation’, the pressure can be higher than the surrounding pressure. This is significant because in conditions where the airways are obstructed such as COPD (a type of lung disease) or severe asthma, the air might not get fully exhaled, this is known as air trapping. This could lead to a condition called ‘auto-positive end-expiratory pressure’, where the pressure inside lung’s air sac is high at the end of a breath. This rise in air and pressure can lead to potential damage to the lungs and reduced blood flow to the heart, making breathing more difficult.
Resistance to airflow or ‘R’ measures how much difficulty air faces when it flows through. It depends on many factors like mucus blockage, curved endotracheal tube, diameter of the tube, spasms in bronchi, and more. Presence of any of these can affect the maximum pressure at the end of inhale, known as ‘Peak pressure’. ‘Plateau pressure’ is the pressure inside the alveoli and varies depending on the flexibility of the lungs. Any condition affecting lungs like ARDS, pneumothorax, pneumonia, etc. can affect the ‘plateau pressure’.
Ee or elastance is the elasticity of the lung system which directly affects the lung’s compliance or its ability to expand or contract.
Why do People Need Positive Pressure Ventilation
Positive pressure ventilation, especially mechanical ventilation, is a method used by doctors to help patients breathe better. This process involves using a machine to push or “push” air into the patient’s lungs when the patient is unable to do so effectively. The reasons to begin this type of ventilation vary and can include several situations:
1. The patient might need help keeping their airway open due to unconsciousness or injuries, also known as trauma. In this case, the ventilation helps to protect the airway and ensure that the patient can breathe adequately.
2. The patient might be experiencing hypercapnic respiratory failure. This condition occurs when there is too much carbon dioxide, a waste gas, in the patient’s blood because they are unable to exhale it out. Ventilation helps by removing some of the excess carbon dioxide.
3. The patient might also be going through hypoxemic respiratory failure. In this case, the patient’s blood does not have enough oxygen, which is necessary for the body to function properly. Mechanical ventilation can help by providing the needed oxygen.
4. Circulatory failure or when the heart is unable to pump enough blood to the entire body can also prompt the use of this method. The ventilation helps by improving oxygenation and thus helping the overall circulation.
In these cases, the ventilation assists patients in maintaining their vital life processes, giving doctors the opportunity to diagnose and manage their conditions effectively.
When a Person Should Avoid Positive Pressure Ventilation
There are certain situations where using NIPPV (non-invasive positive pressure ventilation), a treatment that helps people breathe, may not be recommended or possible:
1. If the person needs to have a tube placed down their throat to help them breathe (intubation).
2. If the person’s brain is not functioning correctly or if their mental state is confused (known as encephalopathy or altered mental status).
3. If the person’s blood pressure and heart rate are unstable (hemodynamic instability).
4. If the person has injuries or abnormalities on their face (facial trauma or facial defects).
5. If something is blocking the airway, like a tumour (airway obstruction secondary to a mass).
6. If the person is predicted to need help from a breathing machine for a long time (prolonged mechanical ventilation).
7. If the person is having bleeding in their stomach or intestines (gastrointestinal bleeding).
Similarly, invasive positive pressure ventilation, which involves using a machine to help you breathe by pushing air into your lungs can’t be used in certain situations:
1. If a patient does not wish to be put on life support.
2. If a less invasive treatment like NIPPV can be used instead, as it poses fewer risks. Some potential complications with classic invasive mechanical ventilation include sleepiness from too much medication (excessive sedation), infection in the lungs from the breathing tube (ventilator-associated pneumonia), and damage to the lungs from too much pressure (barotrauma and volutrauma).
Equipment used for Positive Pressure Ventilation
NIPPV, or “Non-Invasive Positive Pressure Ventilation”, is a type of breathing support delivered via a machine. It can be administered through different devices, most commonly a CPAP or BiPAP machine, but there are others. We can’t go into those in this explanation as it’ll complicate matters.
First, let’s break down what CPAP (Continuous Positive Airway Pressure) is about. The CPAP machine is composed of a pump attached to a tube, which is then connected to a mask that goes over the patient’s face. The job of this device is to constantly provide mild air pressure (usually adjusted between 5-12 cm H2O during sleep) to keep the breathing passageways constantly open. This is especially helpful for persons having trouble with snoring or sleep apnea (a condition where one’s breathing repeatedly stops and starts during sleep).
On the other hand, BiPAP (Bilevel Positive Airway Pressure) machines work slightly differently. While they provide a constant type of pressure like the CPAP machine, they also have an extra feature: when the patient takes a breath, the machine delivers an additional burst of air. This helps the patient inhale more deeply and is therefore great for conditions like sleep apnea, worsened asthma, and chronic obstructive pulmonary disease. However, a tight seal around the face is needed for the mask. If air leaks around the mask, the therapy might not be as effective.
Introducing a more “intense” form of breathing support is invasive positive pressure ventilation. This requires a tube to be either placed into the patient’s windpipe through their mouth or nose (intubation) or directly into their neck (tracheostomy). Once this artificial airway is in place, the patient’s breathing can be either assisted or completely taken over by the machine. While there are many models of these ventilators and different names for the modes of support they provide, all function with the same basic goal: to help a patient breathe by pumping a mix of air or other gasses into the lungs.
Who is needed to perform Positive Pressure Ventilation?
Using a machine that helps patients breathe, known as a ventilator, needs a skilled team of health professionals who are good at communicating with each other. They have extensive knowledge about how ventilators work. Using a ventilator needs to be done very carefully, as research has shown that how much air the machine pushes into the lungs and how much pressure it uses can cause lung injury if not managed correctly.
To look after very sick patients who need help from a ventilator, a team of different specialists is needed. This could include doctors who specialize in breathing and lung issues (pulmonologists), doctors trained for serious illnesses needing immediate treatment (emergency department physicians), professionals that specialize in care for the seriously ill (intensivists and critical care nurses), and specialists in the use of drugs to numb pain or make patients sleep during surgery (‘anesthesiologists), among others.
It’s really important that any changes made to the ventilator settings are clearly talked about between the doctors, the nurses and the respiratory therapists (health care experts who manage ventilators and other breathing machines). This is to make sure that the ventilator is used properly and doesn’t hurt the patient. If there are any alarms from the ventilator, they should never be turned off or ignored without first understanding and dealing with the issue.
Preparing for Positive Pressure Ventilation
Ventilators, machines that help patients breathe, are intricate devices. They are made up of many components like sensors, valves, and tubes, which all require regular upkeep and checks before they are used on a new patient. These machines provide what’s known as “positive pressure ventilation,” which helps push air into the lungs, and can be given either non-invasively (using a mask) or invasively (through a tube inserted into the windpipe). Many of today’s ventilators have the ability to check their own functioning, which is referred to as “self-test”.
How is Positive Pressure Ventilation performed
NIPPV, or Non-Invasive Positive Pressure Ventilation, is a way to help with breathing using a special mask. This mask usually covers both the nose and mouth, but sometimes it can be smaller and only cover the nose. For those who already use a CPAP machine for sleep apnea and low night-time oxygen levels, a nasal device might be preferred. This device releases pressure to help keep the upper airway open. Each NIPPV machine is a little different in how it works, but generally, the person using it will control the pressure levels for the CPAP or BiPAP.
On the other hand, Invasive Positive Pressure Ventilation (IPPV) is a more complex process and needs a medical professional. Here, the doctor creates an artificial airway, most often by inserting a tube into the windpipe or trachea, which is called endotracheal intubation. For this to be done safely, the patient usually needs to be deeply sedated or temporarily paralyzed using medication. Once the tube is in the right place, a cuff on the tube is inflated to make sure it stays put within the trachea. After this, the tube is connected to a machine known as a ventilator, and a healthcare provider adjusts the way it works, or the ventilation mode.
Possible Complications of Positive Pressure Ventilation
If a patient requires positive pressure ventilation, there are several complications that can occur. This is a technique where a machine helps the patient breathe by pushing air into their lungs. Because of its risks, careful and expert use by medical professionals is necessary. Complications can happen more commonly with a more invasive type, called classic mechanical ventilation, but they can also occur with the less invasive kind.
One complication is something called ventilator-associated lung injury and barotrauma. This is damage to the tiny air sacs in the lungs (called alveoli) caused by high pressures from the ventilation. This damage can happen on a small scale initially, but with repeated improper ventilation, it could become severe enough to cause a lung collapse, or air leaking into the chest or skin – conditions which can be deadly. To prevent this, studies recommend using lower volumes of air during ventilation.
Other complications include effects on the heart and blood vessels. The pressure from the ventilation can reduce the amount of blood returning to the heart, which can affect the heart’s function, particularly in people who already have low blood volume. This could also cause irregular heart rhythms or a lack of blood supply to the heart. Risk is higher in patients with imbalances in oxygen and electrolyte levels in the blood. Critically ill patients and those on mechanical ventilation often experience changes in hormones and adrenaline-like substances, which can also affect the heart’s function. Hence, repeated blood tests are necessary to correct these imbalances.
Pneumonia contracted from the ventilator (ventilator-associated pneumonia) is the most common infection in patients on positive pressure ventilation, with a high mortality rate of up to 50%. The tube necessary for ventilation also connects the outside world to the normally germ-free inside of the lungs, providing a direct path for harmful bacteria to infect the lungs, particularly in critically sick patients with weakened immune systems.
On the other hand, breathing in high levels of oxygen, although necessary for some patients, can also harm the body. It can worsen conditions where there’s a mismatch between areas of the lungs receiving air and blood (ventilation-perfusion mismatches). It can also constrict blood vessels supplying the heart leading to heart-related problems.
It’s also important to remember that the process of being on a ventilator can affect the patient’s muscles. Oftentimes, patients needing mechanical ventilation are also sedated, which can lead to nerve and muscle problems. For some, the physical separation from the ventilator can be traumatic, and they may resist the machine (“fighting the vent”), requiring medications to relax their muscles. However, this can lead to muscle weakness or wasting, particularly of the diaphragm, making it hard to get the patient off the ventilator. In some cases, another operation called a tracheostomy might be needed to help the patient breathe by creating a direct airway in their neck.
Lastly, while non-invasive ventilation is generally safer than the invasive kind, it’s not suitable for everyone and has its own complications. These include facial injuries from the seal of the ventilation mask, eye irritation, dry airway passages, and bloating of the stomach. If there’s any risk of the patient accidentally breathing in stomach contents into the lungs (aspiration), inserting a tube directly into the windpipe (intubation) would be safer.
What Else Should I Know About Positive Pressure Ventilation?
Modern medical advancements have greatly improved the treatment of serious heart and lung diseases. A key development in the last century has been the ventilator – a machine that helps people breathe. This device has been continually refined and improved, saving countless lives of people who otherwise might have not survived their illnesses.
There are certain diseases that can certainly cause death without the aid of a ventilator. The machine works by pushing air (providing positive pressure) into the patient’s lungs helping oxygen to circulate in their body. However, the correct use of this equipment requires careful attention and precision, as well as a solid understanding by the care team about when and how to use it.
Healthcare professionals need to work closely together in a team to manage these critically ill patients who need ventilators. Open and frequent communication among team members is vital to keep track of the patient’s condition, as lung-related problems can quickly worsen.
Starting positive pressure ventilation involves a clear understanding of when and how it should be used, the specific features of the equipment, and the risks associated with its use, to ensure that we provide the most effective and safest care to our patients.