Mechanical Ventilation

Mechanical ventilation is a life-saving therapy that helps you breathe when your body cannot do it on its own. Whether during surgery or due to serious illness, a ventilator supports your lung function by delivering oxygen and removing carbon dioxide, giving your body the time it needs to heal.

Table of contents

• What Is Mechanical Ventilation?
• How a Ventilator Works
• Types of Mechanical Ventilation
• Who Needs Mechanical Ventilation?
• How Long Is It Needed?
• Understanding Respiratory Mechanics
• Ventilation Modes and Settings
• Monitoring During Mechanical Ventilation
• Risks and Complications
• Recovery and Life After a Ventilator

What Is Mechanical Ventilation?

Mechanical ventilation is a form of life support that helps you breathe when you cannot breathe on your own^[1]. This therapy can be needed during surgery or when you are very sick. The ventilator is a machine that partially or completely supports your lung functions, similar to how crutches support your weight when you cannot walk normally^[1].

It is important to understand that mechanical ventilation does not directly treat illnesses. Instead, it stabilizes you while other treatments and medications help your body recover^[1]. The therapy is a critical intervention to sustain life in acute or emergency settings, particularly in patients with compromised airways, impaired breathing, or severe oxygen problems^[2].

How a Ventilator Works

A ventilator performs several vital functions to keep your body supplied with oxygen. The machine provides oxygen to your lungs, helps remove carbon dioxide (a waste gas that your body produces) from your lungs, and provides pressure to keep the small air sacks in your lungs, called alveoli, from collapsing^[1].

Healthcare providers can adjust the settings on the machine to meet your specific needs^[1]. The primary goal of mechanical ventilation is to maintain adequate air movement in the lungs and oxygen content in the blood, preventing respiratory acidosis (too much carbon dioxide) and lack of oxygen^[12].

Modern mechanical ventilators use positive pressure to push air into your lungs^[1]. This is different from normal breathing, which generates negative pressure inside your chest to pull air in. In mechanical ventilation, the pressure gradient results from increased pressure of the air source^[3].

Types of Mechanical Ventilation

There are two main types of mechanical ventilation, and the difference between them relates to how air gets from the ventilator into your lungs^[1].

Invasive mechanical ventilation means you have a tube in your airway connected to a ventilator^[1]. This tube can go through your mouth, which is called intubation, or through your neck in a procedure called tracheostomy. When a provider intubates, they put a tube down your throat into your airway, also known as the trachea. Then, a provider will connect the tube to a ventilator^[1].

Noninvasive ventilation uses a face mask connected to a ventilator instead of a tube in your throat^[1]. Straps hold the mask to your head to keep it tight, and the ventilator pushes air into your lungs through the mask. Forms of noninvasive ventilation include devices you might use at home, like CPAP (continuous positive airway pressure) or BiPAP (bilevel positive airway pressure)^[1].

There are some benefits to noninvasive ventilation with a face mask. It can be more comfortable than a breathing tube, it allows you to cough, you may be able to talk and swallow, you may need less sedative and pain medicines, and it lowers some risks, such as pneumonia, that are associated with a breathing tube^[14].

Who Needs Mechanical Ventilation?

You might need mechanical ventilation in several situations. During surgery, general anesthesia decreases your ability to breathe deeply enough on your own^[1]. If you have certain lung conditions or infections, or if a medical emergency blocks your airway or impairs your breathing, you may need ventilator support.

If you have certain brain injuries or conditions, your brain might not communicate well enough with the rest of your body, including your lungs, to allow you to breathe properly^[1]. You may also need mechanical ventilation if you have any conditions that cause your blood to have too much carbon dioxide, called hypercapnia, or not enough oxygen, called hypoxemia. Sometimes ventilation is needed to prevent you from accidentally getting food or mouth contents, like saliva, into your lungs, which is called aspiration^[1].

Specific conditions that might require mechanical ventilation include acute respiratory distress syndrome (ARDS), pneumonia, COVID-19 and other respiratory illnesses, chronic obstructive pulmonary disease (COPD), stroke, traumatic brain injury, coma, and anaphylaxis^[1].

In general, mechanical ventilation should be considered when there are clinical or laboratory signs that the patient cannot maintain an airway or adequate oxygenation or breathing^[3]. Concerning findings include a respiratory rate greater than 30 breaths per minute, inability to maintain oxygen levels above 90 percent despite the use of noninvasive oxygen strategies, blood pH less than 7.25, or carbon dioxide pressure greater than 50 mmHg (unless chronic and stable)^[3].

• Lungs
• Alveoli
• Trachea (windpipe)
• Airways
• Chest wall
• Diaphragm

How Long Is It Needed?

The time you need mechanical ventilation depends on the reason for using it. It could be hours, days, weeks, or, rarely, months or years^[1]. Ideally, you will only stay on a ventilator for as little time as possible. Your healthcare providers will test your ability to breathe without assistance daily or more often.

The majority of patients are on a ventilator for an average of four or five days^[15]. However, a second group of patients require it for 10 to 14 days or more. This second group often has severe acute respiratory distress syndrome, which occurs when fluid builds up in the lungs and prevents them from filling with enough air. People with coronavirus disease 2019 (COVID-19) who end up in the hospital intensive care unit often fall into this second category^[15].

In general, if you need to be on a ventilator for a long time, around two weeks or so, a provider will switch you from a tube through your mouth to a tracheostomy^[1].

Understanding Respiratory Mechanics

Normal spontaneous breathing generates negative pressure inside your chest, which creates a pressure gradient between the atmosphere and the alveoli, resulting in air flowing inward. In mechanical ventilation, the pressure gradient results from increased positive pressure of the air source^[3].

The ventilator measures and displays peak airway pressure, which represents the total pressure needed to push a volume of gas into the lung^[3]. This pressure is composed of several components: pressures resulting from airflow resistance, the elastic recoil of the lung and chest wall, and the alveolar pressure present at the beginning of the breath.

Compliance describes how easily the lungs can expand. It equals the change in volume divided by the change in pressure^[5]. A typical high compliance state is COPD, where the lungs are damaged and suffer from emphysema, making the alveolar units baggy and floppy. It takes very little pressure to fill these lungs up. A typical low compliance state is ARDS, where the lungs are stiff, and it takes a lot of pressure to get a small amount of volume into these lungs^[5].

Resistance describes how difficult it is for air to flow through the airways. It equals the change in pressure divided by the change in flow^[5]. A typical high resistance state is asthma, where the conducting airways are constricted and very tight due to bronchospasm, smooth muscle hypertrophy, and mucus plugging^[5].

Ventilation Modes and Settings

There is no one ventilator mode that is considered the best, except in some very specific cases^[5]. What is important is to understand that in each mode you have dependent and independent variables—things that healthcare providers control and things that are the consequence of the settings as well as the underlying disease state of the patient.

Mechanical ventilation modes can be defined in terms of their control variable and programmed breath sequence^[12]. The control variable determines the gas volume and flow rate delivered for each breath, while the breath sequence determines the frequency of delivered breaths.

Understanding modes starts with understanding the different types of breaths that can be delivered: controlled, assisted, or supported^[5]. In controlled breaths, the ventilator does all the work.

PEEP, or positive end-expiratory pressure, is an amount of pressure applied to the airway at the end of expiration^[5]. On expiration, the elastic forces of the lungs result in forces that want the alveoli to collapse. Pressure helps stent open collapsed airways. PEEP can help open diseased alveoli to allow better flow of oxygen into them in order to participate in gas exchange. This is why PEEP helps improve oxygenation. However, too much PEEP can lead to overdistention of the lung causing injury^[5].

Inspiratory pressure is the pressure delivered by a ventilator with each inspired breath^[5]. On a BiPAP machine, this is called IPAP, or inspiratory positive airway pressure. This pressure helps support each breath. By adding pressure, healthcare providers reduce the amount of work the patient has to do to inhale, thus reducing the work of breathing.

Monitoring During Mechanical Ventilation

People who require ventilators are typically monitored in an intensive care unit^[4]. Various healthcare providers are involved with the use of mechanical ventilation, including doctors, nurses, and respiratory therapists.

Monitoring has to be non-invasive, reliable, and easy to use. Data security needs to be ensured, signals need to be integrated and preferably automatically processed, and monitoring systems need to be based on clinically relevant outcomes^[13].

Healthcare teams monitor gas exchange, ventilator data, and the patient’s breathing pattern. They check oxygen levels, carbon dioxide levels, and other vital signs. Providers also assess patient comfort and watch for signs of complications^[13].

Risks and Complications

Like all treatments, mechanical ventilation has the potential to cause harm if not administered appropriately^[12]. Time on a ventilator can have lasting effects on a person’s mind and body for weeks and even months after leaving the hospital. This is called post-intensive care syndrome^[15].

Post-intensive care syndrome can include physical weakness and cognitive dysfunction, sometimes called brain fog, marked by a loss of intellectual functions such as thinking, memory, and reasoning^[15]. Patients with cognitive dysfunction have trouble recalling words, performing basic math, and concentrating. These thinking problems are caused by the medications needed to sedate patients while they are on the ventilators.

There is also a high rate of PTSD (post-traumatic stress disorder) in those patients and their caregivers^[15]. Symptoms include nightmares and unwanted memories about their stay in the intensive care unit. About 35 percent have anxiety, and about 30 percent experience depression.

Complications of mechanical ventilation include ventilator-induced lung injury and ventilator-associated pneumonia, as well as problems outside the lungs such as stomach ulcers and blood clots in the veins^[6].

The longer you are on a ventilator, the longer it will take for you to recover^[15]. Healthcare providers expect people will not feel back to 100 percent for at least a week for every day they spend on a ventilator. If you spend four to five days on a ventilator, it may take four to five weeks before you are really feeling back to your normal self.

Recovery and Life After a Ventilator

However, the extent of the side effects from being on a ventilator varies from person to person, and data on exactly how patients fare long term is limited^[15]. The world of post-intensive care syndrome follow-up and evaluation is relatively new, and so there is not a great deal yet that is known about all of the issues.

Keep in mind you will need assistance for weeks to months after leaving the hospital^[15]. You may not be able to walk or perform daily functions such as showering or cooking for yourself. The year after a prolonged stay in intensive care, most patients require some degree of care and assistance. That degree of dependence varies among patients. Up to 50 percent of patients may return to work within the first year, but some may not be able to return to the jobs they had before their illness^[15].

If you are a family member of someone in the intensive care unit, there are steps you can take to help minimize the cognitive challenges your loved one may experience^[15]. It can be useful to talk about what day or date it is and what time it is—just share the information, do not quiz them. Bring photographs from home and talk about familiar people, pets, places, and past events. You also can read aloud.

Consider keeping a bedside journal so you can stay on top of what is happening when. This can help reduce stress because your loved one will not feel pressure to remember^[15]. Also, ask a nurse or therapist to show you exercises that keep the patient’s body active; this is good for the brain, too.

Ask for help from the experts: intensive care unit nurses and therapists can connect you with the resources you will need to help your loved one begin the journey to recovery once they leave the hospital^[15].