What is Ventilator-Induced Lung Injury (VILI)?
Ventilator-Induced Lung Injury, or VILI, is a type of lung injury caused or worsened by a machine called a ventilator, which is used during treatment. This injury can occur during both invasive (through surgery) and non-invasive (through masks or other less invasive methods) ventilation. It can play a significant role in causing illness or even death in critically ill patients. While mechanical ventilation can harm all lungs, those already with disease can suffer more severe injury due to greater localised stresses. The term VILI is sometimes used interchangeably with Ventilator-Associated Lung Injury (VALI), particularly when it’s suspected that the lung injury is due to ventilation, but there’s no strong evidence to confirm this.
The idea of lung injury caused by mechanical ventilation has been around since 1744. That year, John Fothergill suggested that mouth-to-mouth respiration could be a safer method of resuscitation compared to machine bellows, which could damage the lungs with an unregulated push of air. This was further supported during the 1952 polio epidemic when researchers recorded physical lung damage caused by mechanical ventilation.
In 1967, scientists coined the term “respirator lung” to describe lung damage seen in autopsies of patients who had been on mechanical ventilators. These lungs showed significant signs of disease, such as widespread inflammation in the alveoli (small air sacs in the lungs), and formation of a substance called hyaline membrane. Further evidence of VILI came from a significant trial concerning a lung condition called Acute Respiratory Distress Syndrome (ARDS). In this trial, ventilators that delivered smaller volumes of air were found to be less damaging than ones that delivered larger air volumes.
What Causes Ventilator-Induced Lung Injury (VILI)?
Damage to the lungs can occur when a patient is being helped to breathe by a ventilator. This is referred to as “ventilator-induced lung injury” and can happen in several ways. It could be from overinflating the air sacs in the lungs, changes in pressure causing injury, lungs partially or fully collapsing, or inflammation due to the body’s response to these injuries.
Other factors that might contribute to lung injury from a ventilator include how it affects the heart, how deflation impacts the injury, and how much effort the patient is putting into breathing. Researchers are also looking into how individual lung mechanics, how often the air sacs in the lungs experience stress, and how much stress the tiny blood vessels in our lungs can handle before they fail.
In a study of 332 patients who didn’t have a lung disease known as ARDS when they started to be helped by a ventilator, larger breath sizes, blood transfusions, acidemia, and a history of a certain type of lung disease called restrictive lung disease were found to be linked to a higher risk of ventilator-induced lung injury. Despite having a connection, certain other factors like rate of breath, blood pressure in the lungs, and body temperature are often considered only secondary influences.
Using too much pressure for a breath can cause the lung to over-inflate, leading to damage. If the breaths are too big and the air pressure in the lungs at the end of an exhaled breath (known as PEEP) is set too low, it can cause the lungs to collapse and become inflamed. On the other hand, if the PEEP is set too high, it can cause the air sacs in the lungs to over-inflate, while if it’s too low, the air sacs may not remain open. This balance is crucial in helping patients breathe.
The mechanical opening and closing of certain under-inflated air sacs in the lungs during the breathing cycle can cause damage to nearby air sacs and airways. This process is referred to as atelectotrauma. To prevent this from happening, an optimal PEEP is necessary.
“Biotrauma” refers to the inflammation caused by over-inflating the air sacs and atelectotrauma. As a part of the body’s response, some cells release inflammatory mediators that can potentially trigger harmful effects locally within the lungs and throughout the body, causing multiple organ failure.
Blood flow in the lungs is significantly affected by the breathing cycle. During the breathing in phase, the blood flow is considerably reduced because the expanding lungs compress the right side of the heart. During the breathing out phase, the blood flow is increased. Constant changes in blood flow from high to non-existent and back to high can damage inner lining of the blood vessels in the lungs. This results in increased permeability of capillaries causing fluid and protein leakage leading to fluid build-up in the lungs.
According to a study conducted in 2018, a sudden release of air after a period of high-pressure breathing can cause injury to the lungs. This can happen if the patient is abruptly disconnected from the ventilator. This effect is similar to what happens when a balloon is suddenly deflated. A sudden disconnection might result in back pressure causing increased pressure in the left side of the heart and fluid build-up in the lungs. Also, high blood flow in the lungs following sudden deflation can cause high pressure in the capillaries, leading to injury.
Patients with already damaged lungs are more prone to injury through spontaneous efforts of breathing. The harm comes from increased negative pressure in the lungs during spontaneous efforts, causing large tidal volumes leading to volutrauma, uneven distribution of air in the lungs, increased pressure across the blood vessels predisposing to fluid build-up in lungs and discrepancies in the rhythm between the patient and the ventilator.
Lastly, “driving pressure” in the context of a ventilator refers to the difference in towards the end of breathing in (plateau pressure), and the air pressure at the end of an exhaled breath (PEEP). It’s been observed that a higher driving pressure in the first week of mechanical ventilation can be associated with a higher mortality rate. As a result, many experts have suggested a ventilatory strategy tailored around maintaining optimal driving pressure to prevent lung injury in ARDS patients on a ventilator.
Risk Factors and Frequency for Ventilator-Induced Lung Injury (VILI)
Right now, there isn’t any specific data on how often ventilator-related lung injuries occur. However, it’s believed that these types of injuries are more common in patients with a severe lung condition called ARDS (Acute Respiratory Distress Syndrome). When someone’s lungs are already damaged or injured, using a ventilator can sometimes cause more harm, especially if certain protective measures aren’t in place. There was a study that looked at this: out of 332 patients who needed a ventilator but didn’t have an acute lung injury to start with, 24% of them ended up with a ventilator-induced lung injury within the first five days.
Signs and Symptoms of Ventilator-Induced Lung Injury (VILI)
Ventilator-induced lung injury is diagnosed in a hospital setting, and it involves a careful evaluation process and the elimination of other potential causes. Patients on mechanical ventilators who develop this condition usually experience a worsening lack of oxygen in their blood, marked by low levels of oxygen and a dip in saturation. A chest X-ray will show widespread infiltrates or substances within the lungs without signs of heart enlargement. In addition, a CT scan of the chest might show uneven consolidation and lung collapse, along with specific areas indicating excessive air in the alveoli, which are tiny air sacks in the lungs.
It’s important for doctors to rule out other related conditions. New lung infections and fluid accumulation in the lungs are two common conditions that need to be initially set aside. Other checks that the doctor might do include listening for signs of bronchospasm, or narrowing of the airways, or the distinctive sounds of crackles in the lungs. They may also check for signs of pneumothorax (collapsed lung), pleural effusion (excess fluid in the chest), swelling in the limbs, fluid buildup in the abdomen, and abdominal hypertension. They may need to investigate the patient’s history for drug allergies or blood product transfusion. Furthermore, the settings on the ventilator need to be cross-checked to look for any settings that may be contributing to the lung injury.
Testing for Ventilator-Induced Lung Injury (VILI)
If a patient is having a low oxygen level while on a ventilator, the doctor needs to find out what might be causing it. This could be due to a range of reasons like choking, infection in the lungs, suffocation, heart problems, blockages in the blood vessels from fat, air, or fluid, a punctured lung, fluid in the chest cavity or a swollen abdomen. To determine the cause, the doctor may conduct a series of tests including a physical examination, X-rays and ultrasound scans of the chest and abdomen, heart monitoring, and echo testing.
For patients with lung injury induced by ventilator usage, the X-ray image could appear quite similar to patients with a severe form of lung disease called Acute Respiratory Distress Syndrome (ARDS). The X-ray would reveal widespread shadows in both lungs without signs of an enlarged heart. A CT scan might show a patchy pattern of solidification and collapse of the lung area coupled with localized areas of over-inflation.
The investigation might also encompass laboratory tests for enzymes linked to the heart and digestive system, along with cultures to identify any present infection. Additional scanning methods evaluating blood flow in the lower leg and lung may also be required in some instances. The use of a device to inspect the airways and retrieving a small tissue sample is rarely required.
A 2016 research proposed the idea that the origins of lung injury from ventilator usage could be translated into one measurement named ‘mechanical power.’ This measurement can be figured out using data such as the volume of air moved into the lungs per breath, breath flow, applied pressure by the ventilator, and the rate of respiration. They suggested the possibility of an easy-to-use software built into the ventilator to calculate this at the patient’s bedside.
In a 2019 review, it was mentioned that by measuring and interpreting changes in ‘dynamic elastance’ (a measure of the lung’s ability to stretch and recoil) could provide insights into the severity and type of lung injury. It could also be used to estimate the contribution of each of two key mechanisms of ventilator-related lung injury, known as ‘volutrauma’ and ‘atelectrauma’. These terms refer to damage caused by overstretching the lung tissue and repetitive collapse and reopening of lung regions, respectively.
Treatment Options for Ventilator-Induced Lung Injury (VILI)
Protecting a patient’s lungs from injuries caused by ventilation (artificial support for breathing) is a high priority. Harm can occur if the lungs get too expanded, causing damage to the small air sacs (alveoli). This distortion is referred to as volutrauma and biotrauma, and can also lead to other lung injuries, like atelectrauma.
In patients with Acute Respiratory Distress Syndrome (ARDS), a condition where fluid builds up in the lungs which can lead to life-threatening organ failure, the concept of “baby lung” is often considered. This refers to the small areas in the lung that remain functional and require protection during mechanical ventilation. These sections, roughly the size of a baby’s lung, are easily damaged if they’re overstretched. It’s also crucial to mention that these functional areas are not static. They tend to shift around when the patient is in different positions.
Studies have shown that in ARDS patients, using a lower amount of air in each breath (tidal volume) during ventilation, based on the predicted body weight, can prevent overstretching of the functional areas and reduce mortality. This approach has also proven beneficial in patients without ARDS.
Maintaining a specific level of pressure at the end of exhalation (positive end-expiratory pressure – PEEP) during ventilation can help avoid lung collapse and improve oxygen absorption. However, the appropriate level of PEEP needs to be tailored for each patient. Too much PEEP can overinflate the lungs and cause damage, while too low PEEP might not be enough to keep the air sacs open.
Using specific techniques to open up the lungs, called recruitment maneuvers, theoretically reduce injury linked to ventilation. Still, they could have side-effects such as compromising blood flow or causing lung rupture, and their effectiveness in clinical practice is still under investigation.
The use of medicine to block nerve impulses (neuromuscular agents) has been proven to lower the levels of inflammation-causing compounds called cytokines. These reductions in cytokines can lead to fewer instances of damage to the lungs and other organs, and ultimately, lower mortality rates.
Placing patients with severe ARDS in a prone position (i.e., laying on their stomach) has negated some effects of lung injury and significantly reduced the mortality rate.
Partial or total support from external machines like ECMO/ECCO2-R (Extracorporeal membrane oxygenation/Extracorporeal CO2 removal) theoretically promises to prevent injuries linked to ventilation. Still, their regular use lacks evidence of clinical benefits.
Finally, strategies to reduce inflammation and the use of specific cells called mesenchymal stem cells are being tested in animal studies to limit damage from ventilation. However, their practical use in humans is yet to be proven.
What else can Ventilator-Induced Lung Injury (VILI) be?
When someone’s lungs endure damage due to being on a ventilator, it is typically diagnosed by eliminating probable causes for breathing trouble while on a ventilator, and commonly known causes of Acute Respiratory Distress Syndrome (ARDS). The following conditions that could result in breathing issues need to be considered:
- New-onset pneumonia
- Cardiogenic pulmonary edema (fluid accumulation in lungs due to heart problems)
- Endobronchial intubation (a tube incorrectly inserted in the bronchus)
- Lung collapse
- Pneumothorax (collapsed lung)
- Pulmonary embolism (blockage in the lung’s blood vessels)
- Auto PEEPing (build-up of pressure in the lungs)
- Pleural effusion (fluid around the lungs)
- Abdominal distension (swelling of the abdomen)
Other conditions that need to be ruled out include:
- Sepsis (a severe reaction to infection)
- Aspiration (inhaling foreign material)
- Infectious pneumonia
- Severe trauma or fractures
- Pulmonary contusion (bruised lungs)
- Burns
- Injuries from inhalation (like smoke, gases, or near drowning)
- Transfusion-associated lung injury (lung damage from blood transfusion)
ARDS can also occur after bypass surgery of the heart and lungs, following major operations, in cases of pancreatitis (inflammation of the pancreas), and in patients who underwent a stem cell transplant.
What to expect with Ventilator-Induced Lung Injury (VILI)
Patients with ventilator-induced lung injury may face the possibility of worsened health conditions and even increased fatality. One of the main causes of mortality could be multiorgan failure, which means a failure of two or more systems in the body, specifically due to biotrauma – a form of injury caused by biological agents. It has also been proven that larger than normal volumes of air moved in and out during respiration, also referred to as higher tidal volumes, can increase the risk of mortality. There is a theoretical chance for long-term respiratory issues, repeated lung infections, and development of the condition referred to as cor-pulmonale – a disease of the heart caused by long-term high blood pressure in the lungs, especially among the survivors with severely damaged lungs.
Possible Complications When Diagnosed with Ventilator-Induced Lung Injury (VILI)
Injury from a ventilator can lead to more severe health problems and can even result in death. Some complications include fluid build-up in the lungs, damage from pressure or puncture (known as barotrauma), worsening low oxygen levels, and the extension of the need for mechanical ventilation. While high volumes of air (or tidal volumes) are shown to increase death rates, multiple organ failure resulting from injury at the cellular level (biotrauma) is a main contributing factor.
In severe cases where extensive inflammation and injury lead to fibrosis (or scarring), this can potentially result in long-term breathing problems and heart-lung conditions for those who survive. Recurring infections are also more common in scarred lung tissue.
Common Complications:
- Fluid build-up in the lungs (pulmonary edema)
- Pressure-induced damage to the lungs (barotrauma)
- Worsening low oxygen levels (hypoxemia)
- Extended need for mechanical ventilation
- Multiple organ failure (biotrauma)
- Scarring leading to long-term respiratory issues
- Heart-lung conditions (cor-pulmonale)
- Recurring infections in scarred lung tissue
Preventing Ventilator-Induced Lung Injury (VILI)
The idea that lung damage can be caused by a ventilator, also known as a breathing machine, is fairly new in the world of medicine. However, doctors around the world are becoming more aware of the harm it can cause and are finding ways to prevent it. The risk of lung damage caused by ventilator use can be discussed by doctors with patients and their families. Please rest assured that at all times, the best possible steps will be taken to prevent any kind of harm to the lungs.
