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Ventilator-associated lung injury (VALI) is an acute lung injury that develops during
mechanical ventilation Mechanical ventilation or assisted ventilation is the Medicine, medical term for using a ventilator, ventilator machine to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, wit ...
and is termed ventilator-induced lung injury (VILI) if it can be proven that the mechanical ventilation caused the acute lung injury. In contrast, ventilator-associated lung injury (VALI) exists if the cause cannot be proven. VALI is the appropriate term in most situations because it is virtually impossible to prove what actually caused the lung injury in the hospital.


Cause

It is generally regarded, based on animal models and human studies, that volutrauma is the most harmful aspect of mechanical ventilation. This may be regarded as the over-stretching of the airways and alveoli. During mechanical ventilation, the flow of gas into the lung will take the path of least resistance. Areas of the lung that are collapsed (
atelectasis Atelectasis is the partial collapse or closure of a lung resulting in reduced or absence in gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the Pulmonary alveolus, alveoli are deflated down to l ...
) or filled with secretions will be underinflated, while those areas that are relatively normal will be overinflated. These areas will become overdistended and injured. This may be reduced by using smaller tidal volumes. During positive pressure ventilation, atelectatic regions will inflate, however, the alveoli will be unstable and will collapse during the expiratory phase of the breath ( atelectotrauma). This repeated alveolar collapse and expansion (RACE) is thought to cause VALI. By opening the lung and keeping the lung open RACE (and VALI) is reduced.Free Full Text
Another possible ventilator-associated lung injury is known as
biotrauma Although the term has occasionally been used in other ways, in medical literature biotrauma is usually defined as a severe inflammatory response produced in the lungs of patients who breathe by means of a Mechanical ventilation, mechanical ventilat ...
. Biotrauma involves the lung suffering injury from any mediators of the inflammatory response or from bacteremia. Finally
oxygen toxicity Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lung ...
contributes to ventilator-associated lung injury through several mechanisms including
oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...
. Possible reasons for predisposition to VALI include: * An injured lung may be at risk for further injury * Cyclic atelectasis is particularly common in an injured lung


Pathogenesis

Overdistension of alveoli and cyclic atelectasis ( atelectotrauma) are the primary causes for alveolar injury during positive pressure
mechanical ventilation Mechanical ventilation or assisted ventilation is the Medicine, medical term for using a ventilator, ventilator machine to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, wit ...
. Severe injury to alveoli causes swelling of the tissues (edema) in the lungs, bleeding of the alveoli, loss of surfactant (decrease in
lung compliance Lung compliance, or pulmonary compliance, is a measure of the lung's ability to stretch and expand (distensibility of elastic tissue). In clinical practice it is separated into two different measurements, static compliance and dynamic compliance. ...
) and complete alveoli collapse (
biotrauma Although the term has occasionally been used in other ways, in medical literature biotrauma is usually defined as a severe inflammatory response produced in the lungs of patients who breathe by means of a Mechanical ventilation, mechanical ventilat ...
). High flow rates are associated with rheotrauma, high volumes with volutrauma and pressures with
barotrauma Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in ...
.


Diagnosis

VALI does not need to be distinguished from progressive
ALI Ali ibn Abi Talib (; ) was the fourth Rashidun caliph who ruled from until his assassination in 661, as well as the first Shia Imam. He was the cousin and son-in-law of the Islamic prophet Muhammad. Born to Abu Talib ibn Abd al-Muttalib an ...
/ARDS because management is the same in both. Additionally, definitive diagnosis of VALI may not be possible because of lack of sign or symptoms.


Prevention


Preventing alveolar overdistension

Alveolar overdistension is mitigated by using small tidal volumes, maintaining a low plateau pressure, and most effectively by using volume-limited ventilation. A 2018 systematic review by The Cochrane Collaboration provided evidence that low tidal volume ventilation reduced post operative pneumonia and reduced the requirement for both invasive and non invasive ventilation after surgery


Preventing cyclic atelectasis (atelectotrauma)

Applied
positive end-expiratory pressure Positive end-expiratory pressure (PEEP) is the pressure in the lungs ( alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration. The two types of PEEP are extrinsic PEEP (PEEP applied by ...
(PEEP) is the principal method used to keep the alveoli open and lessen cyclic atelectasis.


Open lung ventilation

Open lung ventilation is a ventilatory strategy that combines small tidal volumes (to lessen alveolar overdistension) and an applied PEEP above the low inflection point on the pressure-volume curve (to lessen cyclic atelectasis). High frequency ventilation is thought to reduce ventilator-associated lung injury, especially in the context of
ARDS Ards (or ARDS, ARDs) may refer to: Medical * ARDS, Acute respiratory distress syndrome * ARDs, age-related diseases Places * Ards Peninsula, Northern Ireland ** Ards (territory), several historical territorial divisions on the Ards Peninsula ...
and
acute lung injury Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin co ...
. Permissive hypercapnia and hypoxaemia allow the patient to be ventilated at less aggressive settings and can, therefore, mitigate all forms of ventilator-associated lung injury


Epidemiology

VALI is most common in people receiving mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ALI/ARDS). 24 percent of people mechanically ventilated will develop VALI for reasons other than ALI or ARDS. The incidence is probably higher among people who already have ALI/ARDS, but estimates vary widely. The variable estimates reflect the difficulty in distinguishing VALI from progressive ALI/ARDS.


References


External links


Ventilators and COVID-19: What You Need to Know
Yale Medicine {{Mechanical ventilation Respiratory therapy Pulmonology Emergency medicine Medical equipment Intensive care medicine Lung disorders