Ventilator-associated lung injury (VALI) is an acute lung injury that develops during

mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move a ...

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 Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tensio ...

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 The path of least resistance is the physical or metaphorical pathway that provides the least resistance to forward motion by a given object or entity, among a set of alternative paths. The concept is often used to describe why an object or entit ...

. Areas of the lung that are collapsed (

atelectasis Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct ...

) 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 Atelectotrauma, atelectrauma, cyclic atelectasis or repeated alveolar collapse and expansion (RACE) are medical terms for the damage caused to the lung by mechanical ventilation under certain conditions. When parts of the lung collapse at the end ...

). 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. 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, lu ...

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 (

) are the primary causes for alveolar injury during positive pressure

. 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). High flow rates are associated with

rheotrauma Rheotrauma is a medical term for the harm caused to a patient's lungs by high gas flows as delivered by mechanical ventilation. Although mechanical ventilation may prevent death of a patient from the hypoxia or hypercarbia which may be caused by ...

, high volumes with

and pressures with

barotrauma Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tens ...

. Collectively these may be converted into a single unit of

mechanical power : ''For the physics concept, see .'' Mechanical power is a medical term which is a measure of the amount of energy imparted to a patient by a mechanical ventilator. While in many cases mechanical ventilation is a life-saving or life-preserving in ...

Diagnosis

VALI does not need to be distinguished from progressive ALI/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 Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health profess ...

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 (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 Modes of mechanical ventilation are one of the most important aspects of the usage of mechanical ventilation. The mode refers to the method of inspiratory support. In general, mode selection is based on clinician familiarity and institutional pre ...

is thought to reduce ventilator-associated lung injury, especially in the context of

ARDS 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 color ...

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 colo ...

Permissive hypercapnia Permissive hypercapnia is hypercapnia (i.e. high concentration of carbon dioxide in blood) in respiratory insufficient patients in which oxygenation has become so difficult that the optimal mode of mechanical ventilation (with oxygenation in mind ...

and

hypoxaemia Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body ...

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