Ventilator-induced lung injury (VILI) is damage to the lungs caused by mechanical ventilation that exerts stress on the lung alveoli. Mechanical ventilation, although necessary to preserve life, exposes the lungs to high pressures or high volumes and repeated opening and closing of alveoli, which can provoke an inflammatory response.1 Inflammatory response to trauma in the lungs can have systemic effects that can contribute to multiple organ failure and death. Exacerbating factors include ventilator volume and pressure, anesthesia use, length of time the patient is on the ventilator, prior lung injury (such as disease or trauma), and the pressure of the air left in the lungs after expiration.
VILI occurs in three phases:
1) alveolar-capillary permeability causing edema and hemorrhage;
2) cell proliferation causing narrowing and/or obliteration of the airways; and
3) inflammation and fibrosis causing low lung compliance, low tidal volume and CO2 retention.
VILI closely resembles acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). International studies report that 4.5-7 percent of all patients admitted to the ICU have acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) and the incidence increases to 12 percent of patients that are in the ICU for more than 24 hours.2,3 Twenty-three percent of trauma patients who received multiple transfusions (>10 units/24 hours) developed ARDS.4 The mortality rate associated with ALI/ARDS is 40-50 percent,5 with the predominant cause of death being multiple organ failure. Survivors of ARDS are usually young trauma patients who can regain most of their lung function 6 to 12 months after ICU release.
Ventilator-induced lung injury in the ED or ICU can so severely damage patients’ lungs that even if they recover from other traumatic injuries, they may not be able to be removed from the ventilator in a timely fashion and/or may die from VILI-associated causes. Extended periods of time on the ventilator (21-28 days) may also be associated with respiratory muscle atrophy.
Currently accepted protocols for mechanical ventilation include lung protective strategies using limited pressure and limited volume, which have been shown to significantly decrease mortality rates in ARDS patients from 40 percent to 31 percent.5 However, death is still a significant possibility.
Research is being conducted to examine the effects of positive end-expiratory pressure (PEEP; the pressure of air left in the airway after the expiratory cycle), non-invasive ventilation (using a face mask rather than intubation),6 closed-loop ventilation devices that adjust the ventilation strategy automatically using cues from the individual patient,7 air volume control, high frequency ventilation, body positioning (lying face down vs. face up),8 fluid management/restriction, surfactant replacement, glucocorticoids and optimized metabolic rate through nutrition.
Research in this area is extremely challenging due to the variables presented by patients in the ICU. Disease state, age, type of trauma, genetic variability, differences between areas of the lungs within patients, and other existing conditions mean that very large numbers of patients are required to discern statistically significant findings.
To successfully research VILI, it will be necessary to fund and promote national collaborative trials capable of selecting and enrolling enough patients to assess efficacy. Clarification, standardization, optimization and possibly individual customization of protocols to diminish VILI should all be integrated to support cohesive evidence-based changes to clinical practice.
1Dreyfuss, D., and Saumon, G. (1998) From ventilator-induced lung injury to multiple organ dysfunction? Intensive Care Med 24, 102-104
2Hecker, M., Walmrath, H., Seeger, W., and Mayer, K. (2008) Clinical aspects of acute lung insufficiency (ALI/TRALI). Transfus. Med. Hemother. 35, 80-88
3Esteban, A., Anzueto, A., Frutos, F., Alia, I., Brochard, L., Stewart, T.E., Benito, S., Epstein, S.K., Apezteguia, C., Nightingale, P., Arroliga, A.C., and Tobin, M.J. (2002) Characteristics and outcomes in adult patients receiving mechanical ventilation: a 28-day international study. JAMA 287, 345-355
4Chaiwat, O., Lang, J.D., Vavilala, M.S., Wang, J., MacKenzie, E.J., Jurkovich, G.J., and Rivara, F.P. (2009) Early packed red blood cell transfusion and acute respiratory distress syndrome after trauma. Anesthesiology 110, 351-360
5The Acute Respiratory Distress Syndrome Network. (2000) Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. . N Engl J Med 342, 1301-1308
6Barreiro, T.J., and Gemmel, D.J. (2007) Noninvasive ventilation. Crit Care Clin 23, 201-222
7Wysocki, M., and Brunner, J.X. (2007) Closed-loop ventilation: an emerging standard of care?
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8Mentzelopoulos, S.D., Roussos, C., and Zakynthinos, S.G. (2005) Prone position reduces lung stress and strain in severe acute respiratory distress syndrome. Eur Respir J 25, 534-544