Lung protective ventilationBMJ 2012; 344 doi: https://doi.org/10.1136/bmj.e2491 (Published 05 April 2012) Cite this as: BMJ 2012;344:e2491
- Luigi Camporota, consultant intensivist1,
- Nicholas Hart, consultant in respiratory and critical care medicine2
- 1Department of Critical Care, Guy’s and St Thomas’ NHS Foundation Trust, King’s Health Partners, London, UK
- 2Lane Fox Respiratory Unit, St Thomas’ Hospital, Guy’s and St Thomas’ NHS Foundation Trust, King’s Health Partners, London SE1 7EH, UK
Lung protective ventilation—the provision of mechanical ventilation with static inspiratory pressures (plateau pressure) of less than 30 cm of water and tidal volumes normalised to predicted body weight—is the only treatment that has consistently been shown to reduce mortality in patients with acute lung injury. In a linked study (doi:10.1136/bmj.e2124), Needham and colleagues’ present the data from a multicentre prospective North American observational cohort study and report that patients with acute lung injury are at high risk of both short and long term mortality.1 Acute lung injury is a syndrome that is characterised by diffuse alveolar damage and inflammation, increased pulmonary vascular permeability, and a loss of aerated alveolar tissue, all of which have a catastrophic effect on gas exchange. Although mortality attributable to acute lung injury has fallen over the past 40 years, accumulating evidence suggests that a growing number of patients who survive a stay in intensive care have long term disability and high mortality rates years after discharge.2
Because predicted body weight is calculated from height and sex, both of which correlate with lung size in normal people, the delivery of tidal volumes that are based on predicted body weight enables tidal volumes to be proportional to the patient’s estimated lung size. Indeed, the delivery of tidal volumes that are in excess of the available gas lung volume places a mechanical stress on the lungs that worsens acute lung injury and causes ventilator induced lung injury.3 Meta-analyses have shown that using lung protective ventilation reduces the relative risk of 28 day mortality and hospital mortality by about 25%.4
In the current study, Needham and colleagues also show that close adherence to the use of lung protective ventilation was associated with a substantial long term survival benefit—an absolute reduction in mortality at two years of between 4% and 8%, depending on the degree of adherence. Moreover, for each 1 mL/kg increase in tidal volume over that estimated using predicted body weight, there was an 18% relative increase in the risk of mortality at two years.1
What might underpin this association between lung protective ventilation and improved long term mortality? Although the initial insult that causes acute lung injury results in lung damage and acute respiratory failure, respiratory function seems to recover over time, with return to near normal lung function by five years.5 However, survivors of acute lung injury often have ongoing impairment of exercise capacity, with an associated reduction in health related quality of life.5 Attention has recently been focused on the mechanism and effects of critical illness on skeletal muscle wasting, specifically in terms of muscle mass regulation and its association with weakness and physical function.6 It is possible that optimal management of acute lung injury leads to more rapid resolution of lung injury and the inflammatory response, which in turn results in reduced loss of skeletal muscle and better preservation of exercise capacity. This might explain how adherence to a strategy of lung protective ventilation provides long term benefits in physical function. Indeed, lung protective ventilation has been shown previously to reduce local and systemic inflammation and to decrease extrapulmonary organ dysfunction.7
Needham and colleagues’ study highlights the difficulty of translating the findings of clinical trials into clinical practice.1 Although trials of lung protective ventilation have shown that it improves short term and long term survival in patients with acute lung injury, in the current study of a group of clinical academic centres, only 41% of all eligible ventilator settings were adherent with the terms of lung protective ventilation, and 37% of patients did not receive the treatment at all.1 Underuse of lung protective ventilation is common, usually as a result of difficulty in changing the behaviour of clinicians and organisational factors, such as staffing models and unit protocols.8 Despite these limitations, greater adherence to low tidal volumes, or even ultra low tidal volumes in association with extracorporeal oxygenation techniques, could enhance longer term outcomes for patients with acute lung injury who are ventilated in intensive care units. Clinicians need simple tools that can accurately calculate tidal volume for individual patients at the bedside, so that lung stretch during ventilation can be minimised and long term benefits in physical function can be maximised. Furthermore, these efforts need to be underpinned by the consistent and widespread delivery of lung protective ventilation in intensive care practice.
It should also be recognised that the chronic sequelae of acute lung injury place a substantial burden on patients, caregivers, and limited healthcare resources.9 The management of acute lung injury should no longer be the exclusive concern of the intensive care physician but should involve multiple healthcare professionals, including respiratory and rehabilitation specialists, to provide long term management after the acute critical illness has resolved.
Cite this as: BMJ 2012;344:e2491
Competing interests: Both authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Commissioned; not externally peer reviewed.