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Acute Lung Injury — Affecting Many Lives
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     Acute lung injury is the clinical syndrome of rapid-onset bilateral pulmonary infiltrates and hypoxemia of noncardiac origin. When the hypoxemia is severe, the condition is termed the acute respiratory distress syndrome (ARDS).1 As archetypal examples of critical illness requiring intensive care, advanced life support, and considerable health care resources, acute lung injury and ARDS have attracted substantial research interest. An extensive body of laboratory and clinical investigation has been amassed since the original description almost 40 years ago, cataloguing our advancing knowledge of the cause, pathophysiology, and management of these complex and often lethal syndromes. However, estimates of their incidence have varied widely,2,3,4,5 and the true magnitude of these syndromes — and the implications for health care delivery — have been unclear.

    In this issue of the Journal, Rubenfeld and colleagues report the results of the first large prospective study of the incidence of and mortality associated with acute lung injury and ARDS in the United States.6 On the basis of a one-year prospective evaluation of all cases of acute lung injury and ARDS managed in all the adult intensive care units (ICUs) of King County, Washington, the authors generated national estimates of 86 cases per 100,000, or almost 200,000 cases per year, with an in-hospital mortality of 38.5 percent. They exploited the natural and political boundaries around King County to minimize the effects of patient migration and adjusted their data for demographic differences between King County and the U.S. population. They also expended considerable effort to standardize clinical and radiographic criteria for screening and case ascertainment and carefully monitored the quality of their data-collection process. The incidence of these two syndromes as reported by Rubenfeld et al. is considerably higher than previously thought and much higher than that reported from other countries.2,4,5 They also found that acute lung injury and ARDS occur predominantly in elderly patients hospitalized with severe infection, especially pneumonia, and that more than half of the cases occur in community hospitals.

    Although methodologic differences may explain in part why earlier studies from other countries reported lower incidence rates, it seems probable that true variation exists. Acute lung injury and ARDS occur predominantly as consequences of intensive care treatment of patients who have sustained a severe insult, such as severe infection. Consequently, differences either in the frequency and severity of the precipitating events or in the provision of intensive care services could affect the measured incidence. Susceptibility to infection, by far the most common precipitating event, varies among patients but should not vary widely among populations in Western developed nations. Still, the United States has many more ICU beds per person than other countries.7 Thus, an important component of the discrepancy may be a higher treated incidence. Notably, there is a similar pattern of international variation in the treated incidence of severe sepsis, another condition typically managed in the ICU and closely related to acute lung injury and ARDS.8

    This line of argument leads one to speculate on whether the United States overuses — or other countries underuse — intensive care and on how we should define and measure the appropriate use of ICU resources. There are no simple answers to these questions, which require an understanding not only of overall outcome rates as presented here, but also of whether outcomes are improved with intensive care. A potential gain in short-term survival must be weighed against the likelihood of a potentially difficult and protracted ICU course and long-term expectations for survival and quality of life. In this regard, better predictors of both short-term and long-term outcomes for patients with acute lung injury and ARDS would be helpful for clinicians and families as they make difficult decisions about the use of intensive care and life-support measures.

    In recent years, a number of studies have provided guidance on the optimal management of acute lung injury and ARDS, such as the benefits of low-tidal-volume ventilation.9 The large number of cases of ARDS and acute lung injury, their wide distribution across ICUs, in both large and small hospitals, and the high associated mortality all reinforce the need to ensure that evidence regarding best practice is disseminated and applied across broad clinical settings. One important obstacle is case identification. If clinicians do not label a patient as having acute lung injury or ARDS, then they are unlikely to provide interventions shown to improve outcomes.

    The criteria from the American–European Consensus Conference on ARDS were developed for use in clinical trials and are subject to ongoing debate regarding their precision, reliability, and validity. Variations in clinician knowledge, attitudes, and practice affect interpretation of the chest radiograph, suspicion of left atrial hypertension, and the timing and frequency of arterial blood gas measurement. The standardized screening by trained staff in the current study circumvented much of this variation but may be burdensome in daily practice. Practical versions of this strategy or other new approaches to screening need to be developed and incorporated into any efforts designed to promote best practice. In the meantime, all clinicians caring for critically ill patients at the bedside must remain vigilant about identifying patients with these syndromes.

    The main outcome reported by Rubenfeld and colleagues was in-hospital mortality rates. However, it is important to note that many surviving patients were unable to return home at hospital discharge. A number of studies have shown that survivors of acute lung injury and ARDS have generalized weakness, pulmonary dysfunction, cognitive disability, affective disorders, and reduced quality of life after an episode of critical illness.10,11,12,13 Therefore, attention to the postdischarge phase of care is essential if we clinicians are to achieve the best possible outcomes. Yet, there is no standardized approach to the care of patients who have survived these serious syndromes after they leave the hospital. Many relevant lessons can be learned from care strategies that have been developed for survivors of other acute-onset conditions, such as traumatic brain injury and stroke. Emerging paradigms for the care of frail elderly patients, with a focus on managing the transitions from hospital to rehabilitative services to home, may also be instructive.14,15

    As a start, we recommend educational programs for the patient, family, and primary care providers regarding the physical and neuropsychological sequelae of critical illness, acute lung injury, and ARDS. Patient and family education has already been shown to aid recovery in a general ICU population in the United Kingdom.16 Survivors of acute lung injury and ARDS may also benefit from systematic screening and follow-up to facilitate appropriate referrals to expert services for neurocognitive rehabilitation, treatment of depression or post-traumatic stress disorder, physical therapy, and social services. Family members and loved ones need to be included in follow-up care. It has long been recognized that the spouses of patients with stroke and traumatic brain injury have substantial difficulties with depression and post-traumatic stress disorder after these traumatic events, and recent data highlight the neuropsychological burden that critical illness has on family members of patients in ICUs.17 Such strategies may be expensive, and therefore formal evaluation of the costs and benefits of alternative approaches is warranted.

    In summary, Rubenfeld and colleagues have convincingly demonstrated that acute lung injury and ARDS represent a significant public health issue. These syndromes are very common, occurring predominantly in the elderly and often far from a large teaching hospital. Presumably because of prior limitations in our understanding of the epidemiology of acute lung injury and ARDS, broad, system-wide planning for these syndromes does not exist, and care is likely to be heterogeneous and suboptimal. With the looming expansion of the elderly population of the United States, the incidence of acute lung injury and ARDS will grow rapidly, exacerbating the consequences of suboptimal care. As evidence mounts regarding the best practice for the care of patients with these conditions, attention to methods that promote broad dissemination of accurate and consistent criteria for diagnosis and contemporary evidence-based treatment becomes essential. Managing the transition from hospital to home is also crucial, and optimal strategies for rehabilitation and recovery will require a multidisciplinary effort.

    Source Information

    From the Department of Medicine and Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto (M.S.H.); and the Clinical Research, Investigation, and Systems Modeling of Acute Illness Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh (D.C.A.).

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