Acute Lung Injury and ARDS
June 30, 2002 4 minutes read
Acute Lung Injury and ARDS
Abstract & Commentary
Synopsis: Although the survival rate among patients 70 or older was high, these patients were twice as likely to die of acute lung injury compared with their younger counterparts, even after adjustment for covariates.
Source: Ely EW, et al. Ann Intern Med. 2002;136:25-36.
More than half of all days spent in an intensive care unit (ICU) are incurred by patients older than 65, and the number of days per year spent in the ICU is 7-fold higher for persons older than 75. The population of older persons and their respective proportion of health care expenditures are expected to double by 2030. However, previous reports of older patients with respiratory failure from various causes have indicated that recovery and overall prognosis in this age group do not justify using age alone to determine treatment decisions.
The incidence of acute respiratory failure requiring mechanical ventilation increases 10-fold from the ages of 55-85, therefore, health professionals need to understand the effect of age on outcomes of acute lung injury and the acute respiratory distress syndrome (ARDS) to guide their treatment decisions and prognostic discussions.
Ely and associates studied 902 mechanically ventilated patients who participated in the National Heart, Lung, and Blood Institute multicenter trials of the ARDS Network between 18 March 1996 and 28 May 1999. Patients were enrolled from 24 hospitals associated with 10 US medical centers. Patients were eligible if they required mechanical ventilation for acute lung injury, had a PO2/FIO2 ratio of 300 or less, bilateral pulmonary infiltrates consistent with pulmonary edema, and no clinical evidence of left atrial hypertension. If measured, the pulmonary capillary wedge pressure was required to be 18 mm Hg or less.
To determine the rate of recovery of older compared with younger patients, the earliest time at which patients had successfully passed 4 clearly defined recovery landmarks was recorded: 1) the daily weaning screen, 2) the 2-hour spontaneous breathing trial, 3) the date on which the patient began a period of unassisted breathing that lasted 48 hours or more, and 4) discharge from the ICU alive with no mechanical ventilation.
Baseline severity of illness was recorded at enrollment by using the Acute Physiology, Age, and Chronic Health Evaluation III (APACHE III) score. During analysis, a modified APACHE III score that excluded age was used so that age would remain an independent factor of outcome. Outcomes included duration of mechanical ventilation, total length of stay in the ICU, and survival at day 28 and 180.
Median duration of mechanical ventilation was 19 days (7-28 days) for patients 70 or older (n = 173) compared with 10 days (5-26 days) for patients younger than 70 (n = 729; P < 0.001). The duration of ICU stay was 21 days for the older group and 16 days for the younger group (P = 0.004). Survival rates decreased across increasing decades of age (P < 0.001): patients younger than 70 had a greater 28-day survival rate than patients 70 or older (74.6% vs 50.3%; P < 0.001). Older patients did not differ from younger patients with respect to achieving spontaneous breathing trials, but older patients required 1 more day than younger patients to achieve unassisted breathing and 3 more days to leave the ICU (P = 0.005). Of note, the reintubation rate for older patients was more than twice that for younger patients. In a multivariable Cox proportional hazards analysis, age of 70 or older was a strong predictor of in-hospital death (P < 0.001).
Ely et al concluded that patients 70 or older had 28-day and 180-day mortality rates that were nearly twice those of younger patients. Even after adjustment for covariates, age was a strong predictor of mortality. In fact, older persons had a hazard ratio of 2.5 for in-hospital death, and varying the age cut-off by using 65 or 80 years of age did not alter the significance of these results.
Comment by David Ost, MD, & Ali Mojaverian, MD
Survival has improved for patients with ARDS in recent years, and mortality is currently estimated at approximately 35-40%. One study of 918 patients with ARDS at a single institution between 1983 and 1993 found that the mortality from sepsis-related ARDS declined from 67% in 1990 to 40% in 1993; improvements in outcome were most pronounced for patients younger than 60.1
Studies of the natural history of ARDS and the efficacy of therapeutic interventions are complicated by the fact that respiratory failure is unusual as a direct cause of death. In one study of 47 patients, death during the first 3 days usually resulted from the underlying cause of ARDS, not respiratory failure itself.2 Later, nosocomial infections and sepsis accounted for most deaths. The initial Murray Lung Score, designed to describe the severity of lung damage based on hypoxemia, compliance, radiographic appearance, and required positive end expiratory pressure, is a weak predictor of outcome, whereas failure to improve clinically over the first several days more accurately predicts a complicated course and mortality.3
This study emphasizes not only that older patients do worse, but also gives the details of what leads to their worse outcome. In particular, although they reach spontaneous breathing equally quickly compared to younger patients, they fail to come off the ventilator as quickly, require longer ICU stays, and are reintubated more often. This is consistent with prior observations that ARDS mortality is frequently not attributable to respiratory failure, but rather to its complications. Awareness of these complications may lead to earlier diagnosis and improved outcomes.
Dr. Ost, Assistant Professor of Medicine, NYU School of Medicine, Director of Interventional Pulmonology, Division of Pulmonary and Critical Care Medicine, Northshore University Hospital, Manhasset, NY, is Associate Editor of Internal Medicine Alert. Dr. Mojaverian is a Fellow in Pulmonary/Critical Care Medicine, North Shore University Hospital, Manhasset, NY.
References
1. Milberg JA, et al. JAMA. 1995;273:306-309.
2. Montgomery AB, et al. Am Rev Respir Dis. 1985;132: 485-489.
3. Heffner JE, et al. Am J Respir Crit Care Med. 1995; 153:1518-1526.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content