Surviving ARDS: The Chances Are Getting Better
Special Feature
Surviving ARDS: The Chances Are Getting Better
By Doreen M. Anardi, RN
Despite fairly constant and disturbingly high mortality rates since the initial 1967 description of Acute Respiratory Distress Syndrome (ARDS) by Ashbaugh and colleagues, something seems to be changing in the 1990s.1 A number of investigators have reported improved survival, although the reasons for this improvement are unclear.2,3,4 Since its description, ARDS has been recognized worldwide and has been widely investigated.5 Pathophysiology, progression, risk factors, and causes of mortality have been well described, but successful prevention and amelioration strategies have been more elusive. Recent studies have examined quality of life outcomes in survivors of ARDS, as well as sub-group analyses to help understand this trend of improved survival.
Improved Acute Survival in ARDS: Possible Explanations
Can this trend in improved survival reflect variability in patient populations at different institutions or lack of a standardized definition of ARDS?6 The Milberg and associates study reflected a 10-year experience in one institution in which the primary risk factors for the development of ARDS are trauma or sepsis. The definitions used for prospective identification of ARDS patients and the identifying personnel have been constant since 1989. From 1983 to 1987, the survival rate ranged from 32% to 57% with no definite trend. Beginning in 1989, survival began a trend of improvement, reaching a high of 64% in 1993. Further analysis demonstrated that survival rates improved in all risk groups, but was most notable in patients whose etiology for ARDS was sepsis syndrome and who were younger than 60 years old. Survival improved in the trauma patients that developed ARDS, but this could be partially explained by less severe injury and reflected by lower Injury Severity Scores.3 In the Suchyta study, the definitions were also constant in the time periods compared. Patients were referred to their center with severe ARDS for consideration of extracorporeal oxygenation or ventilatory support (ECMO or ECCO2R). Survival was only 11% in the 1979 ECMO trial and by 1991, improved to 55% in the patients treated with ECCO2R. Survival was also improved to 45% in the control group patients who were managed with pressure-control and inverse ratio ventilation, a sign that something was going on.2
In 1994, a Consensus Conference of American and European investigators agreed on common definitions for ARDS and that the "A" in the syndrome acronym should return to the original "acute" instead of "adult," since all age groups are susceptible. These investigators further agreed that ARDS should be regarded as the severe end of the spectrum of Acute Lung Injury (ALI). These definitions have been widely accepted by clinical investigators, improving comparisons of patient criteria in clinical trials.5
Recent clinical trials have used ALI as entry criteria in hope of preventing ARDS. However, some epidemiological studies have found similar mortality rates in patients with ALI and ARDS.
Is improved ARDS survival due to improvements in ICU care? ARDS was described around the time that intensive care units were being organized and developed. Patients who previously would not have survived their initial injury or illness now could be treated and supported long enough for disordered inflammation to take over and for ARDS or multiple organ failure to develop. Clinical research and changes in practice have positively affected the spread of nosocomial infections. The Table shows a few of the improvements in practice that I have seen during my career in the ICU.
Table
Improvements in reducing transmission of nosocomial infections
· Equipment has improved with the development of closed ventilator circuits and humidification.
· Research has supported cost-effective changes in lengthening the frequency with which ventilator tubing is changed.
· Closed in-line suction catheters limit introduction of bacteria into the airway.
· Universal precautions with universal glove-wearing reduce the likelihood of caregiver-to-patient and patient-to-patient transmission of pathogens.
· Many studies have examined and made recommendations for appropriate antibiotic use and how antibiotic prophylaxis is most effective.
· Early nutrition with a host of patient-specific formulae may be playing a role, now that the role of the gut in bacterial translocation and multiple organ failure is recognized.
· Superior enteral feeding devices decrease the risk of gastric aspiration.
Factors Influencing Survival in ARDS
Which patients are still at increased risk of not surviving? In a later study by Suchyta and associates, patients older than age 55 had a significant increase in mortality. Oddly, the older ARDS patients seemed to have less severe ARDS, requiring lower levels of FiO2 and PEEP. Gender, smoking history, presence of sepsis, or organ failure were not associated with the increased mortality. While advanced age may slow or impair tissue repair following inflammatory injury or reduce the ability to adapt to environmental change, withdrawal of support was more likely in older ARDS patients even when there was no terminal illness, potentially contributing to the increased mortality rates. Suchyta et al felt that the recognition of age bias in the management of ARDS is important since it is often not superimposed on a chronic condition with poor long-term prognosis and the assumption of poor quality of life cannot be made.7
In a study of comorbid conditions and ALI in medical ICU patients by Zilberberg and associates, cirrhosis, HIV infection, active malignancy, organ transplantation, age older than 65, and sepsis were all independent predictors of hospital death in patients with ALI. These results generally corresponded to findings in other studies in mixed medical-surgical populations. In the ARDS patients, however, cirrhosis and malignancy were not significantly correlated. Zilberberg et al suggest that one explanation for improved survival is that patients with these comorbid conditions might have foregone mechanical ventilation.8
Although the reasons for improved survival in ARDS patients may never be known, this trend illustrates the folly in using historical controls in clinical trials. Further, inclusion and exclusion criteria and randomization schemes must allow for the fair distribution of high-risk patients in treatment groups.2,8
Health Status of Survivors of ARDS
How well do these ARDS survivors do? Descriptions of recovery of pulmonary function in ARDS survivors have been made since the 1970s, but most of the studies have had small sample sizes, non-consecutive patient selection, and lacked serial measurements of each patient at uniform time intervals.9 A study by McHugh and colleagues attempted to overcome these factors by prospectively identifying ARDS survivors and following their recovery with pulmonary function tests (PFT) at uniform time intervals for one year following extubation. The patient's functional recovery was assessed by administering the Sickness Impact Profile (SIP) with a modification to ascertain the degree that lung function affected the patient's perception of their health status.10
McHugh et al were able to enroll only 63% (n = 52) of the eligible patients, and could obtain complete data on only 20 of these, verifying that this can be a difficult population to study.9,10 They found that pulmonary function steadily improved up to six months following extubation and no significant additional improvement was seen up to one year. Mean pulmonary function values returned to normal or near normal values. Mean total lung capacity (TLC) was within normal limits and mean forced vital capacity (FVC) was slightly below normal. Mean diffusing capacity (DLCO) was below normal but the degree of abnormality varied with the method of measurement used. Although lung volume measurements returned to normal in half of the patients, severity of ARDS did correlate with more severe impairment of TLC, FVC, and DLCO in patients that had been ventilated longer than two weeks.9,10
Evaluation of total health by SIP and lung-related disability improved by the third month and improved to stabilize at low levels thereafter. Most of the patients' complaints were associated with general health rather than lung problems. The results of the SIP generally correlated with the patient's PFTs. The patients who had more severe ARDS also had significantly higher lung-related SIP scores. By one year, only 44% had been able to return to normal work activities. These patients were on the average 12 years older than those who had returned to work.10 The findings of this study are important for patient and family education; by three months, they will experience major pulmonary and functional improvement, and recovery will continue for up to six months.
Quality of Life in Survivors of ARDS
Two recent studies have further investigated recovery from ARDS by examining patient-reported quality of life (QOL) and incidence of post-traumatic stress disorder (PTSD). In the study by Weinert and colleagues, 24 patients with ALI were interviewed by telephone and six participated in a focus group to identify patient concerns and supplement the existing generic and pulmonary-specific QOL scales.11 The patients were evaluated at differing time intervals during their recovery ranging from six to 41 months after their acute illness. The focus group participants voiced concerns about memory problems, bad dreams about their hospitalization, using avoidance behaviors to prevent possible illness, and prolonged recovery.
These complaints are similar to those in post-ICU reports from mechanically ventilated patients. The patients in the focus group tended to have had more severe lung injury, and they reported that it was extremely difficult to mentally move on from their ICU "goal" of simple survival to the more complex, multiple goals of physical and mental rehabilitation and social and occupational reintegration. They felt that the lack of information about their hospital course and ALI may have made their recovery more difficult.11 Health-related QOL results showed significant differences between ALI survivors and the general United States population and that they were more similar to outpatients with serious chronic medical conditions. Weinert et al found that symptoms of depression were more common in patients recovering from ALI than in those with recent non-aphasic strokes, or in elderly patients with an average of five chronic medical conditions.11
In the study by Schelling and colleagues from Germany, 80 ARDS survivors were interviewed and reported a moderate degree of impairment in physical function, but 70% were able to return to work. As in the Weinert study, Schelling et al observed a high frequency of impaired psychosocial function in a subgroup of their patients. Further analysis revealed that this psychosocial dysfunction was the main reason for health-related QOL impairment among patients between the ages of 30 and 50. Patients were queried about their recollections of adverse experiences while they were in the ICU. The incidence of post-traumatic stress disorder (PTSD) increased linearly with the number of traumatic episodes reported by the patients and correlated to impairment in health-related QOL.12
Certainly, making patients and families aware that they have suffered lung injury (which may not have been what initiated their hospitalization) is an important first step in facilitating as full a recovery as possible. Our institution has an ARDS educational pamphlet that is available to patients and families in all of our ICUs. It was written by our ARDS research group in a question and answer format and covers common terminology, pathophysiology, interventions, general course of disease, recovery, and general areas of ARDS research. Although this intervention is untested, it has been well received. As clinical research efforts continue to prevent and improve management of ALI and ARDS, new areas of investigation are apparent. As there are more survivors, studies of physical recovery may be more feasible. As impairments in QOL issues have been identified, interventional programs aimed at patient and family education and psychosocial rehabilitation and resolution of PTSD or other impairment may improve these patient's recovery.
References
1. Ashbaugh DG, et al. Acute respiratory distress in adults. Lancet 1967;2:319-323.
2. Suchyta MR, et al. Increased survival of ARDS patients with severe hypoxemia [ECMO criteria]. Chest 1991;99:951-955.
3. Milberg JA, et al. Improved survival of patients with acute respiratory distress syndrome (ARDS): 1983-1993. JAMA 1995;273:306-309.
4. Sloane PJ, et al. A multicenter registry of patients with acute respiratory distress syndrome. Am Rev Respir Dis 1992;146:419-426.
5. Luce JM. Acute lung injury and the acute respiratory distress syndrome. Crit Care Med 1998;26:369-376.
6. Weiss SM, et al. Outcome from respiratory failure. Crit Care Clin 1994;10:197-215.
7. Suchyta MR, et al. Increased mortality of older patients with acute respiratory distress syndrome. Chest 1997;111:1334-1339.
8. Zilberberg MD, et al. Acute lung injury in the medical ICU. Am J Respir Crit Care Med 1998;157: 1159-1164.
9. Hudson LD, et al. What happens to survivors of the adult respiratory distress syndrome? Chest 1994; 105:123S-126S.
10. McHugh LG, et al. Recovery of function in survivors of the acute respiratory distress syndrome. Am J Respir Crit Care Med 1994;150:90-94.
11. Weinert CR, et al. Health-related quality of life after acute lung injury. Am J Respir Crit Care Med 1997;156:1120-1128.
12. Schelling G, et al. Health-related quality of life and posttraumatic stress disorder in survivors of the acute respiratory distress syndrome. Crit Care Med 1998; 26:651-659.
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