Adult respiratory distress syndrome. Report of survival after two episodes

Long-term assessment of lung function in survivors of severe ARDS

STUDY OBJECTIVES

To investigate the long-term outcome of lung function in survivors of severe ARDS after modern treatment strategies including lung protective mechanical ventilation and prone positioning maneuvers.

DESIGN

Follow-up cohort study.

SETTING

University hospital pulmonary division and level 1 trauma center.

PATIENTS

Sixteen survivors of severe ARDS (from 1992 to 1994) with a lung injury score > or = 2.5.

MEASUREMENTS

The follow-up study (from 1995 to 1996) included interview, physical examination, chest radiographs, static and dynamic lung volumes, diffusion capacity of the lung for carbon monoxide (DLCO), blood gas analysis, and cardiopulmonary exercise testing (CPET).

RESULTS

The mean +/- SD interval between hospital discharge and functional assessment was 29.5 +/- 8.7 months (range, 15.0 to 40.7 months). In approximately one half of the patients, mild abnormalities in static and dynamic lung volumes were found. In 25% (4 of 16 patients), lung function was obstructive; in 25% (4 of 16 patients), lung function was restrictive; and in 6.3% (1 of 16 patients), a combined obstructive-restrictive pattern was revealed. DLCO was impaired in 12.5% (2 of 16 patients); gas exchange during exercise was impaired in 45.5% (5 of 11 patients).

CONCLUSIONS

Residual obstructive and restrictive defects as well as impaired pulmonary gas exchange remain common after severe ARDS. CPET is a very sensitive measure to evaluate residual impairment of lung function after ARDS. Using CPET, reduced pulmonary gas exchange can be detected in many patients with normal DLCO.

Sequelae of the adult respiratory distress syndrome

Most survivors of ARDS have persistent mild reductions of TLCO even as long as a year after their episode. The lung volumes and flows return to normal in most instances, although a subset of patients will have persistent impairment. Both obstructive and restrictive deficits may be seen. This group may be predicted by the degree of acute lung injury assessed by the level of FIO2, PEEP, and gas exchange abnormality that exists in the first few days. In the first year after ARDS most physiological abnormalities will improve, but if deficits persist at one year further improvement is unlikely. Although many patients report dyspnoea following ARDS, the symptom does not correlate with abnormalities of pulmonary function. The possibility that conventional management may augment the degree of acute injury and worsen outcome must be considered. The effects of chronic hyperoxia in humans with acute lung injury or those of high levels of PEEP compared with low levels are not known. Exploring new ventilator management strategies while we await more specific treatment directed at the primary problem of acute lung inflammation will hopefully reduce acute mortality as well as acute and chronic morbidity.

Reduced pulmonary capillary blood volume as a long-term sequel of ARDS

Lung function was evaluated in nine survivors of ARDS. All patients were asymptomatic at rest at the time of the study, ie, 5.5 to 19 months after extubation (mean 12.5). Six had mild to moderate exertional dyspnea. Chest x-ray films showed no gross parenchymal abnormalities. Spirometry and pulmonary mechanics were either normal or minimally altered, particularly in smokers. At submaximal exercise levels, effort was limited by tachycardia in eight patients; one subject showed ventilatory and cardiovascular limitations. It was concluded that spirometry and pulmonary mechanics are restored to normal within six months after extubation, and gas exchange abnormalities persist after ARDS and might be related to intrapulmonary shunts at rest, whereas during exercise a decreased pulmonary capillary blood volume might be the primary factor.

Pulmonary function following severe acute respiratory failure and high levels of positive end-expiratory pressure

In an 18-month period, we treated 561 patients with mechanical ventilation. Fifty-four (10 percent) of these patients had acute respiratory failure, requiring treatment with positive end-expiratory pressure (PEEP) in excess of 20 mm Hg (range, 20 to 40 mm Hg). All patients were allowed to breathe spontaneously between volume-limited mechanical breaths delivered at a rate sufficient to maintain an arterial pH greater than or equal to 7.35. PEEP was applied until calculated pulmonary venous admixture was minimized. Forty-three (80 percent) of these 54 patients were alive and asymptomatic three months after dischage from the hospital, and tests of pulmonary function were performed on ten patients within one year after hospitalization. Abnormalities in pulmonary function appeared to be reversible, and pulmonary function gradually approached normal within one year. It appears that neither acute respiratory failure nor exposure to high airway pressures caused significant permanent pulmonary damage in the ten patients studied.

Pulmonary function after recovery from the adult respiratory distress syndrome

Eight adult patients with acute respiratory distress syndrome were treated with positive end-expiratory pressure (PEEP) ventilation. The results of detailed examinations of pulmonary function in these eight patients obtained after different periods of time following discharge from the respiratory care unit were analyzed to determine the degree of disturbances in pulmonary function. For comparison, examinations of pulmonary function were also performed on two patients who were treated with zero end-expiratory pressure ventilation. This follow-up study showed remarkably few abnormalities. Whe present, restrictive disturbances in pulmonary function, especially decreased static compliance and diffusing capacity, were found. No correlation was found between the pulmonary-function results of the eight patients and the duration of the PEEP treatment, nor between the results and the time interval between treatment at the respiratory care unit and the moment of the pulmonary function studies.