PULMONARY PRESSURE-VOLUME RELATIONSHIP IN ACUTE RESPIRATORY-DISTRESS SYNDROME IN ADULTS - ROLE OF POSITIVE END EXPIRATORY PRESSURE

During the early phase of the acute respiratory distress syndrome in adults (ARDS), pulmonary pressure-volume (P-V) curves exhibit a peculiar pattern, with increased hysteresis and an inflection in the ascending limb (Matamis et al, Chest 86:58-661984). End-expiratory lung volume is also markedly reduced. We traced P-V curves using a 2-L syringe in six patients with ARDS (group 2) and five patients without ARDS (group 1). End-expiratory lung volume, measured using the closed circuit helium dilution technique, was markedly reduced in both groups (39% ± 7% predicted in group 1, and 27% ± 7% in group 2). In the ARDS group, P-V curve was grossly abnormal, with an inflection at low lung volume and increased hysteresis: lung volume difference during inflation and deflation at a pressure 10 cm H2O higher than end-expiratory pressure was 803 ± 127 mL in group 2 and was only 450 ± 189 mL in group 1. Compliance measured during deflation was only slightly reduced in group 2. Application of first positive end-expiratory pressure 10, then 20 cm H2O, restored end-expiratory lung volume in all patients, and, in group 2 (ARDS), suppressed the inflection of the ascending limb, reduced hysteresis, and shifted the P-V trace upward and to the left. We conclude that, in ARDS patients, an abnormal pattern of P-V curve is explained by loss of volume, and by increased surface tension, since lung volume was similarly reduced in both groups. Increasing the level of end-expiratory pressure restores the normal pulmonary P-V relationship by suppressing the airway closure. © 1990.