Elastic pressure-volume curves indicate derecruitment after a single deep expiration in anaesthetised and muscle-relaxed healthy man

Background: in acute respiratory distress syndrome, lung volume is lost imm ediately after positive end-expiratory pressure (PEEP) is removed and is no t immediately regained when PEEP is restored to its original value. The aim of this study was to investigate whether the same phenomenon also occurs i n cardiopulmonary healthy individuals during anaesthesia and muscle relaxat ion. Methods: In 13 anaesthetised and muscle-relaxed patients, inspiratory elast ic pressure-volume (P-el-V) curves were, after lung recruitment, obtained f rom zero end-expiratory airway pressure (ZEEP) and from a PEEP of 5 cmH(2)O . The curves were aligned on a common volume axis. Differences in lung volu mes and compliance (C-rs) were calculated at the different airway pressures . Results: At comparable pressures the ZEEP curve showed significantly lower volumes up to an airway pressure of 25 cmH(2)O. Maximum C-rs was similar on the curves obtained from ZEEP and PEEP However, the lower segments of the curve recorded from PEEP showed lower C-rs compared to the curve recorded f rom ZEEP Conclusion: During anaesthesia and muscle paralysis, the P-el-IV relations change immediately when 5 cmH(2)O of PEEP is removed. This phenomenon is pr obably mainly caused by closure of small airways and only in a minor part, if any, by formation of atelectasis. This study indicates that under these conditions lung volume might easily be normalised by a large breath produci ng an airway pressure of 20 cmH(2)O.