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 immediately after positive end-expiratory pressure (PEEP) is removed and is not immediately regained when PEEP is restored to its original value. The aim of this study was to investigate whether the same phenomenon also occurs in cardiopulmonary healthy individuals during anaesthesia and muscle relaxation.


METHODS
In 13 anaesthetised and muscle-relaxed patients, inspiratory elastic pressure-volume (Pel-V) curves were, after lung recruitment, obtained from zero end-expiratory airway pressure (ZEEP) and from a PEEP of 5 cmH2O. The curves were aligned on a common volume axis. Differences in lung volumes and compliance (Crs) 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 cmH2O. Maximum Crs was similar on the curves obtained from ZEEP and PEEP. However, the lower segments of the curve recorded from PEEP showed lower Crs compared to the curve recorded from ZEEP.


CONCLUSIONS
During anaesthesia and muscle paralysis, the Pel-V relations change immediately when 5 cmH2O of PEEP is removed. This phenomenon is probably 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 producing an airway pressure of 20 cmH2O.
Sigurdsson
S
S
Department of Anaesthesia and Intensive Care, Lund University Hospital, Sweden. sigurdsson.s@telia.com
Svantesson
C
C
Larsson
A
A
Jonson
B
B
D000328:Adult; D000399:Air Pressure; D000758:Anesthesia; D005260:Female; D006801:Humans; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D008170:Lung Compliance / Q000502:physiology; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D009125:Muscle Relaxants, Central / Q000494:pharmacology*; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial
D009125:Muscle Relaxants, Central