title: Dynamic versus static respiratory mechanics in acute lung injury and acute respiratory distress syndrome.
abstract: OBJECTIVE
  It is not clear whether the mechanical properties of the respiratory system assessed under the dynamic condition of mechanical ventilation are equivalent to those assessed under static conditions. We hypothesized that the analyses of dynamic and static respiratory mechanics provide different information in acute respiratory failure.
  
  
  METHODS
  Prospective multiple-center study.
  
  
  METHODS
  Intensive care units of eight German university hospitals.
  
  
  METHODS
  A total of 28 patients with acute lung injury and acute respiratory distress syndrome.
  
  
  METHODS
  None.
  
  
  METHODS
  Dynamic respiratory mechanics were determined during ongoing mechanical ventilation with an incremental positive end-expiratory pressure (PEEP) protocol with PEEP steps of 2 cm H2O every ten breaths. Static respiratory mechanics were determined using a low-flow inflation.
  
  
  RESULTS
  The dynamic compliance was lower than the static compliance. The difference between dynamic and static compliance was dependent on alveolar pressure. At an alveolar pressure of 25 cm H2O, dynamic compliance was 29.8 (17.1) mL/cm H2O and static compliance was 59.6 (39.8) mL/cm H2O (median [interquartile range], p < .05). End-inspiratory volumes during the incremental PEEP trial coincided with the static pressure-volume curve, whereas end-expiratory volumes significantly exceeded the static pressure-volume curve. The differences could be attributed to PEEP-related recruitment, accounting for 40.8% (10.3%) of the total volume gain of 1964 (1449) mL during the incremental PEEP trial. Recruited volume per PEEP step increased from 6.4 (46) mL at zero end-expiratory pressure to 145 (91) mL at a PEEP of 20 cm H2O (p < .001). Dynamic compliance decreased at low alveolar pressure while recruitment simultaneously increased. Static mechanics did not allow this differentiation. The decrease in static compliance occurred at higher alveolar pressures compared with the dynamic analysis.
  
  
  CONCLUSIONS
  Exploiting dynamic respiratory mechanics during incremental PEEP, both compliance and recruitment can be assessed simultaneously. Based on these findings, application of dynamic respiratory mechanics as a diagnostic tool in ventilated patients should be more appropriate than using static pressure-volume curves.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Albert-Ludwigs-University, Freiburg, Germany.
authors.forename: Claudius A
authors.initials: CA
authors.lastname: Stahl
authors.forename: Knut
authors.initials: K
authors.lastname: Möller
authors.forename: Stefan
authors.initials: S
authors.lastname: Schumann
authors.forename: Ralf
authors.initials: R
authors.lastname: Kuhlen
authors.forename: Michael
authors.initials: M
authors.lastname: Sydow
authors.forename: Christian
authors.initials: C
authors.lastname: Putensen
authors.forename: Josef
authors.initials: J
authors.lastname: Guttmann
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D005858:Germany; D006801:Humans; D007362:Intensive Care Units; D008168:Lung / Q000503:physiopathology*; D055370:Lung Injury; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D015656:Respiratory Mechanics / Q000502:physiology*