title: Analysis of dynamic intratidal compliance in a lung collapse model.
abstract: BACKGROUND
  For mechanical ventilation to be lung-protective, an accepted suggestion is to place the tidal volume (V(T)) between the lower and upper inflection point of the airway pressure-volume relation. The drawback of this approach is, however, that the pressure-volume relation is assessed under quasistatic, no-flow conditions, which the lungs never experience during ventilation. Intratidal nonlinearity must be assessed under real (i.e., dynamic) conditions. With the dynamic gliding-SLICE technique that generates a high-resolution description of intratidal mechanics, the current study analyzed the profile of the compliance of the respiratory system (C(RS)).
  
  
  METHODS
  In 12 anesthetized piglets with lung collapse, the pressure-volume relation was acquired at different levels of positive end-expiratory pressure (PEEP: 0, 5, 10, and 15 cm H(2)O). Lung collapse was assessed by computed tomography and the intratidal course of C(RS) using the gliding-SLICE method.
  
  
  RESULTS
  Depending on PEEP, C(RS) showed characteristic profiles. With low PEEP, C(RS) increased up to 20% above the compliance at early inspiration, suggesting intratidal recruitment; whereas a profile of decreasing C(RS), signaling overdistension, occurred with V(T) > 5 ml/kg and high PEEP levels. At the highest volume range, C(RS) was up to 60% less than the maximum. With PEEP 10 cm H(2)O, C(RS) was high and did not decrease before 5 ml/kg V(T) was delivered.
  
  
  CONCLUSIONS
  The profile of dynamic C(RS) reflects nonlinear intratidal mechanics of the respiratory system. The SLICE analysis has the potential to detect intratidal recruitment and overdistension. This might help in finding a combination of PEEP and V(T) level that is protective from a lung-mechanics perspective.
authors.affiliation: Division for Experimental Anesthesiology, Department of Anesthesiology, University Medical Center Freiburg, Germany. stefan.schumann@uniklinik-freiburg.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Schumann
authors.forename: László
authors.initials: L
authors.lastname: Vimlati
authors.forename: Rafael
authors.initials: R
authors.lastname: Kawati
authors.forename: Josef
authors.initials: J
authors.lastname: Guttmann
authors.forename: Michael
authors.initials: M
authors.lastname: Lichtwarck-Aschoff
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D008170:Lung Compliance; D011175:Positive-Pressure Respiration / Q000379:methods*; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D013552:Swine; D013990:Tidal Volume; D036542:Tomography, Spiral Computed