title: Tidal volume is a major determinant of cyclic recruitment-derecruitment in acute respiratory distress syndrome.
abstract: BACKGROUND
  Overdistension and cyclic recruitment-derecruitment contribute to ventilator-induced lung injury. High tidal volumes are thought to increase mortality mainly by inducing overdistension. However, experimental evidence suggests that tidal volume (VT) may also influence cyclic recruitment-derecruitment. Our main goal was to determine whether high tidal volumes increase cyclic recruitment-derecruitment in acute respiratory distress syndrome (ARDS) patients, as measured by dynamic computed tomography (CT).
  
  
  METHODS
  We studied 9 ARDS patients with diffuse attenuations on CT who underwent a protocol including 2 ventilatory modes: (a) VT 6 mL/kg, respiratory rate 30/min, PEEP 9 cmH2O, (b) VT 12 mL/kg, respiratory rate 15/min, PEEP 9 cmH2O. A dynamic computed tomography of 8 seconds on a fixed transverse region was performed during each ventilator mode. Cyclic recruitment-derecruitment was determined as non-aerated tissue variation between inspiration and expiration and was expressed as % of lung tissue weight.
  
  
  RESULTS
  VT 12 mL/kg exhibited less non-aerated tissue at expiration compared to VT 6 ml/kg (40.15 [35.94-56.00] and 45.31 [37.95-59.32], respectively, P<0.05). However, VT 12 ml/kg increased cyclic recruitment-derecruitment compared to VT 6 mL/kg (7.32 [6.58-9.29] mL/kg vs. 4.51 [3.42-5.75] mL/kg, P<0.01). Tidal hyperinflation was also larger at VT 12 mL/kg (0.55 [0.27-2.24] vs. 0.24 [0.18-0.83], P<0.01).
  
  
  CONCLUSIONS
  High tidal volume is a major determinant of cyclic recruitment-derecruitment in ARDS patients with diffuse attenuations.
authors.affiliation: Department of Intensive Medicine, Pontifical Catholic University of Chile, Santiago, Chile. abruhn@med.puc.cl
authors.forename: A
authors.initials: A
authors.lastname: Bruhn
authors.forename: D
authors.initials: D
authors.lastname: Bugedo
authors.forename: F
authors.initials: F
authors.lastname: Riquelme
authors.forename: J
authors.initials: J
authors.lastname: Varas
authors.forename: J
authors.initials: J
authors.lastname: Retamal
authors.forename: C
authors.initials: C
authors.lastname: Besa
authors.forename: C
authors.initials: C
authors.lastname: Cabrera
authors.forename: G
authors.initials: G
authors.lastname: Bugedo
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000000981:diagnostic imaging; D008170:Lung Compliance / Q000502:physiology; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000150:complications; D011175:Positive-Pressure Respiration; D011379:Prognosis; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D015656:Respiratory Mechanics / Q000502:physiology; D018805:Sepsis / Q000150:complications; D013990:Tidal Volume / Q000502:physiology*; D014057:Tomography, X-Ray Computed; D055397:Ventilator-Induced Lung Injury