title: Repeated derecruitments accentuate lung injury during mechanical ventilation.
abstract: OBJECTIVE
  This study was performed to test the hypothesis that derecruitment itself might accentuate lung injury during mechanical ventilation.
  
  
  METHODS
  Randomized, controlled trial.
  
  
  METHODS
  Experimental laboratory.
  
  
  METHODS
  New Zealand White rabbits (2.8-3.5 kg).
  
  
  METHODS
  Twenty-four rabbits were ventilated in pressure-controlled mode with constant tidal volume (10 mL/kg). After lung injury was induced by repeated saline lavage (PaO2 <100 torr, 13.3 kPa), a pressure-volume curve was drawn to calculate the lower inflection point (Pflex), and randomization was done. The control group (n = 8) received ventilation with positive end-expiratory pressure (PEEP) fixed at Pflex for 3 hrs. The nonderecruitment group (n = 8) was ventilated at PEEP of 2 mm Hg (2.7 cm H2O) for the initial hour and then PEEP of Pflex for the remaining 2 hrs. The derecruitment group (n = 8) was ventilated for 3 hrs with six 30-min cycles consisting of 10 mins at PEEP of 2 mm Hg (2.7 cm H2O) and 20 mins at PEEP of Pflex to induce repeated derecruitments.
  
  
  RESULTS
  Variables of gas exchange, mechanics, and hemodynamics were measured, and histologic evaluation was done. In the control group, Pao2 remained >500 torr (66.7 kPa) for 3 hrs. In the nonderecruitment group, PaO2 was 40 +/- 16 (mean +/- SD) torr (5.3 +/- 2.1 kPa) at 1 hr but increased to >500 torr (66.7 kPa) for the remaining 2 hrs after increase in PEEP to Pflex. In the derecruitment group, there was progressive decline in Pao2 with each derecruitment to 220 +/- 130 torr (29.3 +/- 17.3 kPa) at 3 hrs (p <.05 compared with other groups). Histologically there was more hyaline membrane formation in the derecruitment group compared with control (p <.05) and significantly higher mean bronchiolar injury score in the derecruitment group (1.92 +/- 0.78) than both control (0.50 +/- 0.50) and nonderecruitment (0.78 +/- 0.42) groups (p <.05).
  
  
  CONCLUSIONS
  Repeated derecruitments can accentuate lung injury during mechanical ventilation.
authors.affiliation: Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Seoul, Korea.
authors.forename: Gee Young
authors.initials: GY
authors.lastname: Suh
authors.forename: Youngmin
authors.initials: Y
authors.lastname: Koh
authors.forename: Man Pyo
authors.initials: MP
authors.lastname: Chung
authors.forename: Chang Hyeok
authors.initials: CH
authors.lastname: An
authors.forename: Hojoong
authors.initials: H
authors.lastname: Kim
authors.forename: Woo Young
authors.initials: WY
authors.lastname: Jang
authors.forename: Jungho
authors.initials: J
authors.lastname: Han
authors.forename: O Jung
authors.initials: OJ
authors.lastname: Kwon
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D004195:Disease Models, Animal; D006339:Heart Rate / Q000502:physiology; D015601:Injury Severity Score; D008168:Lung / Q000098:blood supply* / Q000473:pathology*; D008170:Lung Compliance; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011175:Positive-Pressure Respiration / Q000009:adverse effects; D011659:Pulmonary Gas Exchange; D011817:Rabbits; D016032:Randomized Controlled Trials as Topic; D012128:Respiratory Distress Syndrome / Q000097:blood / Q000209:etiology* / Q000503:physiopathology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen