title: Adjusting tidal volume to stress index in an open lung condition optimizes ventilation and prevents overdistension in an experimental model of lung injury and reduced chest wall compliance.
abstract: BACKGROUND
  The stress index (SI), a parameter derived from the shape of the pressure-time curve, can identify injurious mechanical ventilation. We tested the hypothesis that adjusting tidal volume (VT) to a non-injurious SI in an open lung condition avoids hypoventilation while preventing overdistension in an experimental model of combined lung injury and low chest-wall compliance (Ccw).
  
  
  METHODS
  Lung injury was induced by repeated lung lavages using warm saline solution, and Ccw was reduced by controlled intra-abdominal air-insufflation in 22 anesthetized, paralyzed and mechanically ventilated pigs. After injury animals were recruited and submitted to a positive end-expiratory pressure (PEEP) titration trial to find the PEEP level resulting in maximum compliance. During a subsequent four hours of mechanical ventilation, VT was adjusted to keep a plateau pressure (Pplat) of 30 cmH2O (Pplat-group, n = 11) or to a SI between 0.95 and 1.05 (SI-group, n = 11). Respiratory rate was adjusted to maintain a 'normal' PaCO2 (35 to 65 mmHg). SI, lung mechanics, arterial-blood gases haemodynamics pro-inflammatory cytokines and histopathology were analyzed. In addition Computed Tomography (CT) data were acquired at end expiration and end inspiration in six animals.
  
  
  RESULTS
  PaCO2 was significantly higher in the Pplat-group (82 versus 53 mmHg, P = 0.01), with a resulting lower pH (7.19 versus 7.34, P = 0.01). We observed significant differences in VT (7.3 versus 5.4 mlKg(-1), P = 0.002) and Pplat values (30 versus 35 cmH2O, P = 0.001) between the Pplat-group and SI-group respectively. SI (1.03 versus 0.99, P = 0.42) and end-inspiratory transpulmonary pressure (PTP) (17 versus 18 cmH2O, P = 0.42) were similar in the Pplat- and SI-groups respectively, without differences in overinflated lung areas at end- inspiration in both groups. Cytokines and histopathology showed no differences.
  
  
  CONCLUSIONS
  Setting tidal volume to a non-injurious stress index in an open lung condition improves alveolar ventilation and prevents overdistension without increasing lung injury. This is in comparison with limited Pplat protective ventilation in a model of lung injury with low chest-wall compliance.
authors.affiliation: Anesthesiology and Critical Care Department, Hospital Clínico Universitario of Valencia, Av. Blasco Ibañez, 17, Valencia, CP: 46010, Spain. cafeoranestesia@gmail.com.
authors.forename: Carlos
authors.initials: C
authors.lastname: Ferrando
authors.affiliation: Section of Anesthesiology and Critical Care, Uppsala University Hospital Uppsala, Uppsala, Sweden. fsuarezsipmann@gmail.com.|CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain. fsuarezsipmann@gmail.com.
authors.forename: Fernando
authors.initials: F
authors.lastname: Suárez-Sipmann
authors.affiliation: Anesthesiology and Critical Care Department, Hospital Clínico Universitario of Valencia, Av. Blasco Ibañez, 17, Valencia, CP: 46010, Spain. andreguti@hotmail.com.
authors.forename: Andrea
authors.initials: A
authors.lastname: Gutierrez
authors.affiliation: Department of Anesthesiology, Hospital Privado de Comunidad, Mar de Plata, Argentina. gtusman@hotmail.com.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Tusman
authors.affiliation: Anesthesiology and Critical Care Department, Hospital Clínico Universitario of Valencia, Av. Blasco Ibañez, 17, Valencia, CP: 46010, Spain. joseacarbonell19@hotmail.com.
authors.forename: Jose
authors.initials: J
authors.lastname: Carbonell
authors.affiliation: Anesthesiology and Critical Care Department, Hospital Clínico Universitario of Valencia, Av. Blasco Ibañez, 17, Valencia, CP: 46010, Spain. marisagarciap@gmail.com.
authors.forename: Marisa
authors.initials: M
authors.lastname: García
authors.affiliation: Clinical Research Foundation, Hospital Clínico Universitario of Valencia, Valencia, Spain. lpiqueras70@hotmail.com.
authors.forename: Laura
authors.initials: L
authors.lastname: Piqueras
authors.affiliation: Pathological Anatomy Department, Hospital Clínico Universitario of Valencia, Valencia, Spain. company_amp@gva.es.
authors.forename: Desamparados
authors.initials: D
authors.lastname: Compañ
authors.affiliation: Radiology Department, Hospital Clinico Universitario of Valencia, Valencia, Spain. susaniefc@gmail.com.
authors.forename: Susanie
authors.initials: S
authors.lastname: Flores
authors.affiliation: Anesthesiology and Critical Care Department, Hospital Clínico Universitario of Valencia, Av. Blasco Ibañez, 17, Valencia, CP: 46010, Spain. soromarina@gmail.com.
authors.forename: Marina
authors.initials: M
authors.lastname: Soro
authors.affiliation: Clinical Research Foundation, Hospital Clínico Universitario of Valencia, Valencia, Spain. allombart@incliva.es.
authors.forename: Alicia
authors.initials: A
authors.lastname: Llombart
authors.affiliation: Anesthesiology and Critical Care Department, Hospital Clínico Universitario of Valencia, Av. Blasco Ibañez, 17, Valencia, CP: 46010, Spain. fco.javier.belda@uv.es.
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: Belda
mesh_terms: D000818:Animals; D018893:Bronchoalveolar Lavage; D004195:Disease Models, Animal; D006439:Hemodynamics; D055370:Lung Injury / Q000628:therapy*; D011175:Positive-Pressure Respiration / Q000379:methods*; D013552:Swine; D035441:Thoracic Wall / Q000502:physiology*; D013990:Tidal Volume