• Emilio García-Prieto, Josefina López-Aguilar, Diego Parra-Ruiz, Laura Amado-Rodríguez, Inés López-Alonso, Jorge Blázquez-Prieto, Lluis Blanch, and Guillermo M Albaiceta.
• From the Servicio de Medicina Intensiva, Hospital Universitario Central de Asturias, Oviedo, Spain (E.G.-P., D.P.-R., G.M.A.); Critical Care Center, Hospital de Sabadell, I3PT, Corporació Sanitaria Parc Taulí, Universitat Autònoma de Barcelona, Sabadell, Spain (J.L.-A., L.B.); Centro de Investigación Biomédica en Red (CIBER)-Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain (J.L.-A., L.B., G.M.A.); Area de Gestión Clínica de Medicina Intensiva, Hospital Valle del Nalón, Langreo, Spain (L.A.-R.); and Departamento de Biología Funcional, Instituto de Oncología del Principado de Asturias (IUOPA), Universidad de Oviedo, Oviedo, Spain (L.A.-R., I.L.-A., J.B.-P., G.M.A.).
• Anesthesiology. 2016 Feb 1; 124 (2): 443-52.

BackgroundLung strain, defined as the ratio between end-inspiratory volume and functional residual capacity, is a marker of the mechanical load during ventilation. However, changes in lung volumes in response to pressures may occur in injured lungs and modify strain values. The objective of this study was to clarify the role of recruitment in strain measurements.MethodsSix oleic acid-injured pigs were ventilated at positive end-expiratory pressure (PEEP) 0 and 10 cm H2O before and after a recruitment maneuver (PEEP = 20 cm H2O). Lung volumes were measured by helium dilution and inductance plethysmography. In addition, six patients with moderate-to-severe acute respiratory distress syndrome were ventilated with three strategies (peak inspiratory pressure/PEEP: 20/8, 32/8, and 32/20 cm H2O). Lung volumes were measured in computed tomography slices acquired at end-expiration and end-inspiration. From both series, recruited volume and lung strain (total, dynamic, and static) were computed.ResultsIn the animal model, recruitment caused a significant decrease in dynamic strain (from [mean ± SD] 0.4 ± 0.12 to 0.25 ± 0.07, P < 0.01), while increasing the static component. In patients, total strain remained constant for the three ventilatory settings (0.35 ± 0.1, 0.37 ± 0.11, and 0.32 ± 0.1, respectively). Increases in tidal volume had no significant effects. Increasing PEEP constantly decreased dynamic strain (0.35 ± 0.1, 0.32 ± 0.1, and 0.04+0.03, P < 0.05) and increased static strain (0, 0.06 ± 0.06, and 0.28 ± 0.11, P < 0.05). The changes in dynamic and total strain among patients were correlated to the amount of recruited volume. An analysis restricted to the changes in normally aerated lung yielded similar results.ConclusionRecruitment causes a shift from dynamic to static strain in early acute respiratory distress syndrome.

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