Published ahead of print on November 12, 2009 Am. J. Respir. Crit. Care Med. 2009, doi:10.1164/rccm.200905-0787OC
Submitted on May 26, 2009 Lung Opening and Closing During Ventilation of Acute Respiratory Distress SyndromePietro Caironi1,1 Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Fondazione IRCCS – Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Università degli Studi di Milano, Milan, Italy; Dipartimento di Anestesia, Rianimazione e Terapia del Dolore, Fondazione IRCCS – Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Milan, Italy, 2 Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Fondazione IRCCS – Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Università degli Studi di Milano, Milan, Italy, 3 Dipartimento di Anestesia, Rianimazione e Terapia del Dolore, Fondazione IRCCS – Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Milan, Italy, 4 Dipartimento di Anestesia, Azienda Ospedaliera San Giovanni Battista-Molinette, Università degli Studi di Torino, Turin, Italy, 5 Anaesthesiologie II, Operative Intensivmedizin, Universitatsklinikum Göttingen, Göttingen, Germany, 6 Departementos de Anestesiologia y Medicina Intensiva, Facultad de Medicina, Pontificia Universidad Catolica de Chile, Santiago, Chile, 7 Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Fondazione IRCCS – Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Università degli Studi di Milano, Via Francesco Sforza, 35, Milan, 20122, Italy; Dipartimento di Anestesia, Rianimazione e Terapia del Dolore, Fondazione IRCCS – Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Via Francesco Sforza, 35, Milan, 20122, Italy * To whom correspondence should be addressed. E-mail: gattinon{at}policlinico.mi.it.
Rationale: The effects of high positive end-expiratory pressure (PEEP) strictly depend on lung recruitability, which widely varies during acute respiratory distress syndrome (ARDS). Unfortunately, increasing PEEP may lead to opposing effects on two main factors potentially worsening the lung injury, i.e., alveolar strain and intra-tidal opening and closing, being detrimental (increasing the former) or beneficial (decreasing the latter). Objectives: To investigate how lung recruitability influences alveolar strain and intra-tidal opening and closing after the application of high PEEP. Methods: We analyzed data from a database of sixty-eight patients with acute lung injury or ARDS who underwent whole-lung computed tomography (CT) at 5, 15 and 45 cmH2O airway pressure. Measurements and main results: End-inspiratory non-aerated lung tissue was estimated from CT pressure-volume curves. Alveolar strain and opening and closing lung tissue were computed at 5 and 15 cmH2O PEEP. In patients with a higher percentage of potentially recruitable lung, the increase of PEEP markedly reduced opening and closing lung tissue (p<0.001), while no differences were observed in patients with a lower percentage of potentially recruitable lung. In contrast, alveolar strain similarly increased in the two groups (p=0.89). Opening and closing lung tissue was mainly distributed in the dependent and hilar lung regions, and it appeared to be an independent risk factor for death (1.10 odds ratio for each 10 g-increase). Conclusions: In ARDS, especially in patients with higher lung recruitability, the beneficial impact of reducing intra-tidal alveolar opening and closing by increasing PEEP prevails on the effects of increasing alveolar strain. Key words: acute respiratory distress syndrome • acute lung injury • ventilator-induced lung injury • mechanical ventilation
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