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Lung Opening and Closing during Ventilation of Acute Respiratory Distress Syndrome

¹ Dipartimento di Anestesiologia, Terapia Intensiva, e Scienze Dermatologiche, Fondazione Istituto Di Ricovero e Cura a Carattere Scientifico–Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Università degli Studi di Milano, Milan, ² Dipartimento di Anestesia, Rianimazione e Terapia del Dolore, Fondazione Istituto Di Ricovero e Cura a Carattere Scientifico–Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Milan, and ³ Dipartimento di Anestesia, Azienda Ospedaliera San Giovanni Battista-Molinette, Università degli Studi di Torino, Turin, Italy; ⁴ Anaesthesiologie II, Operative Intensivmedizin, Universitatsklinikum Göttingen, Göttigen, Germany; and ⁵ Departementos de Anestesiologia y Medicina Intensiva, Facultad de Medicina, Pontificia Universidad Catolica de Chile, Santiago, Chile

Correspondence and requests for reprints should be addressed to Luciano Gattinoni, M.D., Ph.D., Dipartimento di Anestesiologia, Terapia Intensiva, e Scienze Dermatologiche, Fondazione Istituto Di Ricovero e Cura a Carattere Scientifico - Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena di Milano, Università degli Studi di Milano, Via F. Sforza 35, 20122 Milan, Italy. E-mail: gattinon{at}policlinico.mi.it

Rationale: The effects of high positive end-expiratory pressure (PEEP) strictly depend on lung recruitability, which varies widely during acute respiratory distress syndrome (ARDS). Unfortunately, increasing PEEP may lead to opposing effects on two main factors potentially worsening the lung injury, that is, alveolar strain and intratidal opening and closing, being detrimental (increasing the former) or beneficial (decreasing the latter).

Objectives: To investigate how lung recruitability influences alveolar strain and intratidal opening and closing after the application of high PEEP.

Methods: We analyzed data from a database of 68 patients with acute lung injury or ARDS who underwent whole-lung computed tomography at 5, 15, and 45 cm H₂O airway pressure.

Measurements and Main Results: End-inspiratory nonaerated lung tissue was estimated from computed tomography pressure–volume curves. Alveolar strain and opening and closing lung tissue were computed at 5 and 15 cm H₂O PEEP. In patients with a higher percentage of potentially recruitable lung, the increase in PEEP markedly reduced opening and closing lung tissue (P < 0.001), whereas 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 distributed mainly in the dependent and hilar lung regions, and it appeared to be an independent risk factor for death (odds ratio, 1.10 for each 10-g increase).

Conclusions: In ARDS, especially in patients with higher lung recruitability, the beneficial impact of reducing intratidal alveolar opening and closing by increasing PEEP prevails over the effects of increasing alveolar strain.

Key Words: acute respiratory distress syndrome • acute lung injury • ventilator-induced lung injury • mechanical ventilation

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject The response to high levels of positive end-expiratory pressure (PEEP) depends on lung recruitability, which varies among patients with acute respiratory distress syndrome. Its application appears to be appropriate only in patients with a large amount of potentially recruitable lung. Unfortunately, the increase in PEEP may lead to opposing effects on the two major determinants of the development of ventilator-induced lung injury, that is, alveolar strain and intratidal lung opening and closing. What This Study Adds to the Field In patients with greater lung recruitability, the beneficial impact of reducing the amount of opening and closing lung tissue by increasing PEEP appears to prevail over the potentially harmful effects of increasing alveolar strain.

 

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