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Lung Stress and Strain during Mechanical Ventilation for Acute Respiratory Distress Syndrome

¹ Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS–"Ospedale Maggiore Policlinico Mangiagalli Regina Elena" di Milano, Milan, Italy; ² Istituto di Anestesiologia e Rianimazione, Università degli Studi di Milano, Milan, Italy; and ³ Pulmonary and Critical Care, University of Minnesota and Regions Hospital, St. Paul, Minnesota

Correspondence and requests for reprints should be addressed to Prof. Luciano Gattinoni, M.D., F.R.C.P., Istituto di Anestesiologia e Rianimazione, Fondazione IRCCS–"Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena" di Milano, Via Francesco Sforza 35, 20122 Milan, Italy. E-mail: gattinon{at}policlinico.mi.it

Rationale: Lung injury caused by a ventilator results from nonphysiologic lung stress (transpulmonary pressure) and strain (inflated volume to functional residual capacity ratio).

Objectives: To determine whether plateau pressure and tidal volume are adequate surrogates for stress and strain, and to quantify the stress to strain relationship in patients and control subjects.

Methods: Nineteen postsurgical healthy patients (group 1), 11 patients with medical diseases (group 2), 26 patients with acute lung injury (group 3), and 24 patients with acute respiratory distress syndrome (group 4) underwent a positive end-expiratory pressure (PEEP) trial (5 and 15 cm H₂O) with 6, 8, 10, and 12 ml/kg tidal volume.

Measurements and Main Results: Plateau airway pressure, lung and chest wall elastances, and lung stress and strain significantly increased from groups 1 to 4 and with increasing PEEP and tidal volume. Within each group, a given applied airway pressure produced largely variable stress due to the variability of the lung elastance to respiratory system elastance ratio (range, 0.33–0.95). Analogously, for the same applied tidal volume, the strain variability within subgroups was remarkable, due to the functional residual capacity variability. Therefore, low or high tidal volume, such as 6 and 12 ml/kg, respectively, could produce similar stress and strain in a remarkable fraction of patients in each subgroup. In contrast, the stress to strain ratio—that is, specific lung elastance—was similar throughout the subgroups (13.4 ± 3.4, 12.6 ± 3.0, 14.4 ± 3.6, and 13.5 ± 4.1 cm H₂O for groups 1 through 4, respectively; P = 0.58) and did not change with PEEP and tidal volume.

Conclusions: Plateau pressure and tidal volume are inadequate surrogates for lung stress and strain.

Clinical trial registered with www.clinicaltrials.gov (NCT 00143468).

Key Words: acute respiratory distress syndrome • acute lung injury • stress, mechanical • strain • ventilator-induced lung injury

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Lung stress and strain are the primary determinants of ventilator-induced lung injury. Their surrogates are airway pressure and tidal volume normalized for ideal body weight (VT IBW). Prevention of ventilator-induced lung injury is primarily based on recognizing the "harmful" threshold for these surrogates (30 cm H2O airway plateau pressure and 6 ml/kg VT IBW). What This Study Adds to the Field In this study, we demonstrate that VT IBW and airway plateau pressure are inadequate surrogates for lung stress and strain.

 

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Lung Stress and Strain in Acute Respiratory Distress Syndrome: Good Ideas for Clinical Management?

Roy G. Brower, Rolf D. Hubmayr, and Arthur S. Slutsky
AJRCCM 2008 178: 323-324. [Full Text]  

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				R. G. Brower, R. D. Hubmayr, and A. S. Slutsky Lung Stress and Strain in Acute Respiratory Distress Syndrome: Good Ideas for Clinical Management? Am. J. Respir. Crit. Care Med., August 15, 2008; 178(4): 323 - 324. [Full Text] [PDF]