A Method for Determining Optimal Mean Airway Pressure in High-Frequency Oscillatory Ventilation
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A Method for Determining Optimal Mean Airway Pressure in High-Frequency Oscillatory Ventilation Brian Casserly • F. Dennis McCool • Jigme M. Sethi • Eyad Kawar • Richard Read Mitchell M. Levy
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Received: 11 April 2012 / Accepted: 19 October 2012 / Published online: 7 November 2012 Ó Springer Science+Business Media New York 2012
Abstract Background ‘‘Optimal’’ mean airway pressure (MAP) during high-frequency oscillatory ventilation (HFOV) can be defined as the pressure that allows for maximal alveolar recruitment while minimizing alveolar overdistension. Choosing a MAP near or just below the point of maximal curvature (PMC) of the volume–pressure characteristics of the lung can serve as a guide to avoid overdistention during HFOV, while simultaneously preventing derecruitment. The purpose of this study was to assess whether optimal MAP at the PMC can be determined by using measures of PaO2 in patients with acute respiratory distress syndrome (ARDS) undergoing HFOV. Methods We prospectively studied seven patients with ARDS who underwent HFOV after failed conventional ventilation. In addition, 11 healthy subjects were studied to validate measurements of changes in end-expiratory lung volume (DEELV) using magnetometers. Using this validated method, plots of DEELV and MAP were constructed during decremental changes in MAP following a recruitment maneuver in seven ventilated patients with ARDS. The PMC was defined as the point where the slope of the DEELV versus MAP curve acutely changed. The MAP at B. Casserly F. Dennis McCool J. M. Sethi E. Kawar Division of Pulmonary, Critical Care and Sleep Medicine, The Memorial Hospital of Rhode Island, 111 Brewster Street, Pawtucket, RI, USA B. Casserly (&) Pulmonary, Critical Care, and Sleep Medicine, Mid-Western Regional Hospital, Dooradoyle, Limerick, Ireland e-mail: [email protected] R. Read M. M. Levy Division of Pulmonary, Critical Care and Sleep Medicine, Rhode Island Hospital, 593 Eddy Street, Providence, RI, USA
the PMC was compared to that determined from plots of PaO2 versus MAP. Results In the healthy cohort, measurements of DEELV obtained by magnetometry approximated the line of identity when compared to those obtained by spirometry. The MAP determined using either the DEELV or PaO2 techniques were identical in all seven HFOV ventilated patients. Additionally, there was a significant correlation between the MAP associated changes in PaO2 and the MAP associated changes in DEELV (p \ 0.001). Conclusions The finding that MAP at the PMC is the same whether determined by measures of DEELV or PaO2 suggest that bedside measures PaO2 may provide an acceptable surrogate for measures of EELV when determining ‘‘optimal’’ MAP during HFOV. Keywords Mean airway pressure High-frequency oscillatory ventilation Acute respiratory distress syndrome
Introduction Mechanical ventilation remains the cornerstone of therapy for patients with acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Paradoxically, mechanical ventilation has th
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