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Identification of optimal lung volume during high-frequency oscillatory ventilation using respiratory inductive plethysmography

Brazelton, Thomas B. III MD, MPH; Watson, Kenneth F. MS, RRT; Murphy, Maryanne BA; Al-Khadra, Eman MB, BS; Thompson, John E. RRT; Arnold, John H. MD

LABORATORY INVESTIGATIONS
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Objectives  First, to define the relationships between critical opening and closing pressures and oxygenating efficiency, and second, to address whether respiratory inductive plethysmography (RIP) could be used to monitor changes in thoracic volume that follow changes in mean airway pressure during high- frequency oscillatory ventilation (HFOV).

Design  Prospective, interventional animal study.

Setting  University research laboratory.

Subjects  Five anesthetized, paralyzed, and ventilated pigs.

Interventions  The animals were ventilated by using HFOV after lung injury. Pre- and post-HFOV pressure-volume curves were obtained by supersyringe. A pressure-volume curve was constructed during HFOV as mean airway pressure was increased from 10 to 40 cm H2O and then weaned back down to the minimum sustainable. Hemodynamic and oxygenation data were obtained at each data point.

Measurements and Main Results  RIP-derived thoracic volumes correlated with known lung volumes during supersyringe (r2 = .78, p < .00001). During HFOV, three of five animals had an identifiable critical opening pressure of the lung, and four of five had an identifiable critical closing pressure. No consistent relationship between critical opening and critical closing pressures was observed. During the weaning phase of HFOV, a relative decrease in RIP-measured volume of >10% predicted the decrease in oxygenation associated with reaching the critical closing pressure.

Conclusions  The ability of RIP to detect optimal lung volume during the weaning of mean airway pressure may allow clinicians to more directly monitor lung volume changes during HFOV and use the lowest possible airway pressures after lung recruitment.

From the Departments of Anesthesia and Respiratory Care, Children’s Hospital, and Department of Anesthesia (Pediatrics), Harvard Medical School, Boston, MA.

Supported, in part, by SensorMedics, Yorba Linda, CA.

Address requests for reprints to: Thomas B. Brazelton III, MD, MPH, Division of Pediatric Critical Care, University of Wisconsin Children’s Hospital, 600 Highland Avenue, H4/466 CSC, Madison, WI 53792-4108. E-mail: brazeltoniii@facstaff.wisc.edu

Despite the inherent limitations posed by the animal and lavage models and by the technical limitations of the respiratory inductive plethysmography (RIP) technology, this study demonstrates that RIP technology can be a useful, reliable, and noninvasive technique for tracking thoracic volume changes during high-frequency oscillatory ventilation and for identifying the critical opening and closing pressures.

© 2001 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins