Published ahead of print on December 1, 2005, doi:10.1164/rccm.200502-299OC Am. J. Respir. Crit. Care Med., Volume 173, Number 4, February 2006, 414-420 A more recent version of this article appeared on February 15, 2006
Submitted on February 24, 2005 The Deflation Limb of the Pressure Volume Relationship in Infants During High-Frequency VentilationDavid G Tingay1*,1 Department of Neonatology, Royal Children's Hospital, Melbourne, Victoria, Australia; Murdoch Childrens Research Institute, Melbourne, Victoria, Australia; Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia, 2 Department of Neonatology, Royal Children's Hospital, Melbourne, Victoria, Australia, 3 Murdoch Childrens Research Institute, Melbourne, Victoria, Australia; Department of Neonatology, Royal Hobart Hospital, Hobart, Tasmania, Australia * To whom correspondence should be addressed. E-mail: david.tingay{at}rch.org.au.
Rationale: The importance of applying high frequency oscillatory ventilation with a high lung volume strategy in infants is well established. Currently a lack of reliable methods for assessing lung volume limits clinicians ability to achieve the optimum volume range. Objectives: To map the pressure volume relationship of the lung during high frequency oscillatory ventilation in infants, to determine at what point ventilation is being applied clinically and to describe the relationship between airway pressure, lung volume and oxygenation. Methods: In 12 infants, a partial inflation limb and the deflation limb of the pressure volume relationship were mapped using a quasi-static lung volume optimisation manoeuvre. This involved stepwise airway pressure increments to total lung capacity, followed by decrements until the closing pressure of the lung was identified. Measurements and main results: Lung volume and oxygen saturation were recorded at each airway pressure. Lung volume was measured using respiratory inductive plethysmography. A distinct deflation limb could be mapped in each infant. Overall, oxygenation and lung volume were improved by applying ventilation on the deflation limb. Maximal lung volume and oxygenation occurred on the deflation limb at a mean airway pressure of 3 cm H2O and 5 cm H2O below the airway pressure approximating total lung capacity respectively. Conclusions: Using current ventilation strategies, all infants were being ventilated near the inflation limb. It is possible to delineate the deflation limb in infants receiving high frequency oscillatory ventilation, in doing so greater lung volume and oxygenation can be achieved, often at lower airway pressures. Key words: infant newborn, pressure-volume relationship, high-frequency ventilation, plethysmography impedance
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