• J Jane Pillow, Peter D Sly, and Zoltán Hantos.
• Clinical Sciences Division, Telethon Institute for Child Health Research and Centre for Child Health Research, University of Western Australia, Australia.
• Pediatr Crit Care Me. 2004 Mar 1;5(2):172-80.

ObjectivesTo determine whether the low-frequency forced oscillation technique (LFOT) can track changes in lung mechanics resulting from prophylactic intratracheal surfactant and a volume recruitment-derecruitment maneuver during high-frequency oscillatory ventilation (HFOV) and how this relates to the damping of the tracheal pressure waveform (P(tr)).DesignInterventional laboratory study.SettingRural animal research facility in Western Australia.SubjectsSedated newborn preterm lambs.InterventionsTwo separate studies were performed. Study 1 involved a volume recruitment-derecruitment maneuver during HFOV using stepwise changes (4 cm H(2)O) in mean airway opening pressure (P(ao), n = 5). Study 2 involved instillation of 4 mL/kg fetal lung fluid (n = 5) or exogenous surfactant (n = 8) at birth and subsequent intermittent mandatory ventilation for 40 mins.Measurements And Main ResultsArterial blood gases were recorded every 10 mins and ventilation was appropriately adjusted to achieve moderate hypercarbia (Paco(2), 50-60 mm Hg). Lung mechanics were measured using LFOT 10 mins following each adjustment in P(ao) in parallel with measurements of P(tr) and tidal volume (study 1) or after 40 mins (study 2). Both the recruitment-derecruitment maneuver and prophylactic surfactant administration achieved similar improvements (decrease) in tissue impedance (Z(ti)). The coefficient of tissue resistance (G) decreased more than the coefficient of tissue elastance (H), consistent with improved homogeneity of the lung tissue compartment as lung volume was recruited. Minimum Z(ti) coincided with minimum tracheal pressure amplitude (DeltaP(tr)) on the deflation limb of the volume recruitment-derecruitment maneuver during HFOV. There was a linear relationship between DeltaP(tr) and H.ConclusionsIn the preterm lamb, the LFOT can successfully detect changes in lung mechanics resulting from volume recruitment maneuvers during both HFOV and ventilation at conventional rates and may provide information on ventilation inhomogeneity. Minimization of Z(ti) is crucial to damping of P(tr) and may limit potential barotrauma to proximal alveolar units during establishment of HFOV.

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