Monitoring of lung volume recruitment and derecruitment using oscillatory mechanics during high-frequency oscillatory ventilation in the preterm lamb.
OBJECTIVE
To 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)).


METHODS
Interventional laboratory study.


METHODS
Rural animal research facility in Western Australia.


METHODS
Sedated newborn preterm lambs.


METHODS
Two 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.


RESULTS
Arterial 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.


CONCLUSIONS
In 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.
Clinical Sciences Division, Telethon Institute for Child Health Research and Centre for Child Health Research, University of Western Australia, Australia.
J Jane
JJ
Pillow
Peter D
PD
Sly
Zoltán
Z
Hantos
D000818:Animals; D000831:Animals, Newborn; D001784:Blood Gas Analysis; D006612:High-Frequency Ventilation; D008170:Lung Compliance / Q000187:drug effects* / Q000502:physiology; D008176:Lung Volume Measurements; D011663:Pulmonary Surfactants / Q000494:pharmacology*; D015656:Respiratory Mechanics / Q000187:drug effects / Q000502:physiology; D012756:Sheep
D011663:Pulmonary Surfactants