Variable ventilation improves ventilation and lung compliance in preterm lambs
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In adult animals, ventilation with variable tidal volume and rate improves lung mechanics, arterial oxygenation and ventilation compared to a monotonously controlled ventilation pattern. We assessed the physiological consequences of variable ventilation in the immature lung.
Lambs delivered at 129 days (term = 150 days) were euthanised (n = 9) or anaesthetised, tracheostomised and suctioned prior to prophylactic intra-tracheal surfactant instillation (Curosurf®, 100 mg/kg) and commencement of controlled ventilation (50 breaths/min, tidal volume 7.7 ± 0.8 mL/kg). Volume history was standardised at 20 min with two sustained (3 s) inflations to 30 cmH2O followed immediately by measurement of baseline dynamic lung mechanics (FlexiVent™, Scireq, Canada). Ventilation was continued according to prior randomisation (variable or conventional ventilation). For variable ventilation (n = 9), breath-to-breath tidal volume and respiratory rate varied but intra-breath minute volume (MV) and average tidal volume were equivalent to the conventional ventilation group with fixed tidal volume and rate (n = 7). Lung mechanics and gas exchange were measured at intervals. Lambs were euthanised at 2 h. Inflammatory cell counts and protein from bronchoalveolar lavage fluid and lung tissue cytokine mRNA were quantified.
At study completion, PaCO2 (p = 0.026) and mean airway pressure (p = 0.002) were lower and pH (p = 0.047), ventilation efficiency index (p = 0.021) and dynamic compliance were higher (p = 0.003) in lambs on variable rather than conventional ventilation. However, oxygenation indices and post-mortem static compliances were not different between groups.
Variable ventilation improves ventilation efficiency and in vivo lung compliance in the preterm lung, but unlike adult models, had no effect on arterial oxygenation.
KeywordsInfant Preterm Artificial respiration Homeokinesis Respiratory distress syndrome Stochastic resonance
We would like to express our sincere appreciation to the members of the UWA Ovine Research Group for technical assistance and JRL Hall and Co. for provision and early antenatal care of the ewes. We also acknowledge and appreciate the technical assistance of Dr Sven Schulzke, Dr David Baldwin, Dr Roland Neumann and Dr Roshni Sonawane in caring for the lambs. This research was supported by NHMRC 458750, the Women and Infants Research Foundation. Radiant warmer beds were provided by Fisher & Paykel Healthcare™ (Auckland, NZ). Surfactant was donated by Chiesi Group (Parma, Italy). Investigator fellowship support was provided by a Sylvia and Charles Viertel Senior Medical Research Fellowship (JJP) and a NHMRC and NHFA Fellowship (GRP). Partial support was from NIH 1R01HL098976 (BS) and NIH RO1 HD12714 (AHJ).
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