Authors: Marc van Heerde, Karel Roubík, Vít Kopelent, Frans B. Plötz, Dick G. Markhorst
Van Heerde M, Roubík K, Kopelent V, Plötz FB, Markhorst DG. Demand Flow Facilitates Spontaneous Breathing During High-frequency Oscillatory Ventilation in a Pig Model. Critical Care Medicine 2009; 37(3); 1068-1073
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Published in Critical Care Medicine
Objective: In lung protective ventilation strategies the aim is to preserve spontaneous breathing. In high-frequency oscillatory (HFO) ventilation spontaneous breathing is not well tolerated. To facilitate spontaneous breathing during HFO ventilation a demand flow system was designed. Aim of this animal study was to evaluate this system.
Design: Animal experiment. Setting: University animal laboratory.
Subjects: Eight pigs (47 – 64 kg).
Interventions: Lung injury was induced by lung lavage with normal saline. After spontaneous breathing was restored HFO ventilation was applied, in runs of 30 minutes, with continuous fresh gas flow (CF) or the demand flow system operated in two different setups. Pressure to regulate the demand flow system was sampled directly at the Y-piece of the ventilator circuit (DFS) or at the proximal end of the endotracheal tube (DFSPROX) in order to reduce influence of measurement equipment on demand flow system performance. In the end animals were paralyzed. Breathing pattern, work of breathing and gas exchange were evaluated.
Measurements and Main Results: HFO ventilation with demand flow reduced breathing frequency and increased tidal volume compared to continuous fresh gas flow. Comparing HFO modes CF, DFS and DFSPROX, total PTP was 66 cmH2O (IQR 59 – 74), 64 cmH2O (50 – 72) and 51 cmH2O (41 – 63). Ventilator PTP was 36 cmH2O (32 – 42), 8.6 cmH2O (7.4 – 10) and 1 cmH2O (-1.0 – 2.8). Oxygenation, evaluated by PaO2, was preserved if spontaneous breathing was maintained and deteriorated if pigs were paralyzed. Ventilation, evaluated by PaCO2, improved with demand flow. PaCO2 increased using continuous flow and during muscular paralysis.
Conclusions: This animal study confirms that demand flow facilitates spontaneous breathing during HFO ventilation and augments gas exchange. Demand flow decreased total breathing effort quantified by PTP. Imposed work caused by the HFO ventilator was totally reduced by demand flow.
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