title: Demand flow facilitates spontaneous breathing during high-frequency oscillatory ventilation in a pig model.
abstract: OBJECTIVE
  Maintenance breathing is advocated in mechanical ventilation, which is difficult for the high-frequency oscillatory (HFO) ventilation. To facilitate spontaneous breathing during HFO ventilation, a demand flow system (DFS) was designed. The aim of the present study was to evaluate the system.
  
  
  METHODS
  Animal experiment.
  
  
  METHODS
  : University animal laboratory.
  
  
  METHODS
  Eight pigs (47-64 kg).
  
  
  METHODS
  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 DFS operated in two different setups. Pressure to regulate the DFS was sampled directly at the Y-piece of the ventilator circuit (DFS) or between the endotracheal tube and measurement equipment at the proximal end of the endotracheal tube. In the end, animals were paralyzed. Breathing pattern, work of breathing, and gas exchange were evaluated.
  
  
  RESULTS
  HFO ventilation with demand flow decreased breathing frequency and increased tidal volume compared with CF. Comparing HFO modes CF, DFS, and DFSPROX, total pressure-time product (PTP) was 66 cm H2O x sec x min (interquartile range 59-74), 64 cm H2O x sec x min (50-72), and 51 cm H2O x sec x min (41-63). Ventilator PTP was 36 cm H2O x sec x min (32-42), 8.6 cm H2O x sec x min (7.4-10), and 1 cm H2O x sec x min (-1.0 to 2.8). Oxygenation, evaluated by Pao2, was preserved when spontaneous breathing was maintained and deteriorated when pigs were paralyzed. Ventilation, evaluated by Paco2, improved with demand flow. Paco2 increased when using continuous flow and during muscular paralysis.
  
  
  CONCLUSIONS
  In moderately lung-injured anesthetized pigs during HFO ventilation, demand flow facilitated spontaneous breathing and augmented gas exchange. Demand flow decreased total breathing effort as quantified by PTP. Imposed work caused by the HFO ventilator appeared totally reduced by demand flow.
authors.affiliation: Department of Pediatric Intensive Care, VU University Medical Center, Amsterdam, The Netherlands. m.vanheerde@vumc.nl
authors.forename: Marc
authors.initials: M
authors.lastname: van Heerde
authors.forename: Karel
authors.initials: K
authors.lastname: Roubik
authors.forename: Vit
authors.initials: V
authors.lastname: Kopelent
authors.forename: Frans B
authors.initials: FB
authors.lastname: Plötz
authors.forename: Dick G
authors.initials: DG
authors.lastname: Markhorst
mesh_terms: D055371:Acute Lung Injury / Q000503:physiopathology / Q000628:therapy*; D000818:Animals; D006612:High-Frequency Ventilation; D023421:Models, Animal; D012119:Respiration; D013552:Swine