title: Helmet ventilation and carbon dioxide rebreathing: effects of adding a leak at the helmet ports.
abstract: OBJECTIVE
  We examined whether additional helmet flow obtained by a single-circuit and a modified plateau valve applied at the helmet expiratory port (open-circuit ventilators) improves CO(2) wash-out by increasing helmet airflow.
  
  
  METHODS
  Randomized physiological study in a university research laboratory.
  
  
  METHODS
  Ten healthy volunteers.
  
  
  METHODS
  Helmet continuous positive airway pressure and pressure support ventilation delivered by an ICU ventilator (closed-circuit ventilator) and two open-circuit ventilators equipped with a plateau valve placed either at the inspiratory or at the helmet expiratory port.
  
  
  RESULTS
  We measured helmet air leaks, breathing pattern, helmet minute ventilation (Eh)), minute ventilation washing the helmet (Ewh)), CO(2) wash-out, and ventilator inspiratory assistance. Air leaks were small and similar in all conditions. Breathing pattern was similar among the different ventilators. Inspiratory and end-tidal CO(2) were lower, while (Eh) and (Ewh) were higher only using open-circuit ventilators with the plateau valve placed at the helmet expiratory port. This occurred notwithstanding these ventilators delivered a lower inspiratory assistance.
  
  
  CONCLUSIONS
  Additional helmet flow provided by open-circuit ventilators can lower helmet CO(2) rebreathing. However, inspiratory pressure assistance significantly decreases using open-circuit ventilators, still casting doubts on the choice of the optimal helmet ventilation setup.
authors.affiliation: Dipartimento di Anestesia e Rianimazione, Università di Torino, Ospedale S. Giovanni Battista-Molinette, Turin, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Racca
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Appendini
authors.forename: Cesare
authors.initials: C
authors.lastname: Gregoretti
authors.forename: Ilaria
authors.initials: I
authors.lastname: Varese
authors.forename: Giacomo
authors.initials: G
authors.lastname: Berta
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Vittone
authors.forename: Gabriela
authors.initials: G
authors.lastname: Ferreyra
authors.forename: Elisa
authors.initials: E
authors.lastname: Stra
authors.forename: V Marco
authors.initials: VM
authors.lastname: Ranieri
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism*; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000379:methods; D006260:Head Protective Devices; D006801:Humans; D012143:Respiratory Physiological Phenomena
chemical_list: D002245:Carbon Dioxide