title: Heliox enhances carbon dioxide clearance from lungs of normal rabbits during low bias flow oscillation.
abstract: OBJECTIVE
  To evaluate carbon dioxide clearance in normal rabbits during high-frequency oscillatory ventilation with helium-oxygen mixtures by using a low bias flow oscillation (LBFO) system designed to conserve expensive gas.
  
  
  METHODS
  A prospective, paired-controlled, interventional, in vivo animal laboratory study.
  
  
  METHODS
  Animal laboratory of a health science university.
  
  
  METHODS
  Twelve New Zealand White rabbits.
  
  
  METHODS
  Juvenile rabbits were anesthetized, paralyzed, and ventilated through a tracheostomy. LBFO was performed with a modified high-frequency oscillatory ventilation circuit that uses low bias flow (100 mL/kg) and a soda lime cartridge to clear carbon dioxide. LBFO-heliox trials were performed with 20%, 40%, 50%, 60%, and 70% helium (balanced with oxygen) for 30 mins. Each heliox trial was preceded by a paired control trial with 40% oxygen and 60% nitrogen for 30 mins. Ventilator settings in control and heliox trials were identical. During the second part of the study, four rabbits were made hypercapnic by decreasing the power (amplitude), and LBFO was performed with 70% helium against paired-control trials of 40% oxygen and 60% nitrogen. Arterial blood gases were measured at 15-min intervals and airway pressure amplitude was recorded. PaCO2 of control and heliox trials, alveolar PO2-PaO2 gradient of control, and 60% helium trials were compared by paired Student's t-test.
  
  
  RESULTS
  At constant power, amplitude was unaffected by helium. Helium concentrations of 40%, 50%, 60%, and 70% decreased PaCO2 by 12%, 33%, 36%, and 46%, respectively. Alveolar PO2-PaO2 gradient was decreased by 40% during ventilation with 60% helium. Under hypercapnic conditions, 70% helium decreased PaCO2 by 20%.
  
  
  CONCLUSIONS
  Helium concentrations > or = 40% facilitate carbon dioxide clearance from lungs of normal rabbits during LBFO. This could be accomplished inexpensively with LBFO due to preservation of heliox when using this device.
authors.affiliation: Division of Pediatric Critical Care, The Children's Hospital of Buffalo, State University of New York at Buffalo, USA. rajsiddappa@hotmail.com
authors.forename: Rajashekhar
authors.initials: R
authors.lastname: Siddappa
authors.forename: Mark S
authors.initials: MS
authors.lastname: Dowhy
authors.forename: Alexandre T
authors.initials: AT
authors.lastname: Rotta
authors.forename: Lynn J
authors.initials: LJ
authors.lastname: Hernan
authors.forename: Christopher M B
authors.initials: CM
authors.lastname: Heard
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Fuhrman
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism*; D006371:Helium / Q000494:pharmacology*; D006612:High-Frequency Ventilation; D008168:Lung / Q000378:metabolism*; D010100:Oxygen / Q000494:pharmacology*; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange / Q000187:drug effects*; D011817:Rabbits
chemical_list: D002245:Carbon Dioxide; D006371:Helium; C038949:heliox; D010100:Oxygen