title: An evaluation of fresh gas flow rates for spontaneously breathing cats and small dogs on the Humphrey ADE semi-closed breathing system.
abstract: OBJECTIVE
  To evaluate the fresh gas flow (FGF) rate requirements for the Humphrey ADE semi-closed breathing system in the Mapleson A mode; to determine the FGF at which rebreathing occurs, and compare the efficiency of this system to the Bain (Mapleson D) system in spontaneously breathing cats and small dogs.
  
  
  METHODS
  Prospective clinical study.
  
  
  METHODS
  Twenty-five healthy (ASA score I or II) client-owned cats and dogs (mean ± SD age 4.7 ± 5.0 years, and body weight 5.64 ± 3.26 kg) undergoing elective surgery or minor procedures.
  
  
  METHODS
  Anaesthesia was maintained with isoflurane delivered via the Humphrey ADE system in the A mode using an oxygen FGF of 100 mL kg(-1) minute(-1). The FGF was then reduced incrementally by 5-10 mL kg(-1) minute(-1) at approximately five-minute intervals, until rebreathing (inspired CO(2) >5 mmHg (0.7 kPa)) was observed, after which flow rates were increased. In six animals, once the minimum FGF at which rebreathing occurred was found, the breathing system was changed to the Bain, and the effects of this FGF delivery examined, before FGF was increased.
  
  
  RESULTS
  Rebreathing did not occur at the FGF recommended by the manufacturer for the ADE. The mean ± SD FGF that resulted in rebreathing was 60 ± 20 mL kg(-1) minute(-1). The mean minimum FGF at which rebreathing did not occur with the ADE was 87 ± 39 mL kg(-1) minute(-1). This FGF resulted in significant rebreathing (inspired CO(2) 8.8 ± 2.6 mmHg (1.2 ± 0.3 kPa)) on the Bain system.
  
  
  CONCLUSIONS
  The FGF rates recommended for the Humphrey ADE are adequate to prevent rebreathing in spontaneously breathing cats and dogs <15 kg.
  
  
  CONCLUSIONS
  The Humphrey ADE system used in the A mode is a more efficient alternative to the Bain system, for maintenance of gaseous anaesthesia in spontaneously breathing cats and small dogs.
authors.affiliation: Anaesthesia Unit, Faculty of Veterinary Science, University Veterinary Teaching Hospital-Sydney, University of Sydney, Camperdown, NSW, Australia.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Gale
authors.forename: Kim E
authors.initials: KE
authors.lastname: Ticehurst
authors.forename: Sanaa
authors.initials: S
authors.lastname: Zaki
mesh_terms: D000769:Anesthesia, Inhalation / Q000295:instrumentation / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D002415:Cats / Q000502:physiology* / Q000601:surgery; D004285:Dogs / Q000502:physiology* / Q000601:surgery; D004867:Equipment Design; D007530:Isoflurane / Q000008:administration & dosage*; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial / Q000295:instrumentation* / Q000662:veterinary
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane
keywords: anaesthesia; anaesthetic circuits; bain circuit; breathing systems; humphrey ADE