title: Efficiency of breathing systems A and D in the Carden Ventmasta ventilator.
abstract: We have compared the efficiency of the enclosed Magill attachment (System A) and the co-axial System D (Bain) in the Carden Ventmasta ventilator using both systems, each under five different ventilatory conditions, in each of five anaesthetized patients. Efficiency was assessed in terms of the effective alveolar ventilation as a fraction of the fresh gas flow. For System A, efficiency increased from a mean of 0.37 when the total ventilation was only 50% of the fresh gas flow, to a mean of 0.74 when ventilation was 2.3 times the fresh gas flow. The efficiency was substantially and significantly less with System D: 75% of that for System A at the smaller total ventilation (95% CI 65-85%) and 65% at the larger (95% CI 59-71%). A critical examination is made of conflicting definitions and terminology of the efficiency of breathing systems.
authors.affiliation: Department of Anaesthestics, University of Wales College of Medicine, Heath Park, Cardiff.
authors.forename: E J
authors.initials: EJ
authors.lastname: Tham
authors.forename: R
authors.initials: R
authors.lastname: Davies
authors.forename: J M
authors.initials: JM
authors.lastname: Slade
authors.forename: W W
authors.initials: WW
authors.lastname: Mapleson
mesh_terms: D000328:Adult; D000764:Anesthesia, Closed-Circuit; D000769:Anesthesia, Inhalation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011650:Pulmonary Alveoli / Q000502:physiology; D012119:Respiration / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D012122:Ventilators, Mechanical