EFFICIENCY OF BREATHING SYSTEMS A AND D IN THE CARDEN VENTMASTA VENTILATOR

We have compared the efficiency of the enclosed Magill attachment(System A) and the co-axial System D (Bain) in the Carden Ventmastaventilator using both systems, each under five different ventilatoryconditions, in each of five anaesthetized patients. Efficiencywas assessed in terms of the effective alveolar ventilationas a fraction of the fresh gas flow. For System A, efficiencyincreased from a mean of 0.37 when the total ventilation wasonly 50% of the fresh gas flow, to a mean of 0.74 when ventilationwas 2.3 times the fresh gas flow. The efficiency was substantiallyand significantly less with System D:75% of that for SystemA at the smaller total ventilation (95% Cl 65–85%) and65% at the larger (95% Cl 59–71%). A critical examinationis made of conflicting definitions and terminology of the efficiencyof breathing systems. (Br. J. Anaesth. 1993; 71: 741–746). ^*Department of Anaesthetics, East Glamorgan General Hospital,Church Village, Pontypridd, Mid Glamorgan CF38 1ABDepartment of Anaesthesia and Intensive Care, Royal AdelaideHospital, North Terrace, Adelaide, South Australia 5000