Enclosed afferent reservoir breathing systems. Description and clinical evaluation

A new group of breathing systems, namely the Enclosed Afferent Reservoir (EAR) systems, is described. They allow for the selective elimination of alveolar gas in association with both spontaneous and controlled ventilation. A comparison with the Bain system in controlled ventilation demonstrates greater efficiency in eliminating carbon dioxide. A fresh gas flow (VF) of 70 ml kg-1 min-1 using an EAR system gave mild hypocarbia which equated to a VF of 100 ml kg-1 min-1 using the Bain system. Smaller minute volumes of ventilation are required for optimal performance than with the Bain system. The minimum recommended minute volume of ventilation (VI) should equal VF plus anatomical deadspace ventilation (VDanat). The pattern of ventilation appears to have little influence upon the efficiency of carbon dioxide elimination when using an EAR system, whereas the Bain system does appear to be affected.