EFFICIENCY OF THE CARDEN VENTMASTA IN A-MODE AND D-MODE DURING CONTROLLED VENTILATION IN CHILDREN

We have determined the efficiencies of the enclosed Mapleson A and Map leson D modes of the Carden ''Ventmasta'' ventilator during controlled ventilation in 19 anaesthetized children. In addition, we determined the suitability for the A mode of the fresh gas formula, VF = 0.6 x we ight(0.5). Efficiency was assessed in terms of the fraction of fresh g as delivered to the alveoli. When the min ute volume to fresh gas flow ratio exceeded 1.5, fractional delivery of fresh gas was 23 % greater in the A mode than in the D mode (0.74 vs 0.60) (P < 0.0001). Under t he same conditions, mean end-tidal carbon dioxide concentration in 27 children undergoing ventilation in the A mode with VF = 0.6 x weight(0 .5) was 4.6% (range 3.5-5.4%). We conclude that the Carden system is u p to 23% more efficient in the A mode than in the D mode, and that und er the conditions of this study, normocapnia or mild hypocapnia was pr oduced accurately using the formula VF = 0.6 x weight(0.5).