Figure 60-15 Eight types of anesthesia circuits were compared regarding ventilatory losses (circuit efficiency) as a result of compression of anesthetic gases (compression volume) and stretching of the circuit (compliance volume). Compression volume and compliance volume losses vary by as much as a factor of 5, depending on the volume of the circuit and the material from which it is constructed. Low-volume, low-compliance circuits (Mapleson D systems) are the most efficient and give the anesthesiologist the greatest amount of tactile feedback regarding tidal volume and lung compliance in small patients. Although large-volume, high-compliance circuits (adult circle systems) can be used in small patients, it is very difficult to estimate tidal volume and lung compliance because circuit-related losses in compression and compliance volumes are so large. (Redrawn from Coté CJ, Petkau AJ, Ryan JF, et al: Wasted ventilation measured in vitro with eight anesthetic circuits with and without inline humidification. Anesthesiology 59:442–446, 1983.)