Effects of minute volume increases on the rebreathing characteristics of the Bain anaesthesia circuit during controlled ventilation

Oxygen and carbon dioxide concentrations in anaesthetic circuits ventilated with an AGA UV 705 in an oxygen consuming model lung

An oxygen consuming an carbon dioxide producing model lung was used for evaluation of anaesthetic circle systems. Two different circles, the AGA metal circle and the AGA Monosorb circle ventilated by an AGA UV-705 were tested with reference to inspired oxygen concentrations and end-tidal CO2 levels. Carbon dioxide is dependent on alveolar ventilation and CO2 production and thus was stable throughout the experiments. The oxygen concentration of inspired gas decreased progressively with decreasing fresh gas flow. When using the fresh gas inlet on the ventilator outlet block, the inspired oxygen concentration fell 8% as compared to using the fresh gas inlet in the circle. Fresh gas flows under 3 1/min should only be used with oxygen monitoring in the circle. The fresh gas inlet must be directly into the circle, and not in the ventilator outlet block, to avoid hypoxia.