Fresh gas requirements of an enclosed afferent reservoir breathing system in anaesthetized, spontaneously breathing adults.

Using two methods of determining the onset of rebreathing, we have determined the minimum fresh gas flow rate (VF) of the Ohmeda enclosed afferent reservoir breathing system (EAR) in anaesthetized, spontaneously breathing adults. Rebreathing as defined by the Kain and Nunn criteria did not occur when the VF/VE ratio was greater than 0.70. A mathematical model was used to calculate the degree of rebreathing at each VF. From this model, rebreathing did not occur when VF was 0.86 VE or more and this value of VF/VE is considered appropriate to eliminate rebreathing in clinical practice.