Ideal anaesthetic circuit for spontaneously breathing pediatric patient is:-

Mapelson F or Jackson reevs circuit is circuit of choice for for pediatric in both spontaneous and controlled ventilation. It is a modification of Mapleson E by Jackson Rees and is known as Jackson Rees modification or Mapleson F. It has a 500 ml bag attached to the expiratory limb. This bag helps in respiratory monitoring or assisting the respiration. It also helps in venting out excess gases. The bag has a hole in the tail of the bag that is occluded by using a finger to provide pressure. The bags with valve are also available. It is used in neonates, infants, and paediatric patients less than 20 kg in weight or less than 5 years of age. Technique of use For spontaneous respiration. The relief mechanism of the bag is left fully open. For controlled respiration the hole in the bag can be occluded by the user during inspiration and ventilation is done by squeezing the bag.