The Advantages of a Combined T-piece and Non-rebreathing Valve: a Simple Device.

Ayre's T-piece. The Ayre's T-piece (Ayre, 1937) has a very low resistance, is simple, and almost trouble-free. Intermittent positive pressure respiration (IPPR) can be induced by occluding the exhalation reservoir tube intermittently with one finger. However, the pressure, volume, and riming of lung inflation depends on the flow of gases from the anaesthetic machine and the duration of finger occlusion. This manoeuvre is also dangerous because the steep rise of intrapulmonary pressure cannot be estimated by the fingertip (Keuskamp, 1963). While controlled ventilation can be induced fairly well in infants or small children, satisfactory assisted respiration is often hard to attain, because there is no reservoir bag for transmitting respiratory information and for squeezing at an optimal time. Rees (1950) has advocated the addition of an open-ended reservoir bag to the expiratory limb to facilitate intermittent positive pressure respiration. The status of rebreathing is here obscure, because the expiratory gas may remain inside the expiratory limb or in the bag when there is no respiratory pause or if it is too short to enable sufficient fresh gas to accumulate for adequate ventilation. In order to have a properly functioning T-piece it would appear that the fresh gas flow and the expiratory reservoir limb volume should be adjusted to the patient's tidal volume, respiratory rate, duration of inspiration and expiration, and respiratory pause (Ayre, 1956; Collins, Bronner and Rovenstine, 1961; Harrison, 1964; Inkster, 1956; Keuskamp, 1963; Mapleson, 1954; Onchi, Hayashi,