T-PIECE CIRCUIT

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References: 2

Gas anaesthesia is normally applied via a breathing circuit which includes an expiratory valve. This releases excess gas (mainly during exhalation) via a pressure relief valve. One adverse effect of this is to offer some resistance to exhalation. In paediatric anaesthesia this problem can be avoided by using a T- piece circuit (Mapleson classification type E) in which the fresh gas feed is connected to a T-piece which connects on one side to the patient (by a mask or endotracheal tube) and on the other to a length of corrugated breathing tube. Fresh gas fills the tube during the expiratory pause and this is taken in during inspiration. During expiration the waste gases pass out down the tube. Obviously there is some rebreathing but this is limited by the flow rate of fresh gas.

An important modification of this circuit is the inclusion of a double-ended reservoir bag at the end of the length of breathing tube. The distal end of this bag can be occluded with a finger during the inspiratory phase of assisted ventilation and release during the rest of the cycle. This is the Rees T-piece circuit.