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SummaryThe Portex infant breathinglventilation systems with 8.5 mm and I5 mm internal diameter connectors were compared with a standard T-piece which had a I5 mm connector and 22 mm internal diameter tubing. The differential pressures across each system were measured at constant fresh gasjows up to 30 1.min-I dry air. Resistance was calculated at flows compatible with quiet respiration and peak inspiratory pow. Flow resistance of'the 3.0 mm internal diameter tracheal tube in conjunction with the minilink breathing systems were similar to those previously reported for tracheal tubes alone. However, the minilink breathing system assumed a greuter injluence on resistance when tracheal tubes of larger internal diameter were used. It added considerably more resisrance than the standard tubing. This may have a deleterious effect during spontaneous ventilation in older children. Key wordsEquipment; minilink breathing system. A irway : resistance.In accordance with recommendations made by Inkster in 1981 [I], Portex attempted to standardise the size and design of connectors used in paediatric anaesthesia and intensive care. They manufactured an infant breathing system (the minilink) which comprises a T-piece with two designs of cross piece (8.5 mm internal diameter and 15 mm internal diameter) plus dedicated connectors for attachment to a tracheal tube. The cross piece attaches to 6 mm internal diameter (ID) inspiratory and expiratory limbs of 40 cm length. They are made of light weight, flexible and transparent material. The manufacturers claim the advantages of secure fixation, versatility of use and a direct fit onto cut-to-length tracheal tubes. It is considered suitable for spontaneous respiration, manual or mechanical ventilation, humidification and has an additional port for tracheal suction [2].The 8.5 rnm connectors are tapered to avoid excess angulation and rapid changes in diameter so that turbulent flow is minimal and hence resistance to flow is low [3].Although the term infant implies that the system should be used in children aged 0-12 months, the sytem is available with connectors for tracheal tubes up to 6.0 mm ID. We anticipate that it is also suitable for older children.Despite this we were hesitant to use this sytem with spontaneous respiration as it might be a source of resistance to breathing.To assess its suitability for spontaneous respiration in older children, we compared the differential pressure across the Portex breathing systems (the minilink) with the differential pressure across standard 22 mm tubing of the same length as the Portex tubing connected by a standard I5 mm T-piece at flows up to 30 I.min-' of dry air. MethodWecompared the two minilink systems with a standard Tpiece system. The standard T-piece comprised a cross piece with 22 mm connections to the inspiratory and expiratory limbs and a 15 mm I D connector to tracheal tubes. It had a larger dead space than either of the minilink cross pieces (Fig. I). Tracheal tubes of sizes 3.0 mm, 4.0 mm, 5.0 mm and 6.0 mm ID, each cut to leng...