Tracheal tubes and connectors used in neonates--dimensions and resistance to breathing

The dimensions of tracheal tubes and connectors in common use were measured together with the resistance to breathing at flow rates occurring in babies breathing quietly. The outside diameters of rubber tubes varied more than those of plastic tubes. The main factors influencing resistance were the internal diameter and a sudden change in diameter or direction of flow. These are of particular importance in tubes of 2.5 mm i.d. and less and may cause an increase in the work of breathing during spontaneous ventilation. The resistance of small Cole pattern tubes was greater than that of plain tubes of similar o.d.