Internal or external diameter?

Abstract

To the Editor: The size of the tracheal tubes is usually expressed as internal diameter. However, the external diameter may be quite different for tracheal tubes having the same internal diameter. Figure 1 shows a difference of 2 mm in external diameter between two tracheal tubes (produced by Rush and Mallinkrodt, respectively) having the same internal diameter (5 mm).Figure 1.: Different external diameters of two tracheal tubes having the same internal diameter.Interestingly, the ASTM (American Society for Testing and Materials) standards for tracheal tubes contain certain requirements for tracheal tubes (i.e., internal diameter, cuff, Murphy eye, etc.) but do not include recommendations about external diameter (1). While internal diameter is important for the airway resistance, the magnitude of the external diameter may play a role in the development of postintubation airway edema, postintubation croup and subglottic stenosis. in pediatric patients. Therefore, when choosing a certain size of tracheal tube in children, both internal and external diameters should be taken into account. Tiberiu Ezri, MD Marian Weissenberg, MD Ofer Yanai, MD Michael Sullam-Muggia, MD Zion Houri, MD Peter Szmuk, MD