13 3.2 Drainage holes (eyes) The drainage holes (eyes) are positioned about 1 to 2 cm beneath the catheter tip. They allow the drainage of urine. It is, therefore, important that the catheter is placed far enough into the bladder (when urine starts to flow, the catheter should be advanced at least 1 cm further). There are usually two drainage eyes, which are polished to avoid sharp edges. The size of the eyes increases with Charrière size. Catheters with additional eyes (3 to 4) and extra-large eyes, which may be recommended to assist with mucous drainage (e.g., in an augmented bladder), are available from Ch 8. There is also a catheter with micro-hole Technology, which means that the catheter has a lot of micro-eyes. The urine stream comes out in a continuous stream (Luja, Coloplast.) 3.3 Charrière The external diameter (size) of catheters is measured in millimetres and is known as the Charrière scale. 1 Ch corresponds to 0.33 mm. Generally, most types of catheters are available in sizes from 6 to 20 Ch for intermittent catheterisation (Table 4). The size is commonly represented by the international colour coding of the connector at the end of the catheter, and the Charrière is stated on the package. Additionally, for small or premature babies/neonates or difficulties with inserting size six catheters, there are non-coated smaller catheters available: a size four male length (Vygon) and a size five pediatric length (Wycath). The use of feeding tubes is not recommended due to the incidence of knotting in the bladder20 Recommended size by age can be seen in Table 5. Table 4 Catheter connector colour chart Catheter size 6 8 10 12 14 16 18 20 Colour Diameter 2 2.7 3.3 4 4.7 5.3 6 6.7 Table 5 General overview of recommended Charrière per age category Age Charrière 0-1 years Ch 6-8 1-8 years Ch 8-10 8-12 years Ch 10-12 12 years and older Ch 12-14 As the urethra is able to tolerate large sizes of catheter, e.g., a 3-year-old boy can tolerate a size 12 catheter, clinicians may recommend larger sizes than those in the table above in order to promote more effective emptying, reduce time to empty, and minimise infection risks. 3.4 Length A catheter with a length of 20 cm is normally suitable for most boys up to 6 years old. In Charrière sizes 8, 10, and 12, there are catheters available with an ‘in-between’ length of 30 cm (e.g., Wellspect, Coloplast, Teleflex). When boys become older, they can move on to the ‘adult’ length of 40 cm. There is a male compact version available for teenage boys who graduated from a size 12 to 18 within the same catheter. These catheters should only be used in consultation with health professionals.22 For girls, catheter lengths from 7 to 20 cm are available. These lengths can basically be used by children of all ages, with the shortest sizes intended especially for catheterisation when sitting on the toilet. The short catheters are packed in a way that ensures they are easy and discreet to carry. 3.5 Tip design
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