Fig. 1

Study catheters and needle. a + c Self-Coiling Catheter (Sono Long Curl Echo 20 G 100 mm, Pajunk medical products, Geisingen, Germany), a catheter tip; c entire catheter. b + d Regular straight catheter (Sono Long Sono 20 G 100 mm, Pajunk medical products, Geisingen, Germany), b catheter tip; d entire catheter