A catheter assembly is provided. An attachment structure has a proximal end portion of an outer cannula attached to it. A needle is insertable through the outer cannula and the attachment structure. An inner cannula is attached to an inner cannula attachment region of the attachment structure. The inner...http://www.google.co.uk/patents/US5156596?utm_source=gb-gplus-sharePatent US5156596 - Catheter with changeable number of lumens
