barium sulfate or the equivalent the inclusion of the radiopaque material in the material of tip 514 helps to radiographically locate introducer 304 when it is in position by producing a sharply defined distinct radiographic image again referring to fig5 in one embodiment of the present invention cannula 308 includes at least one to a plurality of drainage holes 510 defined between external surface 306 and inner lumen 208 fig3 as shown in fig6 a a typical drainage hole 510 includes a square edge 602 and exhibits perceptible roughness to the touch generally hole 510 is punched through the wall 604 of cannula 308 in one stroke when the punch exits the far side of cannula 308 it may leave a slight burr or raised edge on external surface 302 tissue contacting side of cannula 308 around drainage hole 510 since cannula 308 is to be inserted through skin subcutaneous tissue fat and connective tissue then pushed through the femoral vein up to the right atrium of the heart there is a chance that some of the tissue may be scraped off by the square edged drainage hole 510 this problem is especially evident during percutaneous insertion when the surgeon has to push cannula 308 through the most difficult tissue as shown in fig6 b in accordance with an embodiment.