A hemostasis cannula system includes a cannula, a vessel dilator, an elongate hollow percutaneous needle with clear reservoir, and an obturator. The hemostasis cannula comprises a body having a passage therethrough adapted to receive a catheter as well as a vessel dilator and a specialized obturator. The parts of the system are assembleable in a plurality of configurations including an arrangement for piercing skin, tissue and blood vessels. Another arrangement is adapted for advancing the tubing comprising the cannula, deep within the blood vessel. Lastly, another arrangement is useful for pressure monitoring and fluid introduction directly into the blood vessel of an organism. In the first configuration, the needle is received within the vessel dilator which is in turn received within the tubing comprising the cannula. In the second arrangement, the distal tip needle is withdrawn into the vessel dilator to avoid injury to the vessel when the dilator and cannula are advanced. Lastly, in order to directly monitor the blood pressure, the needle and vessel dilator are replaced with a specialized obturator having a plurality of circumferentially and longitudinally spaced apart openings in fluid communication with the lumen of the obturator as well as with the body of the cannula.