A stainless steel catheter assembly for communicating between a lumen of a blood vessel of a patient's body and a source or drain of fluid. A cannular termination is disposed at a distal portion of the catheter assembly and mechanically connected to respective distal ends of a wire-wound spring guide and a wire core which is disposed along an internal surface of the spring guide. A fitting for coupling to a source of intravenous fluid or a drainage device is disposed at a proximal portion of the catheter assembly and mechanically connected to the spring guide and wire core at respective proximal ends. Embodiments may be provided with a tapering distal termination which is disposed around a slidably retractable cannular needle for facilitating percutaneous access to the interior of a patient's vein. In other embodiments, the catheter assembly is terminated at the distal end in a blunted manner so as to permit the taking of central venous pressures. Such a bluntly terminated embodiment may be slidably disposed within a cannular needle for facilitating venipuncture.