PENETRATION FORCES IN CANNULATION OF THE DORSAL VEINS OF THE HAND .1. A COMPARISON BETWEEN POLYURETHANE (INSYTE) AND POLYTETRAFLUOROETHYLENE (VENFLON) CANNULAE - RESULTS OF A STUDY IN VOLUNTEERS COMPARED WITH THOSE FROM AN INVITRO STUDY

The functional tip tapering design of peripheral venous cannulae (introducer steel needle + catheter) made of polyurethane (PUR-Insyte(R)) and polytetrafluoroethylene (PTFE-Venflon(R)) was studied with 3 techniques: A) Scanning electron microscopy (SEM). B) Measurement of penetration forces in vitro through latex membranes and lamb skins with a tensile-compression apparatus (Instron-1122(R)) at 1) the introducer steel-needle point, 2) the needle heel (the spot marking the passage from the point of the needle to its shaft), 3 the catheter top (i.e. the beginning of the plastic sheath), 4) the catheter tip, i.e. the beginning of the largest diameter of the plastic sheath, and 5) between the catheter tip and its hub (catheter friction). C) Two cannulae (one of each type for every subject) were inserted at random into the dorsal veins of the left and right hand in 37 volunteers, and the penetration forces were measured with a force transducer. Results: A) The PUR-cannulae had a lancet-like appearance and a smoother transition at the catheter top, whilst the PTFE cannulae were arrow-like, cut back and had a less accentuated conical design. B) Penetration forces in vitro through latex membranes were 9-41 times lower (P < 0.0001) than those through the lamb skins. The highest forces (mean +/- s.d.) registered in vitro (lamb skins) were 4.1 +/- 0.2 Newtons (N) with PUR-cannulae at the catheter tip, and 3.4 +/- 0.6 with the PTFE-cannulae at the catheter top (P < 0.05). C). In in vivo (volunteers), significantly (P < 0.001) higher forces were required with the PUR-cannulae than with the PTFE-cannulae for penetration of both the skin (3.9 +/- 1.6 vs 2.7 +/- 0.8 +/- N) and the vein wall with continued penetration of the skin (3.5 +/- 1.2 vs 2.4 +/- 0.9 N). When the highest penetration forces were compared, no significant differences between in vitro (lamb skins) and in vivo (skin and vein with continued skin penetration studies were found with either of the two cannulae studied. We conclude that there were statistically significant differences between penetration forces of the PUR and PTFE-cannulae when inserted into the dorsal veins of the hand. Penetration forces in vitro (lamb skins) may predict with acceptable accuracy the penetration forces in vivo (dorsal veins of the hand).