Advanced Needle Coatings for Improved Lumbar Drain Procedure

Abstract

Lumbar drains are used to remove cerebrospinal fluid (CSF) from the spinal column. This procedure can relieve intracranial pressure, caused by excess CSF, and assist in healing CSF leaks from the brain or spine after surgery or a head injury. To remove the fluid, a catheter is inserted into the subarachnoid space through the vertebrae using a Tuohy needle as shown in Figures 1(a)–1(d)Fig. 1This figure illustrates the process of catheter insertion, where (a) the needle is inserted, (b) the catheter and guide wire are inserted, (c) the needle is removed, and (d) the guide wire is removed.. The needle is inserted first, Fig. 1(a), then the catheter with the guide wire inside is inserted, Fig. 1(b), then the needle is removed, Fig. 1(c), and lastly the guide wire is removed leaving the catheter in place to drain the CSF fluid, Fig. 1(d).Rarely (0.0 – 1.8% of the time) [1], the catheter fractures inside the patient's spine. This can cause major complications, and often requires surgical removal of the catheter fragment. Research has shown that one of the main causes of fracture is intentional or unintentional retraction of the catheter [2]. When difficulty with advancement of the catheter is encountered, there is a tendency to partially withdraw and then re-advance the catheter. Fracture is also caused by the removal of the catheter [2]. If the catheter encountered less frictional wear during insertion, the likelihood of fracture should decrease.Sometimes during the procedure the catheter will be unable to be advanced far enough inside the patient due to a high buildup of forces between the catheter and the needle and subarachnoid space. This requires the needle be reinserted into the patient causing greater pain and increasing the procedures length and risk for complications. A lower insertion force would allow for easier insertion into the body lowering the potential need for needle reinsertion.Often, biocompatible coatings are used in medical tools to improve biocompatibility, thermal stability, and dielectric properties. In this procedure, lubricity is one of the most important properties of the Tuohy needle and can be improved by the use of a coating.Parylene is a plastic, biocompatible coating. It is currently used in many medical applications, such as stents, pacemakers, and hearing aids. In these applications, parylene is mainly utilized for its environmental protection and electrical insulation, rather than its lubricity.Another biocompatible coating is diamond-like carbon (DLC). Its carbon structure is between that of diamond and graphite. DLC is mostly found in mechanical and electrical applications due to its low coefficient of friction, high hardness, chemical inertness, and high electrical resistivity. However, DLC is also used in the body for orthopedic and cardiovascular applications [3]. The lubricity of DLC is utilized in many other applications, but has not yet been thoroughly explored for needles.The objective of this study is to evaluate and compare frictional force of regular uncoated needles to that of parylene and DLC coated needles. Reduction of frictional force would reduce the potential for catheter fracture and needle reinsertion in lumbar drain procedures.The overview of the experimental setup shown in Fig. 2(a) was used to evaluate the frictional force between the needle and catheter. This experimental setup mimics the lumbar catheter insertion procedure by using a pneumatic cylinder to clamp on and push the catheter in 15 mm intervals at 3 mm/s as shown in Fig. 2(b). A small hole was drilled into a water tank, and the needle was inserted into the hole through a small rubber seal to ensure the needle remained stationary and prevent water leakage. The force sensor, attached to the pneumatic clamp, recorded the forces during insertion. The tank of water is of similar density and viscosity of CSF [4]. The pneumatic clamp and linear slide allow for simulation of manual threading of the catheter, while also providing a consistent advancement distance and rate.Three needles were tested: one uncoated, one coated with parylene, and one coated with DLC as shown in Fig. 3. The uncoated needle was used as a baseline for how the current procedure is performed. The 14 gauge Tuohy needles, silicon catheter, and guide wire used were from a standard kit (Integra NeuroSciences).To ensure consistent results, the catheter was placed at the same position for the start of each test, and was advanced five times (five clamping and pushing steps), for a total of 75 mm. The test was repeated for a total of ten runs for each needle. The forces were averaged between 50 and 70% during each advancement, thus eliminating the forces during clamping and release of the catheter. Figure 4 shows an example catheter force profile for five cycles. The black line shown below in Fig. 4 indicates the average value for this portion of the advancement. This value was then averaged for the ten runs of each needle, allowing for an accurate comparison of the frictional forces acting on the three needles tested.The coated needles are able to produce significantly lower insertion forces than the uncoated needle, as shown in Fig. 5. The parylene coating reduced the friction by 34.9% on average, and the DLC coating reduced friction by 24.2%. Overall, the parylene coating provided on average the most significant reduction of friction during insertion.Both DLC and parylene have been reported to have very low coefficients of static and dynamic friction. The coefficient of friction has been reported for parylene to be 0.29 and for DLC less than.01 [5,6]. In water, the frictional coefficient should be even less as it provides lubrication between the moving parts.Though the coefficient of friction for DLC should have been more than 30 times that of parylene, the parylene coated needle experienced slightly less friction on average during insertion.One drawback of the parylene coating is its softness [5]. It is easy to scratch during routine handling. This coating may not be able to withstand the high forces experienced upon needle insertion.It was found that the coatings of DLC and parylene reduced the frictional force between the needle and catheter by 24.2% and 34.9%, respectively compared to a regular uncoated needle. These coatings could help to reduce the potential for catheter fracture and needle reinsertion in lumbar drain procedures. Future work will focus on developing frictional force models to optimize the insertion speed and the surface properties to minimize the frictional forces.