Catheter-over-needle method reduces risk of perineural catheter dislocation.

Editor—We read with great interest the recent study by Marhofer and colleagues which assessed dislocation rates of interscalene and femoral perineural catheters in volunteers. We wish to commend the authors on addressing and reporting a common problem that most anaesthesiologists encounter when placing continuous catheters yet which is largely ignored in the literature. Obviously, there is a significant problem with leakage, as demonstrated by the effort of many clinicians to secure the catheter with glue (e.g. Dermabond), 3 catheter tunnelling, or both. Despite this, most articles focus on reporting high rates of success (and use various definitions of ‘success’) and do not adequately address problems with leakage or dislodgement. We agree completely with the observations made by Marhofer and colleagues and are not surprised at the reported 15% dislocation rate and the positive correlation between time and rate of dislocations. At our institution, catheter dislocation and leakage at the insertion site are significant concerns when placing catheters using the traditional catheter-through-needle (CTN) method. Such problems led us recently to conduct studies examining the underlying cause of leakage and dislodgement. After careful study of the physical mechanisms behind perineural catheter insertion, we concluded thatdislodgement results primarily from the diameter of the catheter (e.g. 20 G) being smaller than that of the needle (e.g. 18 G) used for initial skin puncture (Fig. 1). Thus, the catheter is not held tightly by the skin, leaving space for local anaesthetic to leak upon injection. A simple solution is to borrow from the commonly used i.v. catheter design, in which the catheter is fitted over the needle. In this design, the gauge of the needle (21 G) and catheter (20 G) is reversed relative to the CTN design, such that the puncture hole diameter is smaller than that of the catheter, creating a tight fit in the skin (Fig. 1). Since this time, we have been using acatheter-over-needle (CON)methodsuccessfullyformorethan 1 yr, and we wish to highlight our experience with this method for perineural catheter insertion. We believe that the CON design offers greater stability and less dislocation compared with traditional designs. To test CON and CTN catheters in a controlled system, we carried out a laboratory study which demonstrated the superiority of the CON method over the CTN method in preventing leakage. After this, our initial proof-of-concept clinical study showed that a second bolus of local anaesthetic through a supraclavicular CON catheter after surgery was effective in prolonging the block. Our success with this method suggested that the perineural catheter was stable and did not migrate from its perineural location. Despite the fact that we did not assign specific movements for the patients to undertake after the catheter was inserted, as Marhofer and colleagues did, the patients’ arm and clavicle did move when the patients transferred themselves from the stretcher to the operating table and vice versa and also during skin preparation before surgery. We also conducted a randomized, controlled study which demonstrated that interscalene CON catheters leaked less frequently compared with CTN catheters. Leakage has been described as a complication of the CTN perineural catheter which may disrupt the adhesives, causing potential dislodgement of the perineural catheter. Although our study was