The safety of an interscalene catheter‐over‐needle technique

We read with great interest the case report by Yanovski et al. 1, and the accompanying editorial by Fredrickson et al. 2, reporting the death of a patient following local anaesthetic bolus through an interscalene catheter whose tip was in an intrathecal position. We previously reported a case where the interscalene catheter tip was situated near the phrenic nerve in an asthmatic patient who suffered respiratory embarrassment 3. Together, these reports reinforce the problem of the traditional catheter-through-needle insertion technique: overfeeding of the catheter beyond the needle tip to compensate for subsequent removal of the needle. This can lead to unpredictable catheter tip placement, even under ultrasound guidance. To overcome this problem, we introduced a refined catheter-over-needle (CON) technique 4. We have been using a Pajunk MultiSet 21156-40E CON assembly (Pajunk, Geisingen, Germany) for almost a year and, since its introduction, we have been able to ascertain the final catheter tip position for multiple peripheral block locations, including interscalene, supraclavicular, infraclavicular, femoral and popliteal. The CON technique is relatively simple and relies on two major components: an outer catheter sheath and a flexible, kink-resistant inner catheter (Fig. 1). For interscalene block, a 21-G needle, housed within the outer catheter and with its distal, electrically conductive end protruding, is used to position the distal catheter tip between C6 and C7 nerve roots, just adjacent to the scalenus anterior muscle. A 13-6 MHz high frequency linear ultrasound transducer (HFL 38, M-Turbo; SonoSite, Bothell, WA) provides real-time ultrasound guidance. Subsequently, the needle is withdrawn and the inner catheter, whose length is similar to that of the needle, is inserted into the outer catheter. Thus, the inner catheter literally replaces the needle without the need for overfeeding and enables the inner catheter tip to be in the desired position. The outer catheter provides support, allowing the inner catheter tip to adopt a linear structure that can be observed clearly on the ultrasound screen (Fig. 1). Furthermore, the risk of leakage and dislodgement 5 are substantially lower because the needle puncture hole is smaller than the outer catheter diameter.

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