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We read with interest the recent editorial by Fredrickson and Harrop-Griffiths [1], and agree with the points made regarding techniques to improve the safety of interscalene catheter placement. We propose a novel technique to improve safety further, involving placement of the catheter just within the scalenus medius muscle.

The brachial plexus is imaged in the conventional way and the medial border of scalenus medius is identified at a point where the nerve roots are most closely related. The needle can then be placed just lateral to this border using an out-of-plane technique until the tip lies just lateral to the plexus but just within the body of the scalenus medius muscle (Fig. 1). The catheter can then be inserted and threaded 3–4 cm beyond the needle, in an inferior direction away from the neuraxis, thus providing a degree of protection from misplacement. Scalenus muscle tissue and fascia therefore provide another physical barrier, increasing the safety of the catheter and reducing the likelihood of intravascular placement. Catheter position can be confirmed by observing local anaesthetic spread, and it can be used to administer the first bolus and subsequent infusion of local anaesthetic.

image

Figure 1. Ultrasound image of the interscalene groove with arrow showing the ideal position of the needle tip or interscalene catheter, using an out-of-plane (OOP) technique, just lateral to the medial border of scalenus medius. N = nerve root.

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Combining two recent one-year retrospective surveys at Wrightington Hospital, we found a 100% success rate for interscalene nerve blocks or catheter insertions performed within the scalenus medius border (49 cases). This compares with a 91% success rate for conventional single-shot ultrasound-guided injections into the interscalene groove (171 cases; chi-squared p = 0.0271). Success was measured by lack of opioid use in recovery. In all cases, a low dose of 6–10 ml ropivacaine 0.75% was used, reducing the risk of muscle necrosis; there were no serious complications.

These surveys involve a relatively small number of patients, and we did not look at later analgesic requirements; furthermore, we cannot comment on the complication rate. Our results do, however, provide some evidence that this new technique for interscalene nerve block with catheter insertion is comparable with conventional approaches, and may be inherently safer.

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