The middle interscalene block: cadaver study and clinical assessment.
BACKGROUND AND OBJECTIVES: A variety of brachial plexus block techniques via the interscalene approach have been proposed. We describe here a new middle interscalene perivascular approach to the brachial plexus. To verify its effectiveness, we studied 719 patients scheduled for shoulder arthroscopy. Furthermore, to verify the accuracy of the proposed bony landmarks to use in the case of inability to palpate the subclavian artery pulse, we simulated the block on 10 cadavers. METHODS: The aim of our technique is to cannulate the neurovascular bundle by inserting a 35-mm needle lateral to the subclavian arterial pulse near the midpoint of the upper edge of the clavicle in a horizontal or slightly cephalad direction while pointing toward the seventh cervical vertebra. If the pulse of the subclavian artery is not palpable, we localize the direction of the needle with reference to 3 bony landmarks (the middle point of the clavicle, the spinous process of C7, and the sternoclavicular joint). By connecting these 3 landmarks, we obtain an angle whose apex lies at the midpoint of the clavicle and its bisecting line points to the plexus. The needle is introduced in the transverse plane of C7. RESULTS: The block was performed successfully in 692 of 719 cases (96.2%). Horner's syndrome occurred in 93.5% of the cases, arterial puncture with hematoma occurred in <1%, phrenic nerve block without respiratory impairment in 60%, with transient respiratory failure in <1%, and laryngeal nerve block in <1%. The incidence of severe complications or permanent injuries was zero (upper limit 95% confidence interval = 0.4% or 1:250 patients). The technique performed on cadavers showed that the previously mentioned bony landmarks were reliable reference points in reaching the brachial plexus. CONCLUSIONS: Our technique via a middle interscalene approach is easy to perform and provides a high success rate. Even in the absence of a subclavian artery pulse, the easily recognizable bony landmarks reliably guide us in the insertion of the needle. Furthermore, this technique appears to avoid complications that are theoretically possible in other supraclavicular perivascular approaches (pneumothorax) and paravertebral approaches (injection into the vertebral artery and subarachnoidal injection). However, further comparative studies will be required to assess the clinical relevance of the block.