When is a single-injection nerve block not really a single injection?

To the Editor:—I read, with interest, the case report describing a brachial plexopathy after an ultrasound-guided interscalene block in a patient with multiple sclerosis and the accompanying editorial and would like to make an observation not mentioned in either. Interscalene blocks have been performed using either mechanical paresthesia or electrical nerve stimulation, for decades, with success rates reported to be 94–99%. In both of these techniques, the entire dose of local anesthetic is injected upon eliciting the initial desired response. These true single-injection techniques occur at the first nerve root, and likely the most superficial one, encountered. Perlas et al. used real-time ultrasound to quantify the sensitivity of both paresthesia and motor nerve stimulation techniques. A 22-gauge insulated needle was in the axilla of 103 patients, and after visualizing direct needle–nerve contact, the patients were asked whether they felt any paresthesia. The nerve stimulator was then turned on, and a motor response was sought at 0.5 mA or less. The authors concluded that there are a significant number of false-negative responses (direct needle–nerve contact not resulting in paresthesia or motor response) with these traditional methods of localization. This study showed that direct ultrasound visualization does not prevent intimate needle–nerve contact. Although Koff et al. note that their needle “was not seen to penetrate the epineurium by [their] ultrasound image” after the first injection at C5, one must wonder how that initial volume of injection altered the ability to discern the needle–nerve relation of the three subsequent injections/maneuvers used to complete the block. One of the many questions that needs to be addressed, as we continue to promote the benefits of ultrasound for peripheral nerve blocks, is whether there are any advantages to repositioning a needle multiple times to be able to visualize local anesthetic spread around each of the nerve roots, because our historic success rates imply that this occurs adequately, with the initial injection. That is, does this practice of diving for individual and deeper nerve roots actually increase the risk to patients? The enemy of very good may prove to be better.