To the Editor:-I was interested to read the article by Stoneham et al. in which the efficacy of superficial cervical plexus regional anesthesia for carotid endarterectomy was demonstrated. There are a couple of issues of applied anatomy that warrant further discussion and emphasis.
The superficial technique is inherently simple and safe, because it is a subcutaneous injection along the posterior border of the sternomastoid. The only major structure in immediate proximity is the external jugular vein, which is visible and can be easily avoided. The same cannot be said for the deep technique, which has several major structures in immediate proximity to the advancing needle, including the vertebral artery, dural cuffs, sympathetic chain, phrenic nerve, common carotid artery, and internal jugular vein, and the endpoint can be disconcertingly deep. Clinical confirmation of the relevance of these anatomic relations has previously been reported. 
The authors comment on the possibility of phrenic nerve anesthesia when supplementing the superficial technique. This would in fact be difficult because the nerve lies well lateral to the surgical plane and in a different tissue plane. It would in fact be easier to anesthetize the phrenic nerve when trying to infiltrate subcutaneously during the superficial technique, by inadvertently penetrating the prevertebral fascia adjacent to the nerve. This contrast with the deep technique, which deliberately penetrates the prevertebral fascia to reach its target and has a known incidence of phrenic nerve anesthesia, as noted by the authors. 
The applied anatomy of these techniques would indicate a greater safety profile for the superficial technique, and the authors' demonstration of equivalent intraoperative efficacy should clarify further the issue of which technique to choose.
Philip B. Cornish, F.A.N.Z.C.A.
Consultant Anesthetist; Wellington Hospital; Wellington, New Zealand; Clinical Instructor 1992-1995; Department of Anesthesiology; University of Michigan Medical Center; Ann Arbor, Michigan
(Accepted for publication January 27, 1999.)