Spread of injectate with superficial cervical plexus block in humans: an anatomical study

Background. This study was undertaken to investigate why thesuperficial cervical plexus block for carotid endarterectomyis so effective. Initial consideration would suggest that asuperficial injection would be unlikely to block all terminalfibres of relevant nerves. One possibility is that the localanaesthetic crosses the deep cervical fascia and blocks thecervical nerves at their roots. Methods. Superficial cervical plexus blocks (injections justbelow the investing fascia) were performed using methylene blue(30 ml) in four cadavers. In one additional control cadaver,a deep cervical plexus injection was performed. In a secondcontrol cadaver, a subcutaneous injection (superficial to investingfascia) was performed at the posterior border of the sternomastoidmuscle. Results. Anatomical dissection showed that with superficialblock there was spread of the dye to structures beneath thedeep cervical fascia. In the first control, dye remained inthe deep cervical space. In the second control, dye remainedsubcutaneous. Conclusions. The superficial cervical space communicates withthe deep cervical space and this may explain the efficacy ofthe superficial block. The method of communication remains unknown.Our findings also indicate that the suitable site of injectionfor the superficial cervical plexus block is below the investingfascia of the neck, and not just subcutaneous. Br J Anaesth 2003; 91: 733–5