Background and Objectives: The authors conducted a scanographic study in order to characterize the local anesthetic spread of injectate resulting from a single-injection technique of deep cervical plexus block.

Methods: Six consecutive American Society of Anesthesiologists II and III patients scheduled for elective carotid endarterectomy under regional anesthesia were enrolled. Deep cervical plexus block was placed via an anterolateral approach using a nerve stimulator to guide the injection on contact with the levator scapulae nerve. With specific contractions evoked at a stimulating current intensity ≤0.5 mA, a 40-mL mixture containing local anesthetics and iopamidol was injected. Thirty minutes after the block was placed, sensory and motor neural blockade was evaluated, and a helicoidal scanner of the head-neck and upper thorax was completed. Sequential cross sections spaced at 5 mm were performed from the base of the skull down to T1. A 3-dimensional volume-rendering technique was used to characterize spread of injectate, which calculated volume.

Results: All patients completed C2-C4 dermatomal sensory blockade. None of the patients experienced anesthesia of the C8 and T1 dermatomes. The spread of injectate extended in a cephalocaudal direction from C1 to C7; its wider dimensions were systematically observed at the C3-C4 level. Fascia of the carotid sheath and sternocleidomastoid muscle limited the anterior spread of injectate. The trapezius limited lateral and posterior diffusion of injectate. Spread of injectate had a large volume exceeding twice that of the injectate. It has roughly a hemi cylinder shape with both ends stretched toward C1 and C7.

Conclusion: The authors showed that deep cervical plexus block was associated with a wide spread of injectate. The data show that the spread of injectate is enclosed within to the prevertebral layer of the deep cervical fascia.