HSC Section 3 - Trauma, Critical Care and Sleep Medicine

muscle, and several millimeters inferior (caudal) to the main trunk of the CN XII (Fig. 1A).

OPERATIVE TECHNIQUE The steps involved in implantation of the UAS sys- tem are discussed as follows. The most important aspects to successful implantation are: strict sterile tech- nique, careful attention to neuromonitoring feedback, meticulous dissection and identification of the CN XII branches, and accurate placement of the sensing lead. Induction and Body Positioning The patient is induced under general anesthesia via oral intubation. If it is preferable, nasal intubation can be utilized. The patient’s neck is extended with a shoulder roll and turned to the left. An additional roll or positioning pillow is placed under the patient’s right chest, to facilitate exposure of the lateral chest wall. The intraoral neuromonitoring electrodes are placed. Two Prass paired electrodes (18 mm in length) are used. The first is placed in the right anterior floor of mouth, directed in a vertical direction just posterior to the mandi- ble. This allows monitoring of the GG muscle for purposes of branches to be included in the stimulation cuff. The sec- ond is placed along the ventrolateral aspect of the right tongue directed posteriorly, just underneath the mucosa. This allows monitoring of the SG and HG muscles for con- sideration of branches of the nerve to be excluded. A ster- ile preparation is then performed, encompassing all incisions in a single operative field. The field is covered with an Ioban drape. The mouth is covered with a trans- parent drape (such as a 1010 drape) to allow for visualiza- tion of the tongue and its movement during the procedure. Incision Placement Three incisions are necessary. The first, for the stimula- tor lead placement, is in the right submental neck, starting about a centimeter to the right of midline, and extending back about 3 to 5 cm, to the anterior edge of the submandib- ular gland, about one finger’s breadth below the mandible. The resulting incision line is approximately midway between the hyoid bone and inferior border of the mandible. The second, for the implantable pulse generator (IPG) place- ment, is at the right anterior chest wall, midway along the clavicle, about 3 to 4 cm inferior to it, and 5 cm in length. The third, for the sensor lead placement, is positioned hori- zontally along the lateral chest, at about the fifth or sixth rib. The lateral extent of this incision is the middle of the axilla, and the medial extent is the inferolateral border of the pectoralis major. It is also about 5 cm in length. Placement of the Stimulator Lead The placement of the stimulator lead is the most important and technically demanding part of the proce- dure. The incision is carried through the platysma muscle, Placement of Neuromonitoring Electrodes, Preparation, and Draping

whereupon the anterior belly of the digastric muscle is found, fanning out and overlying the mylohyoid. Once the digastric muscle and tendon have been identified, the anterior edge of the submandibular gland is found, as is the posterior edge of the mylohyoid muscle. In some cases, the gland may overlay the digastric tendon, which then needs to be retracted superoposteriorly before revealing the tendon and mylohyoid (Fig. 2). The latter is retracted anteriorly to expose the HG muscle. The hypoglossal nerve main trunk can be identified in this location, at the ante- rior edge of the submandibular gland. The large ranine vein (vena comitans of hypoglossal nerve) most often over- lies the anterior branching of the hypoglossal nerve, and should be suture ligated and divided to properly dissect out the relevant branches (Fig. 2). Once this has been accomplished, the anterior branching is investigated, isolating the retraction branches to be excluded (HG and SG) and the protrusion branches to be included (GG). The neuromonitor is crucial to this identification. 14 A bipolar probe for the neuromoni- toring is recommended, providing a narrower field of stimulation for selectivity between closely coupled branches. In most of the cases, accompanying vasa nervo- rum are running along the surrounding soft tissue of the nerve, marking the border between lateral and medial branches of the hypoglossal nerve. If the separation of the main fibers can be clearly identified, the next step would be examining with nerve integrity monitoring sys- tem (NIM) to verify that all exclusion and inclusion fibers have been prepared for cuff placement. In some cases, NIM might not provide a clear determination for exclud- ing the lateral branches; the stimulation and resulting contralateral or bilateral tongue protrusion helps to con- firm the targeted fibers are included for the cuff place- ment. Once isolated, the cuff of the stimulator electrode is placed around the nerve. This is accomplished by pass- ing the long outer sleeve of the cuff under a 1-cm seg- ment of the nerve, and positioning the inner sleeve of the Fig. 2. Anatomical landmarks to identify the medial branches of hypoglossal nerve (CN XII). The first step is to identify the digas- tric tendon and its anterior belly (as illustrated, the submandibular gland may need to be retracted). The second step is to retract the posterior border of the mylohyoid anteriorly to reveal the CN XII, which often travels along the ranine vein or vena comitans of hypoglossal nerve.

Laryngoscope 126: September 2016

Heiser et al.: Operative Techniques for UAS

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