Hypoglossal Nerve Stimulator Explantation Technique and Outcomes: A Retrospective Case Series

Abstract

Introduction:

Upper airway stimulation via the hypoglossal nerve stimulator (HGNS) implant is a surgical method for treating obstructive sleep apnea. However, patients may need the implant removed for a variety of reasons. The purpose of this case series is to assess surgical experiences with HGNS explantation at our institution. We report on surgical approach, overall operative times, operative and postoperative complications, and discuss relevant patient-specific surgical findings when removing the HGNS.

Methods:

We performed a retrospective case series of all patients that underwent HGNS implantation at a single tertiary medical center between January 9, 2021, and January 9, 2022. Subjects included adult patients who presented to the sleep surgery clinic of the senior author for surgical management of previously implanted HGNS. Patient clinical history was reviewed to determine the timing of the patient’s implant, reasons for explant, and postoperative recovery course. Operative reports were reviewed to determine overall duration of surgery and any associated difficulties or deviations from the general approach.

Results:

Between January 9, 2021, and January 9, 2022, 5 patients had an explantation of their HGNS implant. Explantation occurred between 8 and 63 months of their original implant surgery. The average operative time from incisional start time to close was 162 min for all cases with a range of 96–345 min. No significant complications were reported including pneumothorax and nerve palsy.

Conclusion:

This reported case series outlines the general steps for Inspire HGNS explantation as well as details the experiences in a case series of 5 subjects explanted over the year at a single institution. The results from the cases suggest that the explantation of the device can be performed efficiently and safely.

Introduction

Upper airway stimulation via hypoglossal nerve stimulator (HGNS) implant is a surgical method for treating obstructive sleep apnea. The Inspire^® Upper Airway Stimulation device (Inspire Medical Systems, Golden Valley, MN) is currently the only FDA-approved HGNS for the treatment of obstructive sleep apnea [1]. Since its approval in 2014, the number of HGNS implantations has steadily increased, with over 4,400 implants being performed in the USA in 2018 [2]. Patients interested in HGNS must meet specific selection criteria for the surgical implant including body mass index <35 events/hr, an apnea-hypopnea index >15 events/hr with <25% central or mixed apnea events, and evidence of anteroposterior collapse patterns of the velum during drug-induced sleep endoscopy. Despite having these selection criteria, response to therapy is not guaranteed with studies showing treatment response to be 66–83% as defined by the Sher Criteria [1, 3].

Nonresponders to therapy can have the device removed. Additional factors that could lead to device explantation include infection of the device, device failure, discomfort from the implant, or intolerance to stimulation settings [4]. Prior to July 2022, implants were not cleared for magnetic resonance imaging of the chest/abdomen at 1.5 T, and patients would have needed the device removed if MRI was medically necessary [5]. Currently, the device remains contraindicated for 3.0 T MRI and would still require implant removal if medically necessary. As more patients are implanted with HGNS, there will likewise be a growing number of patients who will require HGNS explantation. However, there is currently a lack of published literature describing surgical experiences in explanting HGNS.

The purpose of this case series is to assess surgical experiences with HGNS explantation at our institution. We report on surgical approach, overall operative times, operative and postoperative complications, and discuss relevant patient-specific surgical findings when removing the HGNS.

Materials and Methods

We performed a retrospective case series of all patients that underwent HGNS explantation at a single tertiary medical center between January 9, 2021, and January 9, 2022. Subjects included adult patients (aged 18 years or older) who presented to the sleep surgery clinic of the senior author for surgical management of previously implanted HGNS. Patient clinical history was reviewed to determine the timing of the patient’s implant, reasons for explant, and postoperative recovery course. Operative reports were reviewed to determine the overall duration of surgery and any associated difficulties or deviations from the general approach. To determine deviations from the general approach, the operative technique was compared to guidance recommended by Inspire Medical Systems as described below.

Surgical Technique

This section outlines the general approach for HGNS explant. Setup of the explant surgery was nearly identical to that for implanting the device [6]. Patients are placed under general anesthesia and orotracheally intubated. Muscle relaxant is avoided to allow for neuromonitoring. An electromyogram lead is placed on the floor of the mouth on the side of surgery for neuromonitoring of the hypoglossal nerve. A representative from Inspire Medical Systems can be present to provide additional guidance. Incisions are made through the previous surgical incisions, starting with the submental incision to remove the stimulating electrode. The approach in the submentum for explantation is similar to implantation, starting with dissection through the platysma to reveal the anterior digastric muscle that is then retracted anteriorly. The muscle is followed posteriorly to the digastric tendon which will reveal the barrel-shaped anchor of the stimulating electrode that is secured to the tendon with 2 silk sutures. The medial edge of the mylohyoid is then identified and retracted anteriorly, revealing the floor of the neck where the hypoglossal nerve and electrode cuff can be identified using blunt dissection (see Fig. 1 for relevant surgical landmarks in removing the stimulation electrode). The fibrous capsule around the cuff of the electrode is excised using a 15 blade along the spine of the cuff, and the spine is grasped to remove the cuff off the nerve completely. A nerve stimulator can be used to confirm function of the hypoglossal nerve after cuff removal. The electrode wire is then cut just proximal to the cuff, and it is removed from the body. The sutures on the barrel anchor are cut from the digastric tendon, and the barrel is then cut out, leaving the proximal segment of the electrode wire in the neck to be removed later sliding out from the neck through the chest. Attention is then moved to the lateral chest to remove the sensor lead. An incision is made through the previous incision site in the lower lateral chest. Blunt dissection is performed to find any segment of the sensor lead wire. Once identified, the wire is followed to identify the two flanges that anchor the lead to the chest wall. The silk sutures anchoring the flanges are removed, and the distal wire is followed until it inserts into the intercostal space. The sensor lead rests between the external and intercostal muscles in the rib space. The sensor head is gently grasped as it enters the intercostal space and pulled out. The sensor is then cut proximally along with the two flanges securing it into the chest. The surgical bed is filled with saline, and a Valsalva maneuver is performed to assess for pneumothorax. Finally, an incision is made in the anterior chest to remove the IPG. Dissection proceeds down to the fibrous capsule over the IPG which is then cut. Two anchoring sutures on the IPG are cut, and it is pulled out of the body with the electrode wire and sensor wire still connected. The wires are freed from the chest space, and the remaining distal ends in the neck and lateral chest can be pulled out through the anterior chest space. The wounds are irrigated with saline and closed in a layered fashion. Pressure dressing is applied following closure. The surgery is outpatient with patients going home the same day and returning to the clinic 1 week for post-op evaluation.

Fig. 1.

Submandibular approach for explantation.

Results

Between September 2021 and September 2022, 5 patients with previously implanted HGNS presented to the Sleep Surgery Clinic at Emory University Midtown Hospital for evaluation for device removal. Patient demographic information is provided in Table 1 along with individual reasons for surgical explantation. Explantation occurred between 8 and 63 months of their original implant surgery. All patients had right-sided implants with the three-incision implantation technique which included a lower lateral chest incision for the pressure sensor lead of the device.

Table 1.

Explantation demographics

	Age	Sex	PMH	BMI	Reason for explantation	Implant duration	Operative timea	Surgical nonroutine steps	Complications	EBL, mL
Case 1	69	F	OSA, asthma, and HTN	24.3	Mixed tongue activityb and difficulty tolerating a very limited range of stimulation voltages	63 months	345 min	Scarring limited restriction of digastric and proximal portion and the digastric tendon had moved more superiorly under the submandibular gland	None	25
Case 2	72	F	OSA, HTN, HLD, and GERD	23.9	Trouble tolerating optimal settings. Removal for needed MRI	35 months	135 min	Sensor lead was difficult to remove from intercostal space requiring dissection of external intercostal muscle	None	20
Case 3	54	M	OSA	35.6	Residual OSA, switched to BIPAP	50 months	118 min	Ranine vessel bleeding	None	20
Case 4	62	F	OSA, CAD, HLD, HTN, and anxiety disorder	32.1	Trouble tolerating optimal settings	8 months	96 min	No unexpected steps	None	50
Case 5	70	M	OSA, REM behavior disorder, Parkinson, and HTN	33.8	Residual OSA and need for MRI	40 months	118 min	No unexpected steps	None	10

OSA, obstructive sleep apnea; HTN, hypertension; HLD, hyperlipidemia; GERD, gastroesophageal reflux disease; CAD, cardiovascular disease; IBS, irritable bowel syndrome; RLS, restless leg syndrome.

^aTime was recorded from incision to final closing.

^bThis mixed activity may have resulted from inclusion of the hyoglossus branch.

The average operative time from incisional start time to close was 162 min for all cases with a range of 96–345 min. No patients were reported to have a pneumothorax from removal of the respiratory sensor lead or hypoglossal nerve palsies from removal of the electrode lead. The most significant finding post-surgery was neck edema which slowly resolved over several weeks in all patients.

Significant nonroutine steps were reported in 3 of 5 (60%) of surgeries. In case 1, the patient had a dehiscent digastric tendon that was not inserted along the hyoid bone via the intermediate tendon resulting in the tendon, which included the barrel of the stimulation electrode lead, being retracted under the submandibular gland. A proximal segment of the electrode wire was ultimately found and followed distally until the digastric tendon was identified but required additional dissection time resulting in the longest procedure time of the case series. In case 2, difficulty was documented in removing the sensor lead from the intercostal space with concern that pulling the sensor lead could avulse the sensor head, leaving it in the intercostal space. The external intercostal muscle above the sensor head was ultimately cut to free the lead. This patient did not develop a pneumothorax, nor did he complain of any significant chest muscle pain from the additional dissection during his recovery. In case 3, bleeding from a ranine vein occurred while exploring the neck for the electrode cuff which required a difficult suture ligation due to scarring around the area and unconfirmed hypoglossal nerve location. Use of intraoperative neuromonitoring assisted in ruling out the presence of the nerve, and the bleeding was controlled with limited blood loss and no injury to the hypoglossal nerve.

Conclusion

This reported case series outlines the general steps for Inspire HGNS explantation as well as details the experiences in a case series of 5 subjects explanted over the year at a single institution. No significant adverse events occurred after surgery with the most significant finding during postoperative recovery being transient submental edema. Average operative time was 165 min for explantation which is slightly longer than the average implantation procedure time of 142 min reported in the literature [7]. The results suggest that explantation of the device can be performed safely with operative times similar to those of implantation.

Though all patients in the case series had successful removal of their implants without adverse outcomes, there were events that occurred intraoperatively in 3 of 5 patients worthy of discussion. The presence of a dehiscent digastric tendon in 1 patient resulted in difficulty locating the standard landmarks used to identify the location of the implant and hypoglossal nerve. The dehiscence itself may be a result of the initial implantation, and surgeons must be aware that the altered anatomy may make relocating the implant more difficult. If a segment of the stimulating lead can be identified in the neck, it can be followed to its distal end which will lead to the nerve. In removing the sensor lead from the chest, care must be taken while pulling the lead out of the intercostal space. If portions of the lead are adherent in the space, you may risk injuring the lung pleura in attempting to pull the lead. Additionally, the sensor head may tear from the rest of the lead if too much traction is applied. If the sensor head does not easily slide out of the intercostal space with gentle traction, cutting the external intercostal muscle along the sensor until the sensor head is fully identified and freed can be done to ensure the lead is safely removed without further injury to the surrounding structures. It is also advised to always test the chest for leaks by filling the incision with saline and performing a Valsalva maneuver after removal of the lead to ensure no accidental injury to the lung pleura occurred. Finally, the ranine vein is commonly encountered near the hypoglossal nerve during implantation surgery and is not always ligated depending on whether it significantly impedes placement of the stimulating electrode. In explantation, the vessel may be encountered and more difficult to avoid due to scarring. Neuromonitoring of the hypoglossal nerve is advised to help identify the nerve if bleeding from the ranine vein occurs. Additionally, for surgeons performing implantation of the device, it is worth considering ligating the vessel during implantation to reduce the risk of bleeding if future explantation is needed.

This retrospective study was limited by a sample size of only 5 patients. It is expected that additional insights regarding the surgical approach and outcomes will occur as more patients are explanted. Future studies with larger sample sizes can provide further detail regarding intraoperative considerations and postoperative recovery expectations.

The surgical technique for implantation has also changed. In our case series, all patients were implanted using a three-incision technique, with a third incision occurring in the lower lateral chest and the sensor lead being inserted between the intercostal space at the 4th–6th ribs as originally described.¹ More recently, a two-incision technique was approved and widely adopted where the sensor lead is placed at the 2nd intercostal space within the IPG pocket [8]. Future explantation of the two-incision technique will likely be faster saving time from opening and closing an additional incision but may also present different challenges to that of the three-incision technique.

Conclusion

Explantation of HGNS implants is likely to increase in frequency as more patients become interested in this treatment modality. Variations in anatomy and managing a previously operated surgical site add challenges to implant removal; however, explantation of the HGNS can be performed efficiently without significant adverse events.

Data Availability Statement

All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.