Hypoglossal nerve stimulation is a new technology used to treat refractory cases of obstructive sleep apnea (OSA) in appropriately selected adult patients. Use of the stimulator in pediatric patients is limited to research investigations currently, but initial studies suggest this technology may be useful for alleviating upper airway obstruction in adolescents and young adults with Down syndrome who have persistent OSA after adenotonsillectomy. Here we outline the general principles and considerations for hypoglossal nerve stimulator implantation, as well as discuss surgical modifications to allow for implantation in pediatric patients.
20 Pediatric Hypoglossal Nerve Stimulation
Hypoglossal nerve stimulator implantation is an emerging technology for treatment of OSA. The stimulator is an implantable device that senses respiratory variation and delivers electrical impulses to anterior branches of the hypoglossal nerve during inspiration. Stimulation of the genioglossus and geniohyoid muscles results in protrusion of the tongue base, which alleviates nocturnal upper airway obstruction in patients who respond to therapy (▶ Fig. 20.1).
Initial studies published in 2001 1 demonstrated that nerve stimulator therapy reduced the apnea hypopnea index (AHI) in both rapid-eye movement (REM) and non-REM sleep by over 50% as well as reduced oxygen desaturations in adults with severe OSA. Additional trials performed randomized, controlled therapy withdrawal in patients who responded to stimulation and noted that with therapy non-use, AHI increased significantly, as did oxygen desaturations. 2 Thirty-six month follow-up data suggests that nerve stimulation is well tolerated, with up to 81% of patients reporting daily use. In addition, patients with follow-up polysomnography data at 36 months continued to demonstrate significant reductions in AHI (>50%) compared to baseline measurements. 3 The hypoglossal nerve stimulator (Inspire Medical Systems®) is currently approved by the United States Food and Drug Administration (FDA) for implantation in adults age 22 years or older with moderate-to-severe OSA (15≥ AHI ≤65 events/hour) who cannot tolerate or have failed to improve with positive airway pressure therapy and who are without concentric airway collapse at the level of the soft palate. Moreover, eligible subjects should have a central apnea index that accounts for ≤25% of the total AHI on baseline polysomnography.
While the device is only approved for commercial use in adult patients, an investigational device exemption was granted by the FDA for study of this technology in adolescent and young adult patients, aged 10 to 22 years, with Down syndrome (DS) and refractory severe OSA after tonsillectomy and adenoidectomy (T&A) who are nonresponders or nonadherent with positive airway pressure therapy. Patients with DS have an increased risk of OSA in comparison to the general pediatric population (30–80% vs. 2–5.7%), in part due to their unique anatomic and physiologic differences that include decreased muscular tone, macroglossia, maxillary hypoplasia, and lingual tonsil hypertrophy. Up to 67% of children with DS and OSA will have persistent upper airway obstruction after T&A. Initial pilot studies of hypoglossal nerve stimulator implantation in the pediatric DS population demonstrate excellent device adherence and tolerance, quality of life improvement, and a significant (>50%) reduction in AHI at 6 to 12-month follow-up. 4 , 5 With further investigation, we anticipate the device will be approved for use in adolescents and young adults with Down syndrome, and perhaps other special populations as well.
This chapter outlines necessary preoperative investigations, as well as provides step by step guidance on how hypoglossal nerve stimulator implantation is performed in children. We also highlight several modifications to surgical technique that facilitate stimulator placement in smaller patients.
20.2 Preoperative Evaluation and Anesthesia
As with adult patients, successful hypoglossal nerve stimulator implantation begins with appropriate patient selection. In adult patients, prior T&A, lingual tonsillectomy, uvulopalatoplasty, tongue base reduction, and other surgical procedures to reduce the burden of disease are not needed prior to implantation; however, documentation of a patient’s inability to tolerate or failure to respond to positive airway pressure therapy is required. In children and adolescents, because adenotonsillectomy is a first-line therapy for treatment of OSA, surgical removal of the adenoids and both tonsils should be performed prior to considering hypoglossal nerve stimulator implantation. For children with persistent severe OSA (10 ≥ AHI ≤50 events/hour) after adenotonsillectomy, attempts at treatment of residual disease with noninvasive positive airway pressure therapy should be performed. Nerve stimulator implantation may be considered in children who do not respond to or cannot tolerate therapy. All children being considered for implantation should undergo full-night diagnostic polysomnography scored using AASM pediatric criteria within 6 months of planned implantation surgery. Baseline measurements allow for inclusion of children with severe OSA who have ≤25% contribution by central apnea or mixed events to the total AHI. Height and weight measurements should also be obtained so that children with significant obesity, which may be a contributing factor to their persistent disease, are excluded. In adult patients, a body mass index (BMI) >32 kg/m 2 has been associated with a failure to respond to therapy, though a cut-off has not yet been established in children. In children, BMI percentiles calculated through the centers for disease control (CDC) BMI-for-age growth chart are often utilized by the pediatric community. We have utilized the 95th percentile for children under the age of 18 as a cut-off for inclusion in our investigational trials. 5
All candidates should have a thorough examination of the facial bones, nasal cavity, oral cavity, and oropharynx to assess for anatomic factors that could be contributing to airway obstruction and easily corrected. All children should also have a baseline tongue exam to document tongue size, resting position, and hypoglossal nerve function. All candidates should also be screened for behavioral and communication issues that would preclude participation with treatment; in our experience children should be able to communicate and localize any sources of discomfort with their caregivers.
Studies of the hypoglossal nerve stimulator in adult patients suggest that patients with circumferential airway collapse at the level of the velopharynx are less likely to respond to therapy. Therefore, a drug-induced sleep endoscopy (DISE) is required in order to evaluate patterns of obstruction including at the levels of the soft palate, oropharynx, hypopharynx, and larynx. Technique for DISE is beyond the scope of this chapter, but a team approach is critical to the success of this evaluation. During the procedure, the child is sedated using propofol and/or dexmedetomidine until adequate sedation is achieved to initiate obstructive events, which the anesthesiologist should allow to continue during evaluation. The surgeon should be a skilled endoscopist and evaluate and categorize patterns of collapse in the upper airway. Collapse should be evaluated both before and after a jaw thrust maneuver. We have found it useful to utilize the VOTE classification scheme 6 to record and communicate airway findings in a systematic way. Patients without circumferential collapse at soft palate can be considered for implantation.
Beyond anatomic and behavioral considerations, the patient’s medical history must be taken into account to optimize patient selection as well. For example, surgery should be deferred, or at least delayed, in children with active cardiopulmonary disease that will require further thoracic surgical procedures which might disrupt the impulse generator or associated electrodes. With the advent of new generations of the device which are MRI compatible for imaging of the head, abdomen, and extremities, disease processes such as cholesteatoma that could require serial MRI imaging are no longer absolute contraindications to implantation. However, the need for future imaging, particularly of the thorax, should be a consideration because current devices are not compatible with MRI imaging of the chest.
Prior to implantation, a full discussion of the risks and benefits of implantation should be conducted. Patients should be aware of the risks of surgery, including long-term risks of device extrusion or the need for device explantation. Patients and their families must also be informed that the impulse generator battery will need to be replaced after approximately 10 years, and that further surgery will be required to do so. Particularly for the pediatric population, it should be clear that long term data is lacking to determine if device settings will remain stable over time. It should be emphasized that in order for the device to be effective, the patient and/or family will need to activate it each night with a remote control device. Finally, patients and their families should be aware that at least annual follow-up will be required to assess surgical wounds and device functioning.
Once the decision has been made to proceed with surgical implantation, the surgical team and equipment should be assembled. Two of each component of the hypoglossal nerve stimulator, including the sensing lead, stimulation lead, and impulse generator, must be available so that backup hardware can be used if needed. At our institution, a separate nerve monitoring team is utilized during hypoglossal nerve stimulator cases to perform Electromyographic (EMG) monitoring of the hypoglossal nerve during nerve dissection and cuff placement, as well as system validation after implantation is completed.
Because EMG monitoring of the genioglossus and hyo-styloglossus musculature is performed during nerve dissection and cuff placement, the patient’s tongue motion should not be restricted. Therefore, a nasotracheal tube is preferred to an orotracheal tube. Long-term paralytics should be avoided to facilitate nerve stimulation. Particularly in children with Down syndrome, care should be taken in patient positioning to prevent unnecessary neck manipulation and minimize neck extension due to the risk of atlantoaxial instability.
20.3 Surgical Technique
20.3.1 Incision Placement and Preparation
Classically, the stimulator has been placed through three incisions in the right neck and chest: one in the anterior submental region, one inferior to the clavicle over the pectoralis major muscle, and one in the fourth to sixth intercostal region. A 4-cm transverse submental incision should be marked more anterior than the typical incision used for a submandibular approach at the level of or slightly above the hyoid bone, approximately 0.5 cm from the midline. A second incision, approximately 4 to 5 cm, should be marked 3 fingerbreadths below the clavicle over the pectoralis muscle and the approximate outline of the impulse generator should be marked extending inferior from this incision to identify the extent of pocket dissection. Finally, a 5-cm incision should be marked over the fourth to sixth intercostal space for pleural sensing lead placement. We have found that the intercostal incision is best placed anteriorly, inferior to the nipple line, to aid in identification of the costochondral junction where the internal and external intercostal margin is best identified to facilitate the plane of dissection. In younger children with a small thorax, we have described placement of the impulse generator and pleural sensing lead through a single incision rather than two separate incisions, to reduce the risk of impulse generator extrusion. In these smaller children, we have also described lateral positioning, rather than medial positioning, of the pleural sensing lead to reduce the risk of cardiac interference 7 (▶ Fig. 20.2).
The incisions should be injected with local anesthetic.