Drug-Induced Sleep Endoscopy

Drug-induced sleep endoscopy (DISE) is an upper airway evaluation technique in which fiberoptic examination is performed under conditions of unconscious sedation. Unique information obtained from this three-dimensional examination of the airway potentially provides additive benefits to other evaluation methods to guide treatment selection. This chapter presents recommendations regarding DISE technique. It presents the Velum, Oropharynx, Tongue Base, Epiglottis (VOTE) classification for reporting DISE findings, which incorporates the four major structures that contribute to airway obstruction in most patients. The authors review the evidence concerning DISE test characteristics and the association between DISE findings and treatment outcomes, including for upper airway stimulation.

Introduction

Respiratory devices have been the mainstay of treatment for obstructive sleep apnea for decades. However, despite significant technical advances in mechanisms of enhancing patient tolerance, many patients with severe disease have remained deprived of treatment. Alternative treatments for this population were largely unavailable until the introduction of upper airway stimulation therapy. By stimulating the hypoglossal nerve, this therapy activates muscles innervating the intrinsic and extrinsic muscles of the tongue, thus addressing inadequate neural activation. Since its commercial introduction, this innovative therapy has been adopted by multiple medical groups in North America and in Europe.

Special Considerations in the Acute Post-Implantation Period

The introduction of upper airway stimulation (UAS) implantation has offered a novel and effective therapy for patients with moderate to severe obstructive sleep apnea. Procedures for implantable devices are associated with unique risks and considerations. Specific attention should be given to individual factors such as gender, occupation, and medical and surgical history, which are important to consider for comprehensive preoperative counseling, preparation for implant surgery, and postoperative recovery management. This chapter discusses special considerations in the post-implantation period, including adverse events associated with UAS implant surgery and their management; postoperative considerations for patients with preexisting medical conditions; considerations in women; and considerations in patients with occupational requirements for a left-sided implant and other implanted medical devices.

Technical Considerations Following Implantation

The hypoglossal nerve stimulation system provides sleep apnea control and nightly usage when the stimulation is adjusted to meet the patient’s needs. During activation, respiratory sensing is checked and thresholds are set at standard electrode configurations. Follow-up contacts over the next few weeks are very important to ensure therapy adherence and to identify any treatment issues. Polysomnographic titration concentrates on therapeutic voltages, even in the supine position. In-lab polysomnography can be skipped as long as sufficient sleep apnea control is achieved and checked with a home sleep test in the setting of a good clinical response in terms of reduced daytime sleepiness and regular usage. If the latter is not achieved, even with the polysomnographic titration, advanced sleep lab adjustments are indicated in which the effects of modified electrode configuration and correct respiratory sensing are monitored.

The Prevalence and Impact of Obstructive Sleep Apnea and Current Management Landscape

Obstructive sleep apnea (OSA) is characterized by repeated collapse of the upper airway during sleep that leads to reduced airflow and oxyhemoglobin desaturation. The disorder is highly prevalent, with obesity, male sex, and increasing age as risk factors. Consequences of untreated OSA include neurocognitive impairment, such as excessive daytime sleepiness, and an increased risk of cardiovascular and cerebrovascular disease. Positive airway pressure therapy remains the most common treatment for OSA. Over the last few decades, alternative nonsurgical and surgical treatments have been developed. Although surgical approaches are rarely curative, careful patient selection may benefit a subpopulation of people living with OSA. Selective hypoglossal nerve stimulation represents a new treatment strategy for the management of OSA in selected patients.

Surgical Technique

This chapter serves as a practical guide for standard surgical techniques in upper airway stimulation. The major topics covered in this chapter are device implantation, operative device programming, and guidelines for anesthesia. Upper airway stimulation surgery can be technically demanding, particularly in the portions of the procedure involving nerve dissection and cuff positioning as well as placement of the respiratory sensor. Attention to detail during these aspects of surgery is critical in achieving good patient outcomes. Cuff positioning can be guided by proper use of observing the impact of intraoperative nerve stimulation on the tongue musculature as well as the use of nerve integrity monitoring.

Efficacy and Safety

Electrical stimulation of the hypoglossal nerve through implantable neuromodulation systems (UAS) has been demonstrated to be both safe and effective in the management of obstructive sleep apnea (OSA) in a subset of patients meeting specific clinical criteria. After decades of animal and human basic science research confirmed the feasibility and safety of UAS, multiple prospective studies, including the phase III multicenter Stimulation Therapy for Apnea Reduction (STAR) trial, demonstrated the efficacy of UAS in improving both polysomnographic (apnea–hypopnea index, oxygen desaturation index) and patient-reported (Epworth Sleepiness Scale, Functional Outcomes of Sleep Questionnaire, Snoring Visual Analog Scale) outcome measures. Even with the widespread dissemination into routine clinical practice and commercial availability of the therapy across the United States and Europe, these studies also consistently report very low procedure-related or therapy-related serious adverse event rates. Recent comparison studies with upper airway reconstructive surgical procedures suggest that UAS provides treatment that is at least as effective but with reduced postoperative pain and risk, and with preservation of the upper airway anatomy.

Clinical Protocol in the Multidisciplinary Setting

This chapter describes a presurgical protocol for patients with moderate to severe obstructive sleep apnea (OSA) who plan to undergo treatment with upper airway stimulation (UAStim). Patients must receive an initial evaluation including a medical and sleep history and physical examination focused on characteristics suggestive of upper airway narrowing. Criteria related to UAStim therapy and possible exclusion from implantation may be considered at this point. Some patients may be referred to a sleep specialist, but all must undergo in-laboratory or at-home polysomnography to diagnose OSA. Following an OSA diagnosis, treatment with continuous or auto-titrating positive airway pressure should be initiated. Unfortunately, CPAP adherence is low, and while there are several nonsurgical alternatives, many patients who are unable or unwilling to use CPAP will seek surgical treatment. Patients who are referred to otolaryngology for evaluation for UAStim therapy should undergo a medical and sleep history and physical examination including flexible fiberoptic laryngoscopy to evaluate upper airway anatomy. Patients must next undergo drug-induced sleep endoscopy (DISE), during which the upper airway is directly visualized in the operating room with fiberoptic endoscopy under sedation. The most common classification system to describe the location and pattern of upper airway collapse observed during DISE is the Velum, Oropharyngeal walls, Tonsils, Epiglottis (VOTE) system. Patients older than 22 years of age, with an apnea–hypopnea index between 15 and 64 (with central/mixed apneas <25% of the total), a body mass index <32 m/kg2, and without palatal complete concentric collapse may be offered UAStim treatment.

Mechanical Properties, Anatomy, and Control of the Upper Airway

The physiology of the upper airway is fundamental to current and trending therapy for obstructive sleep apnea and neurostimulation in particular. Proper functioning of the upper airway will promote sleep health by supporting the requisite airflow without snoring or significant flow limitation. Dysfunction produces snoring, obstructive hypopneas, and the metabolic sequelae of sleep disordered breathing. How a particular section of the upper airway (e.g., velopharynx, oropharynx, or hypopharynx) remains open while it is suspended from the skull base, maxilla, and mandible is the result of anatomy and neuromuscular control. The genioglossus muscle, originally designed for bringing food into the mouth and swallowing, along with multiple other muscles, participates in the maintenance of patency of the muscular pharynx during wakefulness and sleep. If the genioglossus were the only muscle important for airway stability, then hypoglossal nerve stimulation would likely be universally rather than selectively effective; instead, its effectiveness is predicted by velopharyngeal functions, which in terms of sleep health are poorly described. Literature clearly indicates a fundamental role for muscles other than the genioglossus in maintaining airway diameter, shape, and wall stiffness. Models that incorporate a more complete neuromechanical coupling of these components are necessary to understand a stable airway during sleep and helpful for decisions in management of obstructive sleep apnea.

The Future in Upper Airway Stimulation Therapy

Hypoglossal nerve stimulation therapy for obstructive sleep apnea was first approved by the U.S. Food and Drug Administration in 2014, but it has been under development through various research initiatives for the better part of the last three decades. Currently, multiple lines of research are directed toward optimizing patient selection and device adjustment with available neurostimulation therapies. Additional hypoglossal nerve stimulation devices are in trial or under active development. Future work will focus on iterative improvement of these devices and appropriate patient selection. Additional pharmacological and neurostimulation targets beyond the hypoglossal nerve in the upper airway exist, and current publications provide hints of what is yet to come.