What are the indications, landmarks, and step-by-step procedure for the INSPIRE (Implantable Neurostimulation System for Obstructive Sleep Apnea) procedure, which involves Hypoglossal (cranial nerve XII) Nerve Stimulation for the treatment of Obstructive Sleep Apnea (OSA)?

INSPIRE Implantation Procedure for Obstructive Sleep Apnea

For patients with OSA with an AHI of 15–65/h and a body mass index <32 kg/m² who cannot adhere to PAP, hypoglossal nerve stimulation therapy is recommended as an effective surgical treatment option. 1

Indications for INSPIRE Therapy

The primary indications for hypoglossal nerve stimulation using the INSPIRE system include:

• Moderate to severe obstructive sleep apnea (AHI 15-65 events/hour) 1
• BMI less than 32 kg/m² 2
• CPAP intolerance or inability to adhere to CPAP therapy 1, 3
• Absence of complete concentric palatal collapse (determined during drug-induced sleep endoscopy) 2

Pre-Procedure Evaluation

• Drug-induced sleep endoscopy to rule out complete concentric palatal collapse 2
• Polysomnography to confirm OSA severity (AHI 15-65/hour) 1
• BMI assessment (must be <32 kg/m²) 2
• Evaluation of patient's anatomy to ensure suitability for the procedure

Anatomical Landmarks for Identifying the Hypoglossal Nerve

The hypoglossal nerve (cranial nerve XII) can be identified using these key landmarks:

• Located approximately 2 cm below the mandible in the submandibular region
• Found at the level of the greater horn of the hyoid bone
• Identified within a triangle formed by:
  • Posterior border of the mylohyoid muscle anteriorly
  • Posterior belly of the digastric muscle superiorly
  • Hypoglossal nerve runs parallel to the intermediate tendon of the digastric muscle
• The nerve typically courses deep to the posterior belly of the digastric muscle and superficial to the hyoglossus muscle

Step-by-Step INSPIRE Implantation Procedure

1. Patient Positioning and Preparation

   • General anesthesia administration
   • Position patient supine with neck slightly extended
   • Prepare and drape the neck, upper chest, and right upper quadrant of abdomen

2. Incision Sites

   • Mark three incision sites:
     • Submandibular incision (3-5 cm) for hypoglossal nerve identification
     • Upper chest incision for pulse generator placement
     • Right upper quadrant incision for respiratory sensing lead placement

3. Hypoglossal Nerve Identification and Stimulation Cuff Placement

   • Make submandibular incision 2-3 cm below the mandible
   • Identify and preserve the marginal mandibular branch of facial nerve
   • Retract submandibular gland inferiorly
   • Identify posterior belly of digastric muscle and hypoglossal nerve
   • Carefully dissect the nerve, preserving branches that innervate tongue protrusor muscles
   • Place stimulation cuff electrode around the medial branch of hypoglossal nerve
   • Confirm proper placement with intraoperative nerve stimulation to verify tongue protrusion

4. Pulse Generator Implantation

   • Create a subcutaneous pocket in the right upper chest
   • Place the pulse generator in the pocket

5. Respiratory Sensing Lead Placement

   • Make an incision in the right upper quadrant of the abdomen
   • Create a tunnel between the intercostal muscles
   • Place the sensing lead between the internal and external intercostal muscles
   • Secure the lead in position

6. Tunneling and Connections

   • Create subcutaneous tunnels to connect all components
   • Connect the stimulation lead and sensing lead to the pulse generator
   • Test the system for proper functioning

7. Closure and Final Testing

   • Irrigate all wounds with antibiotic solution
   • Close all incisions in layers
   • Perform final system testing to ensure proper functioning
   • Apply sterile dressings

Post-Procedure Management

• The device is typically activated 4-6 weeks after implantation
• Initial programming session to optimize stimulation parameters
• Regular follow-up visits for device adjustments and monitoring
• Sleep studies to assess effectiveness and make necessary adjustments

Effectiveness and Outcomes

INSPIRE therapy has demonstrated significant improvements in:

• Reduction in AHI from baseline (38.9 ± 9.8 to 10.0 ± 11.0 at 6 months) 2
• Improved quality of life measures 4
• Better adherence compared to CPAP therapy 3
• Sustained effectiveness in long-term follow-up 5

Potential Complications

• Lead displacement
• Infection at implantation sites
• Tongue weakness or discomfort
• Device malfunction
• Nerve injury
• Scarring or seroma formation

Hypoglossal nerve stimulation represents an effective alternative for patients with moderate to severe OSA who cannot tolerate CPAP therapy, with superior outcomes compared to other surgical interventions for appropriately selected patients 5.