Radiofrequency Tissue Effects

Radiofrequency (RF) energy has been used in medicine for numerous applications, including cutting tissue, vessel coagulation, and tissue volume reduction. There are unipolar, bipolar, and even multipolar devices in use at present. The goal of using RF in sleep-disordered breathing (SDB) would be the third application: tissue volumetric reduction.

1 Indications for Treatment

Patients diagnosed with SDB may have obstruction at the following anatomic sites: the nose, palate, and hypopharynx (base of tongue and/or lateral pharyngeal wall).

Surgical therapy in SDB is accomplished by one of the following premises: (1) excision or reduction of the tissue obstructing the airway (turbinectomy, tonsillectomy, uvulopalatopharyngoplasty, laser-assisted uvopalatoplasty, palatal coblation) midline glossectomy, RF tissue reduction of the turbinate, palate, and tongue; (2) constructing a larger airway (transpalatal advancement pharyngoplasty, genioglossus advancement, hyoid myotomy and suspension, tongue suspension, maxillomandibular advancement); (3) providing neural stimulation (hypoglossal nerve stimulation) or preventing neural relaxation to the supporting airway musculature; (4) palatal stiffening procedures (cautery-assisted palatal stiffening, injection snoreplasty, palatal pillar implants); and (5) avoiding the entire upper airway collapse altogether (tracheotomy).

2 Patient Selection

The indication for treatment in an SDB patient using base of tongue (BOT) RF is the following:

1.
A diagnosis of SDB based on sleep study findings
2.
Medical pretreatment workup estimates that the BOT is a factor in the upper airway collapse
3.
Patient elects RF BOT as a treatment option

Patients receiving RF BOT treatments often have macroglossia or relative macroglossia due to retrognathia; however, this is not a prerequisite to treatment. As long as the BOT is determined to be a component of upper airway obstruction, then treatment is indicated. Most patients currently having the procedure performed alone undergo local anesthesia; however, when combined with other upper airway reconstructive procedures, they undergo general anesthesia. This is important, because a limited stomal opening or the presence of trismus makes the procedure difficult, if not impossible, to perform. Patients who demonstrate a significant gag reflex may be treated with diazepam (Valium) to diminish this response. However, if this medication does not work satisfactorily, the procedure requires general anesthesia or the procedure must be aborted. Finally, patients are strongly recommended to use a nasal positive airway pressure (PAP) device to protect their airway for at least 2 weeks posttreatment to avoid airway obstruction during the edema phase of recovery.

3 Sleep-Disordered Breathing Treatment Protocol

Tongue base RF can be done alone or simultaneously with other upper airway surgical procedures. Clinically, the most common adjuvant procedure addresses palatal obstruction: the uvulopalatopharyngoplasty (UPPP).

The author treats every patient with a diagnosis of SDB and suspected BOT obstruction in concert with the genioglossus advancement procedure. It is recommended for these patients to use their PAP device until a posttreatment polysomnograph confirms successful treatment. Posttreatment sleep studies are acquired 3 to 4 months postoperatively. PAP is especially important to protect the upper airway when surgical swelling potentially worsens the severity of their upper airway collapse.

The initial treatment protocol recommended three treatment sessions to attain the optimal airway effects without overtreating the tongue musculature, which may result in motor dysfunction. With the double-pronged RF probe, four lesions can be created with 750 joules (J) per lesion (3000 J per session) and 9000 J totaling three sessions. Each tongue base RF treatment produces more tongue atrophy and, in theory, a larger posterior airway space (PAS) of the oropharynx. Subsequent treatments are spaced at 4- to 6-week intervals to allow the inflammatory response and swelling to subside and scarring to proceed. Collagen synthesis maximizes at about 60 days from the time of tissue injury.

If patients are diagnosed with nasal obstruction, the second RF BOT treatment is performed 4 to 6 weeks after the initial treatment along with nasal septoplasty, inferior turbinoplasty, and nasal valve reconstruction, as dictated by physical examination. A third RF BOT treatment can be performed before the postoperative diagnostic sleep study is completed. Most patients do not wish to wait up to 6 months after surgical reconstruction to undergo a follow-up sleep study, because many are still using PAP devices to protect their airway until receiving confirmation of surgical success.

4 Radiofrequency Tissue Volume Reduction Tongue Base Technique

4.1 Radiofrequency Generator, RF Probe, RF Tissue Effect

The RF generator produces the radiofrequency energy with the circuit penetrating through the body from the RF probe toward a grounding pad. The RF energy creates temperatures that reach up to 100°C, which vaporizes water and injures tissue. The RF generator was programmed to deliver energy in a specific algorithm pattern.

Initial experiments in the porcine model revealed that if the RF energy was increased too rapidly, the tissue in contact with the active probe formed a char and increased tissue impedance. This char limited the transmission of heat beyond the immediate probe treatment area, minimizing the tissue injury radius from the probe. When the energy was increased too slowly, the temperature was less and there was less tissue injury. When the energy was delivered in the moderate range following the algorithm pattern, the lesion injury size was optimized by allowing the heat to spread to the surrounding tissue without excess tissue impedance and char formation.

The RF energy disbursement in the homogenous tissues of the porcine tongue indicated that as the energy increases using the preprogrammed delivery algorithm so does the lesion size. Specifically, as the energy is increased from 500 to 2400 J, the size of the lesion increased from 1.4 cm × 0.5 cm to 1.5 cm × 1.7 cm. The important number to us for comparison was the cross-sectional area of the lesion, which increased from 0.7 cm ² to 1.4 cm ² .

Due to the RF energy initiating an inflammatory response surrounding the central target area of tissue necrosis, the lesion size extended from 2.5 cm ² to 7 cm ² over 48 hours. Peak swelling occurred 48 hours after the RF treatment. With the resolution of the acute inflammatory response and the production of scar tissue, the lesion size progressively shrank over 21 days to less than 1 cm ² . This healing revealed a 26.3% reduction in the overall porcine tongue tissue volume compared with baseline measurements. It was estimated that with a delivery of 2400 J of energy to the porcine tongue, there was a reduction of 0.84 grams (g) of muscle tissue.

The RF probe is 1.6 cm in length with a proximal insulated end and a distal, active, noninsulated end. The probe possessed thermocouples at each end to give continual temperature and tissue impedance feedback pictured on the display. The goal was that the distal target tissue received an energy level creating tissue necrosis while protecting the superficial musculature and mucosa from energy. The target temperature was set at 85°C.

Each lesion is predetermined to receive 750 J of energy, and classically four lesions are created at each treatment session for a total of 3000 J. The treatment regimen is typically two to three treatment sessions for a total of 6000 to 9000 J of total BOT energy delivery. The program had a default impedance level, where the machine stopped delivering energy if the impedance peaked over this level. The typical tissue impedance ranged from 100 to 200 ohms (Ω). When the impedance is increased significantly, it suggests that the probe is either adjacent to bone or is no longer in tissue.

The present protocol was established after attempting higher levels of RF energy complicated by significant experienced pain inhibiting adequate oral fluid intake and a concern for profound tongue swelling producing airway obstruction.

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