Drug induced sleep endoscopy (DISE) is usually performed in the operating room to help diagnose areas of blockage. Endoscopy evaluates obstruction at the level of the nose, the adenoids, the palate, the tonsils, the base of tongue (back part of the tongue), the epiglottis and the supraglottis. Areas of obstruction are then noted and the patient is either awakened and the findings are discussed at a clinic visit, or the patient may undergo surgery based on the counseling and surgical plan.

Sleep endoscopy is a popular method for evaluating the upper airway. Are you going to have sleep endoscopy or know someone who is?

It can be a challenge to find comprehensive and reliable information and we would like to help you.

This sleep endoscopy information guide was written by an ear, nose, and throat (otolaryngology) surgeon who has performed more than 100 sleep endoscopy procedures!

In order to make this more helpful and as part of the research for this information guide, we searched the internet for frequently asked questions and have provided answers.

First, this information guide provides general information about sleep endoscopy for adults and children, what the goals of sleep endoscopy are, what medications are used and how sleep endoscopy could help your ENT surgeon, especially with regard to selecting surgeries that could help breathing during sleep.

This guide provides illustrations that show how sleep endoscopies are performed step-by-step. Over 15 major topics are covered with several illustrations throughout.

Disclaimer: This is an educational blog site. The content is meant for educational purposes only. There is no affiliation with any organization or company. Although we do our best to provide accurate and true information, it is possible that there may be mistakes or errors. The information is not meant to provide specific medical advice and if you rely on any information on this website, it is at your own risk. Even though the writer(s) on this blog site is/are healthcare provider(s), the information is for educational purposes only and you should consult your own healthcare provider for specific information for you. We reserve the right to update, change and manage the blog site at any point.

Woman sleeping, airway blocked by tongue in obstructive sleep apnea at SnoringSchool.com
Woman sleeping, airway is blocked at multiple sites. The soft palate, tongue and epiglottis are blocking the airway. This can be seen in patients with obstructive sleep apnea.
Table of Contents hide

Background information about sleep endoscopy:

Summary:

Snoring and obstructive sleep apnea (OSA) are common disorders. Because patients are seen in clinic when they are awake, a major problem with trying to treat snoring and OSA is that it can be difficult to determine where the blockage of the airway is occurring during sleep. Sleep endoscopy is a procedure that is performed with the patient under general anesthesia and the airway is evaluated when the patient falls asleep. Although it is not natural sleep, sleep endoscopy helps to get the patient into a drug-induced sleep state and when endoscopy is performed in this state it is known as drug-induced sleep endoscopy (DISE).

Background about sleep endoscopy:

How common is sleep endoscopy?

Sleep endoscopy is commonly performed at hospitals with higher volumes of sleep apnea patients.

However, it is not a complex procedure, and there is no reason that a smaller community hospital or surgical center could not do it.

The key is that the surgeon who is doing the sleep endoscopy is comfortable in doing the procedure and interpreting the results.

Who should have sleep endoscopy?

Since sleep endoscopy is meant to evaluate the blockage of the airway during sleep, it is most commonly performed for obstructive sleep apnea patients.

In some cases, surgeons may find benefit in performing the sleep endoscopy in patients who snore but do not have obstructive sleep apnea (snoring without OSA is known as primary snoring).

Knowing the site of snoring and obstruction during sleep endoscopy could be helpful for primary snoring patients who have had previous snoring treatments.

What is sleep endoscopy?

Sleep endoscopy is a procedure that is performed by using a flexible, thin scope that is placed into the nose and the airway can be seen directly through the scope, through a camera and/or on a television screen.

Sleep endoscopy is performed for patients with obstructive sleep apnea as a tool to help determine where the upper airway is obstructed during sleep.

Sleep endoscopy can be performed during natural or drug-induced sleep.

 

Sleep endoscopy in a child scope in place at SnoringSchool.com
Drug-induced sleep endoscopy in a child with the scope in place looking at the airway at the level of the base of tongue.

When should sleep endoscopy be performed?

If patients do not have clear anatomical reasons for obstruction of their airways, then sleep endoscopy can be a helpful tool.

Multiple sites of the upper airway are evaluated during sleep endoscopy, so the additional information obtained during the sleep endoscopy could help the surgeon determine what the most appropriate surgery might be.

Is sleep endoscopy performed for upper airway resistance syndrome?

Upper airway resistance syndrome is when a patient has a respiratory disturbance index (RDI) above 5 events per hour, but the apnea-hypopnea index (AHI) is below 5 events per hour.

This definition changed in 2014 when the international classification for sleep disorders 3 (ICSD-3) reclassified upper airway resistance syndrome and it is now the same as obstructive sleep apnea since the signs and symptoms are basically the same.1

So, if a patient has an RDI above 5 events per hour, and the AHI is less than 5 events per hour, they have obstructive sleep apnea.

Should a patient have sleep endoscopy or awake endoscopy?

An awake examination is standard for patients who have snoring or obstructive sleep apnea.

Upper airway in woman standing palate tongue epiglottis larynx at SnoringSchool.com
Upper airway in woman standing. The airway includes the adenoids, palate, tonsils, tongue, epiglottis, larynx and trachea.

An awake endoscopic examination is also performed if the ENT surgeon believes it is necessary.

The endoscopic examination can help determine potential sites of blockage in the upper airway that may not be obvious by simply examining with direct visualization such as with a speculum, a tongue blade, and a headlight.

The awake endoscopy can provide the following information:

  • Deviated septum that cannot be visualized from the front of the nose,
  • Large inferior turbinates farther back that cannot be seen from the front of the nose,
  • Nasal polyps,
  • Large adenoids,
  • Large tongue at the back part of the tongue (base of tongue), and
  • Floppy tissue behind the tongue (floppy epiglottis or supraglottis)
Awake endoscopy in a woman with upper airway showing adenoids palate tongue epiglottis larynx at SnoringSchool.com
Awake endoscopy. Upper airway in woman standing. The airway includes the adenoids, palate, tonsils, tongue, epiglottis, larynx and trachea.

What is natural sleep endoscopy?

In a European position paper 2 on sleep endoscopy, the recommendation for is to use the term “natural sleep endoscopy” when the airway is evaluated during sleep and the sleep is natural.

In the 1970s, sleep endoscopy was performed without any medications as a method for evaluating breathing during natural sleep.

In adults, natural sleep endoscopy has been described as far back as 1978 by Borowiecki et al.3

In children, natural sleep endoscopy has been described as far back as1979 by Sukerman et al.4

What is drug-induced sleep endoscopy?

Drug-induced sleep endoscopy is when the upper airway is evaluated during sleep and anesthetic medications are used to help put the patient to sleep.

DISE started being using in the late 1980s and early 1990s.

Drug-induced sleep endoscopy in adults (using midazolam) was described in 1991 by ENT surgeons Croft and Pringle.5

Drug-induced sleep endoscopy in children (using “a light general anesthetic”) was described in 1990 by Dr. Croft and colleagues.6

What anesthetic medications are generally used for drug-induced sleep endoscopy?

Propofol, dexmedetomidine, and midazolam are the three anesthetic agents that are most commonly used for DISE.7

In a review article comparing dexmedetomidine and propofol, Dr. Chang and colleagues found that both medications have advantages and disadvantages.7

Dexmedetomidine has been found to provide a more stable profile based on heart and lung vital signs, but propofol was quicker to take effect and showed larger degrees of blockage which actually could more accurately reflect what happens during natural sleep.7

Why should patients have drug-induced sleep endoscopy instead of natural sleep endoscopy?

The advantage of drug-induced sleep endoscopy is that both the surgeon and patient don’t have to wait for the patient to fall asleep during a daytime nap and also the surgeon doesn’t have to perform the sleep endoscopy overnight.

Additionally, having an endoscope in the nose during natural sleep can be uncomfortable and the drug-induced sleep ensures the patient is sleeping and comfortable during the procedure.

Patients also move during sleep and could unintentionally pull the endoscope out during sleep.

Because of how readily available and simple it is to perform DISE, if a patient is going to have sleep endoscopy, then DISE is almost always favored over natural sleep endoscopy.

So to summarize, both natural sleep endoscopy and DISE have been around for decades as a technique to evaluate the upper airway during sleep, but DISE is currently the preferred method.

Who performs sleep endoscopy?

Sleep endoscopy should be performed by the provider who is capable of evaluating the upper airway at the multiple levels of the airway that could be contributing to the blockage during sleep.

ENT surgeons usually perform sleep endoscopy.

General ENT surgeons, ENT sleep surgeons, and pediatric ENT surgeons are the ones who more commonly perform sleep endoscopy.

Is sleep endoscopy performed under twilight sleep?

Twilight anesthesia is when patients are given smaller doses of anesthetics, also known as sedation.

Drug-induced sleep endoscopy involves giving higher concentrations of anesthetic medications than sedation, but lower concentrations than is given for intubating a patient during standard general anesthesia inductions.

It is important to have the anesthesia provider give enough anesthetic to induce upper airway obstruction in the form of snoring and/or blockage.

Is sleep endoscopy really necessary?

Sleep endoscopy, like any elective procedure, has to be evaluated for the risks, benefits, and alternatives in order to decide if it is necessary for you.

Sleep endoscopy can help an ENT surgeon in their surgical planning.

In the 1970s, patients with obstructive sleep apnea were treated with a tracheostomy8 (a hole in the neck that bypasses the upper airway), so sleep endoscopy would not have been helpful back then.

If a patient has already had a tonsillectomy and other throat surgery, then finding other areas of airway blockage during sleep could benefit the surgical planning.

How long does sleep endoscopy take?

If anesthetic medications are used during sleep endoscopy, and the anesthesia provider and ENT surgeon are experienced in the procedure, then it could take as little as 15-20 minutes.

However, if the sleep endoscopy is performed without anesthetic medications, then it could take 1-2 hours because you need to wait for the patient to fall asleep (difficult with a scope in your nose) and then to start snoring or have airway obstruction.

The goal is not to do a quick view, rather it is to try to mimic what is happening at home.

So, it is vital to not give too much anesthetic because that could cause airway structures to exaggerate the amount of collapse and this could lead to overly aggressive surgeries being recommended.

For example, if you have a person who only snores and has no apneas on their sleep study, and you give them a significant amount of anesthetic, then they can block the entire airway, to include their tongue.

But wait, you wouldn’t cut away part of their tongue in that case because snoring only (without apnea) is caused by the soft palate and uvula a majority of the time.

Overall, what are the steps of drug-induced sleep endoscopy?

There are 11 steps that are followed for drug-induced sleep endoscopy to include:

  1. You should expect not to eat anything after midnight,
  2. Then, you come to the hospital or ambulatory surgery center,
  3. You will meet your ENT surgeon, an operating room nurse, and an anesthesia provider and they will each review the procedure with you,
  4. You will then proceed back to the operating room, often you will be wheeled in a rolling bed,
  5. An intravenous (IV) catheter will be placed if it hasn’t been already,
  6. The room lights are darkened and you do your best to relax,
  7. The anesthesia provider then gives the anesthetic medication(s) to help induce sleep,
  8. Once you are asleep, the ENT surgeon will insert a flexible scope that they can use to evaluate the airway,
  9. After airway obstruction starts (for two breath cycles or one minute), the ENT surgeon will grade the obstruction at each of the sites in your airway,
  10. If your oxygen drops during the procedure, then the ENT surgeon will remove the scope, and the anesthesia provider will give you oxygen until your oxygen level is back to normal, and
  11. Some ENT surgeons record the sleep endoscopy and if so, then they can play it back for you at the post-operative, routine clinic follow-up appointment.

What areas of the upper airway are looked at during sleep endoscopy?

Baby with the upper airway shown. As seen during awake airway endoscopy. SnoringSchool.com
Baby with the upper airway showing to include palate, adenoids, tonsils, tongue epiglottis, larynx and trachea. As seen during awake airway endoscopy.

The goal of sleep endoscopy is to evaluate areas of the airway that could potentially become obstructed during sleep.

The nose doesn’t move, in most cases. The exception is that nasal polyps can vibrate during breathing if they are very large.

Overall, the areas evaluated during sleep endoscopy include:

  • Nose and Nasopharynx (adenoids)
Baby upper airway with the adenoids highlighted. As seen during awake airway endoscopy. SnoringSchool.com
Baby upper airway with the adenoids highlighted. As seen during awake airway endoscopy.
  • Velum (soft palate including the uvula)
Baby upper airway with the palate highlighted. As seen during awake airway endoscopy. SnoringSchool.com
Baby upper airway with the palate highlighted. As seen during awake airway endoscopy.
  • Tonsils (palatine tonsils)
Baby upper airway with the tonsils highlighted. Airway Endoscopy. SnoringSchool.com
Baby upper airway with the tonsils highlighted. As seen during awake airway endoscopy.
  • Tongue (base of tongue including the lingual tonsils)
Baby upper airway with the tongue highlighted. As seen during awake airway endoscopy. SnoringSchool.com
Baby upper airway with the tongue highlighted. As seen during awake airway endoscopy.
Baby upper airway with the tongue tonsils highlighted. As seen during awake airway endoscopy. SnoringSchool.com
Baby upper airway with the tongue tonsils highlighted. As seen during awake airway endoscopy.
  • Epiglottis
Baby upper airway with the epiglottis highlighted. As seen during awake airway endoscopy. SnoringSchool.com
Baby upper airway with the epiglottis highlighted. As seen during awake airway endoscopy.
  • Supraglottis/Larynx/Trachea
Baby upper airway with the larynx highlighted. As seen during awake airway endoscopy. SnoringSchool.com
Baby upper airway with the larynx highlighted. As seen during awake airway endoscopy.
Baby upper airway with the trachea highlighted. Awake airway endoscopy. SnoringSchool.com
Baby upper airway with the trachea highlighted. As seen during awake airway endoscopy.

Is there a difference in sleep endoscopy for kids vs adults?

In general, the medications used for sleep endoscopy in children and adults tend to be similar.

A major difference is the dosing of the medications for adults compared to children and also the areas of blockage can be different.

If no surgery has been performed on children or adults, then children will generally tend to show more blockage of the airway at the following areas:

  • Adenoids (palate hitting against the adenoids)
  • Tonsils
  • Epiglottis
  • Supraglottis

For adults, there is often more blockage of the airway at the following areas:

  • Palate
  • Tonsils
  • Base of Tongue
Woman sleeping, open airway, no obstructive sleep apnea at SnoringSchool.com
Woman sleeping. Airway with no obstruction. Air can flow normally and breathing should be quiet.
Woman sleeping, airway blocked by the soft palate during snoring or obstructive sleep apnea at SnoringSchool.com
Woman sleeping, airway blocked by the soft palate. This can be seen in patients with snoring and/or obstructive sleep apnea.
Woman sleeping, airway blocked by tongue in obstructive sleep apnea at SnoringSchool.com (2)
Woman sleeping, airway is blocked at the tongue and epiglottis. This can be seen in patients with obstructive sleep apnea.
Woman sleeping, airway blocked by tongue in obstructive sleep apnea at SnoringSchool.com
Woman sleeping, airway is blocked at multiple sites. The soft palate, tongue and epiglottis are blocking the airway. This can be seen in patients with obstructive sleep apnea.

For adults and children, if there is blockage at the lower levels of the upper airway (level of the epiglottis and supraglottis) in the absence of stridor, then this is known as occult laryngomalacia.

Occult laryngomalacia is important because these patients (more commonly children) do not show symptoms (such as stridor) of a floppy lower airway when they are awake.

Treatment of occult laryngomalacia may include a procedure of the supraglottis (supraglottoplasty) and it may be performed with surgery of the epiglottis (epiglottoplasty) as well.9

When will I know the results of the drug-induced sleep endoscopy?

Your ENT surgeon will have the results right after the surgery and will dictate the results.

Because patients are generally still sleepy after the procedure, the ENT surgeon might share the results with your escort (if you gave permission).

However, in order to devote the necessary time to explain the site(s) of obstruction during the sleep endoscopy, a regular clinic follow-up is recommended.

At that visit, the ENT surgeon can explain what sites had obstruction and can also provide what the recommended treatment may be.

What is the cost for drug-induced sleep endoscopy?

The cost of sleep endoscopy should be covered by insurance companies and government agencies since it is an approved diagnostic tool for airway evaluation.

The costs must take into account the ENT surgeons fee, the anesthesia provider fees, and the hospital or surgical center fees.

What are risks, benefits, and alternatives to sleep endoscopy?

The risks include:

Bloody nose from where the endoscope sits inside the nose,

Risk of airway blockage during the surgery that could require emergency interventions and aborting the procedure, and

Risk of the anesthetic medications – the most serious being malignant hyperthermia (a life-threatening disorder that can be caused by anesthetic medications in which the body temperature increases significantly).

Malignant hyperthermia is treated with a medication called dantrolene sodium.

Dantrolene causes relaxation of the muscles and works by inhibiting calcium ion release (from sarcoplasmic reticulums).

The benefit of sleep endoscopy is that it provides potentially useful information for determining the best treatment option(s) for reducing upper airway obstruction during sleep.

Note: The following section is more advanced, feel free to read on if you would like details about common patterns of airway obstruction, scoring systems and what the suggested anesthetic medication doses are for the sleep endoscopy.

What is the most common pattern for obstruction of the airway based on research?

Lee and Cho 10 performed a review of the literature and summarized as follows:

If the palate and tongue were the only sites evaluated during sleep endoscopy then 10:

  • The soft palate obstructs 92% of the time, and
  • The tongue obstructs about 58% of the time.

If the palate, the tonsil, the tongue, and epiglottis were looked at during sleep endoscopy, then 10:

  • The soft palate obstructs 84% of the time,
  • The tonsils obstruct 33% of the time,
  • The base of tongue obstructs 52% of the time, and
  • The epiglottis obstructs 34% of the time.

Does drug-induced sleep endoscopy help predict the usefulness of transoral robotic surgery?

Dr. Vicini and colleagues,11 who have a high-volume, transoral robotic surgery practice, have reported that sleep endoscopy offers the following information:

The dynamic behavior of the tongue base can be seen,

The opportunity to determine the surgical exposure that can be viewed during surgery, and

If there is collapse from the walls of the throat (lateral wall collapse), then tongue reduction surgery may not work as well. 11

Does drug-induced sleep endoscopy help predict the usefulness of hypoglossal nerve stimulators?

Dr. Vanderveken and colleagues studied how well drug-induced sleep endoscopy works as a method for evaluating how well hypoglossal nerve stimulators might work as treatment for obstructive sleep apnea.12

The authors found that the best outcomes were found in patients that did not have complete soft palate collapse (complete closure of the palate in both the side to side and front to back, known as complete circumferential collapse).12

What are sleep endoscopy scoring systems?

There are several sleep endoscopy scoring systems. A review of the literature 13 found six scoring systems in children and thirty-five scoring systems in adults and one that was used for both children and adults.

The most commonly used system is the VOTE system 13 which evaluates:

  • The Velum (soft palate),
  • The Oropharynx (tonsils),
  • The Tongue base (back part of the tongue), and
  • The Epiglottis.

The second most common scoring system is the Pringle and Croft classification13 which evaluates:

  • The palate,
  • The lateral pharynx/oropharynx,
  • The tongue base (back part of the tongue),
  • The hypopharynx, and
  • The epiglottis/supraglottis.

How is the severity of obstruction during sleep endoscopy graded?

For the VOTE classification,14 the obstruction is graded as:

  • 0 = no obstruction (no vibration)
  • 1 = partial obstruction (vibration)
  • 2 = complete obstruction (collapse), and
  • X = not visualized.

For the Pringle and Croft grading system,15 obstruction is graded as:

  • Grade 1: simple palatal level snoring,
  • Grade 2: single palatal level obstruction,
  • Grade 3: palatal level obstruction and intermittent tonsil lateral wall (orohypopharyngeal) involvement,
  • Grade 4: sustained multi-segmental involvement, and
  • Grade 5: tongue-base level obstruction.15

What are the medication doses that are given during drug-induced sleep endoscopy?

What is the dose for dexmedetomidine for sleep endoscopy in adults?16

Dexmedetomidine loading dose of 1.5 micrograms/kg is given over a period of 10 minutes and then is followed by an infusion given at a rate of 1.5 micrograms/kg/hour. 16

What is the dose for dexmedetomidine for sleep endoscopy in children?17

Dexmedetomidine loading dose of 2 micrograms/kg is given over a period of 10 minutes and then is followed by an infusion given at a rate of 2 micrograms/kg/hour. 17 Ketamine is given at 1-2 mg/kg dosing when the dexmedetomidine loading dose is given. 17

The following suggested medication doses for adults are based on the European position paper for drug-induced sleep endoscopy (2017) Update 2:

What is the dose for propofol for sleep endoscopy in adults?2

Target-controlled infusion:

Starting dose of 2-2.5 micrograms/mL, and then if required, increasing the rate by 0.2-0.5 micrograms/mL every 2 minutes.

Manually controlled infusion:

50-100 mL/hour.

Bolus technique #1: loading dose of 30-50 mg and increase the rate by 10 mg every 2 minutes, or

Bolus technique #2: loading dose of 1 mg/kg and increase the rate by 20 mg every 2 minutes.

What is the dose for midazolam for sleep endoscopy in adults? 2

Bolus technique: First dose at 0.05 mg/kg, observe for 2-5 minutes then increase the rate by 0.015-0.03 mg/kg.

What is the dose for the combination of propofol and midazolam for sleep endoscopy in adults?2 

Midazolam – single dose at 0.05 mg/kg, then

Propofol – two minutes later, start with a loading dose of 1.5-3.0 micrograms/mL and if needed increase rate by 0.2-0.5 micrograms/mL.

What is the CPT code for drug-induced sleep endoscopy?

The Current Procedural Terminology (CPT) code for drug-induced sleep endoscopy is not exact, but typically ENT surgeons will use 31575 (flexible fiber-optic laryngoscopy).

SuperCoder.com has recommended adding modifier 22 (increased procedural service) for DISE. See the reference below:

https://www.supercoder.com/my-ask-an-expert/topic/drug-induced-sleep-endoscopy

References: 

  1. AASM ea. American Academy of Sleep Medicine. International classification of sleep disorders, 3rd ed. (ICSD-3). American Academy of Sleep Medicine Darien, IL. 2014.
  2. De Vito A, Carrasco Llatas M, Ravesloot MJ, et al. European position paper on drug-induced sleep endoscopy: 2017 Update. Clin Otolaryngol. 2018.
  3. Borowiecki B, Pollak CP, Weitzman ED, Rakoff S, Imperato J. Fibro-optic study of pharyngeal airway during sleep in patients with hypersomnia obstructive sleep-apnea syndrome. Laryngoscope. 1978;88(8 Pt 1):1310-1313.
  4. Sukerman S, Healy GB. Sleep apnea syndrome associated with upper airway obstruction. Laryngoscope. 1979;89(6 Pt 1):878-885.
  5. Croft CB, Pringle M. Sleep nasendoscopy: a technique of assessment in snoring and obstructive sleep apnoea. Clin Otolaryngol Allied Sci. 1991;16(5):504-509.
  6. Croft CB, Thomson HG, Samuels MP, Southall DP. Endoscopic evaluation and treatment of sleep-associated upper airway obstruction in infants and young children. Clin Otolaryngol Allied Sci. 1990;15(3):209-216.
  7. Chang ET, Certal V, Song SA, et al. Dexmedetomidine versus propofol during drug-induced sleep endoscopy and sedation: a systematic review. Sleep Breath. 2017;21(3):727-735.
  8. Camacho M, Certal V, Brietzke SE, Holty JE, Guilleminault C, Capasso R. Tracheostomy as treatment for adult obstructive sleep apnea: a systematic review and meta-analysis. Laryngoscope. 2014;124(3):803-811.
  9. Chan DK, Truong MT, Koltai PJ. Supraglottoplasty for occult laryngomalacia to improve obstructive sleep apnea syndrome. Arch Otolaryngol Head Neck Surg. 2012;138(1):50-54.
  10. Lee EJ, Cho JH. Meta-Analysis of Obstruction Site Observed With Drug-Induced Sleep Endoscopy in Patients With Obstructive Sleep Apnea. Laryngoscope. 2018.
  11. Vicini C, Montevecchi F, Gobbi R, De Vito A, Meccariello G. Transoral robotic surgery for obstructive sleep apnea syndrome: Principles and technique. World J Otorhinolaryngol Head Neck Surg. 2017;3(2):97-100.
  12. Vanderveken OM, Maurer JT, Hohenhorst W, et al. Evaluation of Drug-Induced Sleep Endoscopy as a Patient Selection Tool for Implanted Upper Airway Stimulation for Obstructive Sleep Apnea. J Clin Sleep Med. 2013;9(5):433-438.
  13. Amos JM, Durr ML, Nardone HC, Baldassari CM, Duggins A, Ishman SL. Systematic Review of Drug-Induced Sleep Endoscopy Scoring Systems. Otolaryngol Head Neck Surg. 2018;158(2):240-248.
  14. Kezirian EJ, Hohenhorst W, de Vries N. Drug-induced sleep endoscopy: the VOTE classification. Eur Arch Otorhinolaryngol. 2011;268(8):1233-1236.
  15. Pringle MB, Croft CB. A grading system for patients with obstructive sleep apnoea–based on sleep nasendoscopy. Clin Otolaryngol Allied Sci. 1993;18(6):480-484.
  16. Viana A, Zhao C, Rosa T, et al. The Effect of Sedating Agents on Drug-Induced Sleep Endoscopy Findings. Laryngoscope. 2018.
  17. He S, Peddireddy NS, Smith DF, et al. Outcomes of Drug-Induced Sleep Endoscopy-Directed Surgery for Pediatric Obstructive Sleep Apnea. Otolaryngol Head Neck Surg. 2018;158(3):559-565.