The main diagnostic challenge in patients with OSA (obstructive sleep apnea) is to determine the location of obstruction of the upper airway during sleep. This is so, because the otorhinolaryngology examination, which states probable site of obstruction of upper airways, is performed in the awake status. Therefore, drug-induced sleep endoscopy (DISE) has been introduced in the diagnostic algorithm of OSA patients during the last decade. The advantage of DISE is, that the collapse of upper airways, which is not visible during the awake status can be observed and targeted therapy according to the location and degree of obstruction of the upper airway can be applied. As a result, higher treatment success in patients with OSA can be reached.

Materials and Methods The study was approved by the Institutional Ethics Committee and performed in accordance with the Declaration of Helsinki, good clinical practice, and applicable regulatory requirements. Informed written consent was obtained from all participants before initiation of any procedure.

• History, otorhinolaryngology examination, polysomnography Patient history will be taken with emphasis on snoring and OSA symptoms. Daytime sleepiness will be assessed using the Epworth Sleepiness Scale. Moreover, patients will be asked to grade the severity of snoring on a 10-point Visual Analogue Scale (0 = no snoring, 10 = extreme snoring). The body mass index (BMI) will be calculated.

Otorhinolaryngology examination, focusing on nasal, pharyngeal and laryngeal pathologies (enlargement of uvula, soft palate webbing, enlargement of palatal tonsils, base of the tongue hypertrophy, visibility of vallecula, pathology of epiglottis), will be performed.

Thereafter, each patient will undergo polysomnography and patients will be divided according to the severity of OSA into three groups (mild OSA - 5 < AHI ≤ 15, moderate OSA 15 < AHI ≤ 25, and severe OSA with AHI > 25 events per hour of sleep).

According to history, otorhinolaryngology examination and polysomnography, presumably site of obstruction will be stated and therapeutic plan will be designated. Patients with severe OSA will be sent for CPAP (continuous positive airway pressure) treatment, whereas surgery will be recommended for patients with mild and moderate OSA.

• Drug-Induced sleep endoscopy

- Indication and contraindication to DISE DISE will be indicated in patients with mild and moderate OSA and in those with severe OSA who will fail or refuse CPAP treatment. All these patients will be potentially planned for surgery and will have to agree with the surgical treatment.

Patients with ASA (American Society of Anesthesiology) score above 4, as well as patients with central apnea and propofol or midazolam allergies, will be excluded from the study.

• Premedication Patients will be pre-medicated with a combination of 5 mg midazolam and 0,5 mg atropine intramuscularly 30 minutes before DISE.
• Procedure Patients will be lying in a supine position on an operation table, the lights will be dimmed and the room quiet to minimize awaking stimuli. Patients will be standardly monitored: ECG (electrocardiogram), blood oxygen saturation, non-invasive blood pressure, and depth of anesthesia will be monitored by bispectral index (BIS). Local anesthesia of nasal cavity will be performed by Lidocaine 10%, 2 sprays into each nostril.

Anaesthesia will be induced by intravenous bolus of propofol 1 mg per kg of ideal body weight, and maintained by repeated boluses of propofol 10-20 mg every 3-5 minutes for the target BIS (Bispectral Index) value of 50-70. Once the patient reaches a satisfactory level of sedation, a flexible fiber optic. Intubation scope 3.7mm x 65cm coated with anti-condense will be introduced into the nasal cavity. The nasal passage, nasopharynx, velum, oropharynx (including tonsils), tongue base, epiglottis, and larynx will be observed. The length of examination will be 15 minutes minimal in order to detect the obstruction. DISE findings will be reported using the VOTE classification system according to Kezirian. Accordingly, localization of upper airways obstructions will be done.

At the end of endoscopy a jaw thrust (or Esmarch maneuver) will be performed. The mandible will be gently advanced up to 5 mm. The manoeuver will be evaluated as successful when the enlargement of upper airway will be observed and disappearance of apnea mimicking the effect of mandibular repositioning appliance (MRA).

After finishing of endoscopy, patients will be awakened to full consciousness in the operating room and then transferred to recovery room for 1-hour observation.

• Evaluation of changes in indication for site of surgery Indication for surgery made according to otorhinolaryngology examination before DISE and after DISE will be compared. Changes will be noted and the number of patients will be calculated using percentage.

Inclusion Criteria:

• 18-65 years
• obstructive sleep apnoea (mild, moderate Apnea-Hypopnea Index (AHI) <15)
• severe OSA - failed CPAP treatment
• severe OSA - patients whorefused CPAP

Exclusion Criteria:

• ASA 4 (classification of the American Society of Anesthesiologists)
• pregnancy
• propofol or midazolam allergies
• other significant disease with current decompensation