Sleep apneic episodes increase after general anaesthesia up to the third postoperative night. A mandibular advancement device, called MAD, is a small device that is inserted in the patient's mouth during the night and allows the advancement of the mandible, preventing sleep apneic episodes. The objective of this randomized controlled trial is to determine whether a MAD reduces the impact of general anaesthesia on the increase of the sleep apneic episodes in the postoperative period. All patients will have their sleep-related respiratory data measured using a portable respiratory polygraphy recorder (ResMed Embletta® system). This portable recorder allows a non-invasive recording of nasal airflow through a nasal cannula, oxygen saturation (SpO2) via finger pulse oximetry, respiratory efforts through thoracic and abdominal belts, and body position.

Inclusion Criteria:

- adult patient undergoing any lower limb surgery

Exclusion Criteria:

• continuous positive airway pressure (CPAP) treatment for obstructive sleep apnoea,
• presence of severe respiratory or cardiovascular disease
• preoperative consumption of benzodiazepine,
• chronic use of opioids > 30 mg/day morphine equivalent
• no tooth
• patient known for malignant hyperthermia