The investigators aim to assess the respiratory effect of short half-life agents in balanced anesthesia on patients suffering from non-treated or suspected obstructive sleep apnea syndrome (OSA) We will study the impact on OSA of a regimen of remifentanil-desflurane versus a regimen of fentanyl-sevoflurane. Each patient will undergo three respiratory portable polygraphies: the night before the surgery ; the first night following the surgery ; the third night following the surgery.

Inclusion Criteria:

• Physical status I - III
• Patient scheduled to undergo lower limb orthopedic surgery
• Patients known for non-treated obstructive sleep apnea or suspected of having an obstructive sleep apnea

Exclusion Criteria:

• Patients known for treated obstructive sleep apnea ;
• Severe respiratory disease (i.e., chronic obstructive pulmonary disease, asthma, pulmonary fibrosis);
• Severe cardiovascular disease
• Chronic use of opiates ≥ 30mg/j morphine eq.
• Chronic use of benzodiazepine
• Inability to consent
• Refusal