Sleep-disordered breathing has a prevalence of 30~80% in patients with heart diseases. Various studies have revealed a correlation between the incidence and various diseases such as heart failure, hypertension, diabetes, and cerebral infarction. Postoperative acute kidney injury after heart surgery is one of the major complications with incidence with 40~50%, however, there has been no preventive method or treatment yet. Recently, several studies have been published that have shown a correlation between sleep-disordered breathing and renal impairment. In general, sleep-disordered breathing can be regulated easily with continues positive expiratory pressure, which means that early diagnosis and treatment of sleep-disordered breathing might help to reduce the incidence of postoperative acute kidney injury and improve patients' prognosis.

In this study, the investigators investigate the impact of sleep-disordered breathing (diagnosed by oxygen desaturation index ≥5) on the incidence of postoperative acute kidney injury in patients undergoing valvular heart surgery.

Inclusion Criteria:

1. Adult patient aged more than 20 years
2. Patients undergoing valvular heart surgery.

Exclusion Criteria:

1. Emergency
2. Simultaneous surgery with coronary artery bypass graft
3. Previous history of cerebrovascular accident
4. Previous history of sleep disordered breathing (diagnosis & treatment)
5. Previous history of tracheostomy
6. Previous history of surgical treatment of airway (ex: nasopharyngeal cancer)
7. Preoperative oxygen supplement therapy
8. Patients who have participated in other clinical studies that may affect prognosis
9. Patients who cannot read and agree to informed consent (ex: foreigners, cognitive dysfunction)

Adult patients undergoing valvular heart surgery