1. Department of Anesthesiology and Pain Medicine, Gangneung Asan Hospital, Ulsan University School of Medicine, Gangneung, Korea.
2. Department of Anesthesiology and Pain Medicine, Konkuk University Hospital, Konkuk University School of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Konkuk University Hospital, Konkuk University School of Medicine, Seoul, Korea.
4. Department of Chest Surgery, Konkuk University Hospital, Konkuk University School of Medicine, Seoul, Korea.