1. Department of Anesthesiology and Pain Medicine; Korea University Medical Center; Seoul Korea
2. College of Medicine; Korea University; Seoul Korea
3. Biostatistical Consulting Unit; Soonchunhyang University Medical Center; Seoul Korea
4. Department of Preventive Medicine; College of Medicine; Korea University; Seoul Korea
5. Department of Anesthesiology and Pain Medicine; Ilsan Paik Hospital; Inje University; Seoul Korea
6. Department of Thoracic and Cardiovascular Surgery; Korea University Medical Center; Seoul Korea