1. Department of Anesthesiology and Pain Medicine, Wonkwang University College of Medicine, Iksan, Korea.
2. Department of Obstetrics and Gynecology, Wonkwang University College of Medicine, Iksan, Korea.
3. Department of Anesthesiology and Pain Medicine, Wonkwang University Sanbon Hospital, Gunpo, Korea.
4. Department of Anesthesiology and Pain Medicine, Presbyterian Medical Center, Jeonju, Korea.