1. Department of Anesthesiology and Pain Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Korea.
2. The Joun Pain Clinic, Seoul, Korea.
3. Department of Anesthesiology and Pain Medicine, College of Medicine, Ajou University, Suwon, Korea.
4. Department of Anesthesiology and Pain Medicine, Seoul National University College of Medicine, Seoul, Korea.