1. The First Clinical Medical College of Shandong, University of Traditional Chinese Medicine, Jinan 250014, Shandong Province, P. R. China
2. Department of Anesthesiology, Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan 250014, Shandong Province, P. R. China
3. Department of Anesthesiology, University of Connecticut Medical School, 200 Academic Way Farmington, Connecticut 06032, USA