[1] Chungnam Natl Univ Hosp, Dept Anesthesiol & Pain Med, Daejeon, South Korea
[2] Chungnam Natl Univ, Coll Med, Dept Anesthesiol & Pain Med, Daejeon, South Korea
[3] Jeil Neurosurg Hosp, Daejeon, South Korea
[4] Chungnam Natl Univ, Coll Med, Dept Anesthesiol & Pain Med, Munhwa Ro 266, Daejeon 35015, South Korea