Ideal Depth of Guide Wire for Central Catheterization

Inclusion Criteria: * patients receiving general anesthesia requiring central venous catheterization via right internal jugular vein. * ASA (American Society of Anesthesiologist) physical status class I or II Exclusion Criteria: * at the pre-anesthetic evaluation, history of any arrhythmia * when monitoring before the induction of anesthesia in the operating room, newly arrhythmia is observed. * abnormal electrolyte at the pre-anesthetic evaluation * too difficult to access right internal jugular vein for central catheterization (too short neck, infection at the site of right internal jugular vein, ventriculoperitoneal shunt or chemo-port existence at the site of right internal jugular vein. too close site to operating field)