In case of cardiopulmonary bypass, organ transplantation and massive transfusion, the electrolyte(Na+, K+, Ca++) and pH are very changeable, and it is very important to correct the pH and electrolyte immediately. We studied the bedside electrolyte monitoring with VIA(Vascular Intermittent Access) 1-01 and its accuracy validation. We selected 13 patients who went an open heart surgery in the Seoul National University HospitaL The patient was catheterized with 16 G triple lumen catheter into the SVC-right atrium junction via right internal jugular vein. Then we connected VIA 1-01 to one lumen. The electrolyte samplings were done during perianesthetic period. The electrolyte values(Na+, K+, ionized Ca++) of each sample was measured by laboratory, NOVA of PAR(postanesthetic recovery room) and VIA 1-01. We compared the values with correlation. The Pearson product-moment coefficient(r) of laboratory vs VIA 1-01 are 0.9073(Na+), 0.9471(K+) 0.6485(Ca++). The r of NOVA vs VIA 1-01 are 0.6348(Na+), 0.9330 (K+), 0.5206(Ca++ ). The r of laboratory vs NOVA are 0.6719(Na+), 0.9532(K+ ), 0.8221(Ca+). All pvalues of r were lower than 0.01. We conclude that bedside electrolyte monitoring with VIA l- 01 is very useful to critically ill-patient and major operations during anesthesia and it improves the prognosis of such patients.