PREVENTION OF HYPOKALEMIA IN WITH LIDOCAINE DURING MODERATE HYPOTHERMIA IN OPEN HEART SURGERY &/ Lidocaine has membrane stabilising effects and supresses the release of cathecholamines. We aimed to prevent hypokalemia which develops during moderate hypotermia in open heart surgery by adding lidocaine to the priming solution in extracorporeal circulation. Study group consisted of thirty patients with ASA physical status II or III, undergoing open heart surgery for congenital or acquired cardiac problems. Patients were anestheti¬zed with intravenous or inhalation agents and were intubated using medium acting musc¬le relaxant vecuronium. Anesthesia was maintained by inhalation agents until extracorpo¬real circulation and intravenously later on. Moderate hypothermia was applied to all patients. In the first group (18 patients), 1.5 mg/kg lidocaine was added to the priming solution, the second group (12 patients) received no lidocaine. In both groups, blood samples were taken once before extracorporeal circulation and once for every fifteen minu¬tes for the first hour after the beginnig extracorporeal circulation and serum potassium le¬vels were compaired between the two groups. In the first group which received lidocaine. serum potassium levels were found higher than the second group, the difference at the 60 th minute being statistically significant (p