BACKGROUND: Hypoxia often occurs during anesthesia of patients with tetralogy of Fallot (TOF). The factors that determine pulmonary circulation and oxygenation in patient with TOF are the degree of obstruction of right ventricular outflow tract (RVOT), right ventricular filling pressure, systemic vascular resistance, loss of negative pleural cavity pressure by thoracotomy, change of pulmonary vascular resistance due to positive pressure ventilation and degree of arteriopulmonary collateral connection. Hence pulse oximetry is a noninvasive technique for measuring arterial O2 saturation continuously, this study examined the correlation between the change of percutaneous arterial oxygen saturation (delta SpO2) and the change of mean arterial pressure (delta MAP) using pulse oximetry in these patients. METHODS: Twenty pediatric patients undergoing modified Blalock-Taussig shunt or total corrective operation were prospectively investigated. Immediately after induction, baseline values of MAP and SpO2 were determined and if there were some changes in SpO2 from baseline during operation, MAP on that value of SpO2 were collected. If SpO2 reduced, patients were treated with infusion of fresh frozen plasma or pentastach (2-10 ml/kg), injection of phenylephrine (10 microgram/kg) or esmolol (0.5 mg/kg). RESULTS: Intravascular volume loading only was executed in 4 patients, intravascular volume loading and phenylephrine administration was executed in 11 patients, and intravascular volume loading, phenylephrine and beta-blocker administration was executed in 5 patients. There were no significant correlation between delta MAP and delta SpO2 from linear correlation and regression analysis (r=0.23, p<0.05). CONCLUSIONS: Because delta SpO2 were not closely related with delta MAP and above mentioned factors could act closely among each others, meticulous anesthetic management is necessary during palliative or total corrective operation in patients with TOF.