S414 INTRODUCTION: One lung ventilation (OLV) has become increasingly popular during video assisted thoracoscopic surgery (VATS). Compared to bilateral lung ventilation (BLV), OLV could produce a higher rate of complications. Our aim was to examine, retrospectively, for risk factors and possible complications during VATS with OLV. METHODS: With institutional approval, we examined medical and anesthetic records of 1156 patients who underwent VATS in our hospital from Jan. 1991 to Sep. 1997. We examined for hypoxia (SpO2 =95), severe hypoxia (SpO2 =90), hypercapnia (PECO2 >40 mmHg), hypo- or hypertension and brady- or tachycardia (and treatment) during surgery. We also noted gender, age, body weight (BW), body height (BH), anesthetic time (ANT), operation time (OPT) anesthetic method, disease process, and operative body position. Data were expressed as mean +/- S.E and analyzed by ANOVA and Chi-square statistics with p<0.05 considered significant. RESULTS: All patients were anesthetized with inhalation anesthetics with or without epidural anesthesia. BLV was utilized in 141 cases and designated as group I. In the OLV group (group II), all patients but 3 were intubated with Broncho - Cath - LeftTM (Malinchrott). There were no significant differences in gender, BW, BH, tachycardia, bradycardia, and hypo- or hypertension between both groups. ANT and OPT were significantly longer in the BLV group than in the OLV group. However, the occurrence of hypoxia, but not hypercapnia, was significantly higher with OLV than BLV. Table 1 In the OLV group, patients over 30 yr. old had a higher incidence of hypoxia than younger patients (Figure 1). High Body Mass Index (BMI) patients had a higher incidence of hypoxia and patients in the left lateral position had a higher occurrence of hypoxia than those in the right lateral position (Figure 2). However, severe hypoxia occurred more in the right lateral than in the left lateral position (Figure 3). Inhalation anesthetics with or without epidural anesthesia did not affect the occurrence of hypoxia.Figure 1Figure 2Figure 3CONCLUSIONS: Our data indicates that age over 30 yr, high BMI, and left lateral position are risk factor for hypoxia during OLV. This suggests that differences in pulmonary blood flow between right and left decubitus positions can influence the incidence of less than severe hypoxia. Severe hypoxia is more likely to result from inadequate position of the double lumen tracheal tube.