摘要AIM: To clarify the effectiveness of CO_2 insufflation in potentially difficult colonoscopy cases, particularly in relation to the experience level of colonoscopists. METHODS: One hundred twenty potentially difficult cases were included in this study, which involved females with a low body mass index and patients with earlier abdominal and/or pelvic open surgery or previously diagnosed left-side colon diverticulosis. Patients receiving colonoscopy examinations without sedation using a pediatric variable-stiffness colonoscope were divided into two groups based on either CO_2 or standard air insufflation. Both insufflation procedures were also evaluated according to the experience level of the respective colonoscopists who were divided into an experienced colonoscopist (EC) group and a less experienced colonoscopist (LEC) group. Study measurements included a 100-mm visual analogue scale (VAS) for patient pain during and after colonoscopy examinations, in addition to insertion to the cecum and withdrawal times. RESULTS: Examination times did not differ, however, VAS scores in the CO_2 group were significantly better than in the air group (P < 0.001, two-way ANOVA) from immediately after the procedure and up to 2 h later. There were no significant differences between either insufflation method in the EC group (P = 0.29), however, VAS scores for CO_2 insufflation were significantly better than air insufflation in the LEC group (P = 0.023) immediately after colonoscopies and up to 4 h afterwards. CONCLUSION: CO_2 insufflation reduced patient pain after colonoscopy in potentially difficult cases when performed by LECs.