Insufflation of carbon dioxide (CO2) instead of air can reduce pain resulting from colon distension after colonoscopy because CO2 is rapidly absorbed from the colon and excreted through the lungs. This reduces the effects of colonic distension and minimizes intracolonic gas at the end of the examination. The aims of the study were to evaluate the timing of administering CO2 insufflation and to identify predictors of discomfort for colonoscopy.

Inclusion Criteria:

• patients with an appropriate indication for colonoscopy were considered eligible.

Exclusion Criteria:

• Exclusion criteria included severe hematochezia, acute colonic pseudo-obstruction, known obstructive lesions, age <18 years, prior colon resection, fulminant colitis, chronic obstructive pulmonary disease requiring oxygen, and a medical history of CO2 retention. Patients that required only a partial colonoscopy or were unable to read or understand Chinese were also excluded.