The use of carbon-dioxide (CO_2) for colon insufflation as negative contrast media in radiograph is not new. Room air consists of about 80% nitrogen and 20% oxygen. therefore, a buffer system of carbon-dioxide in the human body has limited chemical contact for nitrogen, so that nitrogen gas should stay for a very long time. Thus, the patients may have pain if the gas expansion creates an ischemic situation in the colon blood stream with the body heat. Ninety-eight consecutive patients scheduled for barium enema studies were assigned randomly to insufflation with either air or CO_2 in a double blind, prospective trial. Clinically relevant pain was experienced by 49% of the patients after insufflation with room air, compared with 26% of patients in whom CO_2 was used for insufflation. (p<0.02, x^2)
