Letter: carbon dioxide vs. room air insufflation for gastrointestinal endoscopy

SIRS, Recently, Wang and colleagues’ published a meta-analysis of carbon dioxide (CO2) vs. air insufflation for gastrointestinal endoscopy. Their analyses showed that although CO2 insufflation reduced abdominal pain and distension following colonoscopy, similar benefit was not apparent for endoscopic retrograde cholangiopancreatography (ERCP). We would like to share our experience in this regard. In our retrospective study of 120 ERCP patients, CO2 insufflation reduced both the incidence (P = 0.027) and severity (P = 0.012) of pain based on a visual analogue scale score. However it did not affect the sedation, analgesia or antispasmodic requirements when compared with air. The real advantage of CO2 vs. air, such as diffusibility and rapid absorption, is thus apparent immediately after the procedure when other anatomical and physiological factors come into play. The colon is more capacious and the insufflated air or CO2 can be easily aspirated by controlled suction through the endoscope or vented as flatus by the patient. However, unlike the colon, the small bowel has a narrow lumen and is more pain sensitive to distension. Also the efflux of its luminal contents into the colon is controlled by the ileo-caecal valve which acts as a physiological sphincter. Small bowel, therefore, is more likely to hold onto insufflated gas following ERCP, which is often prolonged and technically challenging. Hence factors like complexity of the procedure, biliary vs. pancreatic endotherapy, simple vs. complicated stone removal techniques, distal vs. hilar biliary strictures, single vs. multiple stenting, duration of the procedure and experience of the endoscopist have a role when comparing the outcome of the two insufflates. Similarly, use of general anaesthesia vs. conscious sedation may have an impact on the recovery phase post-ERCP. This could explain the heterogeneity of the studies compared by Wang et al. and the resultant incongruous results between them.