Colonoscopy is associated with pain and discomfort, and intravenous analgesics and sedatives are widely used. There are several disadvantages regarding this practice, including risk of complications, resources demanded, and amnesia after sedation. In spite of promising results in previous studies, nitrous oxide is rarely used at endoscopy centers around the world.

To investigate the efficiency of nitrous oxide versus placebo as an analgesic during colonoscopy without sedation.

A double-blind, randomized, placebo-controlled trial.

The endoscopy unit at Oslo University Hospital Rikshospitalet, Oslo, Norway, between June 2006 and May 2008.

This study involved patients undergoing elective colonoscopy.

Patients inhaled nitrous oxide or placebo on demand.

The participants filled in a questionnaire regarding their experiences with the examination. Pain was graded from 1 (no pain) to 4 (severe pain).

We recruited 199 patients. We randomized 97 patients to the nitrous oxide group and 102 to the control group. The groups were comparable regarding demographic factors. Median patient-reported pain was 2 in both the nitrous oxide group and the control group (interquartile range 2-3 in both groups). Additional sedatives and analgesics were given equally often and in similar doses in both groups. No side effects related to administration of nitrous oxide were reported.

The questionnaire was returned by 76% of the patients. The study gas was given on demand, not continuously.

Nitrous oxide given intermittently is not an effective substitution for intravenous on-demand sedation and analgesics in the setting of colonoscopy without sedation. (Clinical trial registration number: NCT00318825.)