AIM To compare colonoscopy quality with nitrous oxide gas(Entonox?) against intravenous conscious sedation using midazolam plus opioid.METHODS A retrospective analysis was performed on a prospectively held database of 18608 colonoscopies carried out in Lothian health board hospitals between July 2013 and January 2016.The quality of colonoscopies performed with Entonox was compared to intravenous conscious sedation(abbreviated in this article as IVM).Furthermore,the quality of colonoscopies performed with an unmedicated group was compared to IVM.The study used the following key markers of colonoscopy quality:(1) patient comfort scores;(2) caecal intubation rates(CIRs); and (3) polyp detection rates (PDRs).We used binary logistic regression to model the data.RESULTS There was no difference in the rate of moderate-toextreme discomfort between the Entonox and IVM groups (17.9% vs 18.8%; OR = 1.06,95%CI: 0.95-1.18,P = 0.27).Patients in the unmedicated group were less likely to experience moderate-to-extreme discomfort than those in the IVM group(11.4% vs 18.8%; OR = 0.71,95%CI: 0.60-0.83,P < 0.001).There was no difference in caecal intubation between the Entonox and IVM groups(94.4% vs 93.7%; OR = 1.08,95%CI: 0.92-1.28,P = 0.34).There was no difference in caecal intubation between the unmedicated and IVM groups (94.2% vs 93.7%; OR = 0.98,95%CI: 0.79-1.22,P = 0.87).Polyp detection in the Entonox group was not different from IVM group (35.0% vs 33.1%; OR = 1.01,95%CI: 0.93-1.10,P = 0.79).Polyp detection in the unmedicated group was not significantly different from the IVM group (37.4% vs 33.1%; OR = 0.97,95%CI: 0.87-1.08,P = 0.60).CONCLUSION The use of Entonox was not associated with lower colonoscopy quality when compared to intravenous conscious sedation using midazolam plus opioid. AIM To compare colonoscopy quality with nitrous oxide gas (Entonox®) against intravenous conscious sedation using midazolam plus opioid. METHODS A retrospective analysis was performed on a prospectively held database of 18608 colonoscopies carried out in Lothian health board hospitals between July 2013 and January 2016. The quality of colonoscopies performed with Entonox was compared to intravenous conscious sedation (abbreviated in this article as IVM) .Furthermore, the quality of colonoscopies performed with an unmedicated group was compared to IVM. The study used the following key markers of colonoscopy quality :( (2) caecal intubation rates (CIRs); and (3) polyp detection rates (PDRs). We used binary logistic regression to model the data. RESULTS There was no difference in the rate of moderate-toextreme discomfort between the uninvolved group and the IVM groups (17.9% vs 18.8%; OR = 1.06, 95% CI: 0.95-1.18, P = 0.27) derate-to-extreme discomfort than those in the IVM group (11.4% vs 18.8%; OR = 0.71, 95% CI: 0.60-0.83, P <0.001) .here was no difference in caecal intubation between the Entonox and IVM groups OR = 1.08, 95% CI: 0.92-1.28, P = 0.34). There was no difference in caecal intubation between the unmedicated and IVM groups (94.2% vs 93.7%; OR = 0.98, 95% CI : 0.79-1.22, P = 0.87) .Polyp detection in the Entonox group was not different from IVM group (35.0% vs 33.1%; OR = 1.01, 95% CI: 0.93-1.10, P = 0.79) The unmedicated group was not significantly different from the IVM group (37.4% vs 33.1%; OR = 0.97, 95% CI: 0.87-1.08, P = 0.60) .CONCLUSION The use of Entonox was not associated with lower colonoscopy quality when compared to intravenous conscious sedation using midazolam plus opioid.