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During the procedure, the patient is often given [[sedation]] intravenously, employing agents such as [[fentanyl]] or [[midazolam]]. Although meperidine (Demerol) may be used as an alternative to fentanyl, the concern of seizures has relegated this agent to second choice for sedation behind the combination of fentanyl and midazolam. The average person will receive a combination of these two drugs, usually between 25 and 100{{nbsp}}µg IV fentanyl and 1–4{{nbsp}}mg IV midazolam. Sedation practices vary between practitioners and nations; in some clinics in Norway, sedation is rarely administered.<ref>{{cite journal | vauthors = Bretthauer M, Hoff G, Severinsen H, Erga J, Sauar J, Huppertz-Hauss G | title = [Systematic quality control programme for colonoscopy in an endoscopy centre in Norway] | language = no | journal = Tidsskrift for den Norske Laegeforening | volume = 124 | issue = 10 | pages = 1402–1405 | date = May 2004 | pmid = 15195182 }}</ref><ref>{{cite journal | vauthors = Dossa F, Dubé C, Tinmouth J, Sorvari A, Rabeneck L, McCurdy BR, Dominitz JA, Baxter NN | title = Practice recommendations for the use of sedation in routine hospital-based colonoscopy | journal = BMJ Open Gastroenterology | volume = 7 | issue = 1 | pages = e000348 | date = 2020-02-16 | pmid = 32128226 | pmc = 7039579 | doi = 10.1136/bmjgast-2019-000348 }}</ref>
The first step is usually a [[digital rectal examination]] (DRE), to examine the tone of the anal [[sphincter]] and to determine if preparation has been adequate. A DRE is also useful in detecting anal [[neoplasm]]s and the clinician may note issues with the prostate gland in men undergoing this procedure.<ref>{{cite journal | vauthors = Farooq O, Farooq A, Ghosh S, Qadri R, Steed T, Quinton M, Usmani N | title = The Digital Divide: A Retrospective Survey of Digital Rectal Examinations during the Workup of Rectal Cancers | journal = Healthcare | volume = 9 | issue = 7 | pages = 855 | date = July 2021 | pmid = 34356233 | pmc = 8306048 | doi = 10.3390/healthcare9070855 | doi-access = free }}</ref> The [[endoscopy|endoscope]] is then passed through the [[Human anus|anus]] up the [[rectum]], the [[Colon (anatomy)|colon]] (sigmoid, descending, transverse and ascending colon, the cecum), and ultimately the [[ileum|terminal ileum]]. The endoscope has a movable tip and multiple channels for instrumentation, air, suction and light. The bowel is occasionally insufflated with air to maximize visibility (a procedure that gives the patient the false sensation of needing to take a [[bowel movement]]). Biopsies are frequently taken for [[histology]]. Additionally in a procedure known as [[chromoendoscopy]], a contrast-dye (such as [[indigo carmine]]) may be sprayed through the endoscope onto the bowel wall to help visualize any abnormalities in the mucosal morphology. A [[Cochrane review]] updated in 2016 found strong evidence that chromoscopy enhances the detection of cancerous tumors in the colon and rectum.<ref>{{cite journal | vauthors = Brown SR, Baraza W, Din S, Riley S | title = Chromoscopy versus conventional endoscopy for the detection of polyps in the colon and rectum | journal = The Cochrane Database of Systematic Reviews | volume = 2016 | issue = 4 | pages = CD006439 | date = April 2016 | pmid = 27056645 | pmc = 8749964 | doi = 10.1002/14651858.CD006439.pub4 }}</ref>
In most experienced hands, the endoscope is advanced to the junction of where the colon and small bowel join up ([[cecum]]) in under 10 minutes in 95% of cases. Due to tight turns and redundancy in areas of the colon that are not "fixed", loops may form in which advancement of the endoscope creates a "bowing" effect that causes the tip to actually retract. These loops often result in discomfort due to stretching of the colon and its associated [[mesentery]]. Manoeuvres to "reduce" or remove the loop include pulling the endoscope backwards while twisting it. Alternatively, body position changes and abdominal support from external hand pressure can often "straighten" the endoscope to allow the scope to move forward. In a minority of patients, looping is often cited as a cause for an incomplete examination. Usage of alternative instruments leading to completion of the examination has been investigated, including use of pediatric colonoscope, push enteroscope and upper GI endoscope variants.<ref>{{cite journal | vauthors = Lichtenstein GR, Park PD, Long WB, Ginsberg GG, Kochman ML | title = Use of a push enteroscope improves ability to perform total colonoscopy in previously unsuccessful attempts at colonoscopy in adult patients | journal = The American Journal of Gastroenterology | volume = 94 | issue = 1 | pages = 187–190 | date = January 1999 | pmid = 9934753 | doi = 10.1111/j.1572-0241.1999.00794.x | s2cid = 24536782 }} ''Note:Single use PDF copy provided free by [[Blackwell Publishing]] for purposes of Wikipedia content enrichment.''</ref>
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