Colonoscopy

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Colonoscopy is a procedure in which a flexible fiberoptic endoscope is passed through the anus to visualize the mucosa of the rectum, colon, and, sometimes, the terminal ileum. It is commonly used to diagnose and/or manage lower gastrointestinal (GI) disorders, such as GI bleeding, and for colorectal cancer screening. Bowel preparation involves a combination of dietary restrictions (e.g., a low-residue diet for 1 day) and pharmacological bowel-cleansing agents (e.g., polyethylene glycol-based solutions). Contraindications include known or suspected GI perforation and conditions with a risk of perforation (e.g., toxic megacolon and acute diverticulitis). Complications are rare but include colonic perforation and GI bleeding. For patients unable to undergo colonoscopy, alternatives include video capsule endoscopy and radiography.

• Screening: for colorectal cancer (CRC) ^[2][3]
• Diagnostic ^[2][3]
  • Abnormal bowel imaging findings (e.g., apple core lesion seen on barium enema)
  • Suspected lower GI bleeding (LGIB) based on any of the following:
    • Hematochezia
    • Melena (if upper GI bleed has been ruled out)
    • Positive fecal occult blood test
  • Unexplained iron deficiency anemia
  • Unexplained chronic diarrhea
• Therapeutic intervention ^[2][3]
  • Endoscopic hemostasis for lower GI bleeding
  • Endoscopic mucosal resection or endoscopic ablation for colonic lesions
  • Endoscopic bowel decompression: e.g., for sigmoid volvulus or acute megacolon ^[4]
  • Dilation or stenting: e.g., for palliative treatment of inoperable malignancy, postoperative strictures
  • Management of foreign body ingestion
• Surveillance: e.g., follow-up for CRC, colonic polyps, or inflammatory bowel disease (IBD) ^[2][3]

• Absolute contraindications ^[2]
  • Known or suspected GI perforation
  • Patient is unable to cooperate with the procedure, e.g., due to agitation.
  • Informed consent cannot be obtained.
• Relative contraindications (due to increased risk of periprocedural perforation) include:
  • Acute diverticulitis ^[2]
  • Fulminant colitis, e.g., due to acute severe ulcerative colitis ^[2]
  • Suspected toxic megacolon ^[5]
  • Complicated bowel obstruction, e.g., signs of overt peritonitis ^[4]

We list the most important contraindications. The selection is not exhaustive.

Always obtain and document informed consent from the patient or their legal guardian.

Bowel preparation ^[6]

General principles ^[6]

• A pharmacological agent and dietary restrictions are used to empty the bowel of fecal matter.
• Provide verbal and written patient instructions to improve adherence and ensure adequate bowel preparation.

Dietary modifications ^[6]

• A low-residue diet the day before colonoscopy is sufficient for most patients.
• For patients at risk of inadequate bowel preparation, consider additional modifications, e.g.: ^[6]
  • Restricting high-fiber foods (e.g., vegetables) for 2–3 days
  • Clear liquid diet for 1 day

Agents ^[6][7]

All agents perform similarly. Consider the patient's medical history and the outcomes of previous bowel preparations, if known.

• Polyethylene glycol (PEG) based: preferred for the following
  • Advanced liver disease, chronic kidney disease (CKD), heart failure
  • Increased risk of dehydration and/or electrolyte imbalances
  • IBD
  • Suspected lower GI bleed in patients undergoing rapid bowel preparation
  • Pregnant individuals
• Magnesium citrate with sodium picosulfate (MCSP)
  • Usually better tolerated and causes fewer adverse effects than PEG
  • Contraindicated in patients with heart failure, hypermagnesemia, and CKD stage 4–5 because of hyperosmolarity and magnesium content
• Oral sulfate solution
  • Usually better tolerated than PEG and MCSP
  • Contraindicated in patients with heart failure, ascites, and CKD stage 4–5

Except for simethicone, routine use of bowel preparation adjuncts (e.g., enemas, promotility agents) is not recommended. ^[6]

Dosing ^[6]

• Low-volume (e.g., 2 L): preferred for most ambulatory patients, with or without simethicone as an adjunct
• High-volume (e.g., 4 L): Use in combination with an adjunct (e.g., bisacodyl the day before colonoscopy) for patients at high risk of inadequate bowel preparation.

Timing ^[6][7][8][9]

• Split-dose bowel preparation
  • Preferred for elective colonoscopy ^[6]
  • Administration ^[6]
    • First dose: 12–24 hours before colonoscopy
    • Second dose: starting 4–6 hours before colonoscopy and finishing > 2 hours before colonoscopy
• Single-dose bowel preparation
  • Consider if nonurgent endoscopy is scheduled for the afternoon.
  • Administration: Entire dose is ingested the evening before the procedure.
• Rapid bowel preparation
  • Consider for patients with acute LGIB.
  • Administration: high-volume PEG-based solution over 3–4 hours

Medication management

• Anticoagulants ^[10]
  • Warfarin can usually be continued.
  • Consider holding DOACs, depending on risk of thrombosis.
  • See also “Periprocedural management of oral anticoagulant therapy.”
• Antiplatelet therapy ^[10]
  • Aspirin for secondary prevention can usually be continued.
  • Consider holding ADP receptor antagonists in patients with dual antiplatelet therapy, depending on risk of thrombosis.
• Other medications (e.g., antidiabetics) ^[11]
  • Consider holding scheduled medications based on specialist consultation and/or local protocols.
  • See also “Preoperative medication management” for general recommendations on diuretics.

Preprocedural diagnostic studies ^[12]

• Routine studies are not recommended.
• Consider testing based on patient history, physical examination findings, and procedural risk, e.g.:
  • Pregnancy testing: patients of childbearing age
  • CBC: known anemia, active significant bleeding, or high procedural bleeding risk
  • BMP: known severe renal or hepatic dysfunction (e.g., cirrhosis, renal failure)
  • Coagulation studies: active bleeding
  • Blood typing and crossmatching: active significant bleeding or severe anemia
  • CXR: symptoms of decompensated heart failure or new respiratory symptoms

The following is a general overview and is not intended as a comprehensive guide. ^[13]

• Place the patient in the left lateral decubitus position.
• Place the patient on continuous cardiac monitoring and pulse oximetry.
• Administer procedural sedation.
• Perform a DRE.
• Insert the lubricated endoscope through the anus.
• Insufflate with air via the endoscope to visualize the lumen.
• Advance the scope to the cecum.
• Slowly withdraw the endoscope while systematically inspecting the mucosa of the entire colon and rectum for abnormalities.
• Obtain biopsies and/or perform endoscopic hemostasis if indicated.
• Remove excess insufflated air when removing the endoscope.

While bloating and abdominal pain are common adverse effects of air insufflation, complications from diagnostic colonoscopy are rare. ^[14]

• GI bleeding
• Postpolypectomy bleeding or postpolypectomy coagulation syndrome
• GI perforation
• Complications of procedural sedation
• Bacteremia
• Gas explosion

We list the most important complications. The selection is not exhaustive.

• CT colonography
  • Computed tomography of the abdomen with oral contrast and rectal insufflation of air
  • Requires bowel preparation ^[15]
  • Often used when colonoscopy is incomplete or declined by the patient ^[15][16]
• Video capsule endoscopy
  • Diagnostic procedure involving a small wireless camera inside a capsule that is swallowed by the patient to take pictures of the mucosa as it passes through the GI tract
  • Pictures are analyzed after the capsule is excreted 24–48 hours later.
  • Small-bowel evaluation is the most common indication, e.g., in patients with: ^[17]
    • Obscure GI bleeding
    • Hereditary polyposis syndromes
    • Suspected Crohn disease or celiac disease
  • Colon capsule endoscopy may be used if colonoscopy is not possible or incomplete. ^[15][16][17]
    • Requires bowel preparation similar to preparation for colonoscopy ^[15]
    • Contraindicated in patients with bowel strictures ^[17]
• Double-contrast barium enema
  • Diagnostic procedure in which x-rays of the colon and rectum are taken after rectal administration of a contrast agent
  • Most commonly used to assess for Hirschsprung disease
  • Consider in certain patients to evaluate for diverticulosis or CRC. ^[15][16][17]
• Flexible sigmoidoscopy: may be used in certain cases if endoscopy is recommended but colonoscopy is contraindicated, e.g., toxic megacolon or acute severe ulcerative colitis ^[5][18]
• Mesenteric angiography: may be used in unstable patients with suspected lower GI bleeding