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Colonoscopy

Contents

1. Definition
2. Indications
3. Complications
4. The Colonoscope
5. Preparation
   1. General
   2. Bowel Preparation
6. Procedure
   1. Sedation
   2. Technique
7. Suggested further reading

    

    

    

1. Definition

2. Indications

• Gastrointestinal haemorrhage
• Change in bowel habit > 6 weeks
• Screening for colorectal cancer - It is the first line investigation following a positive Faecal Occult Blood (FOB) test
• Surveillance for groups at high risk of colorectal cancer - this includes
• Patients with ulcerative colitis - Patients with pancolitis of 15 years duration or more should undergo colonoscopy every two years, and of 22 years or more every year
• Family history of colorectal carcinoma - should be seen by a geneticist prior to endoscopic evaluation to assess risk
• Further investigation of abnormalities seen on other imaging modalities that require further assessment e.g. barium enema, CT
• Polyps seen on flexible sigmoidoscopy - rest of the colon therefore needs to be visualised for carcinoma and polyps
• Follow up for adenomatous polyps
• Follow up for colorectal cancer - following resection patients should receive follow up colonoscopy at three years.
  Assessment of inflammatory bowel disease
• Iron deficiency anaemia with a normal OGD and barium enema

3. Complications

• Perforation of the colon - the main risk. 1 in 2000 risk. Can be due to
  • Mechanical reasons such as pushing the tip of the colonoscope against weak sites of the colon wall such as diverticula, areas of inflammation or just before strictures.
  • Pneumatic reasons - over inflation with air
  • Risk is increased with poor bowel preparation
• Bleeding - 1 in 1000 risk. Can be minor which can be treated at the time of colonoscopy by cauterization. Delayed bleeding may occur following polypectomy, and this can occur up to one week after the procedure. Delayed bleeding usually stops on its own but in some severe cases laparotomy may be required.
• Infection - can lead to a gram negative bacteraemia
• Splenic rupture - Can occur due to tearing the spleno-colic ligament using excessive traction or direct trauma to the spleen.
• Anaesthetic complications -
  • Hypotension + bradycardia - over-sedation + instrumentation leading to vagal stimulation.
• for further reading on Complications of Gastrointestinal endoscopy click here

4. The Colonoscope

• Video colonoscope used. Has replaced fibre-optics scopes and allows the endoscopist to view the video monitor whilst manoeuvring the scope instead of an eyepiece

• Tip of the scope is controlled by two wheels
• Wheel closest to the scope moves the tip up and down
• Smaller wheel moves tip left and right

• Two buttons
  • Top button (red) - provides suction
  • Bottom button (Blue) - for air insufflation + washing the lens

• Biopsy channel is found below the buttons (blue cap on channel)

• Tip of the colonoscope
  • note the light channels (top and bottom left 12 o'clock and 7 o'clock)
  • lens for the CCD camera (2 o'clock)
  • washing channel (4 o'clock)
  • suction and biopsy channel (hole at 6 o'clock)

5. Preparation

5.1 General

• Warfarin and aspirin should be discontinued prior to examination to reduce the risk of bleeding
• Clear fluids only should be drunk prior to examination
• Fully informed consent should be obtained

5.2 Bowel Preparation

• For optimal examination and safety, the colon must be empty prior to procedure
• Different options are available for bowel preparation
  • Picolax -
    • Contains sodium picosulphate + magnesium citrate
    • First sachet taken in the morning, the day before colonoscopy
    • Second sachet taken six hours after the first
    • Causes severe diarrhoea
    • Patients need to ensure they are maintaining fluid intake to replace losses
    • Elderly and frail should be admitted the day prior to examination for prep.

   

   

  • Klean prep
    • Contains polyethylene glycol
    • Requires the patient to drink four litres of this solution the prior before colonscopy
    • Impossible task for some patients, therefore picolax is use

6. Procedure

6.1 Sedation

• Light sedation should be used as the patient may be required to change position during the procedure
• Sedative of choice is usually intravenous midazolam combined with pethidine
• Complications include respiratory depression and patients should be monitored throughout the procedure
• Reversal agents should be readily available if required -
  • Flemazenil for benzodiazepines
  • Naloxone for opiates
• For further reading on safety and sedation in endoscopy click here

6.2 Technique

• Patients require intravenous cannulation for administration of drugs
• Positioned in the left lateral decubitus position
• Pulse oximeter is placed and oxygen saturations are monitored throughout the procedure
• Low dose oxygen through nasal specs is added as required
• PR performed - ensures there is no obstruction to the scope as it is passed
• Tip of scope is then passed in to the anal canal
• The scope is only advanced when the lumen can be visualised
• Air, water and suction are utilised to provide optimal views for inspection
• The goal is to visualise the whole colon i.e. to reach the caecum and the terminal ileum if possible
• Biopsies are taken for histology
• Various techniques can be employed for lesions
  • Electrocautery
  • Laser
  • Snare for complete polypectomy
• As the scope is withdrawn it is essential to view the mucosa closely to ensure no polyp/lesion is missed
• For further reading on technique of Colonoscopy see below

7. Suggested further reading