What:
This is a procedure where a long, flexible, thin (13mm diameter) camera is passed through the anus to examine the whole large intestine and a short portion of the small intestine. This is on average 1.5 metres long.
Why:
There are lots of different reasons why you may want to have or have been suggested to have a colonoscopy.
This may include (see other patient information sheets)
- As part of a health check-up to screen for cancer or pre-cancerous polyps
- Screening colonoscopy may reduce the incidence of colorectal cancer by nearly 90%
- Concern about family history of cancer or polyps
- If a 1st degree relative has had colorectal cancer, your risk is increased by over 2 times. If you have had two or more first degree relatives with colorectal cancer, that risk is nearly four times!
- Bleeding from the bottom
- Abdominal pain
- Change in bowel habits, with constipation, diarrhoea or both!
- Unintentional weight loss
- Abnormal blood tests or scans that you have had performed
How:
I hold the camera and with my left hand, move wheels which move and steer the tip of the camera through the bowel, which often has many twists and turns.
Does it hurt?
You will have an intravenous luer inserted into our arm, and sedative medication given to make the colonoscopy more comfortable. Some people prefer to use none, although this is not common. Some patients prefer very light sedation, so they can watch the procedure on the monitor and ask questions. Others prefer to be much sleepier, and it is also possible to arrange to have an anaesthetist give very strong sedation so that you will be completely asleep and unaware of anything. We can talk about what you like before the test.
There are many different techniques that as the endoscopist, I can use to make the procedure both as safe and as painless as possible.
How long it does take:
This is variable depending on the indication for the test, the length and how bendy your bowel is and what is found. It ranges from 20 minutes to one hour, but on average may take 30 minutes.
What happens afterwards?
You will be able to eat and drink as the sedation wears off, and should feel back to normal in 30-60 minutes. I will come to see you to discuss the findings and any follow-up that may be required. We will provide you with everything written down and colour photographs of the inside of the bowel.
More information:
Bowel preparation for colonoscopy - tips and tricks
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ADVANCED INFORMATION:
Colonoscopy is the gold standard for detection and diagnosis of CRC, with the added benefit of the ability to remove polyps in the same setting (see polypectomy section below). A usual adult colonoscope is soft and flexible. They are usually 1.3m long with a 1.3cm-wide shaft.
Colonoscopy is user dependent, with the potential to miss polyps or even cancers. Approximately 85 per cent of interval cancers are thought to develop because of previously missed adenomas or incomplete polyp resection. Quality of bowel preparation, complete caecal intubation rate (total visualisation of the entire colon), and colonoscope withdrawal time (time spent inspecting and visualising the bowel) are modifiable factors that have been shown to influence the performance characteristics of colonoscopy.
In addition, adenoma detection rate (the proportion of patients who have one or more adenomas resected) is an established performance indicator in colonoscopy, validated as a predictor of cancer occurring after colonoscopy. Current recommended minimum thresholds for ADR in screening colonoscopies are 25 per cent overall, 30 per cent in men and 20 per cent in women aged over 50. However, every 1 per cent increase in ADR is associated with a 3 per cent decrease in the risk of CRC.
A variety of measures have been introduced to improve detection rate, including recent widespread interest in artificial intelligence. This uses a technology which processes colonoscopy images in real time and superimposes a green box over suspected polyps on the display monitor. In a retrospective series, we demonstrated that it increased our ADR from 39 to 48 per cent. We are currently performing a prospective randomised trial of 780 patients to confirm this finding.
Colonoscopy is safe, with a perforation rate of one in 10,000 screening colonoscopies. In the context of polypectomy, which may be performed by a number of different methods, this may increase to one in 1000, with bleeding in one to two in 100, depending on the size and method of resection.
Bowel preparation for colonoscopy involves drinking approximately 3L of laxative solution. Patients can expect to pass 12–15 bowel motions with this regimen. Patients are instructed to take it as a “split” preparation, with the final 1L taken on the day of the procedure about three hours before the scheduled start time. This gives the best results in clearing the bowel of residual stool to allow an unimpeded inspection. I suggest cooling the solution down and drinking it through a straw as good methods to assist with what some describe as the most challenging part of the procedure.
The majority of procedures in New Zealand are performed under conscious sedation, with a combination of fentanyl and midazolam used for analgesic and amnestic/anxiolytic effects, respectively. Using this combination, most patients are comfortable throughout the test, which may take on average 25 to 30 minutes. Patients can return home within 30–60 minutes after completion, with someone to observe them. Patients are advised not to drive for 24 hours. Some patients even opt to have colonoscopy without sedation and tolerate this with only mild discomfort.
Computed tomography colonography
CTC uses a CT scan with a small rectal tube and insufflation of the colon after bowel preparation. Scans are taken in multiple patient positions, allowing differentiation of residual stool from polyps, which remain attached in gravity dependent positions on the bowel wall. Images are reconstructed to produce three-dimensional views of the colon for interpretation.
There is ongoing discussion about the performance of CTC for polyp detection compared with standard colonoscopy. Certainly, an agreed-upon drawback is a low sensitivity for flat lesions and polyps smaller than 1cm. For this reason, in my practice, I use it predominantly in older patients or those with significant comorbidity who are less likely to ever come to harm from smaller polyps, which may not be seen with this modality. Sedation is not required, and recovery time is faster.
Additional considerations include exposure to radiation, frequent incidental extracolonic findings, and additional training and skill in radiologist interpretation of findings, which may be confounded by poor bowel preparation or colonic folds. If a mass or polyp is seen, there is still a subsequent requirement for colonoscopy to biopsy or remove the detected lesion.
Polypectomy
Colonoscopic polypectomy is the most commonly performed therapeutic procedure during colonoscopy. This has evolved considerably, and there is a range of equipment and techniques available for different clinical settings, including the use of forceps, metal snares and electrosurgical knives. Colonoscopes can examine polyps in real time, in close detail, with over 50´ high-definition magnification, which allows assessment and characterisation to predict possible pathology and malignant potential.
The endoscopist should select the appropriate technique based on the patients age, comorbidities and, therefore, benefits of removal, as well as suspected pathology and malignant potential based on size, morphological characteristics and the position within the colon.
Polypectomy is safe, with a perforation rate of 0.6 per 1000 colonoscopies with polypectomy. If a perforation occurs, often this can be closed without complication using endoscopic clips.
With advanced techniques, including endoscopic submucosal dissection, whereby a polyp of any size may be resected freehand en-bloc (in one section) with an electrosurgical knife, surgery is infrequently required for resection of non-malignant polyps. In cases where a polyp is extremely large and growing over diverticulum, the appendiceal orifice or ileo-caecal valve, surgical bowel resection may be required.
