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Page: Procedure
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Preparation
The patient may be asked to skip aspirin for up to five days before the procedure to avoid the risk of bleeding if a polypectomy is performed during the procedure. The colon must be free of solid matter for the test to be performed properly. For one to three days, the patient is required to follow a low fibre or clear fluid only diet. Then, on the day before the colonoscopy, the patient is either given a laxative preparation (such as Bisacodyl, sodium picosulfate, or sodium phosphate. and/or magnesium citrate) and large quantities of fluid or whole bowel irrigation is performed using a solution of polyethylene glycol and electrolytes.
The investigation
During the procedure the patient is often given sedation intravenously, employing agents such as midazolam or fentanyl. 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 midazolam and fentanyl. The average person will receive a combination of these two drugs, usually between 1-4 mg iv midazolam, and 25 to 100 µg iv fentanyl. Sedation practices vary between practitioners and nations; in some clinics in Norway, sedation is rarely administered . Some endocoscopists are experimenting with, or routinely use, alternative or additional methods such as nitrous oxide and propofol , which have advantages and disadvantages relating to recovery time (particularly the duration of amnesia after the procedure is complete), patient experience, and the degree of supervision needed for safe administration.
The first step is usually a digital rectal examination, to examine the tone of the sphincter and to determine if preparation has been adequate. The endoscope is then passed though the anus up the rectum, the colon (sigmoid, descending, transverse and ascending colon, the cecum), and ultimately the 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. Biopsies are frequently taken for histology.
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. Maneuvers to "reduce" or remove the loop include pulling the endoscope backwards while torquing the instrument. 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.
For screening purposes, a closer visual inspection is then often performed upon withdrawal of the endoscope over the course of 20 to 25 minutes. Lawsuits over missed cancerous lesions have prompted recent institutions to better document withdrawal time as rapid withdrawal times may be a source of potential medical legal liability. This is often a real concern in private practice settings where high throughput of cases have been postulated as a financial incentive to complete colonoscopies as quickly as possible.
Suspicious lesions may be cauterized, treated with laser light or cut with an electric wire for purposes of biopsy or complete removal polypectomy. Medication can be injected, e.g. to control bleeding lesions. On average, the procedure takes 20-30 minutes, depending on the indication and findings. With multiple polypectomies or biopsies, procedure times may be longer. As mentioned above, anatomic considerations may also affect procedure times.
After the procedure, some recovery time is usually allowed to let the sedative wear off. Most facilities require that patients have a person with them to help them home afterwards (again, depending on the sedation method used).
One very common aftereffect from the procedure is a bout of flatulence and minor wind pain caused by air insufflation into the colon during the procedure.
An advantage of colonoscopy over x-ray imaging or other, less invasive tests, is the ability to perform therapeutic interventions during the test. If a polyp is found, for example, it can be removed by one of several techniques. A snare can be placed around a polyp for removal. Even if the polyp is flat on the surface it can often be removed. For example, the following show a polyp removed in stages.
Risks
This procedure has a low (0.2%) risk of serious complications.
The most serious complication is a tear or hole in the lining of the colon called a gastrointestinal perforation, which is life-threatening and requires immediate major surgery for repair; however, the rate of perforation is less than 1 in 2000 colonoscopies.
Bleeding complications may be treated immediately during the procedure by cauterization via the instrument. Delayed bleeding may also occur at the site of polyp removal up to a week after the procedure and a repeat procedure can then be performed to treat the bleeding site. Even more rarely, splenic rupture can occur after colonoscopy because of adhesions between the colon and the spleen.
As with any procedure involving anaesthesia, other complications would include cardiopulmonary complications such as temporary drop in blood pressure and oxygen saturation, usually the result of overmedication and easily reversed. In rare cases, more serious cardiopulmonary events such as a heart attack, stroke, or even death may occur; these are extremely rare except in critically ill patients with multiple risk factors.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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