(DVT)  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. In rare cases, coma associated with anesthesia may occur. Bowel preparation
Dehydration caused by the laxatives that are usually administered during the bowel preparation for colonoscopy also may occur. Therefore, patients must drink large amounts of fluids during the day of colonoscopy preparation to prevent dehydration. Loss of electrolytes or dehydration is a potential risk that can even prove deadly. In rare cases, severe dehydration can lead to kidney damage or dysfunction under the form of phosphate nephropathy. Other
Virtual colonoscopies carry risks that are associated with radiation exposure.Colonoscopy preparation and colonoscopy procedure can cause inflammation of the bowels and diarrhea or bowel obstruction.During colonoscopies where a polyp is removed (a polypectomy), the risk of complications has been higher, although still low at about 2.3 percent. One of the most serious complications that may arise after colonoscopy is the postpolypectomy syndrome. This syndrome occurs due to potential burns to the bowel wall when the polyp is removed, and may cause fever and abdominal pain. It is a rare complication, treated with intravenous fluids and antibiotics. Bowel infections are a potential colonoscopy risk, although rare. The colon is not a sterile environment; many bacteria that normally live in the colon ensure the well-functioning of the bowel, and the risk of infections is minimal.
In most cases, tea or coffee taken without milk are allowed.The day before the colonoscopy, the patient is either given a laxative preparation (such as bisacodyl, phospho soda, 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 procedure may involve both a pill-form laxative and a bowel irrigation preparation with the polyethylene glycol powder dissolved into any clear liquid, such as a sports drink that contains electrolytes. A typical procedure regimen then would be as follows: in the morning of the day before the procedure, a 238 g bottle of polyethylene glycol powder should be poured into 1.9 litres (64 oz.) of the chosen clear liquid, which then should be mixed and refrigerated. Two bisacodyl 5 mg tablets are taken 3 pm; at 5 pm, the patient starts drinking the mixture (approx. 8 oz. (0.5 litres) each 15-30 min. until finished); at 8 pm, take two bisacodyl 5 mg tablets; continue drinking/hydrating into the evening until bedtime with clear permitted fluids. The procedure may be scheduled early in the day so the patient need not go without food and only limited fluids until later.The goal of the preparation is to clear the colon of solid matter, and the patient may be advised to spend the day at home with ready access to toilet facilities. The patient may also want to have at hand moist towelettes or a bidet for cleaning the anus.