Colonoscopy

Colonoscopy is one of the colorectal cancer screening tests available to people in the US who are 45 years of age and older. The other screening tests include flexible sigmoidoscopy, double-contrast barium enema, computed tomographic (CT) colongraphy (virtual colonoscopy), guaiac-based fecal occult blood test (gFOBT), fecal immunochemical test (FIT), and multitarget stool DNA screening test (Cologuard).[9]

Subsequent rescreenings are then scheduled based on the initial results found, with a five- or ten-year recall being common for colonoscopies that produce normal results.[10][11] People with a family history of colon cancer are often first screened during their teenage years. Among people who have had an initial colonoscopy that found no polyps, the risk of developing colorectal cancer within five years is extremely low. Therefore, there is no need for those people to have another colonoscopy sooner than five years after the first screening.[12][13]

Some medical societies in the US recommend a screening colonoscopy every 10 years beginning at age 50 for adults without increased risk for colorectal cancer.[14] Research shows that the risk of cancer is low for 10 years if a high-quality colonoscopy does not detect cancer, so tests for this purpose are indicated every ten years.[14][15]

Colonoscopy screening is associated with approximately two-thirds fewer deaths due to colorectal cancers on the left side of the colon, and is not associated with a significant reduction in deaths from right-sided disease. It is speculated that colonoscopy might reduce rates of death from colon cancer by detecting some colon polyps and cancers on the left side of the colon early enough that they may be treated, and a smaller number on the right side.[2] Many of these left-sided growths would have been detected by a sigmoidoscopy procedure.

Since polyps often take 10 to 15 years to transform into cancer in someone at average risk of colorectal cancer, guidelines recommend 10 years after a normal screening colonoscopy before the next colonoscopy. (This interval does not apply to people at high risk of colorectal cancer or those who experience symptoms of the disease.)[16][17]

The large randomized pragmatic clinical trial NordICC was the first published trial on the use of colonoscopy as a screening test to prevent colorectal cancer, related death, and death from any cause. It included 84,585 healthy men and women aged 55 to 64 years in Poland, Norway, and Sweden, who were randomized to either receive an invitation to undergo a single screening colonoscopy (invited group) or to receive no invitation or screening (usual-care group). Of the 28,220 people in the invited group, 11,843 (42.0%) underwent screening. A total of 15 people who underwent colonoscopy (0.13%) had major bleeding after polyp removal. None of the participants experienced a colon perforation due to colonoscopy. After 10 years, an intention-to-screen analysis showed a significant relative risk reduction of 18% in the risk of colorectal cancer (0.98% in the invited group vs. 1.20% in the usual-care group). The analysis showed no significant change in the risk of death from colorectal cancer (0.28% vs. 0.31%) or in the risk of death from any cause (11.03% vs. 11.04%). To prevent one case of colorectal cancer, 455 invitations to colonoscopy were required.[18][19]

The CONFIRM trial, a randomized trial on colonoscopy vs. FIT is currently ongoing.[20]

The American Cancer Society recommends, beginning at age 45, both men and women follow one of these testing schedules for screening to find colon polyps and/or cancer:[21]

1. Flexible sigmoidoscopy every 5 years, or
2. Colonoscopy every 10 years, or
3. Double-contrast barium enema every 5 years, or
4. CT colonography (virtual colonoscopy) every 5 years
5. Yearly guaiac-based fecal occult blood test (gFOBT)
6. Yearly fecal immunochemical test (FIT)
7. Stool DNA test (sDNA) every 3 years

In the United States, Medicare insurance covers the following colorectal-cancer screening tests:[22]

1. Colonoscopy: average risk — every 10 years beginning at age 50, high risk — every 2 years with no age restriction[23]
2. Flexible sigmoidoscopy — every 4 years beginning at age 50[24]
3. Double-contrast barium enema: average risk — every 4 years beginning at age 50, high risk — every 2 years[25]
4. (CT) colonography: not covered by Medicare
5. gFOBT: average risk — every year beginning at age 50[26]
6. FIT: average risk — every year beginning at age 50
7. Cologuard: average risk — every 3 years beginning at age 50[27]

The most serious complication is generally gastrointestinal perforation, which is life-threatening and in most cases requires immediate major surgery for repair.[33] Fewer than 20% of cases may be successfully managed with a conservative (non-surgical) approach.[33]

A 2003 analysis of the relative risks of sigmoidoscopy and colonoscopy brought to attention the risk of perforation after colonoscopy is approximately double that after sigmoidoscopy (consistent with the fact that colonoscopy examines a longer section of the colon), a difference that appeared to be decreasing.[34]

As with any procedure involving anaesthesia, other complications would include cardiopulmonary complications such as a temporary drop in blood pressure and oxygen saturation usually the result of overmedication, and are easily reversed. Anesthesia can also increase the risk of developing blood clots and lead to pulmonary embolism or deep venous thrombosis. (DVT)[35]

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.[35] In rare cases, severe dehydration can lead to kidney damage or dysfunction under the form of phosphate nephropathy.[36]

During colonoscopies where a polyp is removed (a polypectomy), the risk of complications has been higher, although still low at about 2.3 percent.[30] One of the most serious complications is postpolypectomy coagulation syndrome, which occurs following about 1% of colonoscopies with electrocautery polypectomy. It results from a burn injury to the wall of the gastrointestinal tract and causes abdominal pain, fever, elevated white blood cell count and elevated serum C-reactive protein. Treatment consists of intravenous fluids, antibiotics, and avoiding any oral intake of food, water, etc. until symptoms improve. Risk factors include right colon polypectomy, large polyp size (>2 cm), non-polypoid lesions (laterally spreading lesions), and hypertension.

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. Infections can occur during biopsies when too much tissue is removed and bacteria protrude in areas they do not belong to, or in cases when the lining of the colon is perforated and the bacteria get into the abdominal cavity.[37] Infection may also be transmitted between patients if the colonoscope is not cleaned and sterilized properly between tests.

Minor colonoscopy risks may include nausea, vomiting or allergies to the sedatives that are used. If medication is given intravenously, the vein may become irritated. Most localized irritations to the vein leave a tender lump lasting a number of days but going away eventually.[38] The incidence of these complications is less than 1%.

On rare occasions, intracolonic explosion may occur.[39] A meticulous bowel preparation is the key to prevent this complication.[39]

Signs of complications include severe abdominal pain, fevers and chills, or rectal bleeding (more than half a cup or 100ml).[40]

The colon must be free of solid matter for the test to be performed properly.[41] For one to three days, the patient is required to follow a low fiber or clear-liquid-only diet. Examples of clear fluids are apple juice, chicken and/or beef broth or bouillon, lemon-lime soda, lemonade, sports drink, and water. It is important that the patient remains hydrated. Sports drinks contain electrolytes which are depleted during the purging of the bowel. Drinks containing fiber such as prune and orange juice should not be consumed, nor should liquids dyed red, purple, orange, or sometimes brown; however, cola is allowed. In most cases, tea or coffee taken without milk are allowed.[42]

The day before the colonoscopy (or colorectal surgery), 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.[43][44] 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 container of PEG (polyethylene glycol or macrogol) with electrolyte used to clean out the intestines before certain bowel exam procedures such as a colonoscopy.

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 patient may be asked not to take aspirin or similar products such as salicylate, ibuprofen, etc. for up to ten days before the procedure to avoid the risk of bleeding if a polypectomy is performed during the procedure. A blood test may be performed before the procedure.[45]

Schematic overview of colonoscopy procedure

During the procedure the patient is often given sedation intravenously, employing agents such as fentanyl or midazolam. 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 fentanyl and midazolam. The average person will receive a combination of these two drugs, usually between 25 and 100 µg IV fentanyl and 1–4 mg IV midazolam. Sedation practices vary between practitioners and nations; in some clinics in Norway, sedation is rarely administered.[46][47]

Some endoscopists are experimenting with, or routinely use, alternative or additional methods such as nitrous oxide[48][49] and propofol,[50] 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. This sedation is called "twilight anesthesia". For some patients it is not fully effective, so they are indeed awake for the procedure and can watch the inside of their colon on the color monitor. Substituting propofol for midazolam, which gives the patient quicker recovery, is gaining wider use, but requires closer monitoring of respiration.

A meta-analysis found that playing music improves tolerability to patients of the procedure.[51]

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 through 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 (a procedure that gives the patient the false sensation of needing to take a bowel movement).[52] Biopsies are frequently taken for histology. Additionally in a procedure known as chromoendoscopy, a contrast-dye (such as indigo carmine) may be sprayed through the endoscope onto the bowel wall to help visualise any abnormalities in the mucosal morphology. A Cochrane review updated in 2016 found strong evidence that chromoscopy enhances the detection of cancerous tumours in the colon and rectum.[53]

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. Manoeuvres to "reduce" or remove the loop include pulling the endoscope backwards while twisting it. 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. Usage of alternative instruments leading to completion of the examination has been investigated, including use of pediatric colonoscope, push enteroscope and upper GI endoscope variants.[54]

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 recently prompted some institutions to better document withdrawal time as rapid withdrawal times may be a source of potential medical legal liability.[55] This is often a real concern in clinical settings where high caseloads could provide financial incentive to complete colonoscopies as quickly as possible.

• 
  Polyp is identified.
• 
  A sterile solution is injected under the polyp to lift it away from deeper tissues.
• 
  A portion of the polyp is now removed.
• 
  The polyp is fully removed.

The pain associated with the procedure is not caused by the insertion of the scope but rather by the inflation of the colon in order to do the inspection. The scope itself is essentially a long, flexible tube about a centimeter in diameter — that is, as big around as the little finger, which is less than the diameter of an average stool.

The colon is wrinkled and corrugated, somewhat like an accordion or a clothes-dryer exhaust tube, which gives it the large surface area needed for water absorption. In order to inspect this surface thoroughly, the physician blows it up like a balloon, using air from a compressor or carbon dioxide from a gas bottle (CO₂ is absorbed into the bloodstream through the mucosal lining of the colon much faster than air and then exhaled through the lungs which is associated with less post procedural pain), in order to get the creases out. The stomach, intestines, and colon have a so-called "second brain" wrapped around them, which autonomously runs the chemical factory of digestion.[56] It uses complex hormone signals and nerve signals to communicate with the brain and the rest of the body. Normally a colon's job is to digest food and regulate the intestinal flora. The harmful bacteria in rancid food, for example, creates gas.

The colon has distension sensors that can tell when there is unexpected gas pushing the colon walls out—thus the "second brain" tells the person that he or she is having intestinal difficulties by way of the sensation of nausea. Doctors typically recommend either total anesthesia or a partial twilight sedative to either preclude or to lessen the patient's awareness of pain or discomfort, or just the unusual sensations of the procedure. Once the colon has been inflated, the doctor inspects it with the scope as it is slowly pulled backward. If any polyps are found they are then cut out for later biopsy.

Some doctors prefer to work with totally anesthetized patients inasmuch as the lack of any perceived pain or discomfort allows for a leisurely examination. Twilight sedation is, however, inherently safer than general anesthesia; it also allows the patients to follow simple commands and even to watch the procedure on a closed-circuit monitor. Tens of millions of adults annually need to have colonoscopies, and yet many don't because of concerns about the procedure.

Colonoscopy can be carried out without any sedation and without problems with pain, which is practised in several institutions in many countries with the patient's agreement. This allows the patient to shift the body position to help the doctor carry out the procedure and significantly reduces recovery time and side-effects.[57] There is some discomfort when the colon is distended with air, but this is not usually particularly painful, and it passes relatively quickly. Unsedated patients can be released from the hospital on their own without any feelings of nausea, able to continue with normal activities, and without the need for an escort as recommended after sedation.

Duodenography and colonography are performed like a standard abdominal examination using B-mode and color flow Doppler ultrasonography using a low frequency transducer — for example a 2.5 MHz — and a high frequency transducer, for example a 7.5 MHz probe. Detailed examination of duodenal walls and folds, colonic walls and haustra was performed using a 7.5 MHz probe. Deeply located abdominal structures were examined using 2.5 MHz probe. All ultrasound examinations are performed after overnight fasting (for at least 16 hours) using standard scanning procedure. Subjects are examined with and without water contrast. Water contrast imaging is performed by having adult subjects take at least one liter of water prior to examination. Patients are examined in the supine, left posterior oblique, and left lateral decubitus positions using the intercostal and subcostal approaches. The liver, gall bladder, spleen, pancreas, duodenum, colon, and kidneys are routinely evaluated in all patients.

With patient lying supine, the examination of the duodenum with high frequency ultrasound duodenography is performed with 7.5 MHz probe placed in the right upper abdomen, and central epigastric successively; for high frequency ultrasound colonography, the ascending colon, is examined with starting point usually midway of an imaginary line running from the iliac crest to the umbilicus and proceeding cephalid through the right mid abdomen; for the descending colon, the examination begins from the left upper abdomen proceeding caudally and traversing the left mid abdomen and left lower abdomen, terminating at the sigmoid colon in the lower pelvic region. Color flow Doppler sonography is used to examine the localization of lesions in relation to vessels. All measurements of diameter and wall thickness are performed with built-in software. Measurements are taken between peristaltic waves.[58]

The terms colonoscopy[62][63][64] or coloscopy[63] are derived from[63] the ancient Greek noun κόλον, same as English colon,[65] and the verb σκοπεῖν, look (in)to, examine.[65] The term colonoscopy is however ill-constructed,[66] as this form supposes that the first part of the compound consists of a possible root κολων- or κολον-, with the connecting vowel -o, instead of the root κόλ- of κόλον.[66] A compound such as κολωνοειδής, like a hill,[65] (with the additional -on-) is derived from the ancient Greek word κολώνη or κολωνός, hill.[65] Similarly, colonoscopy (with the additional -on-) can literally be translated as examination of the hill,[66] instead of the examination of the colon.

In English, multiple words exist that are derived from κόλον, such as colectomy,[63][67] colocentesis,[63] colopathy,[63] and colostomy[63] among many others, that actually lack the incorrect additional -on-. A few compound words such as colonopathy have doublets with -on- inserted.[63][64]