Colonoscopy

Colonoscopy is the endoscopic examination of the colon and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis (e.g. ulceration, polyps) and grants the opportunity for biopsy or removal of suspected lesions.

Virtual colonoscopy, which uses 2D and 3D imagery reconstructed from computed tomography (CT) scans or from nuclear magnetic resonance (MR) scans, is also possible, as a totally non-invasive medical test, although it is not standard and still under investigation regarding its diagnostic abilities. Furthermore, virtual colonoscopy does not allow for therapeutic maneuvers such as polyp/tumour removal or biopsy nor visualization of lesions smaller than 5 millimetres. If a growth or polyp is detected using CT colonography, a standard colonoscopy would still need to be performed.

Colonoscopy can remove polyps as small as one millimetre or less. Once polyps are removed, they can be studied with the aid of a microscope to determine if they are precancerous or not.

Colonoscopy is similar to but not the same as sigmoidoscopy, the difference being related to which parts of the colon each can examine. While colonoscopy allows an examination of the entire colon (measuring four to five feet in length), sigmoidoscopy allows doctors to view only the final two feet of the colon. A sigmoidoscopy is often used as a screening procedure for a full colonoscopy, in many instances in conjunction with a fecal occult blood test (FOBT), which can detect the formation of cancerous cells throughout the colon. Other times, a sigmoidoscopy is preferred to a full colonoscopy in patients having an active flare of ulcerative colitis or Crohn's disease to avoid perforation of the colon. Additionally, surgeons have lately been using the term pouchoscopy to refer to a colonoscopy of the ileo-anal pouch.

Reasons for procedure

Conditions that call for colonoscopies include gastrointestinal hemorrhage, unexplained changes in bowel habit and suspicion of malignancy. Colonoscopies are often used to diagnose colon cancer, but are also frequently used to diagnose inflammatory bowel disease. In older patients (sometimes even younger ones) an unexplained drop in hematocrit (one sign of anemia) is an indication that calls for a colonoscopy, usually along with an esophagogastroduodenoscopy (EGD), even if no obvious blood has been seen in the stool (feces).

Fecal occult blood is a quick test which can be done to test for microscopic traces of blood in the stool. A positive test is almost always an indication to do a colonoscopy. In most cases the positive result is just due to hemorrhoids; however, it can also be due to diverticulosis, inflammatory bowel disease (Crohn's disease, ulcerative colitis), colon cancer, or polyps. However—since its development by Dr. Hiromi Shinya and Dr. William I. Wolff in the 1960s--polypectomy has become a routine part of colonoscopy, allowing for quick and simple removal of polyps without invasive surgery.^[1]

Due to the high mortality associated with colon cancer and the high effectivity and low risks associated with colonoscopy, it is now becoming a routine screening test for people 50^[2] years of age or older. 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.^[3] Patients with a family history of colon cancer are often first screened during their teenage years.

A study published in the New England Journal of Medicine (September 18, 2008) has found that 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.^[4][5]

Procedure

Preparation

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 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 very important that the patient remain hydrated. Orange juice, prune juice, and milk containing fibre should not be consumed, nor should liquids dyed red, purple, orange, or sometimes brown; however, cola is allowed. In most cases, tea (no milk) or black coffee (no milk) are allowed.^[6]

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. Often, the procedure involves both a pill-form laxative and a bowel irrigation preparation with the polyethylene glycol powder dissolved into any clear liquid, preferably a sports drink which contain electrolytes.

In this case, a typical procedure regimen then would be as follows: in the morning of the day before the procedure, a 238 mg bottle of polyethylene glycol powder should be poured into 64 oz. of the chosen clear liquid, which then should be mixed and refrigerated. Two (2) bisacodyl 5 mg tablets are taken 3 pm; at 5 pm, the patient starts drinking the mixture (approx. 8 oz. each 15-30 min. until finished); at 8 pm, take two (2) bisacodyl 5 mg tablets; continue drinking/hydrating into the evening until bedtime with clear permitted fluids. A common brand name of bisacodyl is Ducolax, and store brands are available. A common brand name of polyethylene glycol powder is MiraLax. It may be advisable to schedule the procedure early on a given day so the patient need not go without food and only limited fluids the morning of the procedure on top of having to go through the foregoing preparation procedures the preceding day.

Since the goal of the preparation is to clear the colon of solid matter, the patient should plan to spend the day at home in comfortable surroundings with ready access to toilet facilities. The patient may also want to have at hand moist toilettes or a bidet for cleaning the anus. A soothing salve such as petroleum jelly applied after cleaning the anus will improve patient comfort.

The patient may be asked to skip aspirin and aspirin-like products such as salicylate, ibuprofen, and similar medications 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.^[7][8]

The investigation

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 to 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.^[9][10]

Some endoscopists are experimenting with, or routinely use, alternative or additional methods such as nitrous oxide^[11][12] and propofol,^[13] 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 colour 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 patient tolerability of the procedure.^[14]

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. 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. Manoeuvres 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. 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.^[15]

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.^[16] This is often a real concern in clinical settings where high caseloads could provide 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. Outpatient recovery time can take an estimate of 30–60 minutes. 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. A polyp is a growth of excess of tissue that can develop into cancer. If a polyp is found, for example, it can be removed by one of several techniques. A snare device 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 shows a polyp removed in stages:

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.

Pain

The pain associated with the procedure is not caused by the insertion of the scope but from inflating of the colon in order to do the inspection. The scope is basically a long, flexible tube about a centimeter in diameter, that is, roughly as big around as the little finger. This is less than the diameter of an average stool so just as there is normally no pain from the daily passage of food inside the colon , there should be no pain from a normal insertion.

The colon is wrinkled and corrugated like an accordion, or a clothes-dryer exhaust tube. This gives it the large surface area needed for digestion. But in order to inspect this surface, the doctor must blow it up like a balloon, to get the creases out. This is done using a powered air compressor a lot like the one used to inflate a car's tyres.

The stomach, intestines and colon have a "second brain" wrapped around them. This "second brain" has at least sensor nerves, decision processes, and motor nerves, so that it runs the chemical factory of digestion completely by itself, without the person having to think about it. It uses 95% of all serotonin in the body.^[17] And it uses other 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 to detect when a person gets sick. Harmful bacteria in rancid food create unexpected gas. So the colon has distension sensors that can tell when there is unexpected gas pushing the colon walls out. Then the "second brain" tells the person to feel sick — they are having intestinal difficulties. In the case of bad food, this would involve stopping moving around. The person would sit groaning in the bathroom until the body eliminated the food. This is why doctors often recommend a total anesthesia or a partial "twilight" sedative to lessen the brain's awareness of the pain.

Once the colon has been inflated, the doctor inspects it with the scope on the way out, as it is slowly pulled backwards. If any polyps are found, they can be cut out at this point.

Some doctors prefer to work with totally anesthetized patients at this point, since the lack of pain being reported allows a leisurely examination. Whereas a doctor with a twilight sedated patient might hurry the inspection at this point, because of the groaning. However, twilight sedation is safer than general anesthesia. For this reason, it is generally better to request twilight sedation and ask the doctor to take his or her time, even if the patient groans.

The intensity of the pain may be correlated with the pressure of the air inside the colon. Doctors should use an air pump with a constant pressure source, not a constant volume source. Only enough air to maintain a particular pressure should be pumped into the colon.

Most other known physical means of distending the colon without pumping air in, introduces another physical contact into the system, with corresponding substantial increases in the probability of puncture. It is much safer, from a medical standpoint, to distend the colon with air, even if it does cause pain. The pain is transitory and can be borne.

Tens of millions of adults need to have colonoscopies each year, and yet many don't, because they are afraid of the pain.

If pain is truly an issue, the patient can always request a general anesthetic. In the meantime, knowing that the pain comes from the colon being inflated, and not from the scope itself, makes the pain understandable and bearable.

It is worth noting that in many hospitals (for instance St. Mark's Hospital, London, which specialises in intestinal and colorectal medicine) colonoscopies are carried out without any sedation. This allows the patient to shift their body position to help the doctor carry out the procedure and significantly reduces recovery time and side-affects. Although there is some discomfort when the colon is distended with air this is not usually particularly painful and it passes relatively quickly. Patients can then be released from hospital on their own very swiftly without any feelings of nausea.

Ultrasound duodenography and ultrasound colonography

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 ^[18].

The abdominal quadrants scanned in the order.	The duodenal tri-band wall with folds of Kerckring, showing floaters with water contrast.	A high resolution view of colonic haustration.

Risks

This procedure has a low (0.35%) risk of serious complications.^[19][20]

According to a study published in the Annals of Internal Medicine, for which researchers reviewed colon cancer screening data from 1966 to 2001 the most severe complications from colonoscopy are perforation (that occurred in 0.029% to 0.72% of cases), heavy bleeding (occurring in 0.2% to 2.67% of colonoscopies) and death (occurring in 0.003% to 0.03% of colonoscopy patients).^[21]

The most serious complication generally is the gastrointestinal perforation, which is life-threatening and requires immediate major surgery for repair. An analysis of the relative risks of sigmoidoscopy and colonoscopy, published in the February 5, 2003 issue of the Journal of the National Cancer Institute brought into attention that the risk of perforation after colonoscopy is approximately double that after sigmoidoscopy, even though this difference appeared to be decreasing.^[22]

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 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) ^[23] 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 very rare cases, coma associated with anesthesia may occur. Virtual colonoscopies carry risks that are associated with radiation exposure.

Severe 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 days of colonoscopy preparation to prevent dehydration. Loss of electrolytes or dehydration is potential risk that can even get deadly.^[24] In rare cases, severe dehydration can lead to kidney damage or renal dysfunction under the form of phosphate nephropathy.^[25]

Colonoscopy preparation and colonoscopy procedure can cause inflammation of the bowels and diarrhea or even bowel obstruction.

During colonoscopies where a polyp is removed (a polypectomy), the risk of complications has been higher, although still very uncommon, at about 2.3 percent.^[26] 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. It is however a very rare complication and as a result patients may experience fever and abdominal pain. The condition is treated with intravenous fluids and antibiotics while the patient is recommended to rest.

Bowel infections are a potential colonoscopy risk, although very rare. The colon is not a sterile environment as many bacteria live in the colon to assure the well-functioning of the bowel and therefore the risk of infections is very low. 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.^[27] Infection may also be transmitted between patients if the colonoscope is not cleaned and sterilized properly between tests, although the risk of this happening is very low.^[28]

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.^[29] The incidence of these complications is less than 1%.

On very rare occasions, intracolonic explosion may occur.

High frequency ultrasound duodenography and colonography carry no risks associated with the procedures.

Although complications after colonoscopy are uncommon, it is important for patients to recognize early signs of any possible complications. They include severe abdominal pain, fevers and chills, or rectal bleeding (more than half a cup).^[30]

Results

A recent study published in the Annals of Internal Medicine^[31] implies that colonoscopy screening prevents approximately two thirds of the 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.^[32] This study examined people with colon cancer diagnosed between 1996 and 2001 in Ontario who died of colon cancer by 2003, and hence studied colonoscopies done in the early to mid 1990s. (Since the procedure continues to evolve, more recent colonoscopies may be more effective). The summary result, according to table 3 of the report, show approximately a 37% reduction in the death rate from colorectal cancer, with a significantly lower reduction in death for "incomplete" colonoscopies.

See also

• Anal probe
• Bow and arrow sign
• Rectal examination
• Sigmoidoscopy
• Polypectomy
• Virtual colonoscopy

References

External links

• Florida Hospital Celebration Colorectal in Celebration, Florida
• LearnColoRectalSurgery.com - Colonoscopy pictures
• Colonoscopy. Based on public-domain NIH Publication No. 02-4331, dated February 2002.
• Patient Education Brochures. American Society for Gastrointestinal Endoscopy information