cola is allowed. 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 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 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. a soothing salve such as petroleum jelly applied after cleaning the anus will reduce discomfort. 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. investigation 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. some endoscopists 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. 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. 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). 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. 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. 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. 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. the procedure typically 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 estimated 30–60 minutes. most facilities require that patients have a person with them to help them home afterwards (depending on the sedation method used). one common after-effect 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 management 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. 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. 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. ultrasound 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. economics researchers have found that older patients with three or more significant health problems (i.e., dementia or heart failure) had higher rates of repeat colonoscopies without medical indications. these patients are less likely to live long enough to develop colon cancer. gordon states, "at about $1,000 per procedure, there's clearly an economic incentive". the hemoccult ii fobt (combined with follow-up colonoscopy if indicated by the test) is over 5 times as cost effective as other screening