4.1 General Principles

Colonoscopy was introduced for clinical use in 1970 and was initially used as a diagnostic aid to barium enema studies. Lesions or mucosal abnormalities could be visualized and confirmed by biopsy, but early endoscopists reached the cecum in only 30 to 50% of procedures. The first colonoscopic polypectomy was performed by Hiromi Shinya of New York in 1969. ¹ Increasing experience and technologic advancements have resulted in colonoscopy becoming a major component of colorectal surgery and the ultimate procedure for the detection of colonic diseases. Current colonoscopies (▶ Fig. 4.1) use high-definition video to produce quality images.

Performed properly, the procedure is well tolerated, the complication rate is low, and the cecum is reached in > 95% of procedures. ^{2 , 3 , 4 , 5} The colorectal mucosa or lesions can be biopsied and almost all pedunculated polyps can be removed and most large sessile polyps can be removed piecemeal, in more than one session, or with advanced techniques (e.g., endoscopic submucosal dissection). ^{6 , 7}

Several studies evaluating large numbers of colonoscopies found that approximately 25% of procedures are easy, 50% are more challenging, and 25% are difficult or impossible. ^{8 , 9} The most common cause of difficulty in colonoscopy is recurrent looping or bowing in a long or mobile colon. The colonic length is greater in women (median, 155 cm) compared to men (median, 145 cm) (p < 0.005), with most of the difference being in the transverse colon. ⁹ Many patients also have mobile portions of their colon. ¹⁰

To become a competent colonoscopist, extensive training and hands-on experience in colonoscopy is essential. Although numbers have limitations (performing hundreds of procedures with poor technique does not make one competent), the “learning curve” for colonoscopy is approximately 150 to 200 procedures. ^{11 , 12}

4.2 Indications

Colonoscopy is indicated for the diagnosis of colorectal diseases, treatment of colorectal polyps, surveillance of chronic ulcerative colitis and Crohn’s colitis, preoperative and postoperative examination in patients with carcinoma of the large bowel, and screening for average and high-risk patients for colorectal carcinoma. ¹³ Colonoscopy is also an option to decompress acute pseudo-obstruction of the colon if medical management with neostigmine fails or is contraindicated. ^{14 , 15 , 16 , 17 , 18}

4.3 Contraindications

There are few contraindications to colonoscopy. A patient with poor bowel preparation should be rescheduled and recleansed. The procedure should not be pursued if there is a fixed angle that cannot be straightened. Patients with acute inflammatory bowel disease or acute diverticulitis may benefit from a distal diagnostic exam, but proximal scope passage must be individualized. Colonoscopy is avoided in patients with small bowel obstruction and anal diseases that cause stricture or severe pain. However, patients with large bowel obstruction may benefit from a diagnostic exam or endoscopic placement of a colonic stent. ^{19 , 20} Finally, patients who are too weak or unstable to undergo bowel preparation, or those who have experienced a recent myocardial infarction, are poor candidates for colonoscopy. The most common excuses for not doing colonoscopy are the cost of the procedure and the unavailability of experienced colonoscopists.

4.4 Bowel Preparation

Safe and accurate colonoscopy requires a clean colon. Colon cleansing preparations initially were modifications of barium enema preparations, but have evolved extensively over the years. A variety of methods are currently available. Numerous comparison studies have been performed with mixed results. The patient completing the preparation as directed may be more important than the method chosen. All preparations use some form of dietary limitation and can be divided into isosmotic, hyperosmotic, and stimulant preparations. ²¹

4.5 Sedation

Colonoscopy can be performed without medications in selected patients, but this technique requires a skillful and gentle colonoscopist who uses good techniques. ^{13 , 41} Most colonoscopists, however, prefer to give preprocedural medications. Ideal drugs for endoscopic sedation have a rapid onset and short duration of action, maintain hemodynamic stability, and do not cause major side effects. Commonly used agents include opiates, such as meperidine or fentanyl, benzodiazepines, such as midazolam or diazepam, or a hypnotic, such as propofol (▶ Table 4.2). The choice of agents is often a matter of personal or institutional preference. Combinations of a benzodiazepine and an opiate can be administered by the endoscopist or specially trained nurses. The administration of propofol is governed by state law and facility/hospital rules.

Benzodiazepines induce central nervous system (CNS) depression resulting in anxiolysis, sedation, muscle relaxation, and anterograde amnesia. ⁴² The principal class side effect is respiratory depression. This effect is intensified when coadministered with opiates, and dose reduction of the benzodiazepine, opiate, or both is often required. ⁴³ Midazolam and diazepam are the most commonly used benzodiazepines. In a nationwide survey, midazolam was preferred over diazepam for endoscopic sedation. ⁴⁴ Both drugs demonstrate similar efficacy with regard to sedation. ⁴⁵ Midazolam, however, is associated with greater potency, better amnesic effects, reduced respiratory depression, less injection discomfort, and superior patient satisfaction when compared with diazepam. ^{46 , 47 , 48}

Midazolam has a rapid onset (1–2 minutes), short duration of action (15–60 minutes), and favorable amnesic properties. ⁴⁹ The initial dose is 1 mg, followed by repeat doses (if needed) of 1 mg in 2-minute intervals until the desired effect is achieved. ⁵⁰ When given in combination with an opiate or other sedatives, the dose of midazolam should be reduced by 30%. ⁵¹ Because it is lipophilic, midazolam can be sequestered in adipose tissue resulting in a prolonged sedative effect. ⁴⁹ Patients who are obese or elderly or those with impaired hepatic or renal function are at increased risk for delayed drug clearance. In this population, utilization of lower doses and longer intervals of administration should be considered. ⁴⁹ By comparison, diazepam has less amnesic capabilities, a slower onset of action (2–3 minutes), and prolonged duration of effect (360 minutes). ⁴⁹ The dose for colonoscopy is 2.5 to 5 mg initially. Additional doses of 2.5 mg every 3 to 5 minutes can be given as needed.

The benzodiazepine receptor antagonist flumazenil should be immediately available for administration in all endoscopy suites. The primary effect of flumazenil is reversal of benzodiazepine-induced sedation and psychomotor impairment. It has minimal effect on reversal of respiratory depression. ⁵¹ For this reason, opioid reversing agents (i.e., naloxone) are given prior to flumazenil in situations of benzodiazepine/opioid-induced respiratory depression. The typical flumazenil dose is a 0.2 mg intravenous (IV) bolus and can be repeated three times. ⁵⁰

Similar to benzodiazepines, opioids are efficacious for induction of moderate sedation. ⁵² However, unlike benzodiazepines they provide analgesia as well. This favorable characteristic enhances the overall sedative effect when opioids are adjunctively used with benzodiazepines. Fentanyl and meperidine are two short-acting opioids used for sedation during colonoscopy. Many endoscopists prefer fentanyl due to its pharmacologic profile and reduced incidence of nausea as compared with meperidine. ⁵² Additionally, fentanyl was associated with a shorter procedure time in a recent study comparing meperidine and fentanyl use during upper endoscopy and colonoscopy. ⁵³

Fentanyl is a lipid-soluble, synthetic opioid narcotic with a rapid onset (1–2 minutes) and short duration of action (30–70 minutes). ⁴³ For endoscopic procedures, an initial bolus of 50 µg is given. Subsequent doses of 25 µg in 2- to 5-minute intervals can be administered if necessary. Meperidine has a longer onset (3–6 minutes) and duration of effect (3–5 hours) as compared with fentanyl. ^{43 , 50} The starting dose of meperidine is usually 25 to 50 mg, followed by 25 mg every 2 to 5 minutes if required. Opioids cause synergistic CNS and respiratory depression when used in patients taking other centrally acting medications such as antihistamines, benzodiazepines, narcotics, monoamine oxidase inhibitors, and phenothiazines. ⁵⁴ All opioids reduce seizure thresholds, and narcotic dose reduction or avoidance should be considered in patients with epilepsy. Chest wall rigidity due to increased skeletal muscle tonicity has been reported with high doses of fentanyl. ⁵⁴ This may result in difficulty with assisted ventilation. Meperidine is metabolized in the liver to normeperidine, an active metabolite with a half-life of 15 to 20 hours. ⁴³ Patients with renal and hepatic insufficiency are at risk for normeperidine accumulation, which can cause tremors, myoclonus, and seizures. ⁵⁰ Naloxone does not reverse normeperidine-induced seizures. ⁵⁵ Unlike meperidine, fentanyl does not cause accumulation of active metabolites. ⁵⁶

Naloxone is an opioid receptor antagonist used for reversal of narcotic-induced CNS effects including respiratory depression, sedation, and analgesia. The typical dose is 0.4 mg every 2 to 4 minutes until adequate clinical response has occurred. The duration of effect of naloxone is shorter than that of fentanyl and meperidine, so all patients receiving rescue doses should be closely monitored for relapse of sedation. In such circumstances, repeat administration of naloxone may be required.

Propofol is an ultra-short-acting hypnotic used for induction and maintenance of anesthesia, conscious sedation in minor procedures, and sedation in intensive care unit patients. ⁴³ At doses used during colonoscopy, it provides sedation and mild amnesia but has no analgesic properties. ⁵⁷ It is usually administered in combination with a short-acting benzodiazepine or opioid to enhance each individual drug’s desired effect, a method referred to as “balanced propofol sedation” or “multidrug propofol.” ⁵⁸ Given the lack of analgesic effects, when used alone during endoscopy higher propofol doses may be required to maintain patient comfort. This may result in more profound levels of sedation (i.e., deep sedation) than originally targeted for colonoscopy. Indeed, several studies have demonstrated that utilization of balanced propofol for achieving moderate sedation is associated with fewer instances of deep sedation than when opioids and benzodiazepines are used alone. ^{58 , 59}

Propofol is usually given as an initial 20 to 60 mg bolus, followed by repeat doses of 10 to 30 mg in 30- to 60-second intervals as needed. ⁵⁰ As with benzodiazepines and opioids, use of propofol with other sedatives results in synergistic respiratory depression, and dose reduction of all medications used may be required. ⁶⁰ It has a rapid onset of action (30–45 seconds) and short duration of effect (4–8 minutes). The primary side effects of propofol are respiratory depression and hemodynamic disturbance, including hypotension, decreased cardiac output, and systemic vascular resistance. ⁴³ Unlike benzodiazepines and opioids, there is no medication available to reverse the effects of propofol. ⁵⁹ Instances of propofol oversedation are treated supportively with IV fluids and vasopressors as needed for hypotension and maintenance of ventilation until drug effect wears off. Injection site pain during bolus infusion is reported in approximately 30% of patients and can be minimized by using a large vein and avoiding veins in the dorsum of the hand. ^{52 , 61} Propofol is formulated in a soybean, egg phosphatide, and glycerol emulsion and is contraindicated in patients who are allergic to soy, egg, or sulfite. ⁵⁶ Propofol, however, is not contraindicated in patients with sulfonamide allergy. ⁶¹

Propofol is the most frequently used IV anesthetic today. ⁶² It was originally described in 1977 and subsequently approved for “induction and maintenance of general anesthesia” by the FDA. For this reason, administration of propofol has traditionally been limited to anesthesiologists. However, its utilization and experience by nonanesthesiologists has expanded over the years and now includes a variety of outpatient procedures. A recent survey of gastroenterologists in the United States found that propofol is used in up to 25% of endoscopies; however, 68% of physicians indicated they were reluctant to give propofol due to perceived increased risk of complications. ⁴³

There is a well-established and growing body of literature to support the safety and efficacy of propofol administration by the endoscopist (termed gastroenterologist-directed propofol) or nurse administration of propofol under the direction of the endoscopist for sedation during colonoscopy. ^{62 , 63 , 64 , 65 , 66} Greater than 220,000 cases of gastroenterologist-directed propofol have been reported, with only one reported instance of intubation and no instances of death. ⁶² A recent meta-analysis comparing the effectiveness of propofol to other sedation regimens for colonoscopy found that propofol sedation was associated with faster recovery and discharge times, and increased patient satisfaction without increased side effects. ⁶⁷ Given the amount of supporting data, the American College of Gastroenterology (ACG), the American Gastroenterological Association (AGA), and the American Society for Gastrointestinal Endoscopy (ASGE) jointly conclude that “Compared to standard doses of benzodiazepines and narcotics, propofol may provide faster onset and deeper sedation” and that “with adequate training physician-supervised nurse administration of propofol can be done safely and effectively.” ⁶⁸