concentrating the solution into a smaller volume followed by drinking a predetermined amount of free water or placing PEG in capsules, so the patient does not have to taste the medication. This pill preparation, however, requires ingesting >30 capsules over a short period of time and still requires ingesting large amounts of water or clear soda to provide the fluid volume needed to clean the colon and ensure an isoosmotic concentration in the intestines. Despite these drawbacks, PEG preparations still remain the safest, most effective, and most commonly used preparations.
Scope selection
One decision that needs to be made prior to initiating endoscopy is what instrument to use. There are a number of different types of endoscopes in the gastroenterologist's armamentarium that can be selected to perform lower endoscopy. These include the standard adult colonoscope, pediatric colonoscope, flexible sigmoidoscope, or even a gastroscope that is dedicated to lower procedures (Figure 6.7). Understanding the advantages/disadvantages of each is an important cognitive skill that can improve one's chances of successfully achieving the goals of a lower endoscopy.
In general, the standard adult scope is slightly larger in diameter than the other scopes (measuring roughly 13 mm in diameter) and is one of the most commonly used scopes for colonoscopy. Its thickness results in it being somewhat stiffer than the others. As a result of being slightly stiffer, it tends to loop less than other scopes, especially in patients with a very mobile sigmoid or redundant transverse colon. By the same token, its larger diameter and decreased flexibility can also make it more difficult to navigate through fixed, sharply angulated colons. Such fixation and angulation can be seen in patients with prior abdominal or pelvic surgeries (hysterectomy, C‐sections, etc.), prior radiation, or significant prior peritoneal infection (ruptured appendix or other infection). In these patients, a pediatric scope can sometimes succeed in navigating through a difficult fixed sigmoid where an adult scope could not. This is primarily due to the greater flexibility of this scope resulting from its smaller diameter (11.5 mm diameter). In a long redundant, highly mobile colon, however, this flexibility can result in excessive proximal looping, requiring greater experience and skill to advance the scope to the cecum.
Figure 6.7 Endoscope options. Four different endoscopes can be used for lower endoscopy. Depicted here are: (A) adult colonoscope (13.2 mm diameter), (B) pediatric colonoscope (11.5 mm diameter), (C) sigmoidoscope (12.8 mm diameter), and (D) gastroscope (9.2 mm diameter). The diameter of the endoscope may vary slightly based on the manufacturer.
Gastroscopes are also used in special circumstances for lower endoscopy. Because of their smaller caliber (9.2–9.8 mm diameter), gastroscopes are ideal for lower endoscopy of an ileostomy or in a patient with an ileoanal pouch. The smaller diameter is also useful in patients who have left‐sided colonic strictures (within reach of the shorter gastroscope) that prevent the passage of either of the larger colonoscopes. For routine colonoscopy, however, these scopes loop quite a bit due to their flexibility and their short length prevents them from reaching the cecum in most cases.
Flexible sigmoidoscopes are useful if only the left colon is to be examined. Traditionally, this was the primary method for routine colon cancer screening when paired with testing such as a barium enema or fecal occult blood testing to screen the remaining colon for malignancies. For this purpose, however, colonoscopy has largely replaced flexible sigmoidoscopy (FS). FS is still useful in evaluating the severity of a flare of known ulcerative colitis, suspected ischemic or infectious colitis, to obtain colon biopsies in suspected microscopic colitis, or to evaluate radiographic abnormalities seen in the left colon.
Learning when to use each scope is a skill that comes with guidance and experience and can vary from one individual to another. Just as a golfer learns which club he/she can use most effectively in given circumstances, the endoscopist too must develop an understanding of which scope they can best employ from one case to the next. When a particular type of scope is preferred for a procedure, trainees should get in the habit of including that request at the time of booking, to better ensure that it will be available in the endoscopy unit when it is time to perform the case.
Sedation
From the patient's perspective, sedation and analgesia are two of the most important issues linked to procedure satisfaction. Considering that success of colonoscopy as a screening exam relies on serial evaluations at least every 10 years, a patient's avoidance of pursuing repeat evaluations due to prior bad experiences can lead to potential premalignant lesions or other disease going undetected and advancing to more serious disease. Sedation, analgesia, and patient monitoring in endoscopy are covered in greater detail in another chapter of this text. In general, the use of a benzodiazepine (midazolam or diazepam) in combination with analgesia (meperidine or fentanyl) provides adequate conscious sedation for lower endoscopy. These agents work synergistically in providing sedation while the benzodiazepine provides an added amnestic effect. However, in some instances, deeper sedation may be needed. Propofol or even general anesthesia can be used for these patients.
Indication/contraindications
All trainees need a solid understanding as to when a colonoscopy should be performed, and perhaps more importantly when it should be avoided. One of the most common indications for a colonoscopy is as a screening exam for colorectal cancer. In the general population, these exams traditionally begin at the age of 50 years and if normal, every 10 years thereafter. In 2018, the American Cancer Society has recommended moving this initial screening to 45 years old, which may prompt other societies to follow suit. If a few small polyps are found on a screening exam, this surveillance interval is shortened to 3–5 years depending on the findings. Certain other indications, such as more numerous polyps, larger polyps, advanced dysplasia, villous architecture, or hereditary polyposis syndromes, can result in initiating early screening before the age of 50 or shorten the next interval even further to 1–3 years. In the case of particularly large or advanced polyps, a follow‐up examination in 3 months may be required to ensure complete resection of the lesion. Screening guidelines are frequently updated and every endoscopist must keep current with the most recent recommendations. These guidelines can typically be found online at professional society web sites such as the American Society for Gastrointestinal Endoscopy (ASGE), American College of Gastroenterology (ACG), or American Gastroenterology Association (AGA) [2, 3].
Other indications for colonoscopic examination are primarily symptom driven. Of these, suspicion for GI bleeding (iron‐deficiency anemia, positive stool occult blood tests, or even frank hematochezia) is likely the most common cause for lower endoscopy [4]. A change in bowel habits (stool caliber, constipation, or chronic diarrhea), suspicion of inflammatory bowel disease, abdominal pain, and abnormal radiographic imaging studies are all common indications to pursue colonoscopy as well. Other less common causes include foreign body removal, volvulus reduction, or decompression of colonic pseudo‐obstruction.
As stated earlier, there are times when it is not safe to proceed with colonoscopy. These include recent colon surgery, recent myocardial infarction (MI), the presence of severe colitis, supratherapeutic anticoagulation, or the presence of hemodynamic instability [4]. It is advised to delay colonoscopic exam for 3 months following colonic surgery, such as a new stoma or other colonic anastomosis. In the case of a recent MI, there are no specific guidelines regarding this. For elective procedures, one should wait until well after the event and base timing on the patient's clinical status. Emergent colonoscopy for gastrointestinal bleeding following an MI has been studied. Though there is roughly a ninefold increase in complications (9% vs. 1%), these complications
