Capsule endoscopy, also known as wireless capsule endoscopy or video capsule endoscopy, is a gastrointestinal study that uses a pill camera to take images of the intestinal lumen. The first capsule endoscopy was performed in 1999, and the US Food and Drug Administration approved its use in the United States in 2001. The M2A capsule (mouth to anus) was the first available pill camera and was eventually renamed as PillCam SB (small bowel). The capsule is ingested and transmits images at 2 to 6 frames per second over the course of 8 to 12 hours until the battery expires. It generates 512 by 512-pixel, high-resolution images that allow detailed inspection of the gastrointestinal mucosa. A trained gastroenterologist then reviews the images. Battery life can be a limiting factor during capsule endoscopies, and 16.5% of studies are incomplete due to battery expiration. Capsule endoscopy is a diagnostic procedure and has no therapeutic benefits. It can only localize lesions in the esophagus, stomach, small bowel, and colon but cannot be used for biopsy or therapy. It is used most often for recurrent and obscure gastrointestinal bleeding after traditional endoscopic procedures have failed to identify a bleeding source. It can be a useful study for localizing a lesion prior to angiography, surgery, or further endoscopic procedures. The diagnostic yield of capsule endoscopy has been found to be higher than small bowel barium studies, CT enteroclysis, angiography, and push enteroscopy.
Capsule endoscopy can be used to evaluate the esophagus, stomach, small intestine, and colon. It is ingested just like any other capsule and travels through the esophagus into the stomach. It then passes through the pyloric sphincter into the duodenum, jejunum, and ileum. The capsule proceeds through the ileocecal valve into the cecum. It then advances through the colon and is excreted during a bowel movement. In many cases, the patient will witness the passage of the capsule, but plain abdominal films can be used to evaluate complete passage of the video capsule.
There are many indications for capsule endoscopy. The most common indication is for obscure gastrointestinal bleed thought to be located in the small bowel after upper and lower endoscopic procedures failed to find a bleeding source. Video capsule has a 35% to 77% detection rate of obscure gastrointestinal bleeds. Other indications for small bowel capsule endoscopy are as follows: diagnosis of Crohn's disease and evaluation of Crohn's disease activity, diagnosis of celiac disease, and evaluation of refractory celiac disease, polyposis syndrome surveillance, small-intestine tumors such as neuroendocrine tumors, or carcinoid tumors. Capsule endoscopy is indicated to evaluate the esophagus for esophageal varices screening, Barrett’s esophagus screening, and esophagitis identification. Colon capsule endoscopy is indicated for colon cancer screening in patients with a previous incomplete colonoscopy, patients that have major risks for a colonoscopy itself, and patients that cannot tolerate sedation.
There are several contraindications to capsule endoscopy. Since the procedure requires patient participation, individuals with dementia are usually poor candidates. Swallowing disorders may cause difficulty in ingesting the capsule. There is a relative contraindication in patients with cardiac pacemakers, defibrillators, or left ventricular assist devices due to a concern for possible interference between the capsule and the cardiac devices. However, there has never been a reported case of cardiac device malfunction due to capsule endoscopy. Furthermore, studies have demonstrated that there is no interference with these cardiac devices. Many centers still perform the capsule endoscopy in patients with cardiac devices. Pregnant women should not have capsule endoscopy since there are no studies on the safety of capsule endoscopy in this patient population. The risk of capsule retention is greatest in patients with known or suspected strictures, fistulas, and obstructions. Capsule endoscopy is contraindicated in these patients due to the risk of worsening obstructions or causing obstructions. If capsule endoscopy is necessary for a patient at risk for retention, an Agile Patency Capsule can be ingested. Agile Patency Capsule is a radiopaque capsule without video capabilities. Thirty hours after ingestion a plain abdominal film or hand-held scanner can be used to determine the passage of the capsule. This determines if it is safe to proceed with video capsule endoscopy. If the Agile Patency Capsule is retained, it will dissolve and pass safely through the gastrointestinal tract. The video capsule can also be retained due to achalasia, esophageal diverticula, esophageal strictures, or pyloric stenosis. Gastroparesis may slow the mobilization of the capsule. In these types of patients, an AdvanCE Capsule Endoscopy Delivery System can be attached to the tip of a gastroscope which can then be used by the endoscopist to place the capsule in the stomach or duodenum. Capsules can also be placed into the stomach through the use of an overtube or advanced from the stomach into the duodenum with nets and snares.
There are several different video capsules available for use in the United States. Most are used for diagnosis of small bowel lesions and transmit 2 to 6 images per second. Some capsules are specifically used to visualize the esophageal lumen. The PillCam ESO has a battery life of 20 minutes and a camera at both ends of the capsule. It transmits 18 images per second to evaluate the esophagus. PillCam COLON is used to visualize the colonic lumen and also has a camera on both ends. PillCam COLON activates 2 hours after ingestion to conserve battery life and allow complete colonic evaluation. The capsules range in size but are approximately 1.1 by 1.6 cm in size. The colon capsule is larger and is 1.1 by 3.2 cm. Video capsules transmit data to a wearable receiver through ultra-high frequency band radio telemetry or electric field propagation. A computer with specialized capsule endoscopy software is used to view images and interpret data. The software can detect potential bleeding sources by tagging images that have red pixels.
Trained office or hospital staff such as a medical assistant or nurse can outfit the patient with the external receiver and coach the patient through the capsule ingestion process. After the external receiver captures the transmitted images, they are then downloaded onto a computer. A gastroenterologist competent in evaluating endoscopy then evaluates and documents the findings of the capsule endoscopy in a report. The average time it takes to generate a report is 30 to 120 minutes for small bowel capsules and 5 to 15 minutes for esophageal capsules.
Preparation for a capsule endoscopy is similar to that of colonoscopy preparation and can be performed in an outpatient setting. The day before the procedure patients should remain on a clear liquid diet. Patients need to fast for 10 to 12 hours before video capsule ingestion. Polyethylene glycol solution can be taken the night before the study which helps clear food and stool debris out the gastrointestinal and may improve visualization. For colon capsule endoscopy the patient is required to consume at least 3 liters of polyethylene glycol solution to evacuate the colon. There are mixed reviews whether prokinetic agents such as metoclopramide and erythromycin improve the passage of capsules through the gastroenterology tract. Simethicone solution has been used to improve visualization by decreasing air bubbles in the intestinal lumen.
Prior to video capsule ingestion, the patient is outfitted with a sensor belt which gathers the capsule’s transmitted images. Once a magnet is removed from the capsule, it becomes activated, and the patient can ingest the capsule while in an upright position. As mentioned above, the capsule can also be placed in the stomach or duodenum endoscopically. Patients are advised not to participate in any activities that may cause sensor belt detachment. The patient can resume a clear liquid diet 2 hours after capsule ingestion. They can have a small meal 4 hours after ingestion. Patients undergoing esophageal capsule endoscopy only need to fast for 2 hours before the procedure and will need to consume 100 mL of water just prior to capsule ingestion. The patient will swallow the capsule while lying supine and slowly move into an upright sitting position over a 5-minute period.
Capsule retention can occur in 1.3% to 1.4% of patients undergoing capsule endoscopy and is the most common complication. Capsule retention is usually asymptomatic and diagnosed 2 weeks after capsule ingestion via abdominal plain film x-ray. Patients with known or suspected obstructions, strictures or fistulas should not undergo capsule endoscopy due to their increased risk of retention. Crohn's disease increases a patient’s risk of having capsule retention to 2.6%. A dummy capsule called an Agile Patency Capsule can be used to determine patency of the intestinal lumen for the safe use of capsule endoscopy. Radiographic imaging such as small-bowel follow-through, CT or magnetic resonance enterography can also be used to assess lumen patency prior to the administration of the capsule. Capsules may need to be surgically or endoscopically removed if symptomatic retention occurs. The video capsule can also be retained in a Zenker or Meckel's diverticulum. There is a small risk for aspiration of the capsule or cricopharyngeal impaction of the capsule.
Capsule endoscopy is an important means of evaluating the gastrointestinal tract when traditional endoscopic techniques have failed. It is safe, painless, has no risk for infection and does not require sedation. It has a higher diagnostic yield than many other modalities for evaluating the intestinal lumen and can localize lesions. The shortcomings of capsule endoscopy are its lack of therapeutic capabilities. Its high diagnostic yield and low complication rate make it an appealing choice for evaluation of the intestinal lumen when indicated despite the inability to obtain tissue samples and provide therapy.
Capsule endoscopy does have a role in the detection of some GI disorders but it is rarely the first test of choice. It is most useful for detecting superficial or occult lesions that are not detected by other imaging studies. However, patients need to be educated about the limitations of the test. The nurse should inform the patient that the test may not be covered by some insurance providers. While the test offers great visualization of the GI tract, it does not allow for a biopsy or any type of invasive procedure- hence another procedure is required if a lesion is found. The cost-effectiveness of this study still remains to be determined. In an era where healthcare costs are increasing and patients forced to make large copayments, the decision to offer a patient this study should be done with thought. (Level V)
Overall, there is a lack of good clinical data on the benefits of capsule endoscopy. The yield in patients with bleeding depends on whether the patient is having an overt or occult bleed- in the latter cases, its effectiveness appears to be low. Further, several studies have shown that the technique may miss lesions in the small bowel. The chief complication is retention of the capsule. Capsule endoscopy is best used in combination with other imaging techniques and should not be the test of first choice to assess bleeding. (Level V)