Katie MacBride*, 35, has been suffering with severe reflux and difficulty swallowing for six months. A visit to her physician has her scheduled for an upper endoscopy within two weeks. The procedure reveals evidence of high-grade dysplasia — abnormal, precancerous cells — in her distal esophagus. It also shows evidence of intestinal metaplasia, as seen in Barrett’s esophagus (BE), a potentially premalignant condition, and moderate, chronic esophagitis, with no discrete lesions. Biopsies of the distal esophagus reveal a foci of high-grade dysplasia. To more clearly confirm how extensive these dysplastic changes truly are, Mrs. MacBride’s gastroenterologist performs a repeat endoscopy that includes chromoendoscopy, a colorful endoscopic procedure that uses dyes to localize and identify areas of dysplasia. (Chromo is from the Greek word for color.) Afterward, Mrs. MacBride receives a diagnosis of BE with high-grade dysplasia. Treatment is successful, and Mrs. MacBride will follow-up with her gastroenterologist regularly with surveillance of the treated site.

The goal of any screening endoscopy is the early diagnosis of premalignant and malignant changes of the GI mucosa. By using nontoxic dyes to identify areas of dysplasia, chromoendoscopy provides the ability to visualize mucosa at the cellular level, thus facilitating the diagnosis of abnormal cellular changes and early-stage cancers in the GI tract and biliary tree, the path through which bile is secreted by the liver to its endpoint in the duodenum. Chromoendoscopy reveals otherwise invisible changes of the GI lining, enabling the endoscopist to obtain what would otherwise be an unobtainable directed biopsy. It also improves the definition and thus the ability to evaluate any lesions that are found, more clearly delineating their margins and intrinsic characteristics.

Chromoendoscopy was introduced as a technique for the more thorough diagnosis and surveillance of BE.¹ But now chromoendoscopy also helps diagnose gastroesophageal reflux disease (GERD), esophageal cancer, gastric cancer, inflammatory bowel disease (Crohn’s disease), and ulcerative colitis. It also helps in the diagnosis and evaluation of adenomatous colon polyps and colon cancer. A widely accepted diagnostic technique, chromoendoscopy has been used in a variety of clinical settings — and in all parts of the GI tract that an endoscope can reach. Nurses need to be conversant with this technique because it is emerging as a viable clinical diagnostic tool in many settings.¹

Compared to other evolving diagnostic techniques (e.g., fluorescence spectroscopy, fluorescence endoscopy, and optical coherence tomography), chromoendoscopy is simple, quick, and safe.

Chromoendoscopy requires minimal equipment. Multiple dyes are available for staining. Although some stains require preparation of the tissue beforehand, application of the stain is easy and straightforward.

Colors of the rainbow

Each stain has its own characteristics, and each targets tissue in specific ways. The dye used depends on the type of tissue to be stained and the portion of the anatomy to be evaluated.

A specially designed spray catheter is used to apply chromoendoscopy stains.² The catheters are reusable and extremely long-lived. When passed through the endoscope, the spray catheter delivers a fine mist to the mucosal lining of the GI tract. The endoscopist directs the endoscope and catheter tip toward the mucosa using clockwise-counterclockwise movements while simultaneously withdrawing the endoscope tip.³

The hormone glucagon can be administered immediately before mucosal staining to minimize mucosal contractility, thereby facilitate staining.4 When chromoendoscopy is going to be used in the setting of colonoscopy, a thorough bowel prep is essential because the mucosal wall lining cannot be stained unless it is completely cleaned of stool or debris.

Three major categories of tissue stains are used: absorptive (vital), reactive, and contrast stains. In addition, India ink is used to “tattoo” lesions so they can be easily identified during later procedures.

Absorptive stains

The absorptive stains consist of Lugol’s solution, toluidine blue, methylene blue, and cresyl violet. Absorptive stains are absorbed by the mucosal cells. They are particularly useful in the detection of high-grade dysplasias and early-stage cancers of the esophagus, especially in patients who are at increased risk due to preexisting risk factors, such as chronic GERD, smoking, and alcohol consumption.

Lugol’s solution, named after French physician Jean Guillaume Auguste Lugol, helps detect and evaluate the extent of disease in patients with high-grade dysplasia and early squamous cell cancers of the esophagus. With Lugol’s solution, normal squamous epithelium will stain dark brown while metaplastic columnar epithelium will not stain at all.⁵ (Metaplasia is tissue that should not normally be present in an area, for example, stomach and intestinal columnar cells that have invaded the squamous cell epithelium of the esophagus.) The nonsquamous (nonesophageal) tissue, such as columnar cells normally seen in the stomach or intestine, is not picked up by the Lugol’s stain.

In addition to detecting squamous cell cancers of the esophagus, Lugol’s solution is used in surveillance of BE following mucosal ablation and in detection of reflux esophagitis. Lugol’s solution is formulated from potassium iodine and iodine; both ingredients have an affinity for the glycogen contained in nonkeratinized squamous cell epithelium.⁶ Clinical studies have shown that staining suspected mucosa with Lugol’s solution identified 23% of lesions that contained moderate and severe dysplasia. These lesions were not detected endoscopically without the mucosal staining.⁷

Patients may experience epigastric pain after mucosal staining with Lugol’s solution. An application of sodium thiosulfate solution (20 mL of a 5% solution) following staining can significantly reduce discomfort.⁸ Patients with an allergy to contrast dye should not be given Lugol’s solution, because severe allergic reactions have been reported.⁹

Toluidine blue identifies malignant cells by targeting and staining their nuclei blue. It has been proven useful in the diagnosis of esophageal cancers in patients with a history of alcohol and tobacco abuse or a preexisting head and neck cancer.^10,11 It has also helps to distinguish benign and malignant gastric ulcers.

Before the application of toluidine blue, the endoscopist sprays a 1% acetic acid solution onto the targeted mucosa to dissolve it so it can be washed away. Then comes a 1% aqueous solution of toluididine blue, followed by a second application of acetic acid to wash off any excess dye. No adverse effects have been reported with toluidine blue.

Methylene blue is actively absorbed by the tissues of the small intestine and the colon. This dye diffuses into the cells and stains the nuclei of columnar cells (those found in gastric and intestinal mucosa) blue. Uptake of the dye requires that it come into contact with the epithelial surface. As the stomach and bowel are protected by a mucosal layer, this mucus must be displaced so the stain can be successfully applied. Mucomyst (acetylcysteine) is usually administered as a 10% solution, sprayed by a washing catheter (approximately 20 cc) directly onto the mucosa. While the staining is immediate after Mucomyst is applied, the stain is short-lived and begins to fade within 15 to 20 minutes. Methylene blue causes a blue-green discoloration of the urine, through which it is excreted. It also colors the stool blue. However, neither methylene blue nor Mucomyst is toxic.

Although it’s used throughout the length of the GI tract, methylene blue has been used most extensively in evaluating BE and detecting early esophageal malignancies. Since dysplastic and malignant cells stain differently, the pattern of staining is an important diagnostic tool in the delineation of dysplastic or malignant areas of the esophagus and can help determine treatment. Increasing grades of dysplasia are associated with focal areas of decreased stain intensity and/or increased stain heterogeneity (variation in stain intensity). Methylene blue has also been used to diagnose early gastric cancers and to highlight areas of intestinal-type metaplasia in the stomach.

Methylene blue can also highlight subtle changes in the small intestine, which becomes useful in the diagnosis of celiac disease. It improves the ability to detect the extent of inflammatory changes in the presence of inflammatory bowel disease (ulcerative colitis, Crohn’s disease). Methylene blue is considered safe. Diluted methylene blue can also be used as a contrast stain.

Cresyl violet, another absorptive stain, has recently been used to help diagnose early gastric cancers in conjunction with magnification endoscopy; cresyl violet portrays the characteristic staining pattern commonly noted in early gastric cancers. It can also be used with indigo carmine to enhance the diagnosis of early malignancies of the colon.

Reactive stains

The reactive stains are Congo red and Phenol red, which detect the acid-containing gastric cells and change color when they come into contact with diseased tissue.

Congo red changes color from red to dark blue or black in the presence of acidic conditions. This color change will occur if the acid pH is 3.0 or lower. Used primarily as a stain to detect gastric cancers, Congo red can also be used to detect intestinal metaplasia in the stomach. The staining technique involves the stimulation of the acid production via the administration of oral pentagastrin (Peptavlon). Then, during endoscopy, a 0.5% sodium bicarbonate solution is sprayed over the gastric mucosa, followed by a 0.3 % to 0.5% Congo red solution.

Phenol red targets Helicobacter pylori-infected gastric cells, turning them from yellow to red,¹² thus mapping their distribution in the stomach. (H. pylori can infect portions of the stomach and duodenum, causing many cases of peptic ulcers, gastritis, and duodenitis.) Alkaline pH, secondary to the hydrolysis of urease to NH₃ and CO₂, results in the color change. A solution of 0.1% phenol red and 5% urea is sprayed evenly over the gastric mucosa.

Contrast stains

Indigo carmine is a blue dye derived from the plant dye indigo and a red coloring agent formed from cochineal and alum. Indigo carmine explicitly identifies the borders of a lesion. It isn’t absorbed by the tissue, but pools in the crevices between cells, thereby highlighting small or flat lesions and defining irregularities of the mucosal lining. The stain can be ingested orally in a capsule, sprayed directly onto the mucosa, or introduced through a colon electrolyte lavage.

Indigo carmine has been used to enhance the surveillance and detection of a multiplicity of GI abnormalities, including BE, small gastric cancers, and the villous atrophy in patients with celiac disease; to note mucosal changes evident in ulcerative colitis; and to help detect early colon adenomas. It has proven to be an accurate method of differentiating between hyperplastic and adenomatous colon polyps. Most recently, it has been used to detect colon polyps in patients with hereditary nonpolyposis colorectal cancer.¹³

The ultimate tattoo

India ink is the stain generally used to tattoo the mucosa in the area of a known lesion to precisely demarcate the site. That way, the lesion can easily be relocated for a subsequent endoscopic surveillance or before a surgical excision. The India ink is injected through a long needle (a sclerotherapy needle) that is passed through the endoscope. A permanent tattoo, it’s a colloidal suspension of carbon particles in a solution of stabilizers and surfactants. The diluents include phenol, propylene glycol, shellac, and alcohol. A safe procedure, tattooing with India ink has been used in the esophagus, stomach, small bowel, and colon.

Other agents have been used as part of chromoendoscopy, as well. Acetic acid has only recently been employed in the GI tract as part of chromoendoscopy. Pilot studies have proven that acetic acid is promising in the detection of areas of intestinal metaplasia in the esophagus and in the visualization of areas of mucosal atrophy in patients with celiac disease.¹⁴ A spray catheter containing 3% acetic acid is passed through the gastroscope. The head of the patient’s bed should be elevated to reduce the risk of aspiration. As little as 5 mL to 10 mL is required to coat an area of suspected Barrett’s mucosa. Esophageal and gastric epithelium turn white while the gastric and columnar epithelium of the Barrett’s mucosa turns reddish. This clearly delineates the contrast between normal and metaplastic tissue.

Marriage of mutual convenience

The prognosis for patients with malignancies of the GI tract depends largely upon early diagnosis and treatment. The newer generation video endoscopes with narrow-band imaging (NBI) technology offer high-resolution and magnification to enhance chromoendoscopy, with the marriage of these techniques proving to be a promising diagnostic tool.

NBI technology works by altering the white light emitted by the endoscope to blue. This allows improved visualization of the mucosal lining of the GI tract, thereby delineating the fine capillary patterns in the lining that would otherwise remain undetectable.¹⁵

The new high-resolution endoscopes can discern objects only 10 to 71 microns in diameter. This high resolution is related to pixel density: Most endoscopes have pixel densities of 100,000 to 200,000 while the newer magnification endoscopes have densities as high as 850,000.¹⁶ Magnification of endoscopic images in real time (magnification endoscopy) allows the detection of mucosal abnormalities that would otherwise go unnoticed. Magnification endoscopes include an adjustable focusing mechanism that can enlarge images up to 150 times their original size.¹⁷

In the stomach, magnification endoscopy is useful in detecting premalignant and malignant lesions. In the small and large intestines, magnification endoscopy has allowed a more thorough diagnosis and assessment of flat and depressed lesions, the identification of dysplasia in ulcerative colitis, discrimination among polyps, and assessment of the completeness of endoscopic mucosal resections.¹⁸

Chromoendoscopy enhances magnification, as well. Intestinal metaplasia is frequently translucent when seen through a magnified lens.¹⁹ The addition of chromoendoscopy permits a more thorough and definitive screening by allowing for more precise targeting of areas for biopsy in the esophagus and gastric cardia.

The technique for performing magnification endoscopy generally is the same as that of a usual endoscopic exam. A major difference, especially when the duodenum is under examination, is that glucagon is administered to help reduce mucosal contractility, thereby aiding in visualization and the application of stains.

The new video images are much clearer and cover a larger area of tissue than was previously possible. They improve picture clarity and have greater magnification abilities. When used with the new generation of colonoscopes and gastroscopes, they offer a more defined view of anatomical structures and the fine capillaries of the GI tract. This new technology is designed to be similar to chromoendoscopy, but bypasses the messiness of dye application. But these new generation of endoscopes are very expensive and a fairly recent technology, so they are not widely available.

Although magnification in conjunction with chromoendoscopy has been proven to be a promising technique, some points of contention remain. Inflammation due to illness can occasionally cause a false positive result. Close examination of the mucosa can be difficult secondary to peristalsis and respiratory movements. Although simple to perform, chromoendoscopy still requires careful execution of a multiplicity of steps. Additionally, as with many procedures, much of chromoendoscopy’s success depends the skill of the person operating the technology. As with all new procedures, chromoendoscopy is more efficacious in larger medical centers, where more sophisticated training and research protocols are in effect.

The patient’s end of the scope

From the patient’s point of view, chromoendoscopy is performed in the same way as gastroscopy or colonoscopy. Patients receive sedation and must be NPO after midnight, or per institutional policy. Patients cannot drive afterward and must have a ride home. The primary role of the nurse during endoscopic procedures, including chromoendoscopy, is to be the patient’s advocate and facilitate the procedure. Preprocedure, the nurse discusses the procedure with the patient and significant others, assesses their expectations, answers their questions, and addresses their concerns. During the procedure, the nurse monitors the patient for comfort and stability. Vital signs are closely monitored, and patient safety and comfort are a priority. Afterward, the nurse reports patient and procedure-oriented events to the recovery room nurse at the time of patient transfer to ensure the safe continuity of care.

A procedure nurse or technician assists the physician with all of the technical aspects of the procedure. He or she sets up the room; prepares and cleans the scopes; assembles the required accessories, including the dyes; and assists the physician as necessary.

A view to the future

Chromoendoscopy, in conjunction with the new high-resolution and magnification endoscopes, offers new and improved mucosal examination and diagnosis. Ultimately, neoplastic lesions will be diagnosed rapidly with highly advanced endoscopic imaging techniques. This will allow practitioners to endoscopically diagnose and treat dysplastic and malignant lesions of the GI tract in a single medical visit.

But today, chromoendoscopy and enhanced magnification endoscopic imaging are still evolving. Guidelines on how and when to stain are needed, as is a uniform classification system for the interpretation of results. Additional evidence-based practice studies are needed to investigate the reliability and cost-effectiveness of the multiple emerging techniques and equipment. Electronic digital chromoendoscopy and other evolving endoscopic techniques may one day replace staining of mucosal tissue. The future holds great promise, and what may seem innovative today may become a footnote in the history books tomorrow.

* A fictitious patient.