Some speech-language pathologists use blue dye during the assessment of patients with a tracheostomy via Modified Evans Blue Dye Test (MEBDT), as well as during endoscopic evaluation of swallowing. Questions about the effectiveness and safety of this practice include:
- Is use of blue dye a reliable way to detect aspiration of either oral or tube feeding?
- If dye is used in the above procedures, is there a difference in the use of methylene blue, blue food coloring, or other colors of food coloring compared to naturally colored foods?
- Is use of blue dye safe?
A review of the available literature, as well as discussion with other health care professionals, yields some helpful information for SLPs.
Let’s first clarify what blue dye is. When the term blue dye is used, it most often refers to FD&C Blue No. 1, or what is commonly referred to as "blue food coloring." It was first approved by the U.S. Food and Drug Administration in the 1960s (34 FR 7445; May 8, 1969), based on animal tests, with the most recent safety testing completed in the 1980s (FDA, 1982). Methylene blue is another type of dye, but its chemical composition differs from Blue No. 1.
Recently, information has been reported about patients who have experienced discolored serum, urine, and skin from the Blue Dye No. 1, and several deaths also have been reported. These were patients who were receiving blue-colored enteral feedings. In a letter to the editor in The New England Journal of Medicine , Maloney and colleagues (2000) reported two deaths due to blue-dye absorption. Each patient had sepsis, which increased gut permeability and allowed the dye to enter the patient’s bloodstream. However, many conditions are considered to increase gut permeability, including cardiac bypass, major vascular surgery, renal failure, abdominal aortic aneurysm repair, severe burns, cystic fibrosis, and even nonsteroidal anti-inflammatory drug use (Maloney et al., 2002).
The question of whether blue dye is safe when used during an endoscopic exam or MEBDT is really two questions. First, is the amount of dye used during these exams at all equivalent to the amount a patient would receive in enteral feeding? Typically, a few drops of food coloring are used to tint all the food that will be presented to a patient, whereas 5–10 cc is typically used to color a bag of tube feeding. Therefore, the amount of blue dye used during an endoscopic examination or MEBDT is significantly less than that administered to a patient via enteral feedings. However, as one chief dietitian stated, "Two to three bites of something colored with blue dye is hard to picture as a risk. The trouble is, I would have said that about tube feeding not long ago." (S. Wallace, personal communication, Sept. 3, 2002). It seems there is no definitive answer about whether a few drops of food coloring are potentially harmful to a patient, but Maloney advises to "avoid it in any active conditions that increase gut permeability" (J. P. Maloney, personal communication, March 4, 2002).
The second question about safety of blue food dye is how the blue dye is stored and administered to protect against contamination. In 1995, a medical team described an outbreak of pseudomonas aeruginosa , a ventilator-associated respiratory infection. Nineteen of the 20 patients with this infection had received tube feedings that had been tinted from the same common-use bottle of blue dye (File, Tan, & Thomson, 1995). When the hospital replaced this with single-use vials, the outbreak cycle stopped. Knoll (1993) reported a study in which gram-negative and gram-positive rods (types of bacteria) were found, not only in an open bottle of dye, but also in two unopened bottles. Sterile vials of blue food dye are available, which might alleviate the concern over contamination (Novartis Nutrition, Freemont, MI).
Clinicians must carefully consider this information when deciding whether to use food coloring in the foods presented to the patient during an endoscopic examination of swallowing. The goal is to select materials that will "show up clearly on the monitor, distinct from the mucosal surfaces of the hypopharynx" (Langmore & Aviv, 2001, p. 79). Some foods, like milk, are naturally inclined to meet this specification (Langmore & Aviv, p. 79).
The question of the reliability of the MEBDT, however, may supersede safety concerns about blue dye in some cases. All of the above information, for example, seems moot when deciding whether or not to use suctioning of tracheal secretions to determine if aspiration has occurred. The MEBDT has been used to determine if aspiration has occurred during a bedside evaluation in patients with tracheostomies (Cameron, Reynolds, & Zuidema, 1973; Elpern, Jocobs, & Bone, 1987; Higgins & Maclean, 1997). Brady, Hilldner, and Hutchins (1999) reported on a study in which 20 consecutive simultaneous MEBDTs and modified barium swallow studies were completed on patients with tracheostomies. Overall, the MEBDT showed a 50% false-negative rate. The MEBDT identified aspiration in 100% of patients who aspirated more than trace amounts (greater than 10% of the bolus) but did not identify aspiration of trace amounts.
Donzelli, Brady, Wesling, and Craney (2001) conducted 15 consecutive simultaneous MEBDT and video nasal endoscopic examinations. During these studies, they viewed the subglottis through the tracheostomy site via endoscopy. The MEBDT showed a 50% false-negative error rate for the detection of aspiration compared to the endoscopic view. The MEBDT identified aspiration in 67% of patients who aspirated more than trace amounts, but failed to identify aspiration in trace amounts. These authors concluded that the MEBDT should "be viewed only as a screening tool for the presence of gross amounts of aspiration in patients with a tracheostomy."