The Gamble of Blue Dye Testing
First I want to start off with what this post isn’t:
-The purpose of this post is not to bash the way many therapists have been practicing for years.
-The purpose of this post is not to convince therapists that they should never use blue dye ever again.
-The purpose of this post IS to objectively evaluate the reliability data behind the Modified Evans Blue Dye Test to best determine what we are actually observing when we do a blue dye tracheostomy swallowing exam.
So what is a Modified Evans Blue Dye Test (MEBDT)? This clinical swallowing test was developed to identify aspiration in patients with tracheostomies with the help of suctioning by the respiratory therapist. In the original Evans Blue Dye Test, the clinician would place a few drops of dye on a patient’s tongue and the respiratory therapist would suction the patient every few hours and report back as to whether blue dye was present in suctioned secretions. Speech pathologists modified this to add blue dye to food and drinks to further evaluate aspiration with trials of certain consistencies. The Modified Evans Blue Dye Test was formally introduced in Dysphagia Journal in 1995.
It all makes sense. If the patient is aspirating secretions or food consistencies, the blue dye will go into the trachea/lungs and the respiratory therapist will suction it out. If the respiratory therapist doesn’t suction any blue out, then the patient must not be aspirating. Bingo bango, our job is done!
Unfortunately life just isn’t that simple. Less than 5 years after the introduction of the MEBDT, clinicians performing instrumental swallow exams began reporting on patients who had no blue dye return on MEBDT but who were found to be aspirating on instrumental exam. Bummer. Big bummer.
As SLPs we must critically look at any test we perform to ensure that the test is
Reliable enough to produce the same results under consistent conditions
Sensitive enough to identify those who do have the searched for criteria
Specific enough that those who do not have the searched for criteria are not identified
There have a been many different studies looking at reliability, sensitivity and specificity of the MEBDT. Because we are depending on pretty specific circumstances to obtain our outcome – the patient must aspirate, the respiratory therapist must suction enough and in the right spots to pull out the aspirated material, the dye must be dark enough to perceive in the secretions – many have claimed that the MEBDT may not be sensitive enough to identify everyone who aspirates. The biggest concern with MEBDT is a false negative – this would occur if the MEBDT does not show aspiration but the patient actually is aspirating. This study, from Dysphagia Journal waaaay back in 1999, was one of the first to identify the high likelihood of false negative results with MEBDTs.
Brady SL, Hildner CD, Hutchins BF. 1999. Simultaneous video- fluoroscopic swallow study and modified Evans blue dye procedure: an evaluation of blue dye visualization in cases of known aspiration. Dysphagia 14:146–149. Full Text Here
This investigation analyzed 20 simultaneous MBS exams and MEBDTs to determine if the MEBDT correctly identified each aspiration event that occurred. Before the MBS, the investigators dyed thin, nectar and puree consistency barium blue. During the MBS, if aspiration was observed, the respiratory therapist would suction the patient to identify if blue dye was present in their tracheal secretions. The respiratory therapist also suctioned the patients at the termination of the study. Two SLPs reviewed the MBS exams and identified the quantity of aspiration for the exam as either trace or greater than trace. The investigators then compared the results of the MBS exams and the MEBDTs.
Aspiration occurred in 8/20 of the exams, however, suctioning after the aspiration event only identified aspiration in 4/20 exams. Of those exams that were determined to have greater than trace amounts of aspiration, tracheal suctioning identified the aspiration in 100% of patients. Of those exams which showed only trace amounts of aspiration, tracheal suctioning identified the aspiration in 0% of patients. There were no charts or graphs in this study, so I made my own because I am a visual learner:
In this study, the Modified Evans Blue Dye Test was shown to have a false-negative error rate of 50% in cases of observed aspiration on MBS. Donzelli and colleagues replicated this study in 2001using FEES and found the exact same 50% false-negative error rate and only a 67% identification of aspiration in patients with large amounts of aspiration.
These are grim statistics. Ultimately what we can take from this information is that the MEBDT is not sensitive enough to identify all aspiration events, especially when only trace amounts of aspiration occur. This means that for every two MEBDTs performed that do not identify aspiration, one of the patients likely could be aspirating. That is a gamble – a huge gamble – and a gamble that I don’t want to take with my patients.
So what can a MEBDT be used for? It can be used as a screening device to positively identify aspiration. That’s it. If a test is performed and aspiration is identified, you can be pretty darn sure that aspiration is occurring.
Failure to consistently identify aspiration isn’t the only negative to the MEBDT. Last time I checked, aspiration wasn’t the only indicator of dysphagia. The MEBDT doesn’t identify penetration or significant residue- both of which constitute dysphagia. It doesn’t identify the quantity and consistencies of penetration, aspiration or residue nor does it identify the actual physiological impairments that are causing the dysphagia or give us indications on how to treat them.
So how do we identify if a patient with a tracheostomy has dysphagia? I think you know my answer…
GET AN INSTRUMENTAL SWALLOWING EVALUATION!!
This is the only way to objectively identify aspiration in a patient with a trach or without one. Both MBS and FEES have generally good reliability, sensitivity and specificity. They both will identify on which consistencies penetration, aspiration or residue occur, and they both will provide insight on the physiological deficits causing the dysphagia.
Don’t gamble with aspiration. Get an instrumental exam and know for sure.
Donzelli J, Brady S, Wesling M, Craney M. Simultaneous modified Evans blue dye procedure and video nasal endoscopic evaluation of the swallow. 2001. Laryngoscope;111:1746 –1750.
Peruzzi WT, Logemann JA, Currie D, Moen SG. 2001. Assessment of aspiration in patients with tracheostomies: comparison of the bedside colored dye assessment with videofluoroscopic examination. Respir Care 46:243–247.
Thompson-Henry, S., & Braddock, B. 1995. The modified Evan’s blue dye procedure fails to detect aspiration in tracheostomized patient: Five case reports. Dysphagia,10, 172–174.
O’Neil-Pirozzi TM, Lisieeki DJ, Monsek J, Connors JJ, Milliner MP. 2003. Simultaneous modified barium swallow and blue dye tests: a determination of the accuracy of blue dye test aspiration findings. Dysphagia;18:32-8.
Kelley Babcock, MS, CCC-SLP, BCS-S, is a voice and swallowing therapist from Nashville, Tennessee. She works as a clinician and educator for SA Swallowing Services which provides basic, advanced and custom FEES courses for SLPs across the country. For more information on FEES and dysphagia, check out sasspllc.com or connect with Kelley on Twitter or LinkedIn.
Photo credit flikr for creative commons