FEES is a procedure used to evaluate patients with dysphagia. It is done throughout the US and in all countries that have established programs to evaluate and treat patients with dysphagia. It is also becoming the most common instrumental procedure in developing countries that are forming dysphagia teams and learning more about best clinical practices. FEES has an advantage over fluoroscopy in these countries, as the equipment is less costly and it can be used in a variety of settings, even taken to bedside.
For those who are not familiar with the procedure, using a flexible laryngoscope and camera, the base of tongue, throat and larynx can be visualized. When the person eats and drinks, the examiner is able to assess whether the swallow is normal or impaired. If impaired, the nature of the problem can be determined. Using dietary, behavioral, and postural interventions, the examiner then attempts to remediate the problem and determine how the patient can eat most safely and effectively.
Speech Language Pathologists are the main practitioners who evaluate oropharyngeal swallowing with this tool but some physicians have also developed expertise in using FEES in their practice. In some countries, such as Japan, physicians are the primary endoscopists and the speech pathologist may assist in the exam. In order for any practitioner to be proficient in this procedure, training is needed. This takes the form of skill training (how to handle a laryngoscope) and knowledge-based training (how to identify abnormal findings and know what interventions might be effective). To read more about FEES, I recommend the following articles:
Langmore SE. History of Fiberoptic Endoscopic Evaluation of Swallowing for Evaluation and Management of Pharyngeal Dysphagia: Changes over the Years. Dysphagia. 2017 Feb;32(1):27-38.
I also have a textbook about FEES:
Langmore SE. Endoscopic Evaluation and Treatment of Swallowing Disorders… Hardcover: 263 pages; Publisher: Thieme; 2 edition (January 15, 2001)