Brainstem Auditory Evoked Potentials (BAEP), also known by their English acronyms BERA (Brainstem Evoked Response Audiometry) or BAEP (Brainstem Auditory Evoked Potential), are one of the auditory diagnostic tests we use.
An auditory evoked potential is understood as the neuroelectric response of the auditory system (from the auditory nerve to the inferior colliculus, located in the brainstem) to a sound stimulus. The study of these evoked potentials is of great clinical interest because, by comparing them with responses considered normal, it allows the diagnosis of various pathologies or dysfunctions of the auditory system and neural pathways.
Auditory Evoked Potentials are not exactly a hearing test, but they can be used to identify and quantify hearing loss in children and adults who cannot or do not wish to participate in a subjective test such as audiometry.
At our ENT clinic in Madrid, we perform the necessary tests to achieve an accurate diagnosis. This test does not require direct cooperation from the patient, but it is essential for them to remain calm and relaxed. The examination involves no risk.
To deliver the stimulus, we use insert earphones with disposable tips adapted to the patient’s age and the size of their ear canal. They are comfortable and minimize artifacts and ambient noise. The stimulus used is the so-called click, a very brief sound with a broad frequency spectrum. In this way, we explore the frequency range from 2000 to 4000 Hz (the frequencies that make up most speech sounds).
To record the potentials produced in response to this stimulus, we use disposable self-adhesive electrodes of a size appropriate for the patient’s age.
The potentials obtained consist of well-defined characteristic waves. Those recorded during the first 10 ms after the stimulus are known as short-latency auditory evoked potentials or brainstem auditory evoked potentials (BAEP). In practice, the first five waves (I, II, III, IV, and V) are usually considered; they are consistent in all normal subjects and reflect the function of the auditory nerve and the auditory pathway along the brainstem. The waves are defined by their respective latencies or time of appearance; interwave latencies are also important, especially I–III and I–V.
Main clinical applications of BAEP:
Determination of auditory threshold
Using stimuli of increasing or decreasing intensity, the auditory threshold can be determined by evaluating wave V, which is the wave that persists at lower stimulus intensities. The threshold determined in this way is 10–20 dB higher than the tonal threshold.
It should be noted that BAEP explore frequencies from 2000 to 4000 Hz, not the lower ones, so the absence of a BAEP response is not sufficient to diagnose cochlear deafness (total deafness).
Topographic diagnosis of hearing loss
Each wave corresponds to a specific part of the auditory pathway; therefore, the presence or absence of waves, as well as latency analysis, provides important information about the location of the cause of each hearing loss.
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