Intraoperative Erb's Point-Vertex recording increases brainstem auditory evoked potential wave V amplitude

Recording derivations for intraoperative brainstem auditory evoked potential (BAEP) monitoring consist of a preauricular electrode referenced to Cz'. These derivations are prone to unfavorable signal amplitude. This study analyses whether an alternative noncephalic electrode positioned over ipsilateral Erb's point, thereby generating a new Erb's point-vertex recording derivation, improves BAEP recordings.

Electrodes were placed preauricularly (A1/A2) and at left and right Erb's point (EP1/EP2). They were referenced to Cz'. Click sound stimulation (80-95 dB above hearing level) was applied. At intraoperative baseline conditions, latencies and amplitudes of waves I-V of all derivations were analyzed.

Data of 30 patients (54 ± 15 years/17 females) with normal hearing or mild symmetrical presbycusis undergoing infratentorial surgeries (15 microvascular decompressions) were analyzed. Using EP1-Cz'/EP2-Cz' derivations compared to A1-Cz'/A2-Cz', amplitudes for wave IV (left +65%, p < 0.001; right +43%, p = 0.002) and wave V (left +54%, p < 0.001; right +48%, p < 0.001) were significantly increased. Only in the left (EP1) derivation, there was a tendency towards less reproducibility of wave I, resulting in a decrease of amplitude (-35%, p = 0.005).

Adding an Erb's point electrode derivation resulted in larger amplitudes of waves IV to V. whereas conventional preauricular or mastoid derivation is preferential for wave I assessment.

Increased wave amplitudes facilitate detection of pathologically reduced wave forms (wave V in particular) which represents a significant advancement.