Axillary somatosensory evoked potential response: an alternate peripheral recording site

When recording upper-extremity somatosensory evoked potentials (SSEP), the standard peripheral recording site is Erb's point located near the clavicle. During some surgical procedures, the Erb's point recording site is often either part of the surgical field or is distorted by patient size or trauma. In the present study, we evaluated the usefulness of the axillary fossa as an alternate peripheral recording site. Using standard recording techniques, we studied 29 patients (54 limbs); studied: 19 as outpatients and 10 during surgery. Evoked responses subsequent to median nerve stimulation were recorded with the following montage: Axi-Axc, Epi-Epc, C5S-Cz or Fz, and Cpi-Cpc. The potential recorded at the axillary site, termed axillary response (Ax), produced a waveform similar in morphology to that of the Erb's point response and displayed a generally well defined, prominent negative peak occurring approximately 2.5 ms earlier than that of Erb's point. We conclude that the axillary space in the lateral part of the upper chest and medial side of the arm is an appropriate alternate site for recording peripheral potentials after stimulation of the median nerve. The Ax recording site is useful during surgery when the Erb's point site is unavailable. Further study of this recording site is necessary to determine its diagnostic usefulness.