Bipolar and quadripolar transcranial electrical stimulation: a comparative characteristic

One  of  the  key  methods  for  assessing  the  state  of  the  pyramidal  system  is  transcranial  electrical stimulation (TES). The voltage level used in TES (from 200 V to 800 V) determines the inevitable inconvenience during operation. An alternative method that can significantly reduce the intensity of stimulation is quadripolar transcranial electrical stimulation (quad-TES).

THE   PURPOSE   OF  THE   STUDY:  to  give  a  comparative  description  of  bipolar  and  quadripolar  TES  in  the intraoperative assessment of the state of the corticospinal tract during the removal of neoplasms in the lower spinal cord.

MATERIALS AND  METHOD S .  The study included 15 patients with intradural extramedullary tumors of the spinal cord at the level of Th11-S  2 vertebrae. The minimum intensity of stimulation was assessed to achieve a stable motor response from target muscles during TES (bipolar TES and four variants of quadro-TES). The power of the  m-wave was compared for different montages. R ESULTS .  The average age of the patients was 59.3 ± 10.0 years. In bipolar TES (C 3-C  4), the stimulus intensity was 99 ± 41.6, V.  With quadro-TES: C 3/C 1-C  4/C 2–64.0 ± 30, V (p  < 0.001);  m3/ m1- m2/ m4–59.3 ± 25.6, V (p  < 0.001); C  3/ m1-C  4/m2–52.7 ± 20.2, V (p  < 0.001);  m3/C 1- m4/C 2–52.0 ± 22.2, V (p  < 0.001). With bipolar TES, the highest power of the m-wave was in 1 patient out of 15 (6.67 %). With quadro-TES, 14 out of 15 patients had the highest m-wave power (93.3  %).

CONCLUSION.  To achieve a stable motor response from target muscles using the quadro-TES technique we need a lower stimulation intensity than with bipolar TES. When using the quadro-TES method, the optimal ratio of the intensity of the stimulus and the power of the  m-wave is provided with diagonal mounting m3/C 1- m4/C 2.

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