A comparison between derivation optimization and Cz′–FPz for posterior tibial P37 somatosensory evoked potential intraoperative monitoring

To compare P37 derivation optimization to Cz′–FPz. After induction in 120 patients, monitoring derivations optimized by mapping FPz, Cz, Cz′, Pz, C4′, C2′, C1′ and C3′-mastoid to determine the P37 and N37 maximums for use as inputs 1 and 2 were compared to Cz′–FPz. This was repeated later in 35 surgeries. Eleven optimal derivations occurred and usually differed between sides. Input 1 was Cz′, Pz, Cz, iCi′, or Ci′ and input 2 was Cc′, FPz, Ci′ or Pz. Even the most frequent Cz′–Cc′ derivation was optimal for both sides of an individual in only 17% and this was true for Cz′–FPz in only 4%. Optimization produced higher amplitudes than Cz′–FPz ( P