Related Experiment Video
Updated: Jul 20, 2026
An Experimental Paradigm for the Prediction of Post-Operative Pain (PPOP)
Published on: January 28, 2010
A comparison between derivation optimization and Cz'-FPz for posterior tibial P37 somatosensory evoked potential
D B MacDonald1, B Stigsby, Z Al Zayed
1Section of Neurophysiology, Department of Neurosciences, King Faisal Specialist Hospital and Research Center MBC 76, P.O. Box 3354, Riyadh 11211, Saudi Arabia. dmacdonald@kfshrc.edu.sa
Objective:
To compare P37 derivation optimization to Cz'-FPz.
Methods:
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.
Results:
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<0.001). The ratio was [squareroot of 2] : 1 in 61% of patients and > or =2:1 in 28%, approximately halving or quartering averaging times. Optimization assessed decussation, disclosing non-decussation in one patient while Cz'-FPz did not. Alterations of P37 topography that reduced initially optimal derivation amplitude and made a different derivation optimal were demonstrated by repeat optimization in 13 of 35 patients, preventing misinterpretation in one. While also affected, Cz'-FPz neither detected nor adjusted for potentially misleading topographic changes.
Conclusions:
Higher amplitudes, decussation assessment and topographic adjustment make P37 derivation optimization superior to Cz'-FPz for monitoring this highly variable potential.
