Median somatosensory evoked potential intraoperative monitoring: recommendations based on signal-to-noise ratio analysis.
OBJECTIVE
To form median somatosensory evoked potential (SEP) monitoring recommendations based on signal-to-noise ratio (SNR).


METHODS
Two 1024-sweep right median SEP trials were recorded in 35 patients undergoing spine surgery. The SNR (signal power/noise power) and sweeps to reproducibility (<30% and <20% signal variation) were compared between the following derivations: cubital fossa (CF), Erb's point (EPi-EPc, EPi-M, EPi-Fz), cervical (C5S-EPc, C5S-AC, C5S-M, C5S-Fz), subcortical (CPi-EPc, CPi-M), and cortical (CPc-EPc, CPc-M, CPc-FPz, CPc-Fz, CPc-CPi, CPc-CPz), where M was the mastoid.


RESULTS
Higher SNR produced markedly faster reproducibility. The CF derivation had very high SNR and single-sweep reproducibility. Of cortical derivations, CPc-CPz had highest mean SNR and fastest overall reproducibility (median 50 and 120 sweeps to <30% and <20% signal variation); occasionally CPc-Fz or CPc-CPi was better. Of Erb's point and cervical derivations, EPi-M and C5S-M had highest mean SNR and fastest reproducibility. Subcortical derivations had very low mean SNR and slow or non-reproducibility. High voltage EEG degraded cortical and subcortical derivation SNR and reproducibility in young children.


CONCLUSIONS
The highest SNR derivations should be used to speed surgical feedback; slower low-SNR derivations should be omitted. Consequently, the CF is the best technical control and CPc-CPz should be the standard cortical derivation, with CPc-Fz and CPc-CPi as alternates. EPi-M and C5S-M are the best Erb's point and cervical derivations, but are optional. Subcortical derivations should be omitted. A presence/absence criterion or SEP omission may be indicated for some young children.


CONCLUSIONS
The results should influence future guidelines.
MacDonald
D B
DB
Section of Neurophysiology, Department of Neurosciences, King Faisal Specialist Hospital & Research Center, MBC 76, P.O. Box 3354, Riyadh 11211, Saudi Arabia. dbmacdon@yahoo.com
Al-Zayed
Z
Z
Stigsby
B
B
Al-Homoud
I
I
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004558:Electric Stimulation / Q000379:methods; D004569:Electroencephalography / Q000379:methods; D004576:Electromyography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006287:Health Planning Guidelines; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results; D013057:Spectrum Analysis; D013122:Spinal Diseases / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D055815:Young Adult