Median nerve evoked responses: stimulation modalities for midlatency cortical components.
OBJECTIVE
Median nerve somatosensory evoked responses (MnSSER) are frequently used clinically and scientifically. However, the stimulus-response interrelationship has not been documented for the midlatency components. Therefore we investigated the spinal and cortical midlatency MnSSER, to document the effect of different stimulus intensities.


METHODS
Spinal and midlatency MnSSER were recorded following percutaneous electrical stimulation of the median nerve at the wrist in 32 neurological healthy females. Three different stimulation intensities were applied: threefold sensory threshold (INT 1), motor plus sensory threshold (INT 2), individual level of tolerance (INT 3).


METHODS
Multivariate analyses of variance (independent variable: stimulation intensity).


RESULTS
Three negative and two positive midlatency components were identified after median nerve stimulation. At INT 1 the early waves N20, P25 and N35 were identified in all of the patients. In contrast, the component P45 was identifiable in 23% of the sample at the lowest intensity level and N55, respectively, in 32%. At INT 2 the spinal and the midlatency cortical amplitudes (except amplitude N35P45) were significantly increased (p < 0.014). At INT 3 the amplitudes of the primary cortical complex did not increase further, but the components > 35 ms became identifiable in the whole sample except in one subject. In contrast, there was no change in the MnSSER latencies. The intensity was comfortable for all subjects.


CONCLUSIONS
For monitoring the midlatency MnSSER components > 35 ms the authors suggest a stimulation intensity close to individual tolerance level for optimal cortical responses.
Rundshagen
I
I
Department of Anaesthesiology, University Hospital Charité, Berlin, Germany. ingrid.rundshagen@charite.de
Schnabel
K
K
Schulte
J
J
D000328:Adult; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008475:Median Nerve / Q000502:physiology*; D008875:Middle Aged; D011930:Reaction Time; D012684:Sensory Thresholds