Somatosensory evoked potentials in a head trauma model

Background: To evaluate the diagnostic value of somatosensory evoked potentials in an animal head trauma model.

Methods: Somatosensory evoked potentials (SSEP) were recorded in thirteen male Wistar rats following a standardized head trauma induced with the fluid percussion method (=trauma group). Recordings were also taken in four rats without head trauma, who served as a control group.

Recording technique: A biphasic square wave pulse of 0.5 milliseconds duration and 9 milliamperes strengths was applied with a frequency of 2.1 Hertz to the rats tail, in general anesthesia. Recordings were taken from predefined points from the skull and cervical spine with subcutaneous needle electrodes. Recordings were done four days, one week, two weeks and three weeks following head trauma.

Recordings were evaluated for uni- or bilateral presence of the primary cortical potentials; the central conduction time (CCT) was calculated also.

Results: The evaluation of results was possible in all but two recordings. The mean CCT did differ substantially in moderate (5.1milliseconds) and severe (5.7 milliseconds) head trauma and did increase with time after the trauma. CCT was statistically significantly (p=0.03) longer comparing injured versus non-injured side of the cerebral hemispheres and did also increase with time after trauma.

The primary cortical potentials were present bilaterally in all subjects of the control group, whereas a uni -or bilateral loss of the primary cortical potentials was seen in some recordings of the trauma group.

Conclusions: These results indicate that SSEPs correlate well with the severity of the primary head trauma and secondary injury of the brain following head trauma.

Stable recordings are possible to obtain in nearly all subjects with minimal effort. SSEPs supplement the diagnostic armentarium in animal head trauma models. Further studies are needed to evaluate the prognostic value of SSEPs.