Effects Of Midazolam-propofol And Propofol On Median Nerve Cortical Somatosensory Evoked Potentials

Purpose: To investigate the relationship between the median nerve cortical somatosensory evoked potential ( MnSSEP ) and the depth of aneasthesia as guided bybispectral index ( BIS ) measurement, we compared the effects of midazolam- propofoland propofol on MnSSEP and BIS.Methods: Thirty elective patients were randomly into two groups (n=15). One group received prorofol target control injection (group P, TCI) and the other group received a single dose of Midazolam (0.04mg/kg) before propofol TCI (group M). The initial target effective-site concentration (Ce) of propofol was set at 1.0μg/ml, and was adjusted against BIS value. For every 5-10min, the propofol target concentration was increased by 0.5ug/ml or decreased by 0.2ug/ml as necessary. After the start of the TCI, loss of consciousness (LOC) was tested every 15s by verbal stimulation. To maitain BIS value stable for 5-10min, when LOC, BIS 45-55 and less than 40. The median nerve was stimulated, and the waveform of cortical MnSSEP and the hemodynamics parameters were recorded before induction of anaesthesia, LOC and when BIS was maintained at 45-55 and less than 40.Results: The Ce of group P was always higher than group M (P<0.05). The mean arterial blood pressure and BIS decreased after induction of anesthesia, but there was no difference between two groups.when LOC, the latencie of N55 in grope P increased while there was no change in the latencie of N20 and N35 in both two groups. For the Bis 45-55 and less than 40 range,N35 latency prolonged in group P (P<0.05) but not in group M ; N55 latency increased inboth group P and M (P<0.05); and the wave form of N55 was almost disappeared, when BIS less than 40.Both N20-P25 and P25-N35 amplitudes did not change in group P and M at all times. When LOC, N35-P45 amplitudes decrease both group P and M (P<0.05, P<0.01); P45-N55 amplitudes decrease significantly in group P (P<0.01), but not in group M. Forthe BIS 45-55 and less than 40 range, N35-P45,P45-N55 amplitudes decreased significantly (P<0.05, P<0.01), and the wave form of N55 was almost disappeared,when BIS less than 40.Conclusion: Both short- and middle-latency SSEP components can be depressed by anesthetic, and the middle-latency components is more sensitive. Middle- latency SSEP wave form is associated with the depth of aneasthsia.