Comparative Assessment of Variation in Motor Evoked Potential Recordings in Upper versus Lower Limbs under Propofol-Based Anesthesia

Keywords

anesthesia - propofol - MEP

Introduction: Different anesthetic agents including propofol exhibit variable motor evoked potential (MEP) recordings in upper and lower limbs. Hence, we designed this study primarily to compare effects of propofol on amplitude and latencies in upper versus lower limbs and secondarily to compare requirement of current and stimulating pulse needed to elicit same.

Methodology/Description: After ethics committee approval and informed consent, 25 ASA I/II patients, 18 to 65 years of either gender, undergoing elective neurosurgery were included in a 6-month study. Sample size was calculated using previous studies and power size calculation, 80% statistical power, type-II error = 0.20, Alpha error = 0.05. We performed transcranial electrical stimulation of motor cortex using 200 to 400 V current with 4 to 6 stimulating pulses. MEP responses recorded in 50 upper and lower limbs at abductor pollicis brevis and tibialis anterior, respectively. Baseline MEPs were recorded after standardized induction of anesthesia, before atracurium and repeated at BIS 40 to 60 under propofol anesthesia. We used paired t-test for statistical analysis using SPSS software version 11.5.

Results: Mean age 43.24 years, ASAI/II 10:15 and M:F 13:12. There was a reduction in mean amplitude and increase in mean latency under propofol anesthesia as compared with baseline. These changes were statistically significant in lower limbs (p < 0.05). Overall success rate of MEP recordings was higher in upper limbs. The current and stimulating pulse needed to elicit responses was also higher in lower limbs. Limitations: single institutional study, smaller sample size.

Conclusion: Thus, propofol-based anesthesia appears to suppress MEP recordings in lower limbs as compared with upper limbs.

• References

• 1 Bithal PK. Anaesthetic considerations for evoked potentials monitoring.. J Neuroanaesth Crit Care 2014; 1: 2-12
• 2 Nathan N, Tabaraud F, Lacroix F. et al. Influence of propofol concentrations on multipulse transcranial motor evoked potentials.. Br J Anaesth 2003; 91 (04) 493-497