Evaluation of motor blockade by isometric force measurement and electromyographic recording during epidural anaesthesia--a methodological study.

Methods for assessing motor blockade by means of isometric force measurements and surface electromyographic (EMG) recordings in the lower extremities and abdominal wall were evaluated in 30 volunteers. The coefficients of variation were 10% for force measurements and 14% and 20% for average rectified EMG (RIEMG) recordings over the quadriceps muscle and abdominal muscles, respectively, and 8% overall for TURNS (the number of changes in the sign of the direction of the EMG signal). Seven of the 30 volunteers received epidural anaesthesia with 20 ml of mepivacaine 2% with adrenaline. The mean maximal cephalad analgesic level was T9. At that abdominal segment, RIEMG showed a reduction of 50% and TURNS of 20%. Isometric force and RIEMG recorded simultaneously in the quadriceps muscles during epidural anaesthesia displayed a linear relationship with a correlation coefficient of 0.91. TURNS was insensitive to force variations above 60% of maximum voluntary contraction. During the regression phase, 90% of both the initial force and RIEMG value was noted 180 min after the epidural injection. It is concluded that recording of RIEMG is a good method for quantitative assessment of motor blockade during epidural anaesthesia.