Assessment of motor blockade during epidural anesthesia

Motor blockade during epidural anesthesia was assessed using dynamometry to measure the maximum force of plantar flexion, and the Bromage score method. In a randomized double-blind study, 40 orthopedic patients received one of the following four local anesthetics epidurally: 0.5% bupivacaine-HCl (n = 10), 0.5% bupivacaine-CO2 (n = 10), 1.0% etidocaine (n = 10), and 1.5% etidocaine (n = 10), all without addition of a vasoconstrictor. The decrease of force, measured by dynamometry, followed an e function. This function permits the description of motor blockade development using one single number, its half-life. This finding corresponds to the increase of motor nerve fiber blockade due to diffusion of the local anesthetic into the nerve. Dynamometry was more precise than the Bromage score in describing motor blockade. Both the Bromage score and dynamometry produced roughly comparable results of onset, rate of development, and maximum intensity of motor blockade. These parameters of motor blockade were superior after both etidocaine solutions compared to both bupivacaine solutions. Neither carbonization of bupivacaine nor increased concentration of etidocaine significantly improved motor blockade produced by these drugs. Dynamometry is a time consuming and costly method for accurate quantification of motor blockade during epidural anesthesia; the Bromage score is more practical under clinical considerations and provides useful information.