During anesthesia, neuromuscular blocking agents (NMBA) are routinely used for relaxation of
muscles necessary for the conduction of the surgical procedure. Train-of-four (TOF) test is
based on supramaximal stimulation of peripheral nerve resulting in four twitches: T1 to T4.
The assessment of the NMBA blockade is performed routinely by measurement of the amplitude of
compound muscle action potential (CMAP) and calculation of percentage of CMAP decrement from
T1 to T4.
Train-of-four monitoring is routinely performed during spine surgery by stimulation of the
ulnar nerve. Furthermore motor evoked potentials (MEPs) are routinely used in intraoperative
neuromonitoring to assess the whole motor pathway from the cortical level down to the distal
muscle. During anesthesia MEPs are routinely evoked by transcranial electrical stimulation
with single or short train stimuli. In clinical practice even though full muscle relaxation
of the hand by NMBA can be observed, utilizing the TOF test, remaining muscle tonus can be
observed at the paraspinal musculature during spine surgery.
The goals of this study are to determine (1) if any differences between muscle relaxation of
the hand and foot (measured by TOF test and MEPs) and MEPs of the paraspinal musculature
occur; (2) how much more NMBA must be administered to achieve full muscle relaxation of the
paraspinal musculature in comparison to the hand or foot.