Mechanomyography (MMG) is the gold standard to quantify evoked twitch response during neuromuscular blockade (NMB) in dogs. Limitations of MMG include an elaborate set-up and sufficient immobilization of the limb being assessed. Electromyography (EMG) measures the compound action potential of a muscle when the nerve supplying it is stimulated. The EMG unit is portable, requires less limb immobilization, and has the potential to be used in clinical situations where patient size and position cannot be strictly controlled. Our purpose was to compare MMG and EMG during NMB in anesthetized dogs. Six healthy dogs, 25.3 ± 1.6 kg, were anesthetized with propofol, 6 mg/kg IV, and maintained with isoflurane in oxygen. Normocapnia was maintained with controlled ventilation. Range of means over time for rectal temperature was 36.7 - 37.4 C. Range of means over time for end-tidal isoflurane concentration was 1.3 - 1.6 %. Each dog was studied twice, first for MMG and EMG on opposite rear limbs and second for MMG and EMG on the alternate rear legs. Both methods used supramaximal train-of-four (TOF) stimulation of the superficial peroneal nerve at 20-second intervals. MMG measured evoked twitch response from the paw; EMG measured the integrated compound action potential from the anterior tibialis muscle. Following instrumentation, a 20-minute stabilization period, and recording of baseline twitch response, atracurium, 0.2 mg/kg IV, was administered. First twitch response compared to baseline (T1%) and fourth twitch to first twitch ratio (T4/T1 %) were recorded at 2 minutes, 5 minutes, and then at 5-minute intervals until T1% and T4/T1% returned to baseline values. Data were analyzed for statistical significance using a Student’s paired t-test. Results were considered significant at P < 0.05. After atracurium administration, there was no statistical difference between MMG and EMG for both T1% and T4/T1%. In conclusion, EMG appears to be an acceptable alternative to MMG for assessing NMB in anesthetized dogs.
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