Relationship between stimulating current and accelographic train-of-four response at the great toe

We investigated the accelographic train-of-four response evaluated at the great toe at varying stimulating currents. Fifteen adult patients undergoing elective general anaesthesia were studied. The mean current at which a supramaximal T1 value could be elicited was > 49 (9) mA [mean (SD)]. Ratios of accelographic T1 values at 50, 40, 30, 20 and 10 mA to accelographic T1 value at 60 mA were 0.90 (0. 18), 0.58 (0.37), 0.38 (0.37), 0.19 (0.26) and 0.00 (0.00), respectively [mean (SD), p < 0.05 for 50 mA vs. 30, 20 and 10 mA, p < 0.05 for 40 mA vs. 20 and 10 mA, and p < 0.05 for 30 vs. 10 mA]. Threshold currents for train-of-four (the lowest currents at which any train-of-four response could be elicited) before and after induction of anaesthesia were 30 (10) and 31 (10) mA, respectively. The train-of-four ratio (T4/T1) measured at varying currents did not differ significantly. However, in the patients in whom threshold currents for train-of-four were 40, 30 and 20 mA, the train-of-four ratio recorded at the threshold current was significantly less than at 50 mA. We conclude that at the great toe, the mean current at which a supramaximal response to train-of-four can be yielded is as high as > 49 mA. The mean threshold currents for TOF before and after induction of anaesthesia were 30 and 31 mA, respectively. Train-of-four ratio measured at the threshold current is less than that at 50 mA.