 The purpose of this study would be to determine changes of screw stimulation thresholds under different range of neuromuscular blockade.Therefore, acceptable neuromuscular blockade threshold determined by TOF test acceptable for obtaining reliable screw stimulation test should be determined. Screw stimulation test may be performed when neuromuscular blockade is absent and compared to repeated screw stimulation test when neuromuscular blockade is present. Different levels of neuromuscular blockade may provide different results on screw stimulation test, so if difference is statistically significant, induced neuromuscular blockade level may be set as threshold value, acceptable for obtaining reliable testing results. 