Correlation of train-of-four and double burst stimulation ratios at varying amperages.

The present study was undertaken to document the relationship between train-of-four (TOF) and double burst stimulation (DBS) at varying degrees of blockade, and to determine whether this relationship remained constant over a range of stimulating currents. The neuromuscular responses to the two most commonly employed modes of DBS stimulation, DBS3,3 and DBS3,2, and the responses to TOF nerve stimulation were recorded and compared at 20, 30, and 50 mA. Twenty-two consenting patients undergoing general anesthesia received a vecuronium infusion to achieve a TOF ratio within the range of 0.1-1.0. Train-of-four, DBS3,3, and DBS3,2 were delivered at 20, 30, and 50 mA in random sequence after a steady state of neuromuscular blockade was achieved. At a stimulating current of 50 mA, there was a significant linear correlation between DBS3,3 and TOF (P less than 0.0001; r = 0.98) over the range of blockade. Similarly, there was a high degree of correlation between DBS3,2 and TOF at 50 mA, as the increased "fade" associated with DBS3,2 was maintained throughout the spectrum of blockade (P less than 0.0001; r = 0.95). The high degrees of correlation were maintained at stimulating currents of 20 and 30 mA (P less than 0.0001). In conclusion, the present study revealed that there is a high degree of linear correlation between DBS and TOF, and that this mechanographic relationship is maintained over a wide range of stimulating currents during varying degrees of clinical neuromuscular blockade.