Double burst monitoring during surgical degrees of neuromuscular blockade: a comparison with train-of-four.

Unlabelled: With double burst stimulation (DBS) it is possible to monitor more profound degrees of neuromuscular blockade than with train-of-four stimulation (TOF). It may therefore be indicated to change between DBS and TOF stimulation during moderate to profound degrees of neuromuscular blockade. Consequently, the aim of the study was to evaluate and compare the twitch height of the first twitch (D1) in DBS and the twitch height of the first twitch (T1) in TOF stimulation during moderate to profound degrees of neuromuscular blockade. Thirty-three patients scheduled for gynaecological laparotomy under general anaesthesia were studied. Mechanomyography was used for neuromuscular monitoring. The T1 twitch height before atracurium was administered served as the control twitch height (T1 control). T1 control was considered as 100%. A constant degree of neuromuscular blockade was maintained at a T1 twitch height at a point between 4 and 11% of T1 control, using a continuous infusion of atracurium. Sequences of 16 DBS and 16 TOF stimulations were given. Two different DBS patterns were examined: DBS3,350/50, (3 stimuli at 50 Hz followed 0.75 sec later by 3 stimuli at 50 Hz), and DBS3,380/40, (3 stimuli at 80 Hz followed 0.75 sec later by 3 stimuli at 40 Hz). The data were analysed by the method described by Bland and Altman. The D1 repeatability coefficients of 1.72% for DBS3,350/50 and 1.20% for DBS3,380/40 were significantly greater than the repeatability coefficient of 1.02% for T1 (p <0.05). The D1 bias of 16.7% for DBS3,350/50 was significantly less than the D1 bias of 25.7% for DBS3,380/40 (p <0.05). The limits of agreement between D1 and T1 were 0.1 to 33.3% for DBS3,350/50 and 2.9 to 48.5% for DBS3,380/40.

In Conclusion: The repeatability of responses to DBS and TOF stimulations during moderate to profound degrees of neuromuscular blockade where only one twitch is consistently present is satisfactory. The responses to DBS were greater than responses to TOF as indicated by a positive bias of DBS. The limits of agreement between DBS and TOF responses were so wide that they cannot be used interchangeably.