The effect of different stages of neuromuscular block on the bispectral index and the bispectral index-XP under remifentanil/propofol anesthesia

Facial electromyographic activity and neuromuscular block could influence bispectral index (BIS) depth of anesthesia monitoring. In this study we examined, in 30 patients undergoing general surgical procedures, the effect of different stages of neuromuscular block on BIS monitoring and compared the conventional A-2000 BIS(TM) (BIS3.4) with the new BIS-XP(TM) (BISXP). At deep surgical BIS3.4 anesthesia BIS3.4 of approximately 40, under a propofol 3.61 mug/mL tarpet-controlled infusion and a 0.15-0.3 mug (.) kg(-1) (.) min(-1) remifentanil infusion, mivacurium 0.15 mg/kg was administered. The onset of neuromuscular block triggered a brief transient odd divergence in response that manifested as a BIS3.4 increase from 43 +/- 4 to 49 +/- 7 (P = 0.007) and a BISXP decline from 41 +/- 3 to 35 +/- 3 (P = 0.003) at 1 +/- 0.2 min. Then, 2.5 +/- 1 min after mivacurium administration, both monitors returned to baseline values of 43 +/- 5 and 40 +/- 4, respectively. After that, BIS3.4 and BISXP did not significantly change during complete neuromuscular block or during various levels of neuromuscular recovery. At all phases, BISXP was significantly lower than BIS3.4. Our study indicated that the BIS3.4/BISXP bias and the wide limits of agreement do not allow values given by. the two monitors to be used interchangeably.