The Effect of Different Stages of Neuromuscular Block on the Bispectral Index and the Bispectral Index-XP Under Remifentanil/Propofol Anesthesia

Abstract

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™ (BIS_3.4) with the new BIS-XP™ (BIS_XP). At deep surgical anesthesia BIS_3.4 of approximately 40, under a propofol 3.61 μg/mL target-controlled infusion and a 0.15–0.3 μg·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 BIS_3.4 increase from 43 ±4 to 49±7 (P = 0.007) and a BIS_XP 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, BIS_3.4 and BIS_XP did not significantly change during complete neuromuscular block or during various levels of neuromuscular recovery. At all phases, BIS_XP was significantly lower than BIS_3.4. Our study indicated that the BIS_3.4/BIS_XP bias and the wide limits of agreement do not allow values given by the two monitors to be used interchangeably.