Evaluation of the Effect of Scalp Nerve Block on Bispectral Index Values During Skull Pinning; Prospective Observational Study

<b><i>Background and Objectives</i>:</b> Scalp nerve block (SNB) is hypothesized to attenuate the physiological response to skull pinning more effectively than local anesthetic (LA) infiltration. This study aimed to compare the two techniques using Bispectral index (BIS) as a primary surrogate measure of cortical arousal. <b><i>Materials and Methods</i>:</b> In this prospective observational study, patients undergoing elective craniotomy received either bilateral SNB (Group S, n = 53) or LA infiltration (Group LA, n = 35) based on anesthesiologist preference. Depth of anesthesia was monitored via BIS. The primary outcome was the change in BIS after skull pin insertion. A ΔBIS > 20% from baseline triggered rescue medication (remifentanil/propofol). Secondary outcomes included hemodynamic parameters and rescue requirements. <b><i>Results</i>:</b> There was a significant main effect of time on BIS values (<i>p</i> < 0.001), indicating that BIS values changed significantly across measurement points. Post-hoc examination of parameter estimates revealed that the Group LA showed significantly greater increases in BIS values compared to the Group S at T1 (<i>p</i> = 0.030) and T3 (<i>p</i> = 0.024). No significant between-group differences in BIS changes were observed at T5, T10, or T15 time points (<i>p</i> > 0.05). Hemodynamic responses (mean arterial pressure and heart rate) were also transiently but significantly higher in Group LA at these time points (<i>p</i> < 0.001). The most clinically notable finding was that significantly more patients in Group LA required rescue medication (<i>p</i> < 0.001), indicating a greater frequency of clinically significant physiological trespass. <b><i>Conclusions</i>:</b> Compared to LA infiltration, SNB was associated with statistically significant reductions in immediate BIS and hemodynamic responses to skull pinning. The key potential clinical implication is the corresponding reduction in the need for rescue anesthetic intervention. These findings support SNB as a technique for enhancing physiological stability, though the direct impact on patient-centered outcomes requires further study. BIS may serve as a useful adjunctive indicator of the cortical response to noxious stimuli.