关键词: 功率谱密度, 排序熵, 右美托咪定, 超前镇痛, 大脑时空特征

Abstract: Objective Postoperative pain leading to chronic pain and increased mortality poses a serious threat to public health.Preemptive analgesia,which involves administering analgesic drugs before nociceptive stimulation,can effectively reduce the incidence and severity of postoperative pain.Our previous research has demonstrated that dexmedetomidine (DEX) exhibits significant preemptive analgesic effects without adverse reactions such as respiratory depression.However,the spatiotemporal mechanisms underlying DEX's central analgesic action remain unclear.This study aims to combine linear oscillatory energy (PSD) and nonlinear pattern entropy (PE) to construct a multidimensional brain state assessment system to evaluate the spatiotemporal mechanisms of DEX's central analgesic effects. Methods Twenty patients scheduled for total knee arthroplasty under spinal anesthesia were enrolled.DEX preemptive analgesia was divided into three phases to investigate dynamic functional changes in brain-specific regions during different DEX administration stages:Phase 1(Non-dosing phase):Baseline EEG was recorded for 5 minutes after patient admission before DEX administration.Phase 2 (DEX phase):After spinal anesthesia,DEX was infused continuously at 1.5 μg/kg/h for 30 minutes.Phase 3 (Cease phase):Following DEX cessation,EEG was monitored for an additional hour.Power spectral density (PSD) and permutation entropy (PE) characteristics of EEG signals were compared across the three phases. Results PSD analysis revealed that DEX specifically modulates pain-related brain regions (ACC,PFC).Delta-band (0~4 Hz) power in ACC and PFC progressively increased across Non-dosing,DEX,and Cease phases (more pronounced in PFC),with significantly higher PSD in DEX and Cease phases (P<0.005),possibly due to DEX accumulation.Topographic maps showed a fronto-occipital gradient activation pattern,suggesting α2 receptor-mediated slow-wave synchronization in the prefrontal cortex.PE analysis demonstrated a concentration-dependent reduction in neural complexity in frontal and temporal lobes (most significant in PFC),while parietal and occipital regions remained stable.This confirms DEX selectively suppresses nonlinear dynamics in higher-order cortices for analgesia,without hemispheric lateralization. Conclusion DEX exerts dual analgesic effects by enhancing delta-band PSD in PFC/ACC while suppressing beta/gamma activity—slow-wave synchronization inhibits pain integration,while pathological high-frequency oscillations are reduced,with PFC being more sensitive due to high α2 receptor density;and selectively decreasing PE in frontal/temporal lobes (affecting pain-emotion processing) while preserving parietal/occipital stability.

Key words: Power spectral density, Permutation entropy, Dexmedetomidine, Preemptive analgesia, Spatiotemporal brain dynamics