Frontal Electroencephalogram Phase–Amplitude Coupling Reflects Nociception and the Analgesic Effect of Transversus Abdominis Plane Block in Laparoscopic Surgery

BACKGROUND: Maintaining an optimal nociception-analgesia balance is essential in clinical anesthesia. Traditional monitoring relies on brainstem reflexes, whereas electroencephalography (EEG) indices, such as alpha power attenuation and phase-amplitude coupling (PAC), show promise as markers of nociceptive processing. However, their physiologic mechanisms and relationship to postoperative pain remain unclear. METHODS: This prospective cohort study included 58 patients undergoing laparoscopic surgery under either conventional general anesthesia or general anesthesia combined with a transversus abdominis plane block. Intraoperative EEG recordings were analyzed for frequency band power and PAC across surgical stages (incision, insufflation, and postopioid administration). Generalized estimating equations with Bonferroni post hoc correction were used to assess EEG patterns and their association with postoperative pain. RESULTS: The alpha band power and the delta-alpha PAC modulation index decreased during surgical incision and insufflation, and subsequently recovered after opioid administration. While alpha power changes did not differentiate the effects of the nerve block, delta-alpha PAC changes significantly reflected nerve block effectiveness during incision (coefficient, 0.81; 95% CI, 0.11 to 1.51; P = 0.02). However, no association was observed between perioperative EEG patterns and postoperative pain scores. CONCLUSIONS: Laparoscopic surgical stimulation reduces EEG alpha power and delta-alpha PAC. Delta-alpha PAC demonstrated greater sensitivity than alpha power measures in distinguishing nociceptive input and reflecting the nerve block effects, suggesting its potential as an intraoperative nociception-analgesia marker. However, perioperative EEG patterns showed limited value in predicting postoperative pain, suggesting that postoperative pain perception is shaped by more complex mechanisms requiring further investigation.