The Nociception Level (NOL) Index is a multiparametric, non-invasive monitor that objectively assesses nociception by integrating several autonomic physiological signals. Although the NOL Index has been extensively validated during general anesthesia, its performance in awake patients undergoing regional anesthesia remains poorly understood. During cesarean delivery (CD) under spinal anesthesia, autonomic responses may be influenced not only by nociceptive stimulation but also by anxiety, uterine contractions, hemodynamic changes, uterotonic medications, and other non-nociceptive factors. Understanding the relative contribution of these factors is essential before the NOL Index can be reliably applied in awake surgical patients.

This prospective observational study aims to characterize the behavior of the NOL Index throughout elective CD performed under spinal anesthesia and to evaluate its relationship with subjective pain intensity, anxiety, uterine activity, perioperative autonomic responses, and routine physiological variables.

Approximately 100 women undergoing elective CD under spinal anesthesia will be enrolled at Carmel Medical Center. Continuous NOL monitoring using the PMD-200 system will be performed from before spinal anesthesia until the early postoperative period. Subjective pain (Visual Analog Scale), anxiety (Visual Analog Scale for Anxiety), uterine activity, hemodynamic variables, perioperative medications, and predefined surgical events will be prospectively recorded and synchronized with continuous NOL measurements. Potential confounding factors, including vasopressor administration, uterotonic drugs, nausea, shivering, patient movement, and supplemental analgesia, will also be documented.

This study will provide one of the first comprehensive evaluations of continuous NOL monitoring during CD under spinal anesthesia. The results are expected to improve the understanding of objective nociception monitoring in awake patients, clarify the influence of non-nociceptive autonomic activation on the NOL Index, and help define the clinical role and limitations of NOL monitoring during regional anesthesia, and may contribute to the future development of objective pain assessment strategies in obstetric anesthesia and other clinical settings involving awake patients.