The Nociception Level Index (NOL Index) utilizes various signals to assess the balance of nociception and antinociception during anesthesia. Its correlation with nociceptive stimuli and opioids is known, but its response to isolated heart rate changes remains uncertain. The aim is to investigate how cardiac pacing affects the NOL Index.

The Nociception Level Index (NOL Index) represents an innovative approach to monitoring nociception during general anesthesia, utilizing a combination of signals from photoplethysmography, accelerometry, thermometry, and skin conductance to assess the balance between nociceptive and antinociceptive states. Research has already established how the NOL Index correlates with both nociceptive stimuli and opioid levels, providing valuable insights into patient responses. However, the impact of changes in heart rate, specifically through isolated cardiac pacing, on the NOL Index is not yet clear. The primary goal of this study is to explore and understand how cardiac pacing might influence the readings of the NOL Index, potentially offering a new dimension to managing anesthesia effectively.

Inclusion Criteria:

• Informed consent
• Preoperative and postoperative sinus rhythm (50-90 bpm)
• Norepinephrine support < 100 ng/kg/min

Exclusion Criteria:

• Redo or emergent surgery
• History of any cardiac arrhythmia
• Any cardiocirculatory support other than norepinephrine
• Perioperative treatment with beta-blockers, calcium-channel blockers or ivabradine

Mechanically ventilated postoperative adult patients, admitted to the ICU within 6 hours after elective cardiac surgery.