Adequate analgesia in the perioperative setting is one of the most important pillars of anesthesiology. It is generally understood that poorly managed acute postoperative pain correlates with increased morbidity, prolonged recovery periods, extended opioid utilization, and serves as a predictor for chronic pain onset . On the other hand, the overuse of opioid-based analgesics during surgery may evoke respiratory depression, constipation, nausea, sedation, and opioid-induced hyperalgesia . Thus far, the lack of an objective intraoperative pain monitor has constrained anesthesia practitioners to rely on the interpretation of physiological cues such as tachycardia, hypertonia, and lacrimation as surrogate markers of pain (3). Variability in the educational background and clinical experience among providers may predispose to either excessive or inadequate administration of analgesics, consequently allowing for unfavorable postoperative outcomes. However, recent advancements have introduced novel devices for nociception measurement. Thus, a quantifiable assessment of nociception has become feasible. The most widely approved device is the Nociception Level (NOL®) index developed by Medasense in Israel. This index operates by discerning various sympathetic responses of the body to nociceptive stimuli and has been thoroughly tested on opioid-based analgesic regimens. The NOL® index uses a multiparametric approach including a random forest algorithm to measure the balance between sympathetic and parasympathetic system activity. Recently, a strong correlation has been reported between the response of the NOL® index and analgesia during surgery.

Patients being scheduled for endometriosis surgery do have a significant history of chronic pain thus being more prone to postoperative complications and therefore will benefit the most from a tailored analgesic regimen.

Adequate analgesia in the perioperative setting is one of the most important pillars of anaesthesiology. It is generally understood that poorly managed acute postoperative pain correlates with increased morbidity, prolonged recovery periods, extended opioid utilization, and serves as a predictor for chronic pain onset. On the other hand, the overuse of opioid-based analgesics during surgery may evoke respiratory depression, constipation, nausea, sedation, and opioid-induced hyperalgesia. Thus far, the lack of an objective intraoperative pain monitor has constrained anaesthesia practitioners to rely on the interpretation of physiological cues such as tachycardia, hypertonia, and lacrimation as surrogate markers of pain. Variability in the educational background and clinical experience among providers may predispose to either excessive or inadequate administration of analgesics, consequently allowing for unfavorable postoperative outcomes. However, recent advancements have introduced novel devices for nociception measurement. Thus, a quantifiable assessment of nociception has become feasible. The most widely approved device is the Nociception Level (NOL®) index developed by Medasense in Israel. This index operates by discerning various sympathetic responses of the body to nociceptive stimuli and has been thoroughly tested on opioid-based analgesic regimens. The NOL® index uses a multiparametric approach including a random forest algorithm to measure the balance between sympathetic and parasympathetic system activity. Recently, a strong correlation has been reported between the response of the NOL® index and analgesia during surgery.

Patients being scheduled for endometriosis surgery do have a significant history of chronic pain thus being more prone to postoperative complications and therefore will benefit the most from a tailored analgesic regimen. Patients' existing analgesic regimen, typically comprising Paracetamol, NSAIDs, and Metamizol, will be carefully documented during preoperative anesthetic consultations and taken into account in the study protocols.

Preoperatively, patients will be staged by their gynecologists using the ENZIAN classification. The ENZIAN classification is a diagnostic system for endometriosis that covers various localizations and forms of the disease. It enables a standardized assessment for both non-invasive and invasive diagnostic procedures. The classification considers specific compartments and uses standardized coding for the severity and location of lesions. The classification is performed preoperatively using ultrasound diagnostics as well as intraoperatively and is annotated with the lower-case letters: (s)= Surgical, (u)= Ultrasound (Keckstein J, 2021). Thereby, a comprehensive picture of the disease is obtained. Deeply infiltrating endometriosis requires a more invasive procedure, a longer operating time and a higher consumption of analgesics.

Inclusion Criteria:

• Age ≥ 18 years
• Premenopausal females
• Undergoes any type of laparoscopic surgery for suspected endometriosis or adenomyosis (diagnostic/therapeutic and/or hysterectomy)

Exclusion Criteria:

• Age < 18 years
• Patients with contraindications for opioids and/or ketamine/clonidine (standard medications)
• Pregnant or breastfeeding women
• Lack of ability to follow the study procedure, e.g. due to severe language barriers, mental disorders, dementia
• Patients requiring preoperative or postoperative treatment in the intensive care unit
• Patients with conditions precluding the use of the NOL® sensor, such as neuromuscular deficits affecting hand function
• Regular consumption of opioids (Mankoski Score ≥6)