The role of a single dose of intraoperative clonidine on postoperative opioid requirements, pain intensity and opioid-related side effects in patients undergoing surgical treatment for endometriosis remains scarcely explored. A prospective double-blind, randomised controlled trial investigating the effect of a single-dose of intraoperative clonidine in patients undergoing surgical treatment for endometriosis is therefore conducted.

Background with aim: Acute postoperative pain is a major and common concern for the large number of patients who undergo surgery each year. Despite advances in pain management strategies, many patients continue to suffer from moderate-to-severe pain during the early postoperative period. This is concerning as unrelieved pain can result in decreased patient satisfaction, increased morbidity, prolonged hospital length-of-stay and increased risk of persistent pain. Effective treatment of acute postoperative pain should therefore be prioritized. Opioid analgesics remain the mainstay treatment for postoperative pain. The potential benefits of opioid therapy for acute pain are short-term pain control. However, there are several potential harms associated with opioid use which may outweigh the benefits including sedation, nausea, vomiting, constipation and risk of long-term use. In this respect, a single dose of clonidine could provide stable analgesia and potentially reduce the need for shorter-acting opioids. Therefore, the investigators decided to carry out the present study with the aim to examine the analgesic efficacy and safety of intraoperatively administered intravenous clonidine in patients undergoing surgical treatment for endometriosis on postoperative opioid consumption, pain intensity and opioid-related side effects.

Method: 120 patients undergoing surgical treatment for endometriosis will be included in this prospective, randomized, double-blind, controlled trial with two arms: an intervention arm (clonidine 150 microgram) and a control arm (isotonic saline). The study will be GCP-monitored, and is approved by the Danish Medicines Agency (2022064017) and the National Committee on Health Research Ethics (2209269).

Hypothesis: The investigators hypothesize that a single dose of intraoperatively administered intravenous clonidine will be effective in reducing postoperative opioid requirements, pain intensity and opioid-related side effects.

Inclusion Criteria:

• Patients scheduled for surgical laparoscopic treatment of endometriosis at Aarhus University Hospital

Exclusion Criteria:

• Age < 18 years
• American Society of Anesthesiologists (ASA) physical status IV or V
• Allergy to clonidine
• Inability to provide informed consent
• Known severe renal insufficiency
• Known severe bradyarrhythmia
• Pregnancy, lactation:
• Daily opioid consumption the last 7 days before surgery
• Pain intensity >5 on more than half of the days during the last month

The data will be shared upon reasonable request by other researchers

Randomization and study medication will be handled by the hospital pharmacy. All research team members, caregiving clinicians and enrolled patients will be blinded to the study allocation arms and the randomisation list will be concealed until all statistical analyses are made.