For patients with moderate to severe endometriosis undergoing surgical intervention will the use of methadone and bupivacaine compared to fentanyl alone improve the development of post-operative pain and quality of life

This is a double blinded prospective randomised trial to investigate the effect of methadone and bupivacaine on the development of chronic pelvic pain in women undergoing surgical management of endometriosis. Chronic pelvic pain is common in women with endometriosis, and can develop despite surgical treatment of the disease. Endometriosis causes pain in a variety of mechanisms including direct compression/infiltration of nerves by the lesions, inflammation, and damage to pelvic nerves during surgery and may lead to changes in the central nervous system which propagate chronic pain. The objective of this trial is to prove that active management of intra-operative analgesia with intravenous methadone and intraperitoneal bupivacaine, for women with long-standing pain from moderate to severe endometriosis leads to long-term benefit in terms of pain experience and quality of life. Patients will be recruited from the endoscopy clinic at King Edward Memorial Hospital. They will be eligible if they have an American Fertility Society Score of 2 or 3 on previous laparoscopy and are planned for laparoscopic treatment on endometriosis. At recruitment patients will undergo a visual analogue scale (VAS) assessment for pain and will complete a quality of life (QOL) assessment. Patients will be randomised to either the standard analgesia group (IV fentanyl 5mcg/kg + placebo (200ml saline) intraperitoneal) or the intervention group (IV methadone 0.2mg/kg and 200mL levobupivocaine 0.625% intraperitoneal). Repeat pain scores will be recorded on day 1, and repeat pain scores and QOL scores at 6 weeks, 6 months and 12 months post-operatively.