The effects of depth of volatile general anaesthesia, measured by bispectral index (BIS), on post-operative pain.

This study is looking at whether the amount of anaesthesia given during an operation affects how much pain a person experiences afterwards. Researchers will use a brain monitor to measure the depth of anaesthesia during surgery, and then track pain levels in the recovery period. They also want to explore whether certain genes influence how sensitive a person is to pain and how quickly their body processes pain medication. You may be eligible if: - You are between 18 and 65 years old - You are scheduled for planned (non-emergency) surgery for a non-cancer reason - You are in generally good health (ASA score 1 or 2) - You are able to use a simple pain scale and a self-controlled pain relief device after surgery You may NOT be eligible if: - You are having emergency surgery - You have a malignancy (cancer diagnosis) - You have epilepsy, a neuromuscular disease, a psychiatric illness, or significant lung disease - You regularly use opioid pain medications before surgery - You are allergic to morphine or the anaesthetic drugs used - You are pregnant - You have severe asthma or obesity (BMI over 35 or weight over 120 kg) - Your surgery is expected to last more than 3 hours Talk to your doctor about whether this trial might be right for you.