Orthopaedic surgeries involving the legs can be done under nerve block, where patients will be numb of pain at the operated site but awake during surgery. Sedation can be given to allay anxiety and provide comfort throughout the surgery. Sedation can be given by the anaesthetic doctors by using target-comtrolled infusion pump, or self-administered by patients by means of specialised machines. This study compares two method of administration of sedation, patient-controlled sedation (PCS) versus target-controlled infusion sedation (TCIS) by anaesthetic doctors, in people undergoing orthopaedic surgeries under nerve block.

Central neuraxial block (CNB) is one of the mainstays of anaesthesia methods in various disciplines particularly orthopaedic surgeries. However the state of consciousness can potentially cause patient anxiety thus sedation is often utilized as a mean to improve patient satisfaction and increase patient acceptance of CNB.

Conventionally, the anaesthesiologist administers sedatives for the patients. Propofol is the commonly used drug for sedation due to its favourable pharmacokinetic profile, which results in fast induction, easy control of depth of sedation and rapid recovery. It can be infused by using target-controlled infusion (TCI) devices where the anaesthetists titrates propofol by setting desired target plasma and effect site concentration. However it is difficult to judge precisely patient requirements for adequate patient sedation, comfort and analgesia as patients' needs differ.

Patient-controlled sedation (PCS) is a valid option, initially adapted from post surgery patient-controlled analgesia. It allows patients to titrate sedative medication to their comfort and therefore present an option that addresses the needs of patients with strong desire to maintain sense of control during procedures.

This study was designed to compare total propofol requirement between PCS versus TCI sedation (TCIS), complications and patient satisfaction, in patients undergoing lower limb orthopaedic surgery under CNB.

Inclusion Criteria:

1. American Society of Anesthesiologists (ASA) I or II.
2. Aged 18-65 years.
3. Elective lower limb orthopaedic surgery under CNB anticipated to last for 1.5 to 2 hours

Exclusion Criteria:

1. Body Mass Index (BMI) > 30kg/m2
2. Unable to cooperate (eg. mental disorders, language barrier)
3. Drug abuse
4. Alcoholism (chronic daily alcohol intake greater than 75 g of pure alcohol for ≥ 2 years, where 75g of alcohol = 5 cans of beer, 1 bottle of wine or half a pint of distilled spirit)
5. Contraindications to the study drugs
6. Pregnancy
7. Significant pulmonary or cardiovascular diseases, including obstructive sleep apnoea and obesity hypoventilation syndrome
8. Features of difficult airway