Spinal anaesthesia is a popular form of RA used in many patients undergoing hip arthroplasty. Opioid drugs are frequently added to the spinal injection in order to prolong post-operative pain relief. However, this is associated with side effects including respiratory depression, urinary retention, nausea and vomiting, and pruritus. Such adverse effects may be uncomfortable for the patient and can delay mobilisation, recovery and eventual discharge.