Sedation is often administered to relieve anxiety and discomfort during uncomfortable procedures in elderly patients. Patient control of sedation offers many potential benefits for patients and healthcare professionals, including improved safety and patient satisfaction. The investigators overall goal is to develop a patient controlled intravenous sedation system that is effective but very safe for the patient, and requires minimal supervision by a doctor or nurse. To fulfill these criteria, a sedation system should incorporate fail-safe safety mechanisms. A key safety-critical component is a method of objectively assessing the degree of sedation of the patient, and of preventing him from self-administering unsafe doses of the sedative drug. The investigators have designed a new sedation system that uses a measure of the speed of response of the patient to a defined non-noxious stimulus to determine whether or not it is safe to allow him to self-administer further levels of sedation. Before being able to execute a volunteer study in order to determine a rational selection of optimal threshold response time, a feasibility test on the handset device is required.

Inclusion Criteria:

• age 50-72 years

Exclusion Criteria:

• volunteer refusal
• patient age >72 years
• significant cardiovascular or respiratory disease
• latex allergy

Twenty patients requiring anaesthesia for clinical surgical care. ASA physical status I, II or III