Remifentanil is an ultra-short-acting oppioid, which is quickly metabolized by unspecific blood and tissue esterases . This feature vouches for a predictable pharmacokinetics and makes this drug suitable for administration in continuous intravenous infusion in order to achieve patient conscious sedation during non-invasive surgical procedures. Remifentanil could be particularly useful in day surgery setting, thanks also to its faster elimination than other oppioids. This property ensure a swift recovery from conscious sedation, reducing the period of time during which patient remains in recovery room and decreasing also the incidence of side effects, like PONV and respiratory depression. Conscious sedation with remifentanil can provide patient comfort and cooperation during surgical procedure, since the verbal contact with the patient is kept up. Extracorporeal shock wave lithotripsy (ESWL) is a non-invasive procedure, contemplated as the first-line treatment for renal and upper ureteral stones, if stone diameter is ranged from 5 to 20 mm . It can grind calculi into fine particles, that are expelled through micturition. Although many studies have been published in regard to continuous intravenous infusion of remifentanil, a small number of them focuses on which is the most appropriate infusion rate for ESWL procedure.