The Surgical Pleth index (SPI) has been introduced as a non invasive tool to "measure" stress and pain during surgery. Preliminary studies were performed in patients under general anaesthesia with propofol and remifentanil. These trials showed a good correlation between SPI and aching procedures and a negative correlation between SPI and the remifentanil dosage. Hence, it was concluded that SPI may be a bedside tool to measure `pain` during surgery. So far, no study investigated SPI during regional anaesthesia.