SPI Value Relevance in Clinical Practice

Primary endpoint: Defining The optimal target range for Surgical Pleth index. Surgical Pleth Index (SPI, formerly used SSI = Surgical Stress Index) is a novel multivariate index, which is based on the sum of the normalized pulse beat interval (PBI) and the photoplethysmography. SPI indicates the balance between intensity of surgical stimulation and the level of anti-nociception (opioid analgesia and neural blockade). This study is a Spin off from a larger Adequacy of Anaesthesia study and aims on finding the most appropriate target range for SPI in order to avoid signs of inadequate anaesthesia. Patients are treated without monitoring adequacy of anaesthesia thus the values are collected blinded and analyzed afterwards in accordance of signs for inadequate anaesthesia. The study population will be 150 patients.