Monitoring Pain - Surgical Pleth Index SPI
SPI represents the patient’s hemodynamic responses to surgical stimuli and analgesic medication under general anesthesia.
SPI reflects the patient’s responses, which result from increased sympathetic activity as a
reaction to painful (nociceptive) stimuli. SPI monitoring is based on the acquisition of the readily available plethysmographic pulse wave, which is processed with a unique algorithm. The calculation analyzes the photoplethysmographic amplitude and the photoplethysmographic pulse interval, and then combines these two parameters to create a single digit, the Surgical Pleth Index. The details of the SPI algorithm have been published in an article in the British Journal of Anaesthesia titled “Assessment of surgical stress during
general anaesthesia”.