 Surgical plethysmography index SPI is a device that can noninvasively monitor the balance between the nociception and ant-nociception using pulse photoplethysmographic amplitude PPGA and heart rate obtained through an oxygen saturation measuring device. SPI has recently been studied as a useful tool to monitor the stress response of patients due to surgery or anesthesia and to guide the appropriate use of analgesicsanesthetics. However, these SPI devices have been developed for adults and have not been studied in pediatric patients with relatively high heart rates, and no direct effects on post-operative arousal excitability have been reported. 