Surgical pleth index monitoring in perioperative pain management: usefulness and limitations

Surgical pleth index (SPI) monitoring is a representative, objective nociception-monitoring device that measures nociception using photoplethysmographic signals. It is easy to apply to patients and the numerical calculation formula is intuitively easy to understand; therefore, its clinical interpretation is simple. Several studies have demonstrated its efficacy and utility. Compared with hemodynamic parameters, the SPI can detect the degree of nociception during surgery under general anesthesia with greater accuracy, and therefore can provide better guidance for the administration of various opioids, including remifentanil, fentanyl, and sufentanil. Indeed, SPI-guided analgesia is associated with lower intraoperative opioid consumption, faster patient recovery, and comparable or lower levels of postoperative pain and rates of adverse events compared with conventional analgesia. In addition, SPI monitoring allows for the degree of postoperative pain and analgesic requirements to be predicted through the SPI values immediately before patient arousal. However, because patient age, effective circulating volume, position, concomitant medication and anesthetic regimen and level of consciousness may be confounding factors in SPI monitoring, clinicians must be careful when interpreting SPI values. In addition, as SPI values can differ depending on anesthetic and analgesic regimens and the underlying disease, an awareness of the effects of these variables with an understanding of the advantages and disadvantages of SPI monitoring compared to other nociception monitoring devices is essential. Therefore, this review aimed to help clinicians perform optimal SPI-guided analgesia and to assist with the establishment of future research designs through clarifying current usefulness and limitations of SPI monitoring in perioperative pain management.