Can the SPI properly guide the administration of pain killers during general anesthesia?

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We suggest that the use of SPI guidance is more useful and practical than conventional analgesia for analgesic titration during surgery under general anesthesia in various clinical circumstances. This systematic review shows that SPI-guided analgesia can reduce intraoperative opioid consumption and shorten the extubation time when compared with conventional analgesia during surgery under general anesthesia and has no negative impact on the degree of postoperative pain and incidence of perioperative adverse events (J Int Med Res. 2018;46:4386-98). But further research needs to be performed considering the small number of the included studies, and future systematic reviews should aim to reduce the heterogeneity of the outcome data. In addition, I have another important viewpoint on the SPI. For the measurement of pulse oximetry, the pulse photoplethysmographic amplitude (PPGA) depends on vascular wall distensibility and intravascular pulse pressure, and the greater PPGA is, the better the perfusion is. I demonstrated that since children have a lower vascular tone and higher vascular distensibility compared to adults, they are less likely to show prominent decreases in PPGA from sympathetic stimulation, leading to an underestimation of the surgical pleth index (SPI) during surgery (SPI is an analgesic index tool using the PPGA and heart beat interval [HBI] from pulse oximetry measurements and SPI is calculated using the following equation: SPI = 100 – [0.33 × HBI + 0.67 × PPGA].) and concluded that the SPI value is less likely to reflect the nociception-antinociception balance accurately in children because of their unique cardiovascular structure and physiology and thus, we should use a lower SPI target range than that in adults to more properly assess the degree of pain in children during general anesthesia (Anesthesiology. 2015;122:1280-7). A recent study supported the results of my study by reporting that a lower target (less than 40) than previously published target (50) for SPI may be more appropriate in studies investigating SPI guided anesthesia in children (Br J Anaesth. 2017;119:979-83). Therefore, I am going to focus on identifying appropriate SPI target ranges, and developing new indicators that objectively assess the degree of pain in children in the near future.

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