Surgical pleth index in children younger than 24 months of age: a randomized double-blinded trial.

BACKGROUND: The surgical pleth index (SPI) is a measurement of intraoperative nociception. Evidence of its usability in children is limited. Given that the autonomic nervous system is still developing during the first years of life, the performance of the SPI on small children cannot be concluded from studies carried out in older age groups.

METHODS: Thirty children aged <2 yr, planned for elective open inguinal hernia repair or open correction of undescended testicle, were recruited. The children were randomized into two groups; the saline group received ultrasound-guided saline injection in the ilioinguinal and iliohypogastric nerve region before surgery and ropivacaine after surgery, whereas the block group received the injections in the opposite order. The SPI was recorded blinded and was analysed at the time points of intubation, incision, and when signs of inadequate anti-nociception were observed.

RESULTS: There was a significant increase in the SPI after intubation (P=0.019) and after incision in the saline group (P=0.048), but not at the time of surgical incision in the block group (P=0.177). An increase in the SPI was also seen at times of clinically apparent inadequate anti-nociception (P=0.008). The between-patient variability of the SPI was large.

CONCLUSIONS: The SPI is reactive in small children after intubation and after surgical stimuli, but the reactivity of the SPI is rather small, and there is marked inter-individual variability in reactions. The reactivity is blunted by the use of ilioinguinal and iliohypogastric nerve block.

CLINICAL TRIAL REGISTRATION: NCT02045810.