Measurement of surgical stress in anaesthetized children

Background. The surgical stress index (SSI), derived from a combination of heart rate (HR) and photoplethysmographic amplitude (PPGA) time series, is a novel method for continuous monitoring of intraoperative stress and has been validated in adults. The applicability of SSI and its constituents to monitoring children has not been previously evaluated. Methods. In this controlled trial, 22 anaesthetized patients, aged 4-17 yr, undergoing strabismus surgery were randomized into two groups, Group LL and Group BSS. Patients in Group LL received topical conjunctival anaesthesia with a 1: 1 mixture of lidocaine 2% and levobupivacaine 0.75%, and patients in Group BSS received balanced salt solution. Results. Endotracheal intubation (n=22) increased median (range) SSI from 39.2 (22.6-55.6) to 53.6 (35.8-63.3) (P<0.001), decreased PPGA from 5.62 (2.79-9.69) to 5.27 (2.59-7.54)% (P=0.001), and increased the difference of response entropy (RE) and state entropy (SE) of frontal biopotentials (RE-SE) from 3.1 (0.06-9.1) to 5.7 (0.6-9.4) (P=0.01). Conventional haemodynamic variables also increased, median (range) HR from 72.9 (56.7-113.8) to 84.2 (60.4-124.8) beats min(-1) (P<0.001), and systolic non-invasive arterial pressure (S-NIBP) from 87 (78-143) to 103 (79-125) (P=0.007). When 3 min baseline before surgery was compared with 12 min of surgery, median ( range) SSI increased from 43.3(31.2-58.0) to 49.9 (39.3-57.2) (P=0.042) vs from 46.6 (26.8-57.8) to 52.1 (31.7-60.1) (P=0.024) and PPGA decreased from 6.60 (3.10-8.24) to 5.80 (3.03-7.65)% (P=0.001) vs from 5.51 (3.25-9.84) to 5.06 (3.08-8.99)% ( P=0.042), in Groups LL and BSS, respectively, but SSI or other indicators did not differ significantly between the groups. Conclusions. SSI, PPGA, HR, NIBP, RE, and RE-SE detect autonomic responses to nociceptive stimuli in anaesthetized children undergoing strabismus surgery.