Comparative study of analgesia nociception index (ANI) vs. standard pharmacokinetic pattern for guiding intraoperative fentanyl administration among mastectomy patients

BACKGROUND: The Analgesia Nociception Index (ANI) has been suggested as a non-invasive guide for analgesia. Our objective was to compare the efficacy of ANI vs. standard pharmacokinetic pattern for guiding intraoperative fentanyl administration. METHODS: This was a prospective, randomized, controlled study of adult female patients undergoing elective mastectomy under general anesthesia. The patients were randomized to the ANI-guided group receiving a loading dose of 75 μg of fentanyl followed by 25 μg when the ANI score was under 50. The Control group received the same loading dose followed by 25 μg every 30 min with additional doses when there were signs of inadequate analgesia (viz., tachycardia or hypertension). RESULTS: Sixty patients—30 in each group—were recruited. Although the actual mean ANI score was higher in the ANI-guided than in the Control group (mean difference 2.2; 95% CI: 0.3 to 4.0, P = 0.022), there was no difference in the primary outcome—i.e., intraoperative fentanyl consumption (mean difference − 4.2 μg; 95% CI: − 24.7 to 16.4, P = 0.686 and − 0.14 μg·kg(− 1)·h(− 1); 95% CI: − 0.31 to 0.03, P = 0.105). No difference between groups was shown for either intraoperative blood pressure and heart rate, or for postoperative outcomes (i.e., pain scores, morphine consumption, or sedation scores) in the postanesthesia care unit. CONCLUSIONS: Intraoperative fentanyl administration guided by ANI was equivalent to that guided by a modified pharmacologic pattern. In a surgical model of mastectomy, the ANI-guided intraoperative administration of fentanyl had no impact on clinical outcomes. TRIAL REGISTRATION: The study was registered with ClinicalTrials.gov (NCT03716453) on 21/10/2018.