The Analgesia Nociception Index (ANI) is a promising monitor to evaluate the balance of nociception and anti-nociception based on heart rate variability. This prospective, interventional, monocentric pilot study aimed to verify the effectiveness of the personal analgesic sufficiency status (PASS) measured by pre-tetanus-induced ANI variation for surgical stimuli. After Ethics approval and informed consent, participants were anesthetized with sevoflurane and increased effect-site concentrations of remifentanil step by step (2, 4, 6 ng ml(-1)). At each concentration, a standardized tetanic stimulus was applied (5 s, 60 mA, 50 Hz) with no other noxious stimuli presented. Through all the concentrations, defined the lowest concentration when ANI & GE; 50 as the PASS after tetanic stimuli. The surgical stimulus was conducted under at least 5-min of PASS. Thirty-two participants were analyzed. ANI, systolic blood pressure (SBP), and Heart rate (HR) except the Bispectral Index (BIS) were significantly changed at 2 ng ml(-1) after tetanic stimuli, only ANI and SBP were significantly altered at 4 and 6 ng ml(-1). ANI could predict inadequate analgesia status (an increase in SBP or HR of more than 20% from the baseline) at 2 and 4 ng ml(-1) (P = 0.044, P = 0.049, respectively), but not at 6 ng ml(-1). The PASS under pre-tetanus-induced ANI identification didn't meet the analgesic needs under surgical stimuli. Further investigations are required to provide a reliable prediction of individualized analgesia by objective nociception monitors.Trial registration NCT05063461.
