Analgesia Nociception Index to detect interindividual variability in the sensory effect of paravertebral block for total mastectomy: prospective cohort study.

Background: Single paravertebral block (PVB) injection is widely used for major breast surgery, but its effectiveness can be unpredictable. This study aimed to evaluate whether intraoperative variations of the Analgesia Nociception Index (ANI) could evaluate effectiveness of PVB. Methods: This prospective observational study included 100 women undergoing total mastectomy. PVB was performed under ultrasound guidance in a preoperative regional anesthesia room. Sensory level of efficacy was assessed using an ice cube test. ANI was measured before and one minute after the surgical skin dissection. Statistical analyses compared ANI changes among effective, incomplete, and ineffective PVB groups. Results: Ninety-three patients were analyzed. Effective PVB was observed in 75% and incomplete in 25%. No ineffective block was observed. The mean ANI variation was significantly higher in the effective group (+1.4 ± 10.3 compared to the incomplete group (-11.0 ± 7.1, p<10 ^-4 ). Intraoperative remifentanil consumption was higher in the incomplete group (0.072 µg.kg ^-1 .min ^-1 vs. 0.054 µg.kg ^-1 .min ^-1 , p<10 ^-4 ). Pain score and morphine consumption were significantly higher for patients with incomplete PVB. Conclusion: Early ANI variations after skin dissection were in agreement with PVB effectiveness for total mastectomy. Monitoring ANI may enhance perioperative analgesia management, allowing adjustments to improve patient pain and optimize opioid consumption.