Analgesia nociception index as a tool to assess the effectiveness of paravertebral block in total mastectomy: a prospective cohort study

Abstract

Background

Single-injection Paravertebral Block (PVB) is commonly used for analgesia in major breast surgery; however, its sensory effectiveness may be variable. This study investigated whether intraoperative changes in the Analgesia Nociception Index (ANI) are associated with PVB effectiveness.

Methods

This prospective observational study included 100 women scheduled for total mastectomy. A single-injection PVB was performed preoperatively under ultrasound guidance at the T3 level. Sensory testing was performed from T1 to T10, but block effectiveness was evaluated in the surgical field (T2−T6). PVBs were classified as effective (complete loss of cold sensation in all T2‒T6 dermatomes) or incomplete (partial cold sensation in this range). ANI variations, intraoperative remifentanil consumption, postoperative pain scores, and morphine use were compared.

Results

Ninety-three patients were analyzed. PVB was effective in 75% and incomplete in 25%. The mean ANI variation was significantly greater in the effective group (+1.4 ± 10.3) compared to the incomplete group (-11.0 ± 7.1), with a mean difference of 12.4 (95% CI: 8.8 to 16.0; p < 0.0001). Remifentanil consumption was higher in the incomplete group (0.072 ± 0.018 μg.kg.⁻¹.min⁻¹ vs. 0.054 ± 0.008 μg.kg⁻¹.min⁻¹), mean difference 0.018 (95% CI: 0.010 to 0.026; p < 0.0001). Pain score and morphine consumption were significantly higher for patients with incomplete PVB.

Conclusion

In this observational study, a significant decrease in ANI values following skin dissection was associated with incomplete PVB. Early ANI monitoring may help identify insufficient regional block during total mastectomy, thus guiding intraoperative analgesic adjustment to improve patient comfort.