The Median Effective Volume of 0.375% Ropivacaine for Ultrasound-guided Anterior Suprascapular Nerve Block in Arthroscopic Shoulder Surgery.

Background: The suprascapular nerve (SSN) is an important nerve that contributes to shoulder joint sensation and movement. The anterior suprascapular nerve block (aSSNB) has the potential for noninferior analgesic effect compared with the interscalene block while preserving respiratory function. This study investigated the median effective volume (MEV) of 0.375% ropivacaine in aSSNB for analgesic effect among patients undergoing arthroscopic shoulder surgery.

Objectives: Our primary objective was the MEV. The secondary objectives included the 24 hour sufentanil consumption, 24 hour patient-controlled analgesia (PCA) presses, and incidences of diaphragm impairment.

Study Design: Prospective registered (ChiCTR2300070129), single-armed, volume-finding study.

Setting: This study was conducted in a tertiary, single center.

Methods: There were 23 patients who completed the study. Using an up-and-down process, patients enrolled in the study received different volumes of 0.375% ropivacaine for an aSSNB adjusted based on the success or failure of the previous patient in the study's block by increasing or decreasing the volume by 3 mL. The first patient received 15 mL of 0.375% ropivacaine. The nerve blocks were evaluated by the sensory score of the C5 and C6 dermatomes.

Results: MEV50 (50% of the patients) was 6 mL (95% CI, 5.78 - 6.78 mL), and MEV95 (95% of the patients) was 13.88 mL (95% CI, 13.37 - 14.87 mL). There was no significant difference in the PCA presses, 24 hour sufentanil consumption, and incidences of diaphragm impairments between successful and unsuccessful blocks.

Limitations: Our study focused on the analgesic effect rather than hemi-diaphragmatic paralysis with 0.375% ropivacaine for an aSSNB. The study also did not test varying ropivacaine concentrations while keeping the volume constant. Further investigation with varying concentrations and a larger sample size is indicated to address the optimal volume and concentration to balance analgesia and diaphragm function.

Conclusions: To produce effective analgesic effect, the MEV50 is 6 mL, and the MEV95 is 13.88 mL in patients undergoing arthroscopic shoulder surgery who receive an aSSNB using 0.375% ropivacaine for analgesia.