The 90% minimum effective volume and concentration of lidocaine for ultrasound-guided stellate ganglion blocks in adults: a biased-coin design, up-and-down sequential allocation trial.

Background: As ultrasound imaging technology matured, stellate ganglion blocks (SGBs) have become increasingly precise and safe, and their use in clinical practice has become widespread. However, the 90% minimum effective volume (MEV90) and concentration (MEC90) of lidocaine for ultrasound-guided SGB remain unclear. We aimed to determine the MEV90 and MEC90 of lidocaine used in ultrasound-guided SGBs.

Methods: Patients with indications for an SGB were recruited, without restrictions on sex or disease type. In this two-part study, we first determined the MEV90, and then used these results to determine the MEC90. The MEV90 and MEC90 of lidocaine for each subsequent patient were determined based on the previous patient's response, using a biased-coin design, up-and-down sequential allocation trial. The lidocaine volume and concentration intervals were 0.2 ml and 0.1%, respectively.

Results: In total, 110 patients were enrolled (58 and 52 patients in the MEV90 and MEC90 studies, respectively). The MEV90 for 1% lidocaine was found to be 3.83 ml (95% CI [3.19-3.91]) and the extrapolated MEV99 was 3.97 ml (95% CI [3.95-5.29]). The MEC90 for lidocaine (4.0 ml) was found to be 0.38% (95% CI [0.32-0.41]) and the extrapolated MEC99 was 0.47% (95% CI [0.46-2.55]). Four patients in this study developed hoarseness, but no serious adverse events occurred.

Conclusions: For ultrasound-guided SGB in adults, we have determined the MEV90 of 1% lidocaine as 3.83 ml, and identified the MEC90 of 4 ml of lidocaine as 0.38%.