Minimum effective concentration of ropivacaine for ultrasound-guided transmuscular quadratus lumborum block in total hip arthroplasty: a randomized clinical trial

Abstract

Objective: This trial aimed to identify the Minimum Effective Concentration (MEC₉₀, defined as the concentration which can provide successful block in 90% of patients) of 30 mL ropivacaine for single-shot ultrasound-guided transmuscular Quadratus Lumborum Block (QLB) in patients undergoing Total Hip Arthroplasty (THA).

Methods: A double-blind, randomized dose-finding study using the biased coin design up-and-down sequential method, where the concentration of local anesthetic administered to each patient depended on the response from the previous one. Block success was defined as a Numeric Rating Scale (NRS) score during motion ≤ 3 at 6 hours after arrival in the ward. If the block was successful, the next subject received either a 0.025% smaller dose (probability of 0.11) or the same dose (probability of 0.89); otherwise, the next subject received a 0.025% higher ropivacaine concentration. MEC₉₀, MEC₉₅ and MEC₉₉ were estimated by isotonic regression, and the corresponding 95% Confidence Intervals (95% CIs) were calculated by the bootstrapping method.

Results: Based on the analysis of 52 patients, MEC₉₀, MEC₉₅, and MEC₉₉ of ropivacaine for QLB were estimated to be 0.352% (95% CI 0.334-0.372%), 0.363% (95% CI 0.351-0.383%), and 0.373% (95% CI 0.363-0.386%). The concentration of ropivacaine at 0.352% in a volume of 30 ml can provide a successful block in 90% of patients.

Conclusions: For ultrasound-guided transmuscular QLB in patients undergoing THA, 0.352% ropivacaine in a volume of 30 ml can provide a successful block in 90% of patients. Further dose-finding studies and large sample size are required to verify the concentration.

Keywords: Analgesia; Drug dose-response relationship; Nerve block; Ropivacaine; Total hip arthroplasty.

Figure 1

Ultrasound image of the transmuscular quadratus lumborum block. (A) Probe, needle, and patient set up for transmuscular QLB. (B) The trajectory of the needle is displayed on the ultrasound image. ESM, Erector Spinae mMuscle; PM, Psoas Muscle; QLM, Quadratus Lumborum Muscle; TP, Transverse Process.

Figure 2

Flow diagram depicting patient selection.

Figure 3

The biased coin design up-and-down sequence. Graph of successful () and failed () blocks at different ropivacaine concentrations. The horizontal line represents the calculated minimum effective concentration of ropivacaine providing successful transmuscular QLB in 90% of patients (MEC₉₀). Error bars represent the 95% Confidence Interval.