Minimum effective concentration of ropivacaine for ultrasound-guided pericapsular nerve group block to relieve spinal anesthesia positioning pain in elderly patients with femoral intertrochanteric fracture: a double-blind biased-coin dose-finding study.

BACKGROUND

The optimal ropivacaine concentration for ultrasound-guided pericapsular nerve group (PENG) block to relieve spinal anesthesia positioning pain in elderly patients with femoral intertrochanteric fracture remains unclear. We aimed to estimate the minimum effective concentration (MEC) and explore concentration-related motor impairment.

METHODS

In this double-blind biased-coin up-and-down study, elderly patients scheduled for spinal anesthesia underwent ultrasound-guided PENG block with 20 mL ropivacaine. The initial concentration was 0.10%. For a successful block, the subsequent patient was assigned to the same concentration (probability = 0.89) or a 0.05% lower concentration (probability = 0.11). For a failed block, the concentration was increased by 0.05% for the next patient. The trial was terminated when 45 successful blocks were achieved. Block success was defined as a pain score ≤ 3 at rest and during passive leg raise 30 min after block. The primary outcome was MEC90 estimated by isotonic regression. Secondary outcomes included MEC50, concentration-specific success rates, quadriceps weakness, and onset time of analgesia.

RESULTS

Fifty-two patients completed the sequential trial. Isotonic regression estimated MEC90 at 0.25% (95% CI, 0.20%-0.30%) and MEC50 at 0.20% (95% CI, 0.20%-0.20%). Success rates were 0% at 0.10% and 0.15%, 89.5% at 0.20%, 96.0% at 0.25%, and 100% at 0.30%. Quadriceps weakness at 6 h increased with concentration, occurring in 5.3% at 0.20%, 36.0% at 0.25%, and 50.0% at 0.30% (trend P = 0.007; risk ratio comparing high- with low-concentration groups, 8.72; 95% CI, 1.21-62.72). This safety comparison was exploratory. No local anesthetic systemic toxicity or serious adverse events were observed.

CONCLUSIONS

In elderly patients with femoral intertrochanteric fracture receiving ultrasound-guided PENG block with a fixed 20 mL volume of ropivacaine, the prespecified isotonic regression-estimated MEC90 for relieving spinal anesthesia positioning pain was 0.25%. Exploratory safety analyses suggested that quadriceps weakness at 6 h was more common at concentrations ≥0.25%, but these analyses were underpowered and hypothesis-generating. Future studies should determine whether modifying volume, concentration, or total dose can preserve analgesia while reducing motor impairment.

CLINICAL TRIAL REGISTRATION: identifier ChiCTR2500102032.