Authors: Sunder R.A. et al.
Anesthesiology, September 29, 2025. DOI: 10.1097/ALN.0000000000005775
This pharmacokinetic study revisited infusion rate limitations for continuous lumbar plexus blocks in pediatric patients, addressing the long-standing concern of balancing adequate analgesia with local anesthetic toxicity. The widespread use of ropivacaine for pediatric regional anesthesia has been constrained by limited pharmacokinetic data, leading clinicians to use conservative infusion rates and accept intermittent breakthrough pain.
The investigators enrolled 20 healthy children aged 4 to 18 years undergoing unilateral hip or femur surgery under lumbar plexus blockade. Each patient received an initial bolus of 0.2% ropivacaine (2 mg/kg) followed by a continuous infusion of 0.4 mg/kg/h. Blood samples were obtained at scheduled intervals over 26 hours to measure both total and unbound plasma concentrations of ropivacaine and its active metabolite, 2’,6’-pipecoloxylidide (PPX). Pharmacokinetic modeling and simulation were used to compare standard continuous infusions with alternative bolus-only strategies.
Results demonstrated a fivefold interindividual range in steady-state unbound ropivacaine concentrations and a tenfold variation in PPX concentrations, indicating substantial variability in clearance. Simulations showed that at standard infusion rates (0.4 mg/kg/h) with 6-hour boluses (0.2 mg/kg), the combined unbound plasma concentration of ropivacaine plus one-twelfth of PPX approached the estimated toxic threshold over time—primarily due to the gradual accumulation of PPX at later time points. By discontinuing the continuous infusion after 24 hours and substituting intermittent boluses, modeled plasma concentrations of both compounds remained below toxicity limits while maintaining analgesic coverage.
These findings suggest that continuous ropivacaine infusions at 0.4 mg/kg/h are safe and effective for the first 24 hours of postoperative analgesia in healthy children. Beyond that period, a shift toward scheduled bolus dosing may minimize the risk of cumulative toxicity without compromising efficacy.
What You Should Know
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Continuous ropivacaine infusions (0.4 mg/kg/h) are safe for the first 24 hours of pediatric lumbar plexus analgesia.
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Significant interpatient variability exists in ropivacaine and PPX plasma concentrations.
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Prolonged infusions can lead to late PPX accumulation approaching toxicity thresholds.
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Transitioning to timed bolus dosing after 24 hours maintains safety while sustaining analgesia.
Thank you to Anesthesiology for publishing this important pharmacokinetic analysis refining dosing strategies for continuous lumbar plexus blocks in children and adolescents.