Authors: Sunder, Rani A. et al.
Anesthesiology September 2025 | DOI: 10.1097/ALN.0000000000005775
This prospective pharmacokinetic study examined the safety and dosing parameters of continuous lumbar plexus blocks using 0.2% ropivacaine in pediatric patients. Although lumbar plexus blocks are effective for postoperative analgesia in children, limited pharmacokinetic data have restricted infusion rates due to concerns about systemic toxicity. The study aimed to characterize unbound ropivacaine and its active metabolite 2’,6’-pipecoloxylidide (PPX) to refine dosing limits and reduce breakthrough pain.
Twenty children aged 4–18 years undergoing unilateral hip or femur surgery received a lumbar plexus block with an initial 0.2% ropivacaine bolus (2 mg/kg) followed by a continuous infusion (0.4 mg/kg/h). Serial blood samples collected over 26 hours were analyzed for total and unbound plasma concentrations of ropivacaine and PPX. Pharmacokinetic modeling and simulation were performed to estimate cumulative drug exposure relative to known toxicity thresholds.
Results demonstrated wide interindividual variability in unbound ropivacaine (fivefold) and PPX (tenfold) concentrations. Simulations of standard dosing regimens (0.4 mg/kg/h with intermittent boluses) showed that cumulative exposure to the combined unbound ropivacaine + (1/12 PPX) approached the accepted toxicity threshold after approximately 24 hours, driven largely by delayed PPX accumulation. A modeled adjustment—replacing continuous infusion with larger boluses every six hours—reduced overall plasma concentrations while maintaining analgesic levels.
The authors conclude that continuous infusions of 0.4 mg/kg/h ropivacaine for up to 24 hours are pharmacokinetically safe in healthy children when combined with a 2 mg/kg bolus, but longer durations should favor intermittent bolus dosing to limit systemic accumulation of PPX. These data offer the most detailed pediatric kinetic profile to date for lumbar plexus ropivacaine administration and support evidence-based optimization of postoperative regional analgesia.
What You Should Know
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Continuous lumbar plexus ropivacaine infusions (0.4 mg/kg/h) are safe for the first 24 hours in healthy children.
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After 24 hours, PPX accumulation increases total anesthetic exposure toward toxicity thresholds.
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Transitioning from continuous infusions to scheduled boluses every six hours maintains pain control while reducing systemic risk.
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This pharmacokinetic model provides a framework for refining regional anesthesia protocols in pediatric orthopedic surgery.
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