Local anesthetic dosing for fascial plane blocks to avoid systemic toxicity: a narrative review

Owing in part to the development and popularization of fascial plane blocks (FPBs), high-volume injection of local anesthetic (LA) is becoming more commonplace. Fascial plane blocks typically use high LA volumes to maximize spread, often pushing towards the maximum recommended dosing. This narrative review summarizes the pharmacokinetic literature for several of the most common FPBs.

We searched PubMed®, Embase, the Cochrane Library, and Google Scholar using the following search terms: (plasma concentration, pharmacokinetics, toxicity, local anesthetic systemic toxicity [LAST]) AND (erector spinae plane, serratus anterior plane, parasternal intercostal plane, quadratus lumborum, transversus abdominis plane, fascia iliaca, pericapsular nerve group), as well as FPB acronyms.

Typical LA dosing in studies used concentrations of ropivacaine 0.25-0.5%, levobupivacaine 0.125-0.25%, and bupivacaine 0.25% at volumes of 20-40 mL. While numerous studies found average LA plasma concentrations well below the established thresholds, several patients crossed the toxic threshold. Patients with LA plasma concentrations above toxic thresholds often did not experience LAST symptoms; nevertheless, there are several reports of mild neurologic symptoms and even seizures.

Diligent care should be taken to avoid LAST in FPBs. We recommend the calculation of weight-based doses, aspiration before injection, incremental dosing, close monitoring, and ultrasound observation of injectate when administering high volumes. Clinicians should consider adding low-dose epinephrine to FPBs. The LA concentration should decrease with increasing volume to ensure that the total dose of LA remains below maximum dosing recommendations. Clinicians should use extra caution in those blocks and with patients at a higher risk for LAST.