Background Fascial plane blocks (FPBs) target the space between two fasciae, rather than discrete peripheral nerves. Despite their popularity, their mechanisms of action remain controversial, particularly for erector spinae plane and quadratus lumborum blocks.
Objectives This narrative review describes the scientific evidence underpinning proposed mechanisms of action, highlights existing knowledge gaps, and discusses implications for clinical practice and research.
Findings There are currently two plausible mechanisms of analgesia. The first is a local effect on nociceptors and neurons within the plane itself or within adjacent muscle and tissue compartments. Dispersion of local anesthetic occurs through bulk flow and diffusion, and the resulting conduction block is dictated by the mass of local anesthetic reaching these targets. The extent of spread, analgesia, and cutaneous sensory loss is variable and imperfectly correlated. Explanations include anatomical variation, factors governing fluid dispersion, and local anesthetic pharmacodynamics. The second is vascular absorption of local anesthetic and a systemic analgesic effect at distant sites. Direct evidence is presently lacking but preliminary data indicate that FPBs can produce transient elevations in plasma concentrations similar to intravenous lidocaine infusion. The relative contributions of these local and systemic effects remain uncertain.
Conclusion Our current understanding of FPB mechanisms supports their demonstrated analgesic efficacy, but also highlights the unpredictability and variability that result from myriad factors at play. Potential strategies to improve efficacy include accurate deposition close to targets of interest, injections of sufficient volume to encourage physical spread by bulk flow, and manipulation of concentration to promote diffusion.
- regional anesthesia
Data availability statement
Data sharing not applicable as no data sets generated and/or analyzed for this study.
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Contributors KJC contributed to the conception, research, writing, and editing of the final manuscript. PL, MWH and SKWS contributed to the research, writing, and editing of the final manuscript.
Funding SKWS holds the Dr Jean Hugill Templeton Chair in Anesthesia at The University of British Columbia, supported by the Dr Jean Templeton Hugill Endowment for Anesthesia Memorial Fund (Vancouver, British Columbia, Canada).
Competing interests SKWS is the Editor-in-Chief of the Canadian Journal of Anesthesia/Journal Canadien d’Anesthésie. MWH is Executive Section Editor Pharmacology for the Anesthesia & Analgesia journal; Section Editor Anesthesiology for the Journal of Clinical Medicine, and Associate Editor for the Frontiers in Physiology journal, and Section Editor for the NTvA journal.
Provenance and peer review Commissioned; externally peer reviewed.
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