• Andrej Alfirevic, Federico Almonacid-Cardenas, Esra Kutlu Yalcin, Karan Shah, Marta Kelava, Daniel I Sessler, and Alparslan Turan.
• Division of Cardiothoracic Anesthesiology, Department of Anesthesiology, Cleveland Clinic, Cleveland, OH, USA. Electronic address: alfirea@ccf.org.
• J Clin Anesth. 2024 Aug 1; 95: 111470111470.

Study ObjectiveTo investigate the timing of peak blood concentrations and potential toxicity when using a combination of plain and liposomal bupivacaine for thoracic fascial plane blocks.DesignPharmacokinetic analysis.SettingOperating room.PatientsEighteen adult patients undergoing robotically-assisted mitral valve surgery.InterventionsUltrasound-guided pecto-serratus and serratus anterior plane blocks using a mixture of 0.5% bupivacaine HCl up to 2.5 mg/kg and liposomal bupivacaine up to 266 mg.MeasurementsArterial plasma bupivacaine concentration.Main ResultsSamples from 13 participants were analyzed. There was substantial inter-patient variability in plasma concentrations. A geometric mean maximum bupivacaine concentration was 1492 ng/ml (range 660 to 4650 ng/ml) at median time of 30 min after injection. In 4/13 (31%) patients, plasma bupivacaine concentrations exceeded our predefined 2000 ng/ml toxic threshold. A second much smaller peak was observed about 32 h after the injection. No obvious signs of local anesthetic toxicity were observed.ConclusionsCombined injection of plain and liposomal bupivacaine for pecto-serratus/serratus anterior plane blocks produced a biphasic pattern, with the highest arterial plasma concentrations observed within 30 min. Maximum concentrations exceeded the potential toxic threshold in nearly a third of patients, but without clinical evidence of toxicity. Clinicians should not assume that routine combinations of plain and liposomal bupivacaine for thoracic fascial plane blocks are inherently safe.Copyright © 2024 Elsevier Inc. All rights reserved.

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