Serum concentrations of local anesthetics after unilateral interpectoral-pectoserratus plane block in breast cancer surgery: a pharmacokinetic study.

Introduction: The ultrasound-guided interpectoral-pectoserratus plane block is a fascial plane block for superficial surgery of the anterolateral chest wall. This technique involves injecting a relatively large volume of local anesthetics (typically 30 mL of 0.25%-0.50%, ie, 75-150 mg ropivacaine) underneath the major and minor pectoral muscles of the anterior thoracic wall. There is a potential risk of toxic serum concentrations of local anesthetics due to systemic absorption.

Methods: 22 patients scheduled for elective unilateral breast cancer surgery were included in this study. All surgery was performed with general anesthesia and an ultrasound-guided interpectoral-pectoserratus plane block with 2.5 mg/kg ropivacaine. Ten venous blood samples were collected at 0 (two samples) 10, 20, 30, 45, 60, 90 and 120 min and at 4 hours after performing the block. Free and total ropivacaine levels were measured at each time point. Albumin and alpha-1-acid-glycoprotein were measured to monitor shifts between the free and bound fraction of ropivacaine.

Results: Samples of 20 patients were analyzed. The mean dose of ropivacaine was 172.8 (22.5) mg. In 50% of the patients, the potentially toxic threshold of 0.15 µg/mL free ropivacaine concentration was exceeded. Mean peak serum concentration occurred at 20 min postinjection.

Conclusions: This pharmacokinetic study demonstrated that a 2.5 mg/kg ropivacaine interpectoral-pectoserratus plane block may result in exceeding the threshold for local anesthetic systemic toxicity.