Peak plasma concentration of total and free bupivacaine after erector spinae plane and pectointercostal fascial plane blocks

Purpose: Erector spinae plane blocks (ESPB) and pectointercostal fascial (PIFB) plane blocks are novel interfascial blocks for which local anesthetic (LA) doses and concentrations necessary to achieve safe and effective analgesia are unknown. The goal of this prospective observational study was to provide the timing (Tmax) and concentration (Cmax) of maximum total and free plasma bupivacaine after ESPB in breast surgery and after PIFB in cardiac surgery patients. Methods: Erector spinae plane blocks or PIFBs (18 patients per block; total, 36 patients) were performed with 2 mg⋅kg-1 of bupivacaine with epinephrine 5 μg⋅mL-1. Our principal outcomes were the mean or median Cmax of total and free plasma bupivacaine measured 10, 20, 30, 45, 60, 90, 180, and 240 min after LA injection using liquid chromatography with tandem mass spectrometry. Results: For ESPB, the mean (standard deviation [SD]) total bupivacaine Cmax was 0.37 (0.12) μg⋅mL-1 (range, 0.19 to 0.64), and the median [interquartil...