Local anesthetics and erector spinae plane blocks: a spotlight on pharmacokinetic considerations and toxicity risks.

The Erector Spinae Plane (ESP) block was first described in 2016 and from its inception it has attracted great interest from the scientific community related to anesthesia and pain practice [1]. It is performed by injecting a solution of local anesthetics (LA) in a virtual plane between the transverse processes and the erector spinae muscle group, with the anesthetic solution subsequently spreading for a variable number of vertebral levels (Figure 1). Understanding ESP block pharmacokinetics and related concerns requires two key points. Firstly, a successful ESP block relies on the use of large volumes of anesthetics. Given that the target is not a nerve or a small compartment but a virtual plane where the anesthetic spreads, large volumes are usually necessary to reach the desired effect. In literature, while the injected LA covers a median of one dermatome every 3.4 ml of solution, spread has been reported as being widely variable [2]. Secondly, the ESP is performed in a highly vascularized surface, as on the erector spinae muscle group lies a rich vascular bed [3,4]. Given the above, it is of foremost importance to evaluate the pharmacokinetics of the drugs injected in the ESP to evaluate the possibility of local anesthetic systemic toxicity (LAST).