The ultrasound-guided retrolaminar block: volume-dependent injectate distribution

Abstract

PurposeThe ultrasound-guided retrolaminar block is one of the newer and simpler alternatives to the traditional, often technically challenging, paravertebral (PV) block. Its feasibility, safety, and efficacy have already been clinically demonstrated in patients with multiple rib fractures using higher volumes of local anesthetic, when compared with the traditional approach. The primary aim of this observational anatomical study was to assess the spread of local anesthetic from the retrolaminar injection point to the PV space and its volume dependence. Second, we assessed the incidence of epidural and contralateral PV spread in the both groups.MethodsTen fresh porcine cadavers were randomized into 2 groups (n=5 each) to receive ultrasound-guided retrolaminar injections at Th4-Th5 level with either 10 mL (low-volume group) or 30 mL (high-volume group) of 2% lidocaine and methylene blue mixture. After the procedure, the cadavers were dissected and frozen. Cross-section cuts (~1 cm thick) were performed to evaluate the injectate spread.ResultsIn the high-volume group, injectate spread from the retrolaminar to the PV space was observed in all specimens (5 out of 5; 100%), while in the low-volume group, no apparent spread to the PV space was found (0 out of 5; 0%). No epidural or contralateral PV spread was observed in any of the specimens.ConclusionFollowing ultrasound-guided retrolaminar injections in fresh porcine cadavers, injectate spread from the retrolaminar tissue plane to the PV space is strongly volume dependent, suggesting that, clinically, high local anesthetic volumes maybe critical for achieving regional anesthesia and analgesia consistent with traditional PV blockade.

Analgesic Effect of Double-Level Retrolaminar Paravertebral Block for Breast Cancer Surgery in the Early Postoperative Period: A Placebo-Controlled, Randomized Clinical Trial

“…Our results suggest that a multi-level injection procedure may not be an advantageous technique for RLB. A recent anatomical study on pigs demonstrated that the local anesthetic distribution from the retrolaminar space to the paravertebral space was volume dependent (Damjanovska et al 2018). We cannot directly apply their results to humans due to anatomical differences between the species.…”

Mechanism of action of the erector spinae plane block: distribution of dye in a porcine model

“…Pressure exerted during injection of a large volume of dye in the ESP has also been postulated to favor its spread into the PVS 5 21. However, the pressure exerted during injection should theoretically be ‘consumed’ in the path of least resistance favoring fluid toward the ESP,22 without forcing its passage through the anatomical barrier existing between the epaxial and hypaxial muscle compartments,11 regardless of the volume injected 21. In this study, neither the pressure exerted nor the injection of a large volume (equivalent to 40 mL in a 70 kg human) produced real-time US-visible changes in the PVS compatible with anterior spread of dye.…”

The analgesic efficacy of a single injection of ultrasound-guided retrolaminar paravertebral block for breast surgery: a prospective, randomized, double-blinded study

“…Another cadaveric study, using magnetic resonance imaging and anatomical dissection, demonstrated that the RLB with 20 mL of injectate produced spread into the epidural and neural foramen spaces [ 24 ]. However, the pattern of injectate spread was variable [ 25 ], and the extent of paravertebral distribution could be volume-dependent [ 26 ]. Furthermore, most of these human anatomical studies had in common that the RLB was consistently associated with a large distribution of injectate posterior to the back muscle and with limited spread to the paravertebral block [ 24 , 25 , 27 ].…”