Mechanistic insights into bupivacaine spread through anisotropic tissue planes and fascial barriers: experimental evidence for interfascial block dynamics

Low-volume injectate of bupivacaine spread anisotropically within fresh muscle and permeated fascial barriers in ways not demonstrated by methylene blue or iodinated contrast. The exponential decrease of concentrations provides evidence that diffusion contributes to local anesthetic distribution and may help explain, at least in part, the broad and occasionally disproportionate sensory coverage observed clinically with interfascial plane blocks.