Identification of spread after deliberate intraneural injection in five mammalian species

Abstract

IntroductionThis research endeavors to investigate the phenomenon of intraneural spread across distinct locations: subcircumneurium, extrafascicular intraneural, intrafascicular intraneural, and intraperineurium after deliberate intraneural injections across five mammalian species. The study also aims to propose determinants influencing this spread. Furthermore, the investigation strives to ascertain the optimal animal species and needle configuration for extrapolating intraneural injection outcomes to human contexts.MethodsThis study examined 60 sciatic nerves from 30 fresh and untreated cadavers of rats, rabbits, dogs, pigs, and sheep. The specimens were organized into five groups, each comprising an equal number of nerves. Histological assessments were performed on 30 nerves, involving fascicle metrics. The remaining 30 nerves underwent intentional intraneural injections, facilitated by 19G and 23G needles under ultrasound and direct visualization guidance.Heparinized erythrocytes combined with a methylene blue solution were used as a marker to analyze the extent and patterns of intraneural spread. Needle orifice measurements were obtained, and these data were overlaid onto images of both nerves and needles. This enabled a comparative evaluation of sizes and an assessment of marker diffusion.ResultsThe findings indicated that sciatic nerves in rats, rabbits, and dogs were oligofascicular, characterized by larger fascicles, whereas pigs and sheep exhibited polyfascicular nerves comprised of numerous smaller fascicles. Fascicular diameters were variable across species, with dogs presenting the largest measurements. While intraneural spread was observed and documented, intrafascicular marker spreading was rare, occurring only in one rabbit specimen. Needle orifice attributes were scrutinized and visually depicted.ConclusionsDespite the formidable challenges associated with the practical realization of intrafascicular injection, the utilization of animal models possessing monofascicular or oligofascicular nerves, such as rats, rabbits, and dogs, in conjunction with needles featuring aperture dimensions surpassing those of the fascicles, likely contributes to the compromised reliability of investigations into intraneural injection outcomes.

The Forces Associated with Bolus Injection and Continuous Infusion Techniques during Ultrasound-Targeted Nerve Contact: An Ex Vivo Study

“…Ultrasound guiding has become the standard method for regionally delivering anaesthesia due to its ability to provide the real-time visualization of anatomical structures and the needle trajectory [1]. However, ultrasound has its limitations, particularly in accurately detecting the needle tip, especially in tissues with complex echogenicity, such as nerves [2]. This can make it challenging to achieve precise needle placement and avoid nerve damage during regional anaesthesia interventions.…”

“…Fat-filled circumneural fascial tissue is only visible via histology [4] or experimental 40 MHz microultrasound [6]. Accordingly, different authors [2,5,6] have recommended that the nerve is touched gently [6] so that the aperture of the block needle partially covers the epineurium and the injectate takes the path of least resistance away from the stiff epineurium to the elastic circumneural fat compartments [7].…”