Distribution of in-line fluid injection pressure measurements during 40 MHz microultrasound targeted nerve injection in anaesthetised pigs

Opening pressure >138 kPa (20 psi) during intraneural injection is associated with nerve damage in dogs. The sensitivity of pressure for epineural contact lies between 90% and 97%. Our previous studies showed: (1) in Thiel embalmed soft cadavers, that opening pressure at perineural tissue, epineurium, and subepineurium had a log-normal distribution; and (2) in pigs, the fine detail of needles and nerve anatomy were visible using microultrasound.1 2 Our primary objective was to use 40 MHz microultrasound in pigs to precisely identify the tip of the needle relative to perineural tissue, epineurium, and subepineurium, and measure corresponding opening injection pressures.