Background: Nerve damage after regional anesthesia has been of great concern to anesthetists. Various modalities have been suggested to recognize and prevent its incidence. An understudied area is the measurement of intraneural pressure during peripheral nerve blockade. Previous investigations have produced contradicting results with only one study being conducted on human cadavers. Objectives: The purpose of this investigation was to systematically record intraneural and perineural injection pressures on the median, ulnar, and radial nerves exclusively as a primary outcome. Materials and Methods: Ultrasonography-guided injections of 1 mL of 0.9% NaCl over ten seconds were performed on phenol glycerine embalmed cadaveric median, ulnar, and radial nerves. A total of 60 injections were performed, 30 intraneural and 30 perineural injections. The injections pressure was measured using a controlled disc stimulation device. Anatomic dissection was used to confirm needle placement. Results: Intraneural needle placement produced significantly greater pressures than perineural injections did. The mean generated pressures in median, radial, and ulnar nerves were respectively 29.4 ± 9.3, 27.3 ± 8.5, and 17.9 ± 7.0 pound per square inch (psi) (1 psi = 51.7 mmHg) for the intraneural injections and respectively 7.2 ± 2.5, 8.3 ± 2.5, and 6.7 ± 1.8 psi for perineural injections. Additionally the intraneural injection pressures of the ulnar nerve were lower than those of the median and radial nerves. Conclusions: Obtained results demonstrate significant differences between intraneural and perineural injection pressures in the median, ulnar, and radial nerves. Intraneural injection pressures show low specificity but high sensitivity suggesting that pressure monitoring might be a valuable tool in improving the safety and efficacy of peripheral nerve blockade in regional anesthesia. Peripheral nerves “pressure mapping” hypothetically might show difference amongst various nerves depending on anatomic location, histologic structure, and ultrasonographic appearance. Keywords: Injections; Pressure; Radial Nerves

The aim of the study was to investigate the difference between intraneural and perineural injection pressures in human cadavers. Targeted nerves included the cervical roots, the supraclavicular and infraclavicular brachial plexus, the sciatic-subgluteal nerve and the common peroneal and tibial nerves. Ten readings were obtained for each nerve location. Over ten seconds, 1 mL of 0.9% NaCl was injected - deliberately slower than in clinical practice to eliminate the risk of aberrant readings relating to the speed of injection. Perineural injections occurred at least 1 mm outside the epineurium. After pressure recordings were completed 0.1mL of dye was injected, and dissection performed to confirm needle placement. Ultrasound and dissection images were matched with light microscopy pictures for all locations. The average pressure for intraneural injections was 24.1±5.7 psi and 6.1±2.1 psi for perinereural. The average injection pressure generated for the cervical trunk, supraclavicular, infraclavicular, sciatic subgluteal, peroneal and tibial nerves respectively were 31.2±6.0 psi, 24±15.0 psi, 23.4±9.5 psi, 22.6±8.8 psi 19.7±6 psi, 17±7.3 psi intraneurally and 6.1±2.0 psi, 9.1±5.5 psi, 10±4.9 psi, 6±2.4 psi, 6±2.4 psi and 7±2.5 psi perineurally. For intraneural injections statistically significant differences were demonstrated between the peroneal and tibial nerves compared to cervical roots/trunks/division/cords of brachial plexus. The study has consistently demonstrated statistically significant differences between intraneural and perineural injection pressures. It effectively created a "map" of intraneural injection pressures for the most common peripheral nerves blocks and demonstrated a pattern between proximal and distal locations. The study also revealed limitations of either techniques, ultrasound and injection pressure monitoring reinforcing the concept of their simultaneous application.

Regional anaesthesia, referred to as regional blocks, is one of the most frequently used methods of anaesthesia for surgery and for pain management. Local anaesthetic drug should be administered as close to the nerve as possible. If administered too far away, this may result in insufficient block. If it is administrated too close, severe nerve damage can occur. Neurostimulation techniques and ultrasound imaging have improved the effectiveness and safety of blockade, but the risk of nerve injury with permanent nerve disfunction has not been eliminated. Intraneural administration of a local anaesthetic damages the nerve mechanically by the needle and the high pressure generated by the drug inside the nerve. In many studies, injection pressure is described as significantly higher for unintended intraneural injections than for perineural ones. In recent years, the concept of combining techniques (neurostimulation + USG imaging + injection pressure monitoring) has emerged as a method increasing safety and efficiency in regional anaesthesia. This study focuses on the contribution of nerve identification methods to improve the safety of peripheral nerve blocks by reducing the risk of neural damage.