[Ultrasound-guided peripheral regional anesthesia : placement and dosage of local anesthetics]

Ever since the use of ultrasound guidance in regional anesthesia became more and more popular in recent years, it seemed obvious that so-called intraneural puncture and injection of local anesthetics was much more common than previously assumed. However, neurologic damage was not seen very often. The ultrasound-guided imaging of the nerves showed that intraneural injection has to be seen as an overall term. This term must be characterized in more detail in accordance with nerve anatomy and morphology. Various studies demonstrated that if intraneural puncture occured the needle usually took a path away from the fascicles (intraneural perifascicular), while intraneural transfascicular puncture seemed relatively rare and intraneural intrafascicular placement of the needle even more uncommon. As long as the needle is placed intraneurally but in an extrafascicular fashion a safe injection and the absence of neurologic damage can be assumed. However, if nerve fascicles are affected neurologic dysfunction can occur. In studies investigating the minimal effective local anesthetic volume needed for successful nerve block, a relevant reduction of injected volume was still achieved by intentionally applying the local anesthetic circumferentially around the outermost nerve layer rather than injecting it into neural structures. As an intraneural -intrafascicular injection carries the risk of nerve injury associated with a decrease in quality of life, the potential of ultrasound guidance in regional anesthesia should be considered. Circumferential administration of local anesthetic rather than creating a single point injection appears to be advantageous.