Ultrasound-guided Regional Anesthesia

Abstract

Approaches There are many approaches to regional blocks with ultrasound guidance. Here are some common techniques and some comments on their utility. Offline Markings. This means making skin markings based on ultrasound scans (but not imaging while the needle is placed). This method is limited by changes in patient position, skin mobility, elastic properties of soft tissue, distortion by local anesthetic injection and overall accuracy of the markings. Furthermore, although the required depth can be noted it is difficult to mark the anticipated angle of needle insertion. It is most commonly used today for spinal and epidural blocks. Online approaches (live realtime imaging while the needle is placed) are generally classified as either out-of-plane or in-plane. Out-of-plane (OOP). With this approach the needle tip crosses the plane of imaging as an echogenic dot. This approach is mostly used for shallow blocks and sometimes used for catheter insertion. The advantage is that the needle paths are short but one concern is that anatomic structures may be punctured outside the plane of imaging. In-plane (IP). With in-plane technique the entire shaft and needle tip are within the plane of imaging. This is an increasingly popular technique for regional blockade and provides the most direct form of guidance. The downsides are the longer needle paths and partial lineups are possible (when the shaft is mistaken for the needle tip). The most common error for novices with in-plane technique is to advance the needle without adequately identifying the tip. Hand on needle hub. This technique uses extension tubing and a reservoir syringe. It has the advantage of being a very precise method for needle control. Hand on syringe. This technique is often used with out-of-plane approaches to regional blocks and allows one operator to easily control the injection while the needle is moving. Needle tip visibility. Needle tip visibility is primarily influenced by the needle diameter and angle of insertion. Echogenic needles can be an advantage when steep angles of needle insertion are necessary. Spatial compound imaging also can help improve needle tip visibility over a limited range of angles. The needle bevel is easiest to identify when oriented to face the transducer. Solutions for injection. Injections of clinically degassed solutions of local anesthetic (all visible air removed) are recommended to help outline the visible borders of peripheral nerves with anechoic fluid.