FOREARM BLOCKS AT A GLANCE
Indications: hand and wrist surgery (Figure 32F-1)
Transducer position: transverse on the elbow
Goal: injection of local anesthetic within the vicinity of individual nerves (radial, median, and ulnar)
Local anesthetic: 4–5 mL per nerve
Expected sensory distribution of the radial (blue), median (dark blue) and ulnar nerve blocks (red) proximal to the elbow.
Ultrasound imaging of individual nerves in the distal upper limb allows for reliable nerve blockade. The two main indications for a forearm block are a standalone technique for hand and/or wrist surgery and as a means of rescuing or supplementing an incomplete or failed proximal brachial plexus block. Advantages of rescue block are the reduction of the risk of vascular puncture and in the overall volume of local anesthetic used. There are a variety of locations where a practitioner could approach each of these nerves, most of which are similar in efficacy. In this chapter, we present the approach for each nerve at the level of the elbow.
Ultrasonographic assessment shows that a median nerve block using nerve stimulation alone is commonly associated with intraneural injection.1
Some authors have suggested additional indications for forearm blocks, in combination with a proximal brachial plexus block. Combining proximal and distal blocks allows for a decrease in onset time and improved block consistency.2 It is possible to use these blocks in the setting of wrist or hand surgery involving the bone to provide long-lasting analgesia without blocking the whole limb for many hours; this is done by combining a short-acting brachial plexus block with distal blocks around the elbow, according to the surgical procedure.3 If distal blocks are to be performed after a proximal brachial plexus block, it is of paramount importance to clearly visualize the needle tip at all times in order to avoid intraneural injection.
The radial nerve is best visualized above the lateral aspect of the elbow, lying in the interfascial plane between the brachioradialis and the brachialis muscles (Figure 32F–2). The transducer is placed transversely on the anterolateral aspect of the distal arm, 3–4 cm above the elbow crease. The nerve appears as a hyperechoic, triangular or oval structure with the characteristic honeycomb appearance of a distal peripheral nerve. The nerve divides just distal to the elbow crease into the superficial (sensory) and deep (motor) branches. These smaller divisions of the radial nerve are more challenging to identify in the forearm; therefore, a single injection above the elbow is favored because it ensures blockade of both. The transducer can be slid up and down the arm to better visualize the nerve and the musculature surrounding it. ...