Fig. 23.1
Surface anatomy and landmarks for median nerve block
The patient is placed supine with the arm abducted slightly, the elbow flexed approximately 30°, and the forearm resting on an arm board. Surface landmarks include:
Medial
Medial epicondyle of the humerus
Lateral
Brachial artery pulse: immediately medial to the biceps brachii tendon.
Biceps brachii tendon: lateral to the brachial artery and median nerve, it may be best palpated with slight elbow flexion.
23.1.2 Nerve Stimulation Technique (Table 14.1)
The median nerve is superficially located at the elbow, and a short needle (3–4 cm at most) with a short bevel should be used for the blocks.
Complete elbow extension should be avoided to reduce the chance of elbow joint penetration.
Insert the needle perpendicular to the skin immediately medial to the pulse of the brachial artery.
Twitches will be seen in the lateral three digits (flexion of the thumb, index, or middle finger), although wrist flexion or forearm pronation can also indicate adequate nerve localization.
23.1.3 Ultrasound-Guided Technique
Refer to the VHVS and ultrasound images for the relevant anatomy (Fig. 23.2).
Fig. 23.2
(a) VHVS and MRI images at the antecubital fossa. (b) Ultrasound image of the median nerve at the antecubital fossa
23.1.3.1 Scanning Technique
High-frequency (10+ MHz) probes should be used for visualizing the median nerve in children.
Place the probe in the axial plane with the center of the probe just medial to the biceps tendon in order to capture a transverse view of the nerve (medially) and adjacent brachial artery (laterally).
Both the nerve and artery lie quite superficial, and the nerve can be larger than the artery at this location.
Color Doppler may be used to confirm the identity of the artery and of the nerve on its medial aspect.
23.1.3.2 Sonographic Appearance
The nerve appears oval/peanut-shaped and lies medial to the artery, which is often circular and smaller than the nerve (Fig. 23.2b).
23.1.3.3 Needle Insertion
An in-plane (IP) or out-of-plane (OOP) approach may be used to block the median nerve at the level of the elbow.
For the IP approach (Fig. 23.3), insert the needle medial to the median nerve in order to avoid the brachial artery. The needle will be perpendicular to the median nerve, and the goal will be to inject local anesthetic around the nerve. This approach may cause more discomfort in an awake patient due to a longer needle path compared to the OOP technique.
Fig. 23.3
In-plane needling approach for ultrasound-guided median nerve block. Blue rectangle indicates probe footprint
For the OOP approach (Fig. 23.4), position the nerve at the center of the ultrasound screen, and insert the needle in cross section to the transversely placed probe in a cephalad direction.
Fig. 23.4
Out-of-plane needling approach for ultrasound-guided median nerve block. Blue rectangle indicates probe footprint
Place the needle initially at a small distance (e.g., 1 cm) from the probe in order to view the needle tip once the needle has reached the nerve.
23.1.4 Local Anesthetic Application
The median nerve can be blocked using a 3–4 cm needle, insulated if using nerve stimulation, with 2–3 mL of 0.25–0.5 % ropivacaine.
Performing a test dose with D5W is recommended prior to local anesthetic application to visualize the spread and confirm nerve localization.
Aim to spread approximately 1–3 mL of local anesthetic around the nerve in a circular fashion in order to avoid nerve contact but obtain a complete block.
The local anesthetic injection will appear as an expansion of hypoechogenicity surrounding the nerve.
23.1.5 Case Study
Median Nerve Block at the Elbow (Contributed by A. Spencer)
A 12-year-old girl, 44 kg in weight, presented for hand surgery. An X-ray showed a mildly displaced intra-articular fracture of the distal portion of the proximal phalanx of the left thumb without involvement of the epiphyseal growth plate. The patient required an open reduction and internal fixation of the proximal phalanx and underwent a general anesthetic combined with an ultrasound-guided median nerve and radial nerve block at the elbow. Both blocks were performed with a 40 mm, 22G needle using an in-plane approach (see Figs. 23.5 and 23.10). Four mL of 0.5 % bupivacaine was used for each block; block duration was 6–12 and 8–12 h for the median and radial nerve blocks, respectively. The duration of surgery was 1 h, 10 min. Pain reporting was 0/10 at both 30 and 60 min post-op with sensory block noted in the median and radial territories. Postoperative analgesia consisted of acetaminophen 500 mg po q4h prn and ibuprofen 400 mg po q6h prn.
Fig. 23.5
Ultrasound-guided median nerve block. M median nerve, BA brachial artery, arrowheads indicate needle position (see Case Study for details)
23.2 Radial Nerve Block
The radial nerve innervates muscles which produce extension (dorsiflexion) of the wrist and digits. The nerve carries fibers from the upper and middle trunks, the posterior division, and the posterior cord of the brachial plexus and emerges from the posterior aspect of the plexus.
The nerve’s origin lies posterior to the second and third parts of the axillary artery, and it descends within the axilla across the subscapularis, teres major, and latissimus dorsi muscles (the nerve lies on the insertion of this latter muscle).
It then passes between the medial and lateral heads of the triceps brachii muscle and descends obliquely across the posterior aspect of the humerus along the spiral (radial) groove at the level of the deltoid muscle insertion (Fig. 10.11). It travels posterior and medial to the deep brachial artery of the arm at this location.
The nerve reaches the lateral margin of the humerus above the elbow before crossing over the lateral epicondyle and entering the anterior compartment of the arm in a deep groove between the brachialis and brachioradialis muscles proximally and the extensor carpi radialis longus muscle distally.
In front of the lateral epicondyle of the humerus, the nerve divides and continues as the superficial radial (sensory) and the deep posterior interosseous (motor) nerves.
The radial nerve supplies the posterior compartments of the arm and forearm, including the skin and subcutaneous tissues. It also supplies the skin on the posterior aspect of the hand laterally near the base of the thumb and the dorsal aspect of the index finger and the lateral half of the ring finger up to the distal interphalangeal crease.
23.2.1 Surface Anatomy (Fig. 23.6)
Fig. 23.6
Surface anatomy and landmarks for radial nerve block
The patient is placed supine with the arm abducted slightly, the elbow flexed approximately 30°, and the forearm resting on an arm board. Surface landmarks include:
Deltoid tuberosity: internal rotation of the arm accentuates the posterior deltoid region and enables the deltoid muscle to be traced to its point of insertion on the tuberosity. The spiral groove lies just distal to the tuberosity.Related posts:
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