Mid-humeral block

Intermediate. Each nerve is superficial and easy to see, but the radial nerve needs a second probe position on the outer side of the arm, and four separate injections take time. It suits learners who are already comfortable with the axillary block.

At the level of the upper and middle thirds of the arm the brachial plexus has already split into its terminal nerves, and each one has taken its own path.

The median nerve lies on the brachial artery, usually on its superficial (anterior) side, in the medial bicipital groove under the deep fascia. It crosses from lateral to medial over the artery as it runs down the arm.

The ulnar nerve starts next to the artery but moves backwards as it goes down, piercing the medial intermuscular septum to lie on the medial head of triceps. At mid-arm it is usually 1–2 cm behind the artery, near the basilic vein.

The musculocutaneous nerve has left the sheath higher up. It runs between biceps and brachialis, where it is a flat, bright oval in the fascial plane. Its sensory end is the lateral cutaneous nerve of the forearm.

The radial nerve winds round the back of the humerus in the spiral (radial) groove with the profunda brachii artery. On the lateral side of the arm, about 10–14 cm above the lateral epicondyle, it lies directly on bone under the lateral head of triceps, then passes through the lateral intermuscular septum to the front of the arm.

The medial cutaneous nerves of the arm and forearm run superficially near the basilic vein and are often blocked with a small extra injection.

• The pulse of the brachial artery in the groove between biceps and triceps on the inner arm.
• The junction of the upper and middle thirds of the humerus, about a hand's breadth below the axillary fold.
• The lateral epicondyle and the line of the humerus on the outer arm (for the radial nerve).

• Surgery on the forearm, wrist and hand, as an alternative to an axillary or infraclavicular block.
• When one nerve needs adding to an incomplete block (rescue).
• When a selective block is wanted, for example sparing the radial nerve to allow some movement.
• Analgesia after injury to the hand or forearm in the emergency department.

• Median nerve: front of the forearm flexors, thenar muscles, and the skin of the radial palm and the thumb, index, middle and half the ring finger.
• Ulnar nerve: flexor carpi ulnaris, the small muscles of the hand, and the skin of the little finger and ulnar side of the hand.
• Radial nerve: wrist and finger extensors, skin of the back of the forearm and the back of the radial hand.
• Musculocutaneous nerve: biceps and brachialis, and the skin of the lateral forearm (lateral cutaneous nerve of the forearm).
• With a small subcutaneous injection: medial cutaneous nerves of the arm and forearm.

Surface anatomy, relevant structures and landmarks

The brachial artery pulse at the junction of the upper and middle thirds of the arm. The needle entry is just above the pulse, aimed at each nerve in turn.

Positioning

Supine, arm abducted to 80–90° with the elbow straight or slightly bent and the forearm supinated.

Block technique

This was described by Dupré as a nerve-stimulator technique. From one skin entry over the artery, the needle is directed towards each nerve: median (superficial to the artery), ulnar (behind the artery), radial (deep, towards the humerus, below the artery) and musculocutaneous (into biceps, lateral to the artery). Each nerve is found by its motor response and given a separate injection.

Needle choice

22 G, 50 mm insulated short-bevel needle.

Neurostimulation technique

• Median: wrist flexion, thumb opposition and finger flexion.
• Ulnar: flexion of the ring and little fingers, thumb adduction.
• Radial: extension of the wrist and fingers.
• Musculocutaneous: elbow flexion (biceps).
• Accept each response at 0.3–0.5 mA.

Choice of local anaesthetic (including volume)

8–10 mL per nerve with a stimulator alone, so a total of 30–40 mL.

Show scan

Ba.V Basilic veinMn Median nerveBr.m Brachialis muscleBm Biceps muscleBa Brachial artery

Show scan

ECR.m Extensor carpi radialis muscleBRa.m Brachioradialis muscleTrm Triceps muscleRn Radial nerveHumerus HumerusBrm Brachialis muscle

Positioning

Supine, arm abducted to about 90°, elbow straight or slightly bent, forearm supinated. The operator sits or stands at the head or beside the arm with the screen in line with the probe.

Scanning technique

• Place the probe across the inner arm at the junction of the upper and middle thirds, over the brachial artery.
• Find the brachial artery (pulsatile, does not compress) with its two veins. The median nerve is the honeycomb oval on top of the artery.
• Slide the probe slightly backwards to find the ulnar nerve, which lies deeper and further back, on triceps near the basilic vein. Trace it up and down: it moves away from the artery as you go down.
• Slide forwards to the plane between biceps and brachialis to find the musculocutaneous nerve, a flat bright oval.
• For the radial nerve, move the probe to the outer side of the arm, a little above the middle. Look for the bright line of the humerus with the nerve lying directly on it, next to the small profunda brachii artery (colour Doppler helps).

Structures to identify

• Biceps
• Brachialis
• Triceps
• Humerus
• Brachial artery and veins
• Basilic vein
• Median nerve
• Ulnar nerve
• Musculocutaneous nerve
• Radial nerve and profunda brachii artery

Position / ergonomics

Sit beside the abducted arm with the screen beyond the hand, so you look along the needle to the screen. Move round to the outer side of the arm, or rotate the arm inwards, for the radial nerve.

Probe

High-frequency linear probe (10–15 MHz).

Settings

Nerve or small-parts preset, focus at the level of the nerve, colour Doppler to identify the profunda brachii artery.

Depth

2–3 cm on the medial side; 3–4 cm for the radial nerve.

Needle size

22 G, 50 mm short-bevel needle.

Needling technique

In-plane, from the front of the arm, through biceps. Block the deepest and most distant nerve first if possible, so that air or local anaesthetic does not spoil the view of the rest. A common order is musculocutaneous, median, ulnar. Then block the radial nerve from the outer side, in-plane from posterior or anterior, with the needle tip resting next to the nerve on the bone.

Optimal needle-tip position

• Median: next to the nerve, away from the artery, so the solution surrounds the nerve.
• Ulnar: next to the nerve, keeping clear of the basilic vein.
• Musculocutaneous: in the fascial plane between biceps and brachialis, next to the nerve.
• Radial: next to the nerve, between the nerve and the profunda brachii artery, on the humerus.

Drug choice

For surgery: 1.5–2% lidocaine with adrenaline, 1.5% mepivacaine, or 0.5% levobupivacaine / 0.5% ropivacaine for long analgesia. Mixtures of short- and long-acting agents are common.

Volume

4–6 mL per nerve with ultrasound (16–24 mL in total). Add 2–3 mL subcutaneously over the basilic vein for the medial cutaneous nerves if a tourniquet is used.

Optimal current if nerve stimulation is used

0.3–0.5 mA at 0.1 ms.

Muscle responses acceptable

• Median: wrist and finger flexion, thumb opposition
• Ulnar: ring and little finger flexion, thumb adduction
• Radial: wrist and finger extension
• Musculocutaneous: elbow flexion

Testing block success

• Median: pinprick on the pad of the index finger; thumb-to-little-finger pinch.
• Ulnar: pinprick on the pad of the little finger; finger spreading.
• Radial: pinprick on the back of the first web space; wrist extension.
• Musculocutaneous: pinprick on the lateral forearm; elbow flexion against resistance.

Indication

Rarely used at this level, because the nerves are separate. For long analgesia a catheter in the axillary or infraclavicular region is more practical.

Kit

Not routinely used.

Catheter

A catheter next to one nerve (for example the median) only covers that nerve.

Regime

Not applicable in routine practice.

• Trace each nerve up and down before you inject. The median follows the artery; the ulnar leaves it.
• Block the deepest nerve first so later injections do not obscure the view.
• For the radial nerve, find the bone first and then look for the nerve on it with the small artery beside it.
• The musculocutaneous nerve can occasionally run inside the median nerve sheath: if you cannot find it between biceps and brachialis, check near the median nerve.
• A tourniquet on the upper arm also needs the medial cutaneous nerves and the intercostobrachial nerve blocked.

• Bouaziz and colleagues (1997) compared the mid-humeral approach with a single-injection axillary block. Success was higher with the multi-injection mid-humeral approach, but it took longer to perform.
• Carles and colleagues (2001) reported the mid-humeral block in 1417 patients with about 95% success and a low rate of complications.
• With ultrasound, the separate-nerve approach at the axilla and mid-arm allows small volumes per nerve with high success, and is the basis of modern selective distal blocks (Dufeu 2014).

• Bouaziz H, Narchi P, Mercier FJ, et al. Comparison between conventional axillary block and a new approach at the midhumeral level. Anesth Analg 1997;84:1058–1062. PubMed
• Carles M, Pulcini A, Macchi P, et al. An evaluation of the brachial plexus block at the humeral canal using a neurostimulator (1417 patients): the efficacy, safety, and predictive criteria of failure. Anesth Analg 2001;92:194–198. PubMed
• Dufeu N, Marchand-Maillet F, Atchabahian A, et al. Efficacy and safety of ultrasound-guided distal blocks for analgesia without motor blockade after ambulatory hand surgery. J Hand Surg Am 2014;39:737–743. PubMed
• McCartney CJ, Xu D, Constantinescu C, Abbas S, Chan VW. Ultrasound examination of peripheral nerves in the forearm. Reg Anesth Pain Med 2007;32:434–439. PubMed