Landmark-based approach

As for all regional anesthetic procedures, after checking that emergency equipment is complete and in working order, intravenous access, ECG, pulse oximetry, and blood pressure monitoring are established. Asepsis is observed.

The patient is placed supine and the arm abducted at 90°. At the junction between the upper and middle thirds of the arm, a line is drawn over the brachial artery. The needle insertion point is infiltrated with local anesthetic using a 25-G needle. A 50-mm 22-G insulated needle connected to a peripheral nerve stimulator is inserted almost tangentially to the skin, between the brachial artery and the palpating finger, in the direction of the axilla, in order to locate the median nerve (Fig. 20.3). The stimulating current is set at 1.0 mA, 2 Hz, and 0.1 ms. The needle is advanced slowly until the appropriate muscle response is obtained. The needle position is adjusted while decreasing the current to 0.35 mA with maintenance of the muscle response. Stimulation of the median nerve will produce contraction of the flexor carpi radialis and flexor digitorum superficialis of the fingers. Incremental injections of local anesthetic (6–8 mL) are made with repeated aspiration.

Figure 20.3 Midhumeral block technique: locating the median nerve. The needle is inserted anterior and parallel to the brachial pulse to locate the median nerve.

After blocking the median nerve, the current is increased to 2 mA, and the needle withdrawn and redirected beneath and medial to the artery (Fig. 20.4). Stimulation of the ulnar nerve induces contraction of the flexor carpi ulnaris muscle. Incremental injection of local anesthetic (6–8 mL) is made with repeated aspiration.

Figure 20.4 Midhumeral block technique: locating the ulnar nerve. The needle is inserted medial and perpendicular to the brachial pulse to locate the ulnar nerve.

The needle is now withdrawn and, with a high level of stimulation in the subcutaneous position, redirected toward the radial nerve. This nerve is posterior to the artery, close to the humerus (Fig. 20.5). Stimulation of the radial nerve causes contraction of the extensor muscles of the forearm. Incremental injections of local anesthetic (6–8 mL) are made with repeated aspiration.

Figure 20.5 Midhumeral block technique: locating the radial nerve. The skin is retracted inferior to the brachial pulse and oriented perpendicular to the artery and toward the humerus to locate the radial nerve.

To block the musculocutaneous nerve, the needle is directed from its initial subcutaneous position beneath the biceps muscle (Fig. 20.6). Stimulation of this nerve induces contraction of the biceps muscle and flexion of the elbow. Incremental injections of local anesthetic (6 mL) are made with repeated aspiration. A final 3 mL is injected medial to the artery to block the medial cutaneous nerves of the arm and the forearm.

Figure 20.6 Midhumeral block technique: locating the musculocutaneous nerve. The needle is inserted superior to the brachial pulse and under the biceps to locate the musculocutaneous nerve.

Ultrasound-guided approach

The ultrasound machine and block tray should be placed in positions which allow the operator to simultaneously scan the patient and take items from the block tray with minimal movement. This setup may take some forethought but is a worthwhile exercise, and will facilitate successful regional anesthesia.

The operator stands on the side to be blocked, and with the patient supine and the arm abducted at 90 ° (Fig. 20.7). The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The humeral canal region is scanned with a 7–13 MHz linear transducer. The ultrasound screen should be made to look like the scanning field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

Figure 20.7 Global view of the block field for the ultrasound-guided humeral block.

With transverse imaging of the humeral canal, in half of the cases, when the point of puncture is situated cephalic to the ultrasound transducer the needle crosses the basilic vein in order to reach the ulnar nerve. Similarly, the radial nerve cannot be blocked through this pathway because the humerus is situated on the pathway of the needle in 58% of cases (Fig. 20.2). It would be possible to introduce the needle on the caudal side of the probe, but in this configuration, movements of the needle are impeded by the upper limb layout.

Two points of puncture are thus used for the ultrasound-guided humeral block: the first is dedicated to the blockade of radial and ulnar nerves (moving the transducer caudally); and the second is dedicated to the blockade of musculocutaneous and median nerves. This technique allows a reduction of the skin-to-radial nerve distance to facilitate visualization of the radial nerve otherwise hidden by the humerus.

In this configuration, the radial nerve is initially blocked through an out-of-plane approach. After the transducer has been re-directed anterior to the vessels, the ulnar nerve is blocked within the same point of puncture through an in-plane approach (Fig. 20.8). Nerves from the cephalic compartment are both blocked through an in-plane approach. The deepest nerve is always blocked first; otherwise the injected local anesthetic impedes location of the deepest structures.

Figure 20.8 (A) Position of the patient, the ultrasound transducer, and the needle during block of the radial nerve. (B) Position of the patient, the ultrasound transducer, and the needle during block of the ulnar, the median, and the musculocutaneous nerves. The ultrasound transducer is repositioned more cephalad and slightly laterally compared to the position of the transducer described in A; for the block of the ulnar nerve, the needle is re-orientated in an in-plane position. (C) A second point of puncture is performed on the cephalad side of the ultrasound transducer in order to block the musculocutaneous nerve and the median nerve through an in-plane approach.

A 22-GA × 50-mm insulated needle (B. Braun, Bethlehem PA) is attached to sterile extension tubing, which is connected to a 20 mL syringe and flushed with local anesthetic solution to remove all air from the system. It is then introduced as indicated above. It is important not to advance the needle without good visualization. This may require needle or transducer adjustment.

Once the needle has approached each individual nerve, 1–2 mL of local anesthetic may be injected to confirm correct needle placement. Local anesthetic appears as a hypoechoic image. Correct needle placement is confirmed by observing solution surrounding each individual nerve (Fig 20.9). Should this not occur, the needle may need to be repositioned, and the procedure repeated. Following confirmation of correct needle placement, 4–6 mL of local anesthetic solution can be injected to achieve blockade of each nerve.

Figure 20.9 (A) Sonoanatomy of the radial nerve at the humeral canal. RN: radial nerve; HB: humerus; HA: humeral artery. (B) Sonoanatomy of the median and ulnar nerves. UN: ulnar nerve; MN: median nerve; HA: humeral artery; BV: basilic vein; HB: humerus. (C) Sonoanatomy of the musculocutaneous nerve. MCN: musculocutaneous nerve; CBM: coracobrachialis muscle; BB: biceps brachialis muscle; HB: humerus; HA: humeral artery.

Continuous technique

Continuous midhumeral techniques have not been described, but it may be possible to provide continuous anesthesia of an individual upper arm nerve at this location. Ultrasound can be used to assist catheter placement.