Distal median/ulnar and radial blocks

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Introduction: Ultrasound guided SS distal median/ulnar and radial blocks can be used as the primary regional anesthesia for wrist and hand surgery, however, because of the usual requirement for tourniquet analgesia, distal median nerve block, ulnar nerve block and radial nerve blocks are more commonly used to supplement a more proximal brachial plexus block e.g. infraclavicular block. Supplementation in this situation means either to complete a "patchy" brachial plexus block, or to accelerate the onset of upper extremity anesthesia.


Skill level: Simple.


Procedure time: 2-5 mins per nerve (2 mins for experienced practitioners)


Common indications

Common: Supplementation of a more proximal brachial plexus block e.g. to complete a "patchy" brachial plexus block, or to accelerate the onset of upper extremity anesthesia.

Less common: Primary anesthesia for wrist and hand surgery.


Sedation: e.g. midazolam 2 mg + alfentanil 250-500 mcg


Anatomy: See below


Surface landmarks: Median nerve block=midline anterior point of the forearm at its midpoint (from elbow to wrist) . Ulnar nerve block=ulnar aspect of forearm at the junction of middle and proximal thirds (from elbow to wrist). Radial nerve block=lateral arm at the junction of middle and distal thirds (from shoulder to elbow).


Needle: 22G blunt needle.


Setup

1. High resolution linear array probe e.g. SonoSite L38

2. 2 inch 22G blunt needle

3. 12 mL LA filled syringe


Procedure

Median, ulnar and radial nerve blocks are performed with an in-plane needle imaging technique and 4 ml ropivacaine 0.50-0.75% for each nerve. The sites described have been shown to be the optimum sites for nerve visualisation. All nerves appear hyperechoic compared to the surrounding muscles. The procedural objective of distal blocks is to place LA in proximity, in at least 2 positions (ideally each side) around the nerves but specifically avoiding intraneural injection as follows.

1.      Median nerve block (Video 1 and 2). At the mid forearm level (prox. to distal) between the flexor digitorum superficialis and muscles flexor digitorum profundus muscles (Fig. 1). 1


 Median nerve at the mid-forearm level

Fig. 1.Median nerve block: ultrasound image of median nerve at the mid-forearm level. Nerve is located between flexor digitorum superficialis and flexor digitorum profundus muscles. Blue arrow=nerve. Red arrow=needle shaft

 

The median nerve runs down the forearm in the middle of the compartment, therefore, probe placement is usually at the forearm midpoint (from radial to ulnar). The arm is abducted and externally rotated with the palm facing up. Needle advancement is in-plane from the radial to the ulnar side of the forearm, therefore the needle puncture site is usually on the radial side of the forearm (Fig. 2).

 

medianpic

 Median nerve at the mid-forearm level sonography

Fig. 2. Median nerve path (a) and median nerve block (b). Needle insertion on radial side of midforearm. Here the US machine is such that the operator must turn the head 90 degrees right to view the screen. Block performance is easier if the machine is directly in front of the operator (i.e. on the opposite side of the bed in this figure).

 

2.       Ulnar nerve block (Video 3 and 4). At approximately the junction of the middle and proximal thirds of the forearm (prox. to distal) just proximal to where the nerve diverges from the ulnar artery (Fig. 3). 2


 Ulnar nerve at the proximal forearm level

Fig. 3. Ulnar nerve block: ultrasound image of ulnar nerve at the proximal forearm level. UA=Ulnar artery. UN=Ulnar nerve. Access to the nerve is facilitated by tracing the nerve proximally until it diverges away from the ulnar artery.

 

The arm is abducted and externally rotated with the palm facing up. Probe placement is on the ulnar side of the forearm. Needle advancement is in-plane from anterior to posterior (Fig. 4).


ulnarpic


ulnar nerve block

 Fig. 4. Ulnar nerve path (a) and ulnar nerve block (b).

 

3.      Radial nerve block (Video 5). At approximately the junction of the middle and distal thirds of the arm (shoulder to elbow) just distal to the nerve leaving the spiral groove of the humerus (Fig. 5). 2, 3

radial nerve block

Fig. 5. Radial nerve block: ultrasound image of radial nerve in the distal (upper) arm. 


The arm is adducted and internally rotated with the forearm resting on the chest. The probe is placed on the outer aspect of the arm. Needle advancement is in-plane from anterior to posterior (Fig. 6). In our experience, the radial nerve is the most challenging nerve to image. Move the probe from the mid arm distally towards the elbow and look for a hyperechoic structure swinging around from behind the humerus towards the extensor compartment. The radial nerve is often accompanied by the deep brachial artery, which when present is a useful landmark. Colour doppler can assist its identification.


radialpic


radial nerve block at distal humerus

Fig. 6. Radial nerve path (a) and radial nerve block (b). N.B. Here the hand holding the probe is not well stabilised against the patient. A more ideal hand position involves resting the side of the wrist to rest against the distal arm near the elbow, thus assisting probe stabilisation and minimisation of inadvertent probe "sliding".


Local anesthetic regimen: 4 mL ropivacaine 0.5-75% per nerve.


Specific Complications: None of note


Clinical PEARLS

1.To facilitate nerve visualisation:

a) Median nerve block – slide the probe proximally/distally at the midforearm level and tilt forward and back to optimise nerve visualisation.

b) Ulnar nerve block – first visualise the ulnar artery at the junction of middle and proximal thirds of the forearm then slide probe proximally and look for a hyperechoic structure diverge from the artery.

c) Radial nerve block – place probe at approx. the mid arm level on its posterior(extensor) aspect. Slide probe distally watching for a hyperechoic structure swing around laterally from behind the humerus.

 


Videos

Video 1. Median nerve block



Video 2. Median nerve block (US). Aim for LA spread immediately adjacent to the nerve. LA injection superficial to nerve not captured on this video


Video 3. Ulnar nerve block.


Video 4. Ulnar nerve block (US). The ulnar artery is visualised first then the nerve. Tracing the nerve proximally until it diverges away from the artery facilitates access to the nerve.




Video 5. Radial nerve block (sonography). Only radial nerve identification displayed here (not LA injection). The first few seconds of the video illustrates the nerve swinging anteriorly around the lateral humerus as the probe is moved distally towards the elbow. Concomitant neurostimulation can be used to assist nerve identification (wrist extension). LA is injected on both sides of the radial nerve.


 

Video 5b. Radial nerve block 2 (sonography). Includes LA deposition. In this video, right is anterior as suggested by the origin of the advancing needle.

 


References

 

1.         McCartney CJ, XD, Constantinescu C, et al. Ultrasound examination of peripheral nerves in the forearm. Reg Anesth Pain Med 2007;32:434-9.

2.         Kathirgamanathan A, French J, Foxall GL, et al. Delineation of distal ulnar nerve anatomy using ultrasound in volunteers to identify an optimum approach for neural blockade. Eur J Anaesthesiol 2009;26:43-6.

3.         Foxall GL, Skinner D, Hardman JG, et al. Ultrasound anatomy of the radial nerve in the distal upper arm. Reg Anesth Pain Med 2007;32:217-20.