Monday, October 1, 2018

Wrist Block (Landmark Technique)

While a majority of injuries on hand can be managed by local infiltration of anesthetics, wrist nerve blocks may be required in instances such as diffuse lesions, deep lacerations, deep contaminated abrasions, hydrofluoric acid and thermal burns. Wrist blocks are also particularly useful when the injured extremity is swollen and local infiltration may lead to severe pain.

Nerves at the level of the wrist are more easily accessible anatomically and can be blocked more reliably. All three nerves (Median, Radial, Ulnar) lie in the volar aspect of the wrist near easily palpated tendons. However, a full wrist block may have a slow and unreliable onset and can require more time to take effect.

Right wricrossectionalonal view

1. Median Nerve

Location - Just below the palmaris longus (PL) tendon OR slightly radial to it between the PL and flexor carpi radialis (FCR) tendons. The nerve lies relatively superficially (1cm or less from skin) but deep to the fascia of the flexor retinaculum.

PL tendon is located by having the patient make a fist with the wrist flexed against resistance. Use a 25-gauge needle and go perpendicular to the skin on the radial border of the palmaris longus tendon just proximal to the proximal wrist crease. Advance the needle slowly until a slight “pop” is felt as the needle penetrates the retinaculum. Inject 3 to 5 mL of anesthetic in the proximity of the nerve at a depth of 1 cm under the tendon.

https://www.researchgate.net/figure/Peripheral-nerve-blocks-at-the-wrist-A-Median-nerve-block-B-Ulnar-nerve-block-C_fig2_320883196

Caveats - PL may be absent in up to 20% of patients, in which case you inject at about 1 cm in the ulnar direction from the FCR tendon. The superficial position of the median nerve at the wrist is a major cause of failure of this block as the anesthetic is often instilled too deep.

2. Radial Nerve

Nerve block of radial nerve requires an injection in close proximity to the artery and a field block that extends around the dorsal aspect of the wrist. Radial nerve follows the radial artery into the wrist but gives off sensory nerve branches proximal to the wrist. These branches wrap around the wrist and fan out to supply the dorsal and radial aspect of the hand.

Insert a 25-gauge needle and inject 2-5ml of LA immediately lateral to the palpable artery at the level of the proximal palmar crease. Inject another 5 to 6 mL of anesthetic subcutaneously from the initial point of injection to the dorsal midline. Withdraw the needle and reposition it to complete the block.

3. Ulnar NerveThe ulnar nerve follows the ulnar artery into the wrist, where they both lie deep to the flexor carpi ulnaris (FCU) tendon (The nerve lies between the tendon and the artery). The FCU tendon is palpated just proximal to the prominent pisiform bone by having the patient flex the wrist against resistance.

Use a lateral approach to ulnar nerve block rather than volar approach due to risk of ulnar arterial puncture. Use a 25-gauge needle and inject on the ulnar aspect of the wrist at the proximal palmar crease and deposit a wheal of anesthetic horizontally under the flexor carpi ulnaris tendon. Then direct the needle toward the ulnar bone at a point deep to the flexor carpi ulnaris tendon and inject 3 to 5 mL of anesthetic solution as the needle is withdrawn. Block the dorsal cutaneous branches by subcutaneously injecting 5 to 6 mL of anesthetic from the lateral border of the flexor carpi ulnaris tendon to the dorsal midline.

Images from:

Roberts and Hedges’ Clinical Procedures in Emergency Medicine

Posted by:

Lakshay Chanana

ST4 Trainee

Royal Infirmary of Edinburgh

Department of Emergency Medicine

Edinburgh

Scotland

@EMDidactic

Monday, September 17, 2018

Ankle Block (Landmark Technique) - Procedures

Ankle block covers the five nerves around the ankle joint. Three nerves are located anteriorly and supply the dorsal aspect of the foot. Two nerves are located posteriorly and supply the volar aspect. A complete nerve block of the foot requires blocking three subcutaneous nerves and two deeper nerves. Overlap of the sensory distribution frequently necessitates blocking multiple nerves for adequate anesthesia.

Deep peroneal - Deep - Supplies Anteriorly
Posterior tibial - Deep - Supplies Posteriorly
Saphenous - Superficial - Supplies Anteriorly
Superficial peroneal - Superficial - Supplies Anteriorly
Sural nerves - Superficial - Supplies Posteriorly

Depending on the desired area of anesthesia, one or more of the five nerves are blocked. Nerve block of the sural and posterior tibial nerves together anesthetizes the bottom of the foot and is the most useful combination.

Indications

Procedures on the foot (lac repair, I&D, FB removal, wound irrigation). The rationale for using Ankle block over infiltration anesthesia on the sole is that skin of the sole is thicker and more tightly bound to the underlying fascia making skin puncturing quite difficult and painful. Large amounts of anesthetic on sole may lead to painful distention of the tissue and circulatory compromise of the microvasculature.

Relevant Anatomy and Sensory supply of 5 nerves around Ankle Joint

Image from Roberts & Hedges - Clinical Procedures in Emergency Medicine

Site of Injections (2 deep injections and 3 bands)

1. Posterior Tibial Nerve - Posterosuperior to the posterior tibial artery between medial malleulus and Achilles. At a depth of 1 cm, inject 3 to 5mls of anesthetic.

2. Deep Peroneal Nerve - Palpate the EHL and anterior tibial tendons (Ask the patient to dorsiflex the foot and big toe) and inject 3-5mls LA 1 cm superior to the medial malleolus under the EHL tendon until it strikes the tibia.

3. Superficial Peroneal - Inject 4 to 10 mL of anesthetic subcutaneously in a band between the EHL tendon and the lateral malleolus.

4. Saphenous - Inject 3-5ml of LA subcutaneously in a band between the medial malleolus and the anterior tibial tendon.

5. Sural Nerve - Block at the lateral aspect of the ankle between Achilles and the lateral malleolus. Inject 3 to 5 mls of anesthetic subcutaneously in a band like fashion at about 1 cm above the lateral malleolus.

All five nerves can be blocked by placing subcutaneous band blocks around 75% of the ankle circumference and two deep injections: one next to the palpable posterior tibial artery (Post Tibial Nerve) and the other under the extensor tendon of the big toe (Deep Peroneal Nerve).