Nerve blocks provide a fast and efficient method of providing adequate analgesia to facilitate treatment or repair of injuries such as fractures, dislocations, lacerations or removal of foreign bodies.
Caution must be taken in choosing patients suitable for regional anaesthetic; a cooperative patient is absolutely essential and therefore, it may be more appropriate to use procedural sedation in very young children. As well as a struggling child, there are other contraindications to regional techniques. These include:
- Local anaesthetic sensitivity/allergy
- Circulatory compromise
- Overlying skin infection
Choosing an appropriate local anaesthetic agent
The choice of agent depends on the type of injury and the desired onset and duration of pain relief. Commonly, short-acting agents alone are used for digital and auricular blocks, while a combination of short and long-acting agents are useful for femoral nerve blocks.
Lignocaine 1% or Procaine: onset 5-10 mins, duration 30-40mins
Max dose 3mg/kg
Long acting agents
Bupivacaine (Marcaine): 0.25%, onset 5-10mins, duration 2 hrs
Max dose 2.5mg/kg
*It is thought that the combined use of lignocaine and adrenalin (1:100,000) can increase the risk of digital ischaemia and is best avoided. Actually the evidence isn’t that clear cut. Adrenaline is added to a local anaesthetic to prolong its effect. The concern it will constrict end arteries, leading to localized ischaemia, has led to the recommendation to avoid adrenaline in fingers and toes. Cochrane published a review in 2015 which concluded, “from the limited data available, the evidence is insufficient to recommend use or avoidance of adrenaline in digital nerve blocks.” So there we are, still on the fence.
There’s a bit of a Catch-22 when it comes to injecting local anaesthetic. It hurts, because it’s an acid, and causing pain can lose the trust and rapport you just spent the last 15 minutes building with a child. Even worse, adding adrenaline makes it even more acidic and therefore even more painful to inject. There are two things we can do to make lignocaine less painful to inject:
- Buffer it to bring the pH up to a more physiological pH. Mix 10ml of 1% lignocaine (or 1% with 1:100,000 adrenaline) with 1ml of 8.4% bicarbonate (using a ratio of 8.4% bicarbonate : 1% lignocaine of 1:10)
- Warm it to room temperature. An EMJ review in 2007 suggested that warming local anaesthetic solution can significantly reduce the pain of infiltration.
The preparation for regional nerve blocks is the same at any site; clean the area with iodine or chlorhexidine solution to reduce the risk of infection. Soaking a digit in a bath of the antiseptic solution may be easier.
So, let’s look at some specific blocks.
Digital nerve block
On assessment, Harry has a closed injury of his 5th finger, with no neurovascular compromise. There is an obvious deformity of the proximal phalanx, with reduced movement at the joint. An x-ray reveals a dorsal dislocation of the proximal interphalangeal joint, with no evidence of an associated fracture. Harry needs that finger relocating but you think to yourself, you’d better put in a ring block.
Repair or treatment of injuries such as dislocations, lacerations, foreign bodies to the digits of the upper or lower extremities
- Two dorsal digital nerves at the 10 and 2 o’clock positions of the phalanx.
- Two palmar digital nerves at the 4 and 8 o’clock positions.
- Each palmar digital nerve is closely associated with a digital artery and vein.
- Place the hand or foot flat on a sterile surface.
- Clean the skin
- Hold a syringe containing a short-acting anaesthetic, such as 1% lignocaine, perpendicular to the digit and insert the needle into the subcutaneous tissue of the digital webspace.
- After aspirating to ensure you’re not in a vessel, slowly inject 2 ml of anaesthetic into the subcutaneous tissue and infiltrate, surrounding the nerve, as you withdraw
- Withdraw needle and repeat procedure on the opposite side of the digit.
- Allow 5 to 10 minutes for the local anaesthetic to work before performing the procedure.
Ulnar nerve block
The management of injuries to the ulnar border of the palm, as well as the 5th finger such as lacerations to or manipulation of metacarpal or interphalangeal fractures.
- The ulnar nerve passes between the ulnar artery and tendon of the flexor carpi ulnaris (FCU). The ulnar nerve is deep to the tendon flexor carpi ulnaris, and medial to the ulnar artery.
- The palmer and digital branches of the ulnar nerve supply the medial aspect of the palm and ring finger, as well as the entire little finger, respectively.
- Insert needle deep to the FCU, proximal to its attachment at the styloid process of the ulna
- advance the needle 5-10mm further beyond the tendon on the FCU, injecting 3-5ml of local anaesthetic
- If blood is visible on aspiration, redirect the needle superficially and medially to avoid the ulnar artery
Have a look at this fabulous video from Mike Stone for some in-action ulna nerve blockade.
Auricular nerve block
Treatment of injuries to the external ear such as lacerations, haematomas requiring drainage, and removal of foreign bodies, such as embedded earrings, while preserving anatomy.
- The outer portion of the auricle receives its innervation from the greater and lesser auricular nerves and auriculotemporal nerve
- The medial portion receives innervation from the auriculotemporal nerve and auricular branch of the vagus nerve
To anaesthetise the greater auricular nerve (for all things earlobe related):
- Clean the skin
- Insert a 25 gauge needle containing a short-acting local anaesthetic such as 1% lignocaine subcutaneously below the earlobe in line with the external auditory meatus.
- Direct the needle behind the ear towards the mastoid process, advance it parallel to the skin, aspirate to ensure you’re not in a vessel, then inject 2-3ml as you withdraw the needle
- Withdraw the needle back to the first position.
If the procedure also involves the upper half of the ear, rather than just the earlobe, continue with the following steps:
- Direct the needle anterior to external ear towards the area just anterior to the tragus, aspirate, then inject as you withdraw the needle completely.
- Insert the needle subcutaneously directly above the ear again in line with the external auditory canal
- Repeat the above steps with the needle facing caudally towards the mastoid process and anterior to the tragus
Posterior tibial nerve block
Freddie, an active 9-year-old, was running barefoot in the garden when he stood on something sharp, sustaining a large cut to the sole of his foot. He hops into the emergency room, supported by this dad. He’s taken Calpol prior to arrival in the department. On examination, there is a 5cm wound on the sole of his foot and you are concerned that there may be glass in the wound. You give further analgesia and arrange an x-ray. You think to yourself, ‘Posterior tibial blocks are great for foreign bodies or wounds in the sole of the foot. I’ll get things ready while he’s in x-ray.’
Provides sensory paraesthesia to the anterior 2/3 of the sole of the foot, allowing for the management of lacerations and wound in this area. It is not suitable for injuries on the extreme medial or lateral aspect of the sole.
Posterior tibial nerve is located at the medial aspect of the ankle, between the medial malleolus and the Achille’s tendon.
- Position the patient lying supine with the foot partially dorsiflexed.
- Locate the posterior tibial artery, the nerve lies posterior to this.
- Inject 2 -4 ml local anaesthetic at the level of the upper edge of the medial malleolus, aspirating prior to injection
- If the artery cannot be felt, the point of injection is the midpoint between the medial malleolus and the achilles tendon.
Freddie’s x-ray confirms a shard of glass in the sole of his foot. With a posterior tibial block in place, you successfully remove the glass and are able to washout and close the wound without him even noticing. Freddie’s dad confirms he’s had all his vaccinations, including tetanus. Freddie is discharged home with wound care advised and promises to always wear his shoes in the garden.
Once again, Mike Stone shows us how it’s done.
Femoral nerve block
Sam is a 15-year-old brought to the emergency department by ambulance following a fall from a tree. The ambulance crew have given paracetamol and ibuprofen en route but Sam is very distressed, complaining of severe pain in his right leg, as he is moved from the trolley to the bed. Following a primary survey, you are satisfied Sam is stable with no airway, c-spine, breathing or circulatory compromise. His right thigh is grossly swollen and tense. You place it in a traction splint, give Sam intranasal fentanyl and organise an urgent x-ray of his right femur, which confirms a proximal femur fracture.
Anterior thigh wounds requiring exploration and washout
- Ultrasound machine with a linear probe. Ultrasound-guided is the gold standard.
- Sterile drape, probe cover and gloves
- Needle for injection
- Specific nerve block needle or a spinal needle with trocar removed
- Monitoring; continuous ECG and pulse oximetry
- Consider adjunct analgesic eg: intranasal fentanyl
- The femoral nerve is located at the midpoint of the inguinal ligament; half way between ASIS and pubic tubercle.
- Moving lateral to medial: Femoral nerve > artery > vein
- Clean the skin and palpate the artery.
- In an adolescent, the site of local anaesthetic injection if 5cm lateral to the artery towards ASIS. This distance is smaller in children. Using ultrasound will help find the femoral nerve accurately.
- Prepare the ultrasound machine: Choose the correct probe, position yourself on the opposite side of the bed, apply gel to the probe and apply a probe cover.
- Prepare a dressing pack with 1-2% lignocaine, appropriate needle, sterile dressing and low-pressure tubing
- Clean the area and drape appropriately.
- Use the ‘in-plane’ ultrasound probe orientation with the marker pointing to ASIS
- Observe landmarks (lateral > medial)
- Infiltrate 1-2ml of 1-2% lignocaine superficially lateral to the artery
- Pierce the skin the with block needle through anaesthetised skin
- Advance the needle slowly ensuring tip of the needle is always visible
- When lateral to the nerve and between layers of fascia iliaca, aspirate the needle to ensure it is not within a vessel, and then infiltrate local anaesthetic slowly, aiming to fully encircle the nerve (total 10-20ml in an adolescent)
- Apply a sterile dressing over injection site; label the block time and date.
You have completed the nerve block and are tidying up your equipment when Sam complains of a funny sensation around his lips and says he feels sick. As you turn towards Sam you notice he is heart is racing and he looks really unwell…
Local Anaesthetic Systemic Toxicity (LAST)
LAST is a severe and life-threatening condition which can occur when local anaesthetic reaches significantly high levels in the circulation. The causes are often iatrogenic; accidental injection into a vein or artery or excessive doses of anaesthetic used.
Signs and symptoms of LAST are:
STOP the infusion of local anaesthetic, MOVE the patients to the resus area if not already there and CALL for HELP.
A: Maintain airway, if necessary prepare for intubation
B: Ventilate with 100% oxygen
C: Confirm or establish IV access
D: Treat seizures with benzodiazepines. Check glucose.
E: Perform ECG, looking for treatable arrhythmias
Give lipid emulsion therapy, as per your local hospital guideline. Lonnqvist (2012) designed a user-friendly guideline for management of paediatric local anaesthetic toxicity.
You ask a colleague to repeat Sam’s observations and perform an ECG, as you call your ED consultant for help. You call the anaesthetics registrar asking for an urgent review and you search for the local anaesthesia toxicity guidelines. Lipid emulsion therapy is initiated and Sam is transferred to PICU for close observation. Thankfully it all ends well. A few days later Sam is well enough to undergo surgery for his femoral fracture, and recovers without complication. You complete an incident report and develop a teaching session on femoral nerve blocks and LAST.
With thanks to Aarani Somaskanthan for her excellent teaching on auricular nerve blocks.
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Ultrasound guided nerve blocks for hip fractures & femoral fractures; Barts Health. National Health Service 2014.https://www.rcem.ac.uk/docs/Local%20Guidelines_Audit%20Guidelines%20Protocols/12u.%20Ultrasound%20guided%20nerve%20block%20for%20hip%20and%20femoral%20fractures%20(Barts%20Health,%202014).pdf
Martin N, Darcey M. Local Anaesthetic systemic toxicity (LAST) in children. The Royal Children’s Hospital Melbourne 2012. https://www.rch.org.au/uploadedFiles/Main/Content/anaes/LAST_submission_draft6-2.pdf
Lonnqvist PA. Toxicity of local anaethetic drugs: a paediatric perspective. Paediatric Anesthesia, 22 (2012), 39-43.
Frank SG, Lalonde DH. how acidic is the lidocaine we are injecting, and how much bicarbonate should we add? Can J Plast surg 2012;20(2):71-74.
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