• Scalenus medius lies posterior to the subclavian artery and thus need not be divided to expose the artery. Whereas, sternocleidomastoid & scalenus anterior lie anteriorly and omohyoid lies superiorly and thus are cut during exposure of the subclavian artery.

Ans.B. Ulnar nerve
The roots of the brachial plexus are found in the inter scalene groove (defined by the anterior and middle scalene muscles)deep to the sternocleidomastoid.
Interscalene block is used to provide anesthesia or analgesia for shoulder surgery as it targets the proximal roots of the plexus (C4-C7).
The more distal roots of the plexus such as ulnar nerve (C8-T1) is usually spared.

C i.e. Systemic toxicity of Local Anaesthetics

• Systemic toxicity of LA includes – CNS toxicity, cardiovascular system, methemoglobinemia & Allergies.

CNS is particularly vulnerable to toxicity & is the site of premonitory signs of overdose in awake patients. Cortical inhibitory pathways are most susceptible resulting in the excitatory motor phenomenon in the initial stages of LA toxicity.

• Hypercapnia, respiratory & metabolic acidosis exacerbates CNS toxicity. Increased PaCO₂ increases cerebral blood flow delivering a greater dose of LA more rapidly to the brain. And decreased intracellular pH favors formation of non-diffusible cationic (protonated) form of LA, which is trapped within the neuron. Finally, plasma protein binding of LA is decreased in an acidic environment resulting in increased availability of the free drug for diffusion into the brain.
• But the involvement of the peripheral nerve is characterized by paresthesias, numbness, hypoaesthesia, pain and neurological dysfunction.
• So, this patient is having a peripheral nerve injury. It could have happened d/t:

– Open (crush) injury t/ t laceration of nerves. As the patient underwent debridement, so he is a case of open injury.

Nerve injury during debridement.

Nerve injury during reduction & manipulation.

Tourniquet pressure palsy

Nerve injury d/t tight bandage or cast.

B i.e. Brachial Plexus block
Brachial plexus block with interscalene approach provides most intense anesthesia in C₅-C₇ dermatomes and least intense in C₈-T₁ (ulnar nerve) area.

Ans. is `B’ i.e., Supraclavicular 

Brachial plexus block

• This is the second most commonly practised block after central neuraxial block (spinal & epidural anaesthesia). Brachial plexus block is used for upper limb surgeries.
• Brachial plexus can be blocked by 4 approaches : –

1.  nterscalene approach

• Brachial plexus is blocked between anterior and middle scalene. This approach is not used routinely due to close proximity of vital structures. Ulnar nerve is usually spared by this approach because injection is given in close proximity of upper nerve roots and inferior nerve roots (C8-T 1) may be spared.
• This technique provides excellent anaesthesia and analgesia for shoulder and upper arm procedures. (in contrast to other three approaches which do not provide adequate shoulder anaesthesia).
• Complications include Horner syndrome (due to stellate ganglion block), phrenic nerve block, intravascular injection into carotids and epidural or intrathecal injections.

2.  Supraclavicular approach   

• This is the most commonly used approach. It involves the injection of local anaesthetic in close proximity to
• the trunks of the brachial plexus by inserting the needle lateral to subclavian vessels. The supraclavicular
• block is performed where the brachial plexus is most compact, consequently, it produces reliable and rapid
• onset anaesthesia and is particularly useful in a fast paced ambulatory surgery centre.
• Pneumothorax is the most common complication. Other complications include phrenic nerve block, intravascular injection in subclavian artery or vein, Horner syndrome, hematoma formation.

3. Infra-clavicular approach

•  Infraclavicular block involves the injection of local anaesthetic in close proximity of cords of the brachial plexus. The axillary nerve may be spared as this nerve exits the brachial plexus sheath proximal to the level of infraclavicular block.

4. Axillary approach

• Axillary block involves the injection of local anaesthetic in close proximity of terminal branches of the
• brachial plexus. The major disadvantage of this approach is that mucocutaneous and intercostobrachial nerves are spared. So arm surgery cannot be performed. In contrast to interscalene approach, most intense
• block occur in (C7-T1) ulnar dermatomes and least in C5-C6 dermatomes.