Brachial Plexus Blocks

Regional anaesthesia of the upper limb hinges on accurately depositing local anaesthetic around the brachial plexus at one of four classic levels. Each approach has a distinct anatomical target, a characteristic "spared" or "missed" segment, and a signature complication that examiners love to test.

Relevant anatomy — the roadmap

The brachial plexus arises from the ventral rami of C5–T1 (with variable contributions from C4 "prefixed" and T2 "postfixed"). It is organised, proximal to distal, as:

Mnemonic: Read That Damn Cadaver Book → Roots → Trunks → Divisions → Cords → Branches.

• Roots (C5–T1): lie between the anterior and middle scalene muscles (the interscalene groove).
• Trunks (3): Superior (C5–C6), Middle (C7), Inferior (C8–T1) — sit over the first rib, posterolateral to the subclavian artery.
• Divisions (6): behind the clavicle.
• Cords (3): Lateral, Medial, Posterior — named by their relation to the axillary artery, surround it in the infraclavicular/axillary region.
• Branches (5 terminal): Musculocutaneous, Axillary, Radial, Median, Ulnar.

The plexus is wrapped in a fascial sheath continuous from the prevertebral fascia, allowing a single large-volume injection to spread along the neurovascular bundle.

Level	Anatomical landmark	Surrounding structure
Interscalene	Roots/upper trunks	Between scalenus anterior & medius
Supraclavicular	Trunks/divisions	First rib, lateral to subclavian artery
Infraclavicular	Cords	Around 2nd part of axillary artery, deep to pectoralis
Axillary	Terminal branches	Around axillary artery in axilla

The four approaches at a glance

High-yield: The level of block determines which part of the arm is reliably anaesthetised and which nerve is classically spared. This single concept generates most MCQs.

Approach	Target	Best for surgery on	Classically SPARED	Signature complication
Interscalene	Roots/upper trunk (C5–C6)	Shoulder, proximal humerus	Ulnar (C8–T1) — "inferior trunk spared"	Phrenic nerve palsy (≈100%), Horner syndrome
Supraclavicular	Trunks/divisions	Whole arm below shoulder ("spinal of the arm")	Rarely ulnar; most complete	Pneumothorax (highest risk)
Infraclavicular	Cords	Elbow, forearm, hand	— (good for all but musculocutaneous occasionally)	Vascular puncture (axillary vessels)
Axillary	Terminal branches	Forearm and hand	Musculocutaneous & axillary nerves	Intravascular injection (LAST), no shoulder cover

Interscalene block

Target: Roots/upper trunk in the interscalene groove at the level of the cricoid cartilage (C6).

Indications: Shoulder arthroscopy, rotator cuff repair, clavicle and proximal humerus surgery, shoulder dislocation reduction.

Why the ulnar nerve is spared: The needle deposits drug around the superior and middle trunks (C5–C7); the inferior trunk (C8–T1) lies most caudal and is reached last/poorly. Hence interscalene is a poor choice for hand surgery.

High-yield: Interscalene block causes ipsilateral phrenic nerve (C3–C5) palsy in nearly 100% of patients due to anterior spread. It is therefore contraindicated in patients with significant respiratory compromise or contralateral phrenic/diaphragmatic palsy or pneumonectomy.

Other classic complications / associations:

• Horner syndrome (ptosis, miosis, anhidrosis, enophthalmos) — from spread to the stellate ganglion / cervical sympathetic chain.
• Recurrent laryngeal nerve block → hoarseness.
• Inadvertent neuraxial spread — subarachnoid, epidural, or vertebral artery injection (causing immediate seizures with tiny volumes) because the vertebral artery is close.

Approaches: Classic Winnie approach; modern practice uses ultrasound guidance — the trunks appear as the "traffic-light / stoplight sign" (stacked hypoechoic circles) between scalenus anterior and medius.

Supraclavicular block

Target: Trunks and divisions as they cross the first rib, lateral and superficial to the subclavian artery.

High-yield: Called the "spinal anaesthesia of the arm" because at this point the plexus is most compact, giving the fastest onset and most complete, dense block of the entire upper limb below the shoulder.

Indications: Surgery of the elbow, forearm, and hand; anything distal to the mid-humerus.

Ultrasound landmark: Plexus appears as a "bunch of grapes" / cluster lateral and superficial to the pulsatile subclavian artery, sitting on the hyperechoic first rib (which acts as a backstop) with the pleura visible medially.

High-yield: The supraclavicular approach carries the highest risk of pneumothorax owing to proximity of the cupola of the pleura. Always confirm the first rib and pleural line on ultrasound; avoid in patients with respiratory reserve concerns.

Other complications: Phrenic palsy (lower incidence than interscalene, ~50%), Horner syndrome, subclavian artery puncture.

Infraclavicular block

Target: The three cords around the second part of the axillary artery, deep to pectoralis major and minor, below the clavicle (coracoid approach).

Indications: Elbow, forearm, wrist, and hand surgery; ideal for catheter placement (stable, away from the neck, good for continuous analgesia).

Advantages: Lower pneumothorax risk than supraclavicular; the arm need not be abducted (useful in trauma where the patient cannot move the shoulder); reliable coverage of all terminal nerves.

Complications: Vascular puncture of axillary vessels (deep target → harder to compress), and the block is deeper, requiring careful needle visualisation.

Axillary block

Target: Terminal branches around the axillary artery in the axilla, with the arm abducted to ~90°.

High-yield: The musculocutaneous nerve leaves the sheath early (it pierces coracobrachialis proximally), so it is frequently missed in an axillary block → forearm flexion/lateral forearm sensation spared. A separate injection into coracobrachialis is needed to block it. The axillary nerve (shoulder) is also not covered.

Mnemonic for needle-relative nerve positions around the axillary artery (transarterial / surface view):

• Median — superior/anterior (12 o'clock-ish, lateral)
• Ulnar — inferior/medial
• Radial — posterior
• Musculocutaneous — within coracobrachialis, away from artery.

Memory aid: "M-A-R-M" around the artery, or recall Median above, Ulnar below, Radial behind, Musculocutaneous in the muscle.

Indications: Forearm and hand surgery — safest approach as there is no risk of pneumothorax or phrenic palsy (lies well away from pleura and phrenic nerve).

Complications: Intravascular injection → Local Anaesthetic Systemic Toxicity (LAST); haematoma; the transarterial technique deliberately punctures the artery.

Stepwise clinical approach to choosing a block

Surgery on shoulder? → Interscalene → accept phrenic palsy unless contraindicated → if respiratory risk → consider supraclavicular/combined or alternative.

Surgery on elbow/forearm/hand and want a dense complete block? → Supraclavicular → confirm pleura on USG.

Need a continuous catheter / arm cannot be abducted? → Infraclavicular.

Hand/forearm surgery in a patient with respiratory disease (want to avoid pleura/phrenic)? → Axillary → remember to supplement musculocutaneous.

A simplified decision line:

Shoulder → Interscalene ➜ Whole arm/dense → Supraclavicular ➜ Catheter/no abduction → Infraclavicular ➜ Hand + lungs at risk → Axillary

Local anaesthetics and dosing principles

Common agents: lignocaine (1–2%, with adrenaline) for shorter cases, bupivacaine / levobupivacaine / ropivacaine (0.25–0.5%) for prolonged analgesia.

High-yield: Adrenaline 1:200,000 (5 µg/mL) is added to (a) prolong block duration, (b) reduce systemic absorption/peak plasma levels, and (c) act as an intravascular marker (a rise in heart rate on test dose suggests intravascular placement).

Maximum safe doses (memorise):

Drug	Plain	With adrenaline
Lignocaine	3 mg/kg (≈4.5)	7 mg/kg
Bupivacaine	2 mg/kg	3 mg/kg
Ropivacaine	3 mg/kg	—

Volume for a brachial plexus block is typically 15–30 mL; ultrasound has allowed reduction in volume while maintaining efficacy.

Local Anaesthetic Systemic Toxicity (LAST)

High-yield: Brachial plexus blocks (especially axillary/supraclavicular near vessels) are a leading site for LAST. CNS symptoms (perioral numbness, tinnitus, metallic taste, seizures) precede cardiovascular collapse. Bupivacaine is the most cardiotoxic agent.

Management flow:

1. Stop injection, call for help, secure airway with 100% oxygen.
2. Control seizures (benzodiazepine; avoid large propofol doses if cardiovascularly unstable).
3. Intravenous lipid emulsion (Intralipid 20%) — bolus 1.5 mL/kg over 1 min, then infusion 0.25 mL/kg/min (lipid sink theory).
4. Modify ACLS — avoid vasopressin, calcium channel blockers, β-blockers, and reduce adrenaline doses (<1 µg/kg boluses).
5. Prolonged resuscitation; consider cardiopulmonary bypass if refractory.

Techniques to localise the plexus

• Paraesthesia technique — older; eliciting paraesthesia in the nerve distribution.
• Peripheral nerve stimulator — motor twitch at 0.2–0.5 mA / 0.1 ms; a twitch persisting below 0.2 mA suggests intraneural placement → withdraw.
• Ultrasound guidance — current gold standard; real-time visualisation reduces vascular puncture and improves success with lower volumes.

High-yield: High injection pressure during deposition (>15 psi) signals possible intrafascicular/intraneural placement and risk of nerve injury — stop and reposition.

Complications — summary table

Complication	Most associated approach	Mechanism
Phrenic nerve palsy	Interscalene (≈100%) > supraclavicular	Anterior spread to C3–C5 / phrenic
Horner syndrome	Interscalene / supraclavicular	Stellate ganglion block
Recurrent laryngeal palsy (hoarseness)	Interscalene	Spread in carotid sheath
Pneumothorax	Supraclavicular (highest)	Proximity to pleural cupola
Vertebral artery / neuraxial injection	Interscalene	Vessel/foramen proximity → seizures, total spinal
LAST	Axillary, supraclavicular	Intravascular uptake
Nerve injury / neuropraxia	Any	Intraneural injection, high pressure
Missed musculocutaneous nerve	Axillary	Nerve exits sheath early

Contraindications

• Patient refusal, local infection at site, coagulopathy (relative — deep blocks near non-compressible vessels are higher risk).
• Interscalene/supraclavicular: severe respiratory disease, contralateral phrenic/recurrent laryngeal palsy, contralateral pneumonectomy.
• Pre-existing neurological deficit in the limb (relative — document before block).

Key differentials / contrasts to keep straight

• Interscalene vs supraclavicular: Both can cause phrenic palsy and Horner; pneumothorax is supraclavicular's hallmark, near-universal phrenic palsy is interscalene's.
• Axillary vs infraclavicular: Both for distal limb; axillary needs arm abduction and misses musculocutaneous; infraclavicular does not need abduction and covers cords more completely.
• Spared nerve clues: Ulnar spared → interscalene; Musculocutaneous spared → axillary.

Recently asked / exam angle

• "100% incidence of phrenic nerve palsy" → Interscalene block (most repeated single-line fact).
• Block most associated with pneumothorax → Supraclavicular.
• Horner syndrome after a nerve block → think interscalene/supraclavicular (stellate ganglion).
• Nerve most commonly spared in axillary block → Musculocutaneous (and axillary nerve).
• Block called "spinal anaesthesia of the arm" → Supraclavicular.
• Ultrasound "traffic light/stoplight sign" → interscalene trunks; "bunch of grapes" lateral to subclavian artery → supraclavicular.
• Best approach for a continuous catheter / when shoulder cannot be abducted → Infraclavicular.
• First-line drug for LAST → 20% lipid emulsion (Intralipid).
• Most cardiotoxic local anaesthetic → Bupivacaine.
• Nerve stimulator current for correct placement → 0.2–0.5 mA.
• Maximum lignocaine with adrenaline → 7 mg/kg.

Rapid revision

1. Plexus = C5–T1; organised Roots → Trunks → Divisions → Cords → Branches.
2. Interscalene = shoulder surgery; ulnar spared; ~100% phrenic palsy; Horner & hoarseness possible.
3. Supraclavicular = "spinal of the arm"; densest block; highest pneumothorax risk; "bunch of grapes" on USG.
4. Infraclavicular = cords; ideal for catheters and when the arm cannot be abducted.
5. Axillary = terminal branches; musculocutaneous nerve missed; no pneumothorax/phrenic risk.
6. Horner syndrome = ptosis + miosis + anhidrosis from stellate ganglion spread (interscalene/supraclavicular).
7. Vertebral artery injection in interscalene → seizures with tiny volume.
8. Adrenaline 1:200,000 prolongs block, reduces absorption, marks intravascular injection.
9. Bupivacaine is the most cardiotoxic LA; treat LAST with 20% Intralipid 1.5 mL/kg bolus.
10. Nerve stimulator twitch at 0.2–0.5 mA; high injection pressure = stop (intraneural risk).
11. Ultrasound is the modern standard — lowers volume needed and vascular/pleural complications.
12. Spared-nerve shortcut: Ulnar → interscalene; Musculocutaneous → axillary.