AS5.{1-3,5-6} | Regional Anaesthesia — Practice Quiz

Correct. Neuraxial anaesthesia avoids endotracheal intubation, positive-pressure ventilation, and systemic volatile agents — all of which are particularly hazardous in severe COPD and low EF. It also enables early mobilisation and reduces opioid consumption postoperatively.

Regional anaesthesia is the preferred primary technique for lower-limb orthopaedic surgery in patients with severe respiratory or cardiac disease, chiefly because it avoids airway instrumentation and systemic anaesthetic agents.

Incorrect. Spinal does not abolish tourniquet pain (sympathetic fibres may escape the block), and sympathectomy-induced hypotension is a significant risk with impaired cardiac output. The key rationale is avoidance of airway and ventilatory compromise.

Correct. The midline sequence is: skin, subcutaneous fat, supraspinous ligament, interspinous ligament, ligamentum flavum (the densest and most identifiable resistance), epidural space, dura mater, subdural space (potential), then arachnoid mater into the subarachnoid space.

Memorise the midline sequence: skin → subcutaneous fat → supraspinous → interspinous → ligamentum flavum → epidural space → dura → arachnoid → subarachnoid space. The 'give' felt as the needle enters the epidural space, and then CSF flow on stylet removal, are the two key tactile landmarks.

Incorrect. The order matters clinically — supraspinous ligament precedes interspinous ligament (not the reverse), and the ligamentum flavum is encountered before the epidural space and dura, not after.

Correct. The mnemonic is Robert Taylor Drinks Cold Beer: Roots → Trunks → Divisions → Cords → Branches. The cords are named by their relationship to the axillary artery — lateral, posterior, and medial.

Brachial plexus: Roots C5–T1 → upper/middle/lower Trunks → Divisions → lateral/posterior/medial Cords (named by relation to axillary artery) → terminal branches (musculocutaneous, axillary, radial, median, ulnar).

Incorrect. The sequence must follow Roots → Trunks → Divisions → Cords → Terminal branches. Reversing trunks and cords, or placing cords before divisions, is a common error that will prevent correct identification of block levels.

Correct. Local anaesthetic systemic toxicity (LAST) from bupivacaine is treated with 20% intralipid emulsion — 1.5 mL/kg IV bolus, repeated once if needed, followed by 0.25 mL/kg/min infusion. Lignocaine would worsen LA toxicity; naloxone is for opioid overdose; bicarbonate alone does not treat LAST.

Bupivacaine maximum safe dose is 2 mg/kg (no adrenaline formulation for IV regional). LAST: early CNS excitation → seizures → cardiovascular collapse. Treatment: 20% intralipid emulsion 1.5 mL/kg IV bolus + supportive care.

Incorrect. This is LAST (local anaesthetic systemic toxicity) — peri-oral tingling is an early CNS excitatory sign followed by seizures. The specific antidote is 20% intralipid emulsion. Note: 30 mL × 5 mg/mL = 150 mg bupivacaine = 2.5 mg/kg for a 60 kg patient, exceeding the safe limit of 2 mg/kg.

Correct. The differential block sequence follows: small-diameter, lightly myelinated fibres first — B fibres (preganglionic sympathetic), then C fibres (pain/temperature), then A-delta (sharp pain/light touch), and finally A-alpha (motor). Sympathetic block extends approximately 2 dermatomes above the sensory level.

Differential block in neuraxial anaesthesia: sympathetic first (2 dermatomes above sensory), then sensory, then motor. This explains vasodilation/hypotension preceding surgical anaesthesia.

Incorrect. Because sympathetic (B) fibres are smallest, they are blocked first and at the lowest LA concentration. This is why hypotension (sympathectomy) can precede adequate sensory block and why sympathetic block extends higher than sensory block.

Correct. Ipsilateral phrenic nerve palsy occurs in essentially all interscalene blocks because C3, C4, C5 are all involved and the phrenic nerve (C3–C5) is invariably affected. This causes ipsilateral hemidiaphragm paresis and a 25–30% reduction in FVC. In patients with contralateral lung disease, this is contraindicated.

Interscalene block invariably causes ipsilateral phrenic nerve palsy (~100%) with 25–30% FVC reduction. It is contraindicated in patients with severe contralateral lung disease. Horner's syndrome and recurrent laryngeal nerve palsy also occur but are less clinically significant in healthy patients.

Incorrect. While pneumothorax, recurrent laryngeal nerve palsy, and Horner's syndrome are all recognised complications of interscalene block, the near-universal complication explaining ipsilateral respiratory reduction is ipsilateral phrenic nerve palsy — it is an expected consequence, not an avoidable complication.

Correct. The Armitage formula for lumbar coverage is 1 mL/kg. For a 16 kg child, this is 16 mL of 0.25% bupivacaine. The dose of bupivacaine = 16 mL × 2.5 mg/mL = 40 mg = 2.5 mg/kg, which is at the upper limit of the safe dose (2 mg/kg plain) — so in practice 0.2% bupivacaine is preferred for volumes exceeding 1 mL/kg.

Armitage formula for paediatric caudal: sacral = 0.5 mL/kg, lumbar = 1 mL/kg, mid-thoracic = 1.25 mL/kg. Always calculate the total LA dose (mg/kg) separately to confirm it stays within the safe range.

Incorrect. The Armitage formula: sacral/lumbar = 0.5 mL/kg; thoracolumbar = 1 mL/kg; midthoracic = 1.25 mL/kg. For 16 kg at 1 mL/kg = 16 mL. 8 mL would be the sacral dose; 32 mL is twice the needed volume.

None of the above is an ideal single answer as presented. The correct interpretation: very low resistance AND severe headache suggests intrathecal placement (the dural sac in adults may extend lower than expected, and a misplaced needle can puncture it). Aspiration alone does not fully exclude dural puncture if the aperture is partially outside the sac.

In adult caudal block, the dural sac ends at S2 but anatomical variants place it lower. Always use a test dose (3 mL containing adrenaline 1:200,000), watch for tachycardia (intravascular) or rapidly spreading block (intrathecal) before full injection.

The combination of very low resistance (no epidural 'pop' or tissue resistance) with immediate headache is a red flag for inadvertent dural puncture and subarachnoid injection. In adults the dural sac ends at S2; however, anatomical variants exist. This scenario underscores the importance of test-dose technique.