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

Correct. Severe aortic stenosis produces a fixed cardiac output dependent on adequate preload and afterload. Single-shot spinal causes rapid sympathectomy, reducing both preload (venous pooling) and afterload — precipitating catastrophic hypotension. CSE or epidural (titrated slowly) is safer than single-shot spinal if neuraxial is chosen; general anaesthesia with haemodynamic monitoring is also appropriate.

Severe AS (fixed CO, dependent on preload+afterload) is a relative contraindication to single-shot spinal due to abrupt sympathectomy. Titrated epidural or general anaesthesia with invasive monitoring is preferred. Avoid rapid haemodynamic shifts.

Incorrect. The core issue is the SPEED and unpredictability of single-shot spinal sympathectomy in a patient who cannot compensate. Severe AS is a relative contraindication to single-shot spinal, not to all neuraxial techniques. Titrated epidural can be used carefully. And general anaesthesia, while not without risk, allows more haemodynamic control.

Correct. The lateral cord gives the musculocutaneous nerve and the lateral root of the median nerve. The posterior cord divides into the axillary and radial nerves. The medial cord gives the ulnar nerve and the medial root of the median nerve (which joins the lateral root to form the median nerve).

Lateral cord → musculocutaneous + lateral root of median. Posterior cord → axillary + radial. Medial cord → ulnar + medial root of median. Median nerve requires lateral AND medial cord contributions — blocking both is essential for complete hand surgery anaesthesia.

Incorrect. The axillary nerve arises from the posterior cord (not the lateral). The musculocutaneous nerve comes from the lateral cord. Median nerve formation requires contributions from BOTH lateral and medial cords — this is the key point that distinguishes infraclavicular and axillary blocks.

Correct. Lignocaine 6.4 mg/kg is within the 7 mg/kg limit (with adrenaline). Bupivacaine 1.43 mg/kg is within the 2 mg/kg limit (plain). However, concurrent use of two LA agents is additive for systemic toxicity — the combined central nervous system and cardiovascular toxicity threshold is lower than the individual limits suggest. This warrants close monitoring.

LA safe limits: lignocaine 3 mg/kg plain, 7 mg/kg with adrenaline; bupivacaine 2 mg/kg (no IV regional use). Always calculate mg/kg from concentration (%). Concurrent LAs have additive toxicity risk even when each is below its individual ceiling.

Incorrect. The key calculation: lignocaine 1.5% = 15 mg/mL × 30 mL = 450 mg ÷ 70 kg = 6.4 mg/kg (within 7 mg/kg limit with adrenaline). Bupivacaine 0.5% = 5 mg/mL × 20 mL = 100 mg ÷ 70 kg = 1.43 mg/kg (within 2 mg/kg plain limit). Both are individually within safe doses, but additive toxicity risk exists.

Correct. The dorsal web space between the thumb and index finger (anatomical snuffbox region) is exclusively supplied by the superficial branch of the radial nerve. Intact pinprick there indicates the radial nerve was not adequately blocked — the most common failure in axillary blocks because the radial nerve lies deepest in the axilla and is most easily missed.

Radial nerve sensory landmark = dorsal web space between thumb and index finger. Ulnar = little finger dorsal/palmar; Median = palmar lateral 3 digits; Musculocutaneous = lateral forearm. In axillary blocks, the radial nerve is most often missed as it lies posteriorly.

Incorrect. The ulnar nerve supplies the little finger and medial palm. The median nerve supplies the palmar surface of the lateral 3.5 digits. The musculocutaneous nerve supplies the lateral forearm. The dorsal thumb web space (first dorsal interosseous territory) is the radial nerve's sensory landmark.

Correct. In neonates and infants, the dural sac extends more caudally, to approximately S3–S4, compared to S2 in adults. Advancing the needle more than 1–2 cm past the sacrococcygeal membrane risks dural puncture. The textbook warning is: in neonates, never advance beyond 1.5 cm past the hiatus.

Neonatal dural sac extends to S3–S4 (vs S2 adults). Never advance caudal needle more than 1–2 cm past the sacrococcygeal membrane in neonates. This is the primary safety constraint distinguishing paediatric from adult caudal technique.

Incorrect. The critical anatomical reason for depth limitation is the caudal extension of the dural sac in neonates. The sacrococcygeal membrane is actually thinner and more easily identified in neonates. Pelvic organ injury is a real risk but not the primary concern limiting needle advancement depth.

Correct. Current obstetric anaesthesia guidelines (SOAP, OAA) suggest neuraxial techniques are generally acceptable down to platelet counts of 70–80 × 10⁹/L when the trend is stable and there is no coagulopathy. A count of 92 × 10⁹/L with no DIC is within acceptable range. However, individual assessment of trend, rate of fall, and coagulation profile is mandatory.

Neuraxial block in pre-eclampsia: generally acceptable at platelets ≥70–80 × 10⁹/L with no falling trend or DIC. Individual risk-benefit assessment is mandatory. Epidural provides haemodynamic benefits in pre-eclampsia and can be extended for emergency caesarean.

Incorrect. The 100 × 10⁹/L threshold is a conservative institutional policy, not a universal contraindication. The actual decision threshold varies between 70–80 × 10⁹/L in most current guidance, provided there is no falling trend or DIC. The benefit of epidural analgesia in pre-eclampsia (reduced sympathoadrenal response, haemodynamic stability, ability to extend for caesarean) often outweighs risk at 92 × 10⁹/L.

Correct. At the supraclavicular level, the brachial plexus lies posterolateral to the subclavian artery on the surface of the first rib. On ultrasound, the artery appears as a pulsatile hypoechoic circle, and the plexus appears as a cluster of hypoechoic nodules (like a cluster of grapes) superior and lateral to the artery.

Supraclavicular block: plexus lies posterolateral to subclavian artery on first rib. Ultrasound shows 'cluster of grapes' pattern. Pneumothorax risk from medially-directed needle — always direct laterally. Most complete block for upper limb surgery.

Incorrect. The plexus lies posterolateral to the subclavian artery. The key safety point: the pleural dome lies medial and inferior — the needle must be directed laterally to avoid pneumothorax. At this level the plexus is compact (trunks/divisions), making supraclavicular the most reliably complete brachial plexus block.

Correct. Bupivacaine alone in a caudal epidural does not cause respiratory depression — local anaesthetics block sodium channels and have no direct central respiratory depressant effect at conventional doses. Respiratory depression in a child after caudal block should prompt immediate investigation for concurrent opioid use (intraoperative IV opioids or caudal opioid additives such as morphine, fentanyl, or clonidine).

Bupivacaine caudal alone does NOT cause respiratory depression. Post-caudal desaturation in a child = suspect opioid (IV or caudal additive). Treat with naloxone and supplemental oxygen. Avoid opioid additives in caudal blocks performed as outpatient techniques.

Incorrect. Caudal bupivacaine at lumbar doses (1 mL/kg = 22 mL of 0.25%) does not spread high enough to block intercostal nerves, and phrenic nerve palsy would require cervical spread — impossible at these volumes. The combination of bupivacaine + IV opioids is the classic cause of respiratory depression post-caudal in children.

Correct. The femoral nerve (L2–L4) supplies the quadriceps — the primary knee extensor and 'locking' mechanism for weight-bearing. A dense femoral nerve block causes profound quadriceps motor block, eliminating the patient's ability to control knee extension. Falls with femoral nerve blocks in ambulatory settings are a recognised patient safety issue, driving adoption of adductor canal blocks (which spare more motor function) for outpatient ACL procedures.

Femoral nerve block = quadriceps motor block = fall risk. This is why adductor canal blocks are preferred for outpatient ACL surgery — they preserve more motor function. Always counsel patients on fall precautions and ensure physiotherapy supervision for ambulation post-femoral block.

Incorrect. While sensory loss and proprioceptive impairment contribute, the primary fall risk is MOTOR block of the quadriceps. The femoral nerve carries motor fibres to quadriceps (knee extension). Without quadriceps control, patients cannot prevent the knee from buckling on weight-bearing. This is why adductor canal blocks (sparing most motor function) are now preferred for outpatient ACL repair.

Correct (best single mechanism). With T6 sensory block, the sympathetic block may reach T1–T4 — the origin of the cardioaccelerator fibres. Blockade of these fibres abolishes sympathetic acceleration of the heart, and, with venous pooling reducing venous return, unopposed vagal tone causes bradycardia. This is the classic 'high spinal' bradycardia mechanism.

High spinal (sensory to T6 or higher) → sympathectomy of cardiac accelerator fibres (T1–T4) → bradycardia. Combined with venous pooling → hypotension. Treat with IV fluids, vasopressors (ephedrine/phenylephrine), and atropine for bradycardia.

Incorrect. While the Bezold-Jarisch reflex can contribute to bradycardia with high spinal blocks (it is a recognised additional mechanism), the primary cause of bradycardia with T6 or higher sensory block is sympathectomy of the cardioaccelerator fibres (T1–T4). Baroreceptor-mediated vagal activation would actually cause bradycardia, not tachycardia, but the sympathetic block is the dominant mechanism here.