Regional Anesthesia and Pain Management Flashcards

A 58-year-old patient undergoes ultrasound-guided erector spinae plane (ESP) block at the T5 level for thoracic surgery. Postoperatively, pain control is inadequate laterally. Which anatomical limitation best explains this failure?

Answer: The injectate spreads primarily in the fascial plane deep to erector spinae, with unreliable lateral cutaneous branch coverage

The ESP block deposits local anaesthetic in the plane between erector spinae muscle and the transverse process. While it reliably blocks the medial and posterior branches of the dorsal rami, spread to the lateral cutaneous branches of the intercostal nerves is variable and often incomplete. This explains residual lateral chest wall pain despite adequate posterior coverage.

During a continuous femoral nerve block for post-total knee arthroplasty analgesia, the patient develops progressive quadriceps weakness on day 2 despite a low-dose infusion (0.1% ropivacaine at 5 mL/h). Which mechanism is the most pharmacologically plausible explanation?

Answer: Catheter migration placing the tip closer to the femoral nerve motor branch

At 0.1% ropivacaine and 5 mL/h, differential blockade should theoretically spare motor fibres. Progressive worsening of motor block on day 2 most likely reflects catheter tip migration toward the motor branches of the femoral nerve, increasing local drug concentration at those fibres. α1-acid glycoprotein saturation affects free plasma levels but not local tissue concentration, and systemic motor inhibition from epidural/perineural doses of ropivacaine is not a recognised clinical phenomenon.

A patient with known CRPS type I of the right upper limb is scheduled for stellate ganglion block. After negative aspiration and injection of 8 mL 0.5% bupivacaine at C6, the patient develops Horner's syndrome but reports no temperature change in the limb and pain is unchanged at 30 minutes. What is the most likely explanation?

Answer: Horner's syndrome confirms successful stellate ganglion block; CRPS I is not reliably sympathetically maintained in all patients

Horner's syndrome (ptosis, miosis, anhidrosis) confirms cephalad spread to the superior cervical ganglion and does not reliably confirm complete stellate ganglion block of the upper limb sympathetics. More importantly, CRPS type I is heterogeneous — a substantial proportion of patients have 'sympathetically independent pain' (SIP) rather than 'sympathetically maintained pain' (SMP). Absence of limb temperature change and pain relief in the context of adequate Horner's sign suggests this patient's pain is SIP, not SMP. Repeating the block or changing agents would not address this distinction.

Which of the following correctly describes the risk of intravascular injection during a transforaminal epidural steroid injection (TFESI) at L4-L5, and the most appropriate mitigation strategy according to current evidence?

Answer: Digital subtraction angiography (DSA) detects vascular uptake more reliably than live fluoroscopy alone, particularly for arterial flow to the Adamkiewicz artery at lower lumbar levels

Catastrophic spinal cord infarction from TFESI has been reported even at lower lumbar levels, as the artery of Adamkiewicz can arise as low as L2 and there are anatomical radicular feeders throughout the lumbar spine. Live fluoroscopy with contrast can miss rapid arterial washout, whereas digital subtraction angiography (DSA) identifies vascular patterns that are invisible on single-frame fluoroscopy. Non-particulate steroids (e.g. dexamethasone) are now recommended, particularly for cervical and upper lumbar TFESI, to reduce the risk of embolic infarction even if intravascular injection occurs. Stating the Adamkiewicz artery is exclusively thoracic is anatomically incorrect.

A 70 kg patient receiving an intravenous regional anaesthesia (Bier's block) with 40 mL of 0.5% prilocaine develops methaemoglobinaemia postoperatively. At what total prilocaine dose threshold is this complication most likely to occur, and which metabolite is responsible?

Answer: Above 200 mg total; o-toluidine is the responsible metabolite

Prilocaine is metabolised in the liver to o-toluidine (ortho-toluidine), which oxidises haemoglobin to methaemoglobin. Clinically significant methaemoglobinaemia (>10%) becomes likely above approximately 600 mg total dose in adults, but symptoms can appear at lower cumulative exposures in susceptible patients. A 40 mL dose of 0.5% prilocaine = 200 mg — this is near the safe upper limit for Bier's block, and cuff deflation before full hepatic redistribution can unmask toxicity. MEGX is a lignocaine metabolite, not prilocaine's. Hydroxyprilocaine and ortho-chlorotoluidine are distractors; o-toluidine is the correct culpable species.

In the context of the PROSPECT guidelines and multimodal analgesia for major abdominal surgery, which combination is currently supported by the highest level of evidence for reducing opioid consumption while preserving early mobilisation?

Answer: Epidural analgesia (thoracic) + paracetamol + NSAID/COX-2 inhibitor, with epidural reserved as first-line only when no contraindication exists

PROSPECT (Procedure-Specific Postoperative Pain Management) guidelines for major abdominal surgery recommend thoracic epidural analgesia as first-line regional technique when no contraindication exists (Grade A), combined with scheduled paracetamol and NSAID/COX-2 inhibitor as the analgesic backbone. This combination has the strongest evidence base for opioid sparing and functional recovery. Intrathecal morphine is a second-line option but carries pruritus/nausea burden. TAP blocks do not provide visceral analgesia and are inferior for open abdominal surgery. Thoracic paravertebral blocks have good somatic coverage but also lack reliable visceral spread, and evidence for routine replacement of epidural is not established in this surgical population.