Regional Anesthesia and Acute Pain Management
Core concepts
Know the anatomy, dermatomes, and block-specific risks for neuraxial and peripheral techniques. Understand local anesthetic pharmacology: pKa determines onset, lipid solubility determines potency, protein binding determines duration; maximum safe doses differ for lidocaine, bupivacaine, and ropivacaine, and epinephrine prolongs duration and reduces systemic absorption. Recognize local anesthetic systemic toxicity (LAST) presentation (perioral numbness, tinnitus, seizures, cardiovascular collapse) and its management, including lipid emulsion therapy. Understand spinal versus epidural differences in onset, block height, hypotension, and post-dural puncture headache. Acute pain management includes multimodal regimens, opioid-sparing strategies, and awareness of opioid tolerance and hyperalgesia.
Traps in questions
- Confusing the level of a spinal with the dermatome tested; do not assume a block height from the needle insertion point alone.
- Forgetting that bupivacaine is more cardiotoxic than lidocaine and that LAST can present without seizures.
- Missing that epinephrine-containing solutions can cause tachycardia and that intravascular injection is the real danger.
- Assuming a peripheral nerve block is contraindicated in every anticoagulated patient; risk depends on technique and site.
- Overlooking that a high spinal can cause hypotension and bradycardia (Bezold-Jarisch-like reflex).
Worked example / rule of thumb
For a 70 kg adult, lidocaine maximum without epinephrine is about 3 mg/kg (210 mg) and with epinephrine about 7 mg/kg (490 mg); bupivacaine is roughly 2 mg/kg (140 mg). Rule of thumb: calculate the maximum dose before drawing up, and if a block fails, do not simply top up with a second full dose.
Exam framing
Questions often ask the next best step after a failed block or a suspected intravascular injection. Prioritize stopping injection, airway and hemodynamic support, and lipid emulsion for severe LAST.