Regional Anesthesia
Block pharmacology and complications
Start with dose ceilings. Lidocaine maximum is 4.5 mg/kg plain and 7 mg/kg with epinephrine; bupivacaine 2–3 mg/kg; ropivacaine about 3 mg/kg. Onset tracks pKa (chloroprocaine fast, bupivacaine slow), duration tracks protein binding and vasoactivity.
Neuraxial: hyperbaric bupivacaine spreads with gravity and patient position; hypobaric spreads opposite. Anticipate sympathectomy-induced hypotension, high block, urinary retention, and postdural puncture headache (postural, treated initially with caffeine and hydration, then an epidural blood patch).
Peripheral blocks pair anatomy with ultrasound. Know the complication signature: interscalene causes phrenic palsy and hoarseness; supraclavicular risks pneumothorax; axillary risks hematoma; adductor canal spares the posterior knee.
Local anesthetic systemic toxicity presents as CNS excitation followed by cardiovascular collapse. Stop injection, secure the airway with 100% oxygen, treat seizures with benzodiazepines, give 20% lipid emulsion 1.5 mL/kg bolus then 0.25 mL/kg/min, and continue resuscitation.
Traps: epinephrine in a test dose detects intravascular injection rather than prolonging block; ultrasound does not prevent intraneural injection; a negative aspiration does not exclude intravascular placement.
Worked example: 70 kg adult, lidocaine 1% with epinephrine. Maximum 7 mg/kg = 490 mg, and 1% contains 10 mg/mL, so the ceiling is 49 mL. Plain lidocaine would cap at 315 mg, or 31.5 mL.