Spinal anesthesia hemodynamics — predictable drop
Why spinal anesthesia drops BP and what to do
Mnemonic device
Sympathectomy-Block-Treat
Mapping
Sympathectomy
Spinal blocks T1-S2+ sympathetic chain → vasodilation below the block + venous pooling
Block
Above T4 sympathetic block → blocks cardiac sympathetics (T1-T4) → bradycardia (Bezold-Jarisch reflex amplifies)
Treat
Phenylephrine 50-100 mcg, ephedrine 5-10 mg if bradycardic, fluid bolus 250-500 mL, leg elevation, atropine if HR < 50
Clinical note: Prevent rather than chase — give 500 mL crystalloid + co-load with vasopressor as block sets in. In OB, phenylephrine is preferred (less placental transfer of CV effect).