Spinal Anesthesia — Patient + Drug Selection

🫀Inject below the conus to avoid cord injury — most commonly L3-L4 or L4-L5.

The Tuffier line connects the iliac crests and crosses L4 vertebral body — useful landmark, but unreliable in obese + elderly (off by 1-2 levels in 30%).

Ultrasound landmark identification recommended in difficult anatomy.

Median vs paramedian approach: paramedian bypasses calcified ligaments in elderly + can be easier in flexion-limited patients.

Standard hyperbaric: 0.75% bupivacaine in 8.25% dextrose.

Isobaric (matches CSF density) — stays near the injection site, less position-dependent; useful when you want a tight band of anesthesia.

Hypobaric (lighter than CSF) — flows to non-dependent areas; clinical use is limited (some hip surgery in lateral position with non-operative side down).

Patient position IMMEDIATELY after injection and through the first 10-15 minutes is critical for level control — once the LA is fixed in the cord, you can't adjust the level.

Knee + thigh: T10.

Hip + pelvis: T6-T8.

Lower abdominal (hernia, TURP): T6-T8.

Upper abdominal: T4-T6 (rarely chosen because of higher hemodynamic + respiratory impact).

Cesarean section: T4 (level of nipple line — verified by ice/cold test before incision).

Hemorrhoid / urologic anal procedures: S2-S4 saddle block — small volume + reverse Trendelenburg.

Test the block bilaterally before incision: cold, pinprick, and motor — all three matter, sympathetic block extends 2 dermatomes above sensory.

💊Duration 2-3 hours surgical.

Ropivacaine: 15-25 mg — slightly faster recovery + less motor block, useful for ambulatory.

Lidocaine 5% hyperbaric: short duration (~60-90 min) but has been associated with transient neurologic symptoms (TNS, especially lithotomy + outpatient knee scope) — use is limited; isobaric 2% lidocaine sometimes preferred.

Chloroprocaine 3% (preservative-free): 40-50 mg, very short duration (~60 min), excellent for ambulatory cases — historic concerns about adhesive arachnoiditis with old preservative formulations are no longer relevant.

Tetracaine 0.5% hyperbaric: 6-12 mg, duration 2-4 hr.

Morphine 100-200 mcg (preservative-free morphine — Duramorph/Astramorph PF): 18-24 hr postop coverage; DELAYED respiratory depression peak at 6-12 hr requires extended SpO₂ monitoring + naloxone availability.

Sufentanil 5-10 mcg: similar to fentanyl, less commonly used.

Clonidine 30-100 mcg: prolongs sensory + motor block, hypotension.

Dexmedetomidine 5 mcg: prolongs block similarly.

Epinephrine 0.2 mg: meaningfully prolongs lidocaine + tetracaine, minimal effect on bupivacaine in clinical practice.

Sympathectomy from a T4 block: vasodilation throughout the venous + arterial bed + bradycardia (T1-T4 cardiac accelerator fibers blocked) → hypotension is essentially universal at this level.

Treatment: PHENYLEPHRINE 50-100 mcg IV bolus first-line, OR phenylephrine infusion 25-50 mcg/min.

In OB cesarean, phenylephrine is now PREFERRED over ephedrine (less neonatal acidosis from less placental transfer + less fetal stimulation).

Co-load IV fluid 500-1000 mL crystalloid at induction of spinal (not pre-load — coadministration during onset is more effective per modern evidence).

Bradycardia: atropine 0.4-1.0 mg if HR <50 + symptomatic.

Left lateral tilt 15° in pregnant patients > 20 wk (relieves aortocaval compression).

Persistent or refractory hypotension → rule out high block, hidden hemorrhage, embolism.

Action: WAIT 20-30 min before declaring failure (slow-onset isobaric blocks can mature).

Document specifically what was inadequate.

Total spinal: block reaches the brainstem → apnea + loss of consciousness + cardiovascular collapse + pupil dilation.

Treatment is the same and immediate: intubate + ventilate (don't wait for arrest), IV fluids wide open, phenylephrine + epinephrine for BP, atropine for bradycardia, vasopressin if refractory.

Trendelenburg is NOT helpful once block is already cephalad.

The block self-resolves over 1-3 hours as LA redistributes — supportive care + ICU monitoring until resolution.

Common precipitants: dural puncture during epidural attempt with subsequent re-injection through epidural catheter, excessive dose in elderly/obese/short patients.

Treatment: conservative (hydration, caffeine 300-500 mg, lying flat, NSAIDs) for 24-48 hr; if persistent or severe → epidural blood patch (15-20 mL autologous blood injected at the puncture level, ~70-90% effective first patch).

Sphenopalatine ganglion block or greater occipital nerve block can be intermediate options.