Peripheral Nerve Blocks: Lower Extremity

PNBs: Basics & Nerve Atlas - Laying the Groundwork

• Peripheral Nerve Blocks (PNBs): Precise Local Anesthetic (LA) deposition near target nerves/plexuses.
• Goal: Surgical anesthesia, postoperative analgesia, chronic pain management.
• Advantages: Opioid-sparing, ↓ Postoperative Nausea & Vomiting (PONV), improved rehabilitation.
• Nerve Localization Methods:
  • Ultrasound (USG): Gold standard; real-time needle/spread visualization.
  • Peripheral Nerve Stimulator (PNS): Elicits motor response at <0.5 mA.
  • Anatomical Landmarks/Paresthesia: Historically used, less precise.
• Key Lower Limb Nerve Plexuses & Branches:
  • Lumbar Plexus (L1-L4):
    • Femoral n.: Anterior thigh, knee, medial leg/foot.
    • Obturator n.: Medial thigh (adduction).
    • Lateral Femoral Cutaneous n.: Anterolateral thigh (sensory).
  • Sacral Plexus (L4-S4):
    • Sciatic n.: Posterior thigh, entire leg & foot below knee (via Tibial & Common Peroneal nn.).

⭐ Ultrasound guidance significantly improves PNB success rates and safety by allowing direct visualization of neural structures, vasculature, and LA spread, reducing risk of intraneural or intravascular injection.

Anterior Blocks - Thigh High Relief

• Femoral Nerve Block (FNB)
  • Targets: Femoral nerve (anterior thigh, medial leg/foot via saphenous).
  • Indications: Hip, femur, knee surgery.
  • Technique: Inguinal crease, lateral to femoral artery. US: "target sign".
  • Volume: 15-25 mL.
  • ⚠️ Quadriceps weakness, ↑ fall risk.
• Fascia Iliaca Compartment Block (FICB)
  • Targets: Femoral, lateral femoral cutaneous, +/- obturator nerves.
  • Indications: Hip fractures, broader analgesia than FNB.
  • Technique: US: inject deep to fascia iliaca, lateral to femoral artery. "Double pop" (landmark).
  • Volume: 30-40 mL.
• PENG Block (Pericapsular Nerve Group)
  • Targets: Articular branches to hip capsule (femoral, obturator, accessory obturator).
  • Indications: Hip fracture, THA. Motor-sparing.
  • Technique: US: AIIS & iliopubic eminence.
  • Volume: 15-20 mL.

⭐ FICB is often preferred for pre-operative hip fracture analgesia due to its relative ease and broader coverage. oka

Posterior Blocks - Sciatic & Co. Secrets

• Sciatic N. (L4-S3): Forms Tibial (TN) & Common Peroneal (CPN).

  • Covers: Post. thigh, leg, foot (sensory); hamstrings, lower leg/foot muscles (motor). Excludes saphenous area.
  • Proximal Blocks: Transgluteal, Subgluteal. US-guided. Vol: 15-20 mL.

• Popliteal Block (Sciatic in fossa): TN & CPN targeted.

  • For: Foot, ankle, calf surgery. Spares quads & hamstring motor.
  • Approaches: Posterior (prone/lat), Lateral (supine).
  • Vol: ~20 mL total; or ~10 mL each TN/CPN.
  • 

• Pearls:

  • ⚠️ CPN injury risk (superficial/lateral) → foot drop.
  • ⭐ > iPACK block (Interspace Popliteal Artery & Capsule of Knee) often complements popliteal sciatic for posterior knee analgesia.

Distal Blocks & Management - Ankle Deep & Aware

• Ankle Block (5 Nerves):
  • Saphenous, Tibial, Deep Peroneal (DPN), Superficial Peroneal (SPN), Sural. 📌 (STPDS)
  • Landmark/USG-guided. Volume: 3-5 mL/nerve.
  • Patient often awake.

• Adjuvants for PNBs:

  • Epinephrine (1:200k-1:400k): ↑duration, vascular marker.
  • Dexamethasone (4-8 mg): ↑analgesia (IV/perineural).
  • α2-agonists (Clonidine/Dexmed): ↑analgesia; monitor side effects (sedation, bradycardia).

• Management of Complications:

  • Nerve Injury: Stop if pain/paresthesia.
  • LAST (Local Anesthetic Systemic Toxicity):
    • CNS (early): Tinnitus, metallic taste, seizures.
    • CVS (late): Arrhythmias, cardiac arrest.
    • Tx: Stop LA; ABCs (100% O2); Benzos (seizures); Mod. ACLS.
    • ⭐ Lipid Emulsion (20%): Bolus 1.5 mL/kg, then infusion 0.25 mL/kg/min.

⭐ Bupivacaine-induced cardiac arrest (LAST): prolonged CPR & lipid emulsion are vital. Use smaller Epi doses (<1 mcg/kg) in ACLS.

High‑Yield Points - ⚡ Biggest Takeaways

• Femoral block: Anterior thigh/knee analgesia; causes quadriceps weakness. Saphenous often spared.
• Sciatic block: Posterior thigh, leg, & foot anesthesia (spares medial leg/saphenous).
• Adductor canal block: Knee analgesia with quadriceps motor sparing; mainly sensory.
• Popliteal block: For foot/ankle surgery; blocks tibial & common peroneal nerves.
• Ankle block: Targets five nerves for foot procedures (tibial, peroneals, sural, saphenous).
• PENG block: Hip fracture analgesia via articular branches (femoral, obturator); motor-sparing.
• Ultrasound guidance crucial for safety (avoiding LAST) and efficacy.