Ultrasound-Guided Regional Anesthesia & Nerve Blocks
Evidence-based emergency regional anesthesia: Pericapsular Nerve Group (PENG) block for hip fractures, Serratus Anterior plane block for multiple rib fractures, forearm nerve blocks (radial, median, ulnar), popliteal/tibial blocks, local anesthetic toxic dose limits, and 20% lipid emulsion rescue.
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Ultrasound-guided regional anesthesia (UGRA) provides dense, targeted opioid-sparing analgesia, reduces delirium in the elderly, and facilitates painless fracture reductions. Always calculate max toxic doses (Lidocaine plain 4.5 mg/kg, with Epi 7 mg/kg; Bupivacaine plain 2.5 mg/kg, with Epi 3 mg/kg). For hip/femur fractures, the PENG (Pericapsular Nerve Group) block targets articular sensory branches of femoral, obturator, and accessory obturator nerves while completely sparing quadriceps motor function. Have 20% Lipid Emulsion (Intralipid) at the bedside for LAST rescue (1.5 mL/kg bolus, then 0.25 mL/kg/min).
Point-of-care ultrasound (POCUS) has transformed emergency pain management. Direct real-time visualization of the needle tip, target neural/fascial planes, and surrounding vascular structures ensures rapid onset, high procedural success, and dramatic reduction in vascular injection risks:
| Block Name | Clinical Indications | Probe & Patient Position | Sonoanatomy Landmarks & Target Plane | Injectate & Volume |
|---|---|---|---|---|
| PENG Block (Pericapsular Nerve Group) | Femoral neck and acetabular fractures; hip dislocations | Curvilinear or high-frequency linear probe in transverse orientation over anterior inferior iliac spine (AIIS) | Identify AIIS, iliopubic eminence (IPE), and psoas tendon. Advance needle in-plane from lateral to medial; place tip in fascial plane between psoas tendon and pubic ramus | 15–20 mL of 0.25% Bupivacaine or 0.2% Ropivacaine. SENSORY ONLY: Completely spares quadriceps motor function. |
| Fascia Iliaca Compartment Block (FICB) | Femoral shaft fractures, hip fractures (infra- or supra-inguinal) | Linear probe transverse at junction of lateral 1/3 and medial 2/3 of inguinal ligament | Identify femoral artery, femoral nerve, and iliopsoas muscle covered by hyper-reflective fascia iliaca. Advance in-plane from lateral to medial; penetrate fascia iliaca ('pop'); confirm hydrodissection beneath fascia | 30–40 mL dilute local anesthetic (0.25% Bupivacaine or 0.2% Ropivacaine). Volume-dependent spread to femoral, lateral femoral cutaneous, and obturator nerves. |
| Serratus Anterior Plane Block (SAPB) | Multiple traumatic rib fractures, thoracostomy pain, flail chest | Linear probe at 4th or 5th rib along the midaxillary or anterior axillary line | Identify rib shadow, pleura, intercostal muscles, serratus anterior muscle, and latissimus dorsi. Advance in-plane; deposit local anesthetic superficial or deep to serratus anterior | 20–30 mL of 0.2% Ropivacaine or 0.25% Bupivacaine. Blocks lateral cutaneous branches of intercostal nerves T2–T9. |
| Superficial Cervical Plexus Block | Clavicle fractures, acromioclavicular (AC) dislocations, neck lacerations | Linear probe transverse over midpoint of posterior border of sternocleidomastoid (SCM) muscle | Identify SCM, carotid sheath, and prevertebral fascia. Advance needle in-plane from posterior to anterior; inject into fascial tapering behind SCM margin | 5–10 mL of 0.25% Bupivacaine or 1–2% Lidocaine. Anesthetizes C2–C4 sensory dermatomes. |
| Forearm Nerve Blocks (Median, Ulnar, Radial) | Hand lacerations, digital amputations, metacarpal fractures, abscess drainage | High-frequency linear probe transverse at mid-forearm (5–10 cm proximal to wrist crease) | Median: between FDS and FDP muscles ('honeycomb' nerve); Ulnar: immediately medial to ulnar artery; Radial: lateral to radial artery deep to brachioradialis | 3–5 mL of 1–2% Lidocaine per nerve. Circumferential 'donut' spread around each nerve trunk. |
Exceeding maximal weight-based local anesthetic thresholds causes life-threatening systemic absorption. Calculate total allowable milligrams before drawing up the medication, especially when combining local infiltration with regional blocks:
| Local Anesthetic Agent | Max Dose (Plain) | Max Dose (with Epinephrine 1:200,000) | Onset of Action | Duration of Anesthesia |
|---|---|---|---|---|
| Lidocaine (Xylocaine) | 4.5 mg/kg (max 300 mg) | 7.0 mg/kg (max 500 mg) | Rapid: 2–5 minutes | Intermediate: 1–2 hours (2–4 hours with epi) |
| Bupivacaine (Marcaine) | 2.5 mg/kg (max 175 mg) | 3.0 mg/kg (max 225 mg) | Moderate: 10–20 minutes | Prolonged: 4–8 hours (up to 12 hours) |
| Ropivacaine (Naropin) | 3.0 mg/kg (max 200 mg) | 3.5 mg/kg (max 250 mg) | Moderate: 10–15 minutes | Prolonged: 4–8 hours (lower cardiotoxicity than bupivacaine) |
Local Anesthetic Systemic Toxicity (LAST) occurs from accidental intravascular injection or rapid systemic absorption. Lipophilic agents (Bupivacaine > Ropivacaine > Lidocaine) bind to cardiac sodium channels and intracellular mitochondrial enzymes, triggering a progression from CNS excitation to catastrophic refractory cardiovascular collapse.
| Phase of Toxicity | Clinical Signs & Symptoms | Physiologic Mechanism | Immediate Emergency Interventions |
|---|---|---|---|
| Early CNS Toxicity | Perioral numbness, metallic taste, tinnitus, lightheadedness, facial tingling, slurred speech | Inhibition of inhibitory cortical interneurons leading to unopposed excitation | STOP local anesthetic injection immediately; administer 100% O2 via NRB; call for LAST rescue kit. |
| Excitative CNS Phase | Visual disturbances, muscle twitching, myoclonus, generalized tonic-clonic seizures | Diffuse cortical epileptogenic activity | Administer Midazolam 2–4 mg IV or Lorazepam 1–2 mg IV immediately. AVOID Propofol in cardiovascular compromise. |
| Cardiovascular Collapse | Severe conduction block (prolonged PR, wide QRS), ventricular dysrhythmias (VT/VF), profound bradycardia, asystole | Fast inward sodium channel blockade, inhibition of cardiac fatty acid metabolism and ATP synthesis | INITIATE 20% LIPID EMULSION IMMEDIATELY. Follow ACLS modified guidelines (avoid vasopressin; use low-dose epinephrine < 1 mcg/kg). |
The Official ASRA LAST Treatment Protocol: 1) Administer 20% Intravenous Lipid Emulsion (Intralipid) 1.5 mL/kg IV bolus over 1 minute (~100 mL for standard adult); 2) Immediately initiate continuous IV infusion of 0.25 mL/kg/min (~1,000 mL/hr); 3) If cardiac stability not restored, repeat 1.5 mL/kg bolus up to 2 times, and double infusion rate to 0.5 mL/kg/min; 4) Continue CPR for at least 30–60 minutes (lipid sink extracts local anesthetic from myocardium); 5) In ACLS, use small epinephrine boluses (<= 1 mcg/kg; 10–50 mcg in adults) to avoid exacerbating arrhythmias and lipid binding interference.
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