Ultrasound-Guided Regional Principles

Ultrasound-guided regional anesthesia (UGRA) has been shown to: reduce time to block onset, increase block success rate, decrease total local anesthetic dose required, reduce vascular punctures, and reduce LAST incidence vs landmark or nerve-stimulator-only techniques.

Multiple Cochrane reviews confirm faster onset and higher success for major upper-extremity blocks.

Nerve stimulator retains a confirmatory role — but ultrasound is the modern standard.

The combination of US guidance + small (3-5 mL) test injection of LA observed spreading around the nerve is the highest-yield workflow.

Linear high-frequency (8-15 MHz): superficial structures (<5 cm depth) — brachial plexus (interscalene, supraclav, infraclav, axillary), femoral, ankle, popliteal in lean patients, fascial plane blocks (TAP, ESP).

Best resolution.

Curvilinear low-frequency (2-5 MHz): deeper structures (5-10 cm) — lumbar plexus, sciatic via posterior approach, paravertebral in some patients, popliteal in obese, neuraxial in difficult anatomy.

Lower resolution but better depth.

Phased-array small-footprint probes: rarely used in regional except for very tight intercostal spaces — primarily a cardiac probe.

Depth: adjust so target is in middle 1/3 of screen — too shallow misses spread, too deep wastes resolution.

Gain: ensures cortical bone bright + vessels black; over-gain washes out detail.

Focus: position the focal zone at or just below the target.

Doppler: confirm vessels are vessels (rules out lymph nodes + hypoechoic tissue) and identifies them in the needle path before injection.

Tissue harmonic imaging reduces clutter in obese patients.

Preferred for most peripheral blocks because you SEE the entire path and avoid vessels + nerves.

Useful for central line access, occasional deep peripheral nerves where in-plane is geometrically impossible.

Hydrodissection (small saline test injection) confirms tip location when out-of-plane.

Watch the fluid spread on the screen.

If you see expected tissue plane spread + the nerve floats free: proceed.

If you see abnormal swelling of the nerve itself (intraneural): STOP, withdraw, reposition.

If you see fluid flow into a vessel: STOP.

Hydrodissection also reduces the risk of injection injury — saline is harmless if mispositioned; LA is not.

Echogenic needles substantially improve tip visualization in deep blocks (popliteal, infraclavicular, paravertebral, lumbar plexus).

Acoustic shadowing: bone + calcium + needle artifacts cast hypoechoic shadows below them — useful for identifying bony landmarks (transverse process, rib, hyoid) but can hide structures.

Watch LA surround the target nerve circumferentially — the 'donut sign' — for optimal block.

Adequate spread of ~15-20 mL around a major plexus is typical; less for individual peripheral nerves.

Inadequate spread → reposition the needle and re-inject (small aliquots, never push more LA hoping it will spread).

Asymmetric spread → block may be incomplete; consider supplemental injection in the deficient sector.

This visualization distinguishes a successful block from an inadequate one AT THE MOMENT of injection rather than 20 minutes later when you discover the patient still has sensation.

STOP IMMEDIATELY, withdraw 1-2 mm, reposition.

Intravascular: blood return on aspiration, ultrasound visualization of LA flowing into a vessel rather than spreading in tissue.

Aspirate every 3-5 mL during injection.

Monitor the patient continuously for LAST symptoms (peri-oral numbness, tinnitus, metallic taste, agitation, seizure) — prompt cessation of injection + lipid emulsion preparation are time-critical.

💉Photograph the ultrasound image with needle-tip-at-target as a static record.

ASRA documentation standards.