High-definition ultrasound in regional anesthesia.

Purpose of review: Ultrasound has become the standard imaging technique for regional anesthesia. Traditional guidelines discourage direct needle-nerve contact to prevent fascicle impalement and nerve injury from high-pressure injections. However, despite its widespread usage, efficacy remains inconsistent, with significant rates of secondary continuous block failure and unchanged side-effect profiles. Current ultrasound (8-14 MHz) provides insufficient resolution to reliably differentiate nerve structures from surrounding tissues, particularly in patients with conditions affecting tissue differentiation, such as rheumatoid arthritis.

Recent findings: Recent microultrasound studies (>30 MHz) challenge conventional paradigms by revealing multiple fascicles and distinct adipose tissue compartments that are critical for anesthetic distribution. These studies indicate that the needle-tip location relative to adipose tissue, rather than mere proximity to nerves, dictates clinical outcomes. Intraneural injections into adipose compartments seem to be common and clinically beneficial, in contrast to traditional beliefs that associate intraneural injections exclusively with harm.

Summary: Innovative technologies such as ultra-high-resolution ultrasound and fiber-optic needle integration promise significantly improved visualization and accurate pressure monitoring for precise anesthetic placement. Until these technologies mature, a combined approach that utilizes ultrasound for anatomical guidance and nerve stimulation to confirm accurate needle and catheter positioning is recommended to enhance block reliability and patient safety.