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Ultrasound-Guided Interfascial Injection For Peripheral Obturator Nerve Block In The Thigh
Published 2009 · Medicine
To the Editor: Identification of vascular structures during regional anesthesia procedures with ultrasound can help to identify target nerves and plan for an appropriate needle approach to avoid puncture and intravascular injection. Arteries can be identified by their relative resistance to collapse from pressure exerted by the ultrasound probe along with the characteristic pulsatile flow demonstrated by color or pulse wave Doppler. Veins often go unidentified, leading to patient morbidity and potential mortality. Because of their ease of collapse with minimal ultrasound probe pressure and their low-velocity-flow states that are not always well represented on ultrasound by color Doppler, veins can be difficult to recognize with ultrasound. We describe a novel technique to identify small or collapsed veins using any standard ultrasound with color Doppler. Once an area is identified that could contain venous structures, color Doppler is activated. During real-time ultrasound, any distal part of the patient’s corresponding extremity is compressed or squeezed. This compression of the distal muscles and veins significantly increases venous blood flow that is then represented more reliably by color Doppler on ultrasound (Fig. 1). This technique may be repeated several times for complete evaluation of veins in an area and is well tolerated by patients. Other techniques can be used to visualize low-flow blood vessels such as probe tilt, adjustment of pulse repetition frequency, and increasing color gain, but none of these are effective in evaluating veins that are collapsed. Squeezing a distal extremity, as described here, results in the ability to evaluate both low-flow and completely collapsed venous structures. We have found this distal compression technique to be very useful in the identification of veins that are often closely associated with nerves. We routinely use this technique in the axillaq and the popliteal regions by squeezing the arm and calf, respectively.