With the growth of ultrasound-guided regional anesthesia, so has the requirement for training tools to practice needle guidance skills and evaluate echogenic needles. Ethically, skills in ultrasound-guided needle placement should be gained in a phantom before performance of nerve blocks on patients in clinical practice. However, phantom technology is varied, and critical evaluation of the images is needed to understand their application to clinical use. Needle visibility depends on the echogenicity of the needle relative to the echogenicity of the tissue adjacent the needle. We demonstrate this point using images of echogenic and nonechogenic needles in 5 different phantoms at both shallow angles (20 degrees) and steep angles (45 degrees). The echogenicity of phantoms varies enormously, and this impacts on how needles are visualized. Water is anechoic, making all needles highly visible, but does not fix the needle to allow practice placement. Gelatin phantoms and Blue Phantoms provide tactile feedback but have very low background echogenicity, which greatly exaggerates needle visibility. This makes skill acquisition easier but can lead to false confidence in regard to clinical ability. Fresh-frozen cadavers retain much of the textural feel of live human tissue and are nearly as echogenic. Similar to clinical practice, this makes needles inserted at steep angles practically invisible, unless they are highly echogenic. This review describes the uses and pitfalls of phantoms that have been described or commercially produced.
Needle tip visualization is fundamental to the safety and efficacy of ultrasound-guided regional anesthesia (UGRA). It can be extremely challenging especially at steep insertion angles. We assessed whether an echogenic needle improved tip visibility during UGRA by anesthesiologists performing their normal in-plane technique. The visibility of the Pajunk Sonoplex (echogenic) and the Pajunk Uniplex (control) needle were compared during 60 nerve blocks (30 femoral, 30 sciatic) in this randomized controlled trial. All ultrasound imaging was recorded for analysis. The anesthesiologist subjectively estimated the percentage time they had visualized the needle tip (5-point scale: 1 [0%-20%], 2 [20%-40%], 3 [40%-60%], 4 [60%-80%], 5 [80%-100%]). The actual time the tip was in view, angle of needle insertion, target depth, and procedure time were subsequently measured objectively by a single investigator. The Sonoplex group had both subjectively and objectively better tip visibility (P=0.002), despite having larger mean body mass index (29.0 vs 25.0 kg/m(2), P=0.01) and steeper mean insertion angle (31 vs 22 degrees, P=0.03). Objective percentage tip visibility, during in-plane UGRA, reduced by 12% for every 10-degree increase in insertion angle with the control. Tip visibility with the Sonoplex was independent of insertion angle over the range studied (0-57 degrees, P=0.95). This finding occurred when nonexpert anesthesiologists performed their standard UGRA technique. A needle that is visible for a greater percentage of time has potential safety and efficacy implications.
We assessed whether echogenic needles reduce tip location error, by comparing three echogenic designs (Pajunk Sonoplex, Lifetech, B. Braun Stimuplex D+) with a non-echogenic control (Pajunk Uniplex), using a novel assessment technique in unembalmed human cadavers. Multiple images were taken of each needle at shallow (15 to 25°), moderate (35 to 45°) and steep (55 to 65°) insertion angles. Twenty anaesthetists with varied experience in ultrasound-guided nerve blocks identified needle tip position and stated their confidence level in estimates. Actual tip position was determined at the time of image generation but concealed from the anaesthetists. Two-dimensional mapping of ‘tip-error’ involved measurement of the distance and orientation of each clinician's estimate of tip position in relation to the actual tip position. There were no significant differences in confidence or overall needle visibility at shallow insertion angles. At steeper angles, the Sonoplex showed significantly higher confidence and visibility scores. The remaining echogenic designs did not show any significant differences from the non-echogenic control. Objective measurements of tip error followed the same pattern as the subjective data, although were not universally significant. Two-dimensional mapping showed that as needle visibility deteriorated, so precise tip location was lost but the needle shaft/insertion path remained well-identified. As visibility deteriorated further, accuracy in this axis was also lost. When inaccurate, clinicians generally assessed the needle tip to be more superficial and inserted less far than it actually was. This has important implications for the safety of ultrasound-guided regional anaesthesia. Effective echogenic needle technology has the potential to address these concerns.
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