A new score for characterizing the visibility of anatomical structures during ultrasound guided regional anesthesia: a retrospective cohort study.

BACKGROUND: To identify anatomical structures using sonography can be challenging, yet it is a basic requirement for effective and safe ultrasound guided nerve blocks. In clinical routine, we find a wide variety in the visibility of anatomical structures. Aim of this study was to evaluate the feasibility of a newly developed visibility score for anatomical structures in ultrasound guided regional anesthesia. METHODS: We retrospectively evaluated the blockades from the routine documentation of ultrasound-guided regional anesthesia over an arbitrary period of 15 months at a university hospital with a Visibility Score (VIS) of one (best) to five (worst visibility). RESULTS: The study analyzed 983 blockades (femoral, saphenous, infragluteal and popliteal sciatic, transversus abdominis plane, interscalene, supraclavicular, axillary and suprascapular blockades). The following VIS were found: 1: 80.6%; 2: 14.0%; 3: 4.0%; 4: 1.2%; 5: 0.2%. The mean Body Mass Index (BMI) was 27.9 kg/m2. The best cut-off for poor VIS was a BMI of 28.9 kg/m2. For infragluteal sciatic nerve block VIS was significantly higher (mean VIS 1.71±1.0) compared to all the other recorded blockades except the supraclavicular block. CONCLUSIONS: VIS was feasible in clinical routine. Compared to the other evaluated blocks, the VIS for the infragluteal access to the sciatic nerve was rated worst. VIS is found to be worse in obese patients. Further research is needed to evaluate VIS and its suitability for specific questions as for instance anesthetists' learning curves, comparison of different patient populations, ultrasound devices or different nerve blocks.