Background This cadaveric dose-finding study investigated the minimum effective volume of dye in 90% of cases (MEV90), required to stain the femoral, lateral femoral cutaneous and obturator nerves for ultrasound-guided suprainguinal fascia iliaca block (SIFIB).
Methods In cadaveric specimens of the lower limb, the block needle was advanced, medial to the anterosuperior iliac spine, until its tip was positioned between the internal oblique and iliacus muscles underneath the fascia iliaca. The dye was injected inside the fascia iliaca compartment. Volume assignment was carried out using a biased coin design, whereby the volume of dye administered to each cadaveric specimen depended on the response of the previous one. In case of failure, the next one received a higher volume (defined as the previous volume with an increment of 2.5 mL). If the previous cadaveric specimen had a successful block, the next one was randomized to a lower volume (defined as the previous volume with a decrement of 2.5 mL), with a probability of b=0.11, or the same volume, with a probability of 1–b=0.89. Success was defined as the staining of the femoral, lateral femoral cutaneous, and obturator nerves on dissection.
Results Thirty-six cadavers (60 cadaveric specimens) were included in the study. Using isotonic regression and bootstrap CI, the MEV90 for ultrasound-guided SIFIB was estimated to be 62.5 mL (95% CI 60 to 65).
Conclusion For ultrasound-guided SIFIB, the MEV90 of dye required to stain the femoral, lateral femoral cutaneous and obturator nerves is 62.5 mL. Further studies are required to correlate this finding with the MEV90 of local anesthetic in human subjects.
- lower extremity
- nerve block
Data availability statement
All data relevant to the study are included in the article.
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Contributors PK, NM, AS, PM and PL participated in the planning, conception, design, conduct, reporting, acquisition of data, data analysis and interpretation of data. DQT participated in the planning, conception, design, data analysis and interpretation of data.
Funding This research received a grant from the Teacher Assistant or Research Assistant (TA/RA) Scholarship from the Graduate School of Chiang Mai University, and the Faculty of Medicine Research Fund (grant number 054-2564) of Chiang Mai University, Chiang Mai, Thailand.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.