Background and Aims Ultrasound-guided lumbar plexus block(ULPB) can be performed using two approaches: a parasagital (PSA) or transversal(TA). The PSA and TA have been described targeting the location of transverse process of the 4th lumbar vertebra (L4). A higher approach may promote organ puncture complication. We hypothised that TA ULPB might promote a higher level of puncture than expected.
Methods After informed consent, 50 volunteers were studied. Each volunteer was landmarked bilaterally, using PSA and an invisible ink pen from T12 to L5 transverse process location. A landmarked horizontal line parralel from both iliac crests was drawn. We named this line ”C”. Once we obtained the typical image of ULPB using TA passing from line C, we oriented caudaly and cephalad the probe to visualise the lumbar plexus on the level directly above and under. We named these lines ”>C” for the level above and ”<C” for the level under.
Results The demographic characteristics are described on the table below. On 100 compared approaches,we reported that a ULPB with a TA is projected between the transversal process of L3 and L4 ( 51%), L4 (21%) and L3 (9%). By tilting the probe we can access up to L1 transverse process ( 1%). Lumbar plexus was not visualized in 12% of cases in PSA and in 1% in TA.
Conclusions A TA for an UPLB leads to an unexpected higher level than L4. We recommend to perform a previsualization with a PSA to strictly identify a L4 level of puncture.
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