Ultrasound standard for lumbar plexus block.

Editor—The lumbar plexus block (LPB) has been traditionally performed with the needle puncture guided by landmark and the injection point confirmed by nerve stimulator. Various ultrasound approaches could help improve the safety, but each has its own problems. Not until the advent of the ‘Shamrock method’ did I routinely, perhaps more easily, apply ultrasound for real-time guidance during LPB. Personally, I recommend the ‘Shamrock method’ to be the standard of ultrasound monitoring for LPB in combination with pressure and stimulator monitoring, the so-called triple monitoring. Several advantages could be found while applying the ‘Shamrock method’ compared with others. Firstly, the ‘Shamrock method’ is the real needle in-plane one without changing the practice of traditional landmarkguided LPB, all the same besides additional information of needle trajectory. The lumbar plexus is almost always located ventral to the medial half of the transverse process on shamrock view. Although absolute posterior–anterior approach could also be accomplished and assisted by the famous ‘trident sign’, most clinicians consider it an out-of-plane technique and hard to prevent inadvertent needle puncture during LPB, at least possible for the kidney and intestines. Using the ‘Shamrock method’, the needle shaft usually could be found after slightly tilting the transducer. Personal experience revealed that to obtain the complete shamrock view with the transverse process centred, sometimes the curve transducer needed to be slid more posterior, even with some part of it off the skin (Fig. 1). Secondly, although the paramedian transverse scan (PMTS) of the lumbar paravertebral region with the ultrasound beam being insonated through the intertransverse space (ITS) provides a possible solution for in-plane LPB, PMTS-ITS in-plane view is not so easy and straightforward as the vertical ‘Shamrock method’ to get the needle in plane. Furthermore, lateral-to-medial PMTS-ITS approach will direct the needle towards the neuraxis, which is not recommended if the needle is not easily visible, especially for deeper targets, such as the lumbar plexus close to the intervertebral foramen. Medialto-lateral PMTS-ITS in-plane approach inherently has the risk of introducing jelly throughout the path because the jelly will inevitably flow to the dependent part where the needle inserts nearby. Jelly introduction into the central part of the body should be avoided whenever possible, even if it is aseptic. Thirdly, one-man technique is possible by using the ‘Shamrock method’. The vertical direction of the needle to the skin usually will ensure the needle anchored by the flank muscle; therefore, the needle-holding hand could be safely free without changing the position of the needle tip after confirmation of the patella twitch by 0.5–1.0 mA current. With the transducer in situ, the original needle-holding hand could then be used to adjust the stimulating current, execute half-the-air opening pressure test (better to have a luer lock syringe tip at the connection point for one-hand test), record the image during injection, . . . and so on; thus, one-man Shamrock saves manpower for one-shot LPB. Another point is the contact area for the transducer is far away from the needle injection point (Fig. 1), which also saves time because there is no need to routinely make the transducer aseptic. Currently, a clinical trial regarding the minimally effective volume of ‘Shamrock’ LPB is being carried out by the inventor (http://clinicaltrials.gov/ct2/show/NCT01956617). Although the anaesthetic volume is probably the same compared with the traditionally landmark-guided technique, we are expecting more details about the ‘Shamrock method’ explored from the trial.