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Ultrasound-guided psoas compartment block

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Introductory Remark

The psoas block has established itself in only a few anaesthesia departments as a routine procedure. The primary reason for this appears to be the fear of complications such as damage to the kidneys or intraabdominal organs. On the positive side is the all-round effectiveness of this block, which we see demonstrated almost every day, in the lumbar plexus area. The psoas block can with justification be designated as the true „3-in-1-block“.

We now look back on more than 5,000 psoas blocks in the last 15 years without a single clinically apparent kidney or abdominal puncture. Compared with blocks near the surface (e.g. the femoral nerve) in which nerve structures can usually be ultrasonographically distinguished with ease, some limitations in this regard must be accepted with the psoas block. Because the lumbar plexus is deeply embedded in the greater psoas muscle in the area of the lumbar spinal column, high-frequency ultrasound probes reach their limits here for reasons of ultrasound physics. Nevertheless, it is (usually) also possible with low-frequency sector ultrasound probes to distinguish the block-relevant anatomy, including its relationships to the surroundings (kidney!!). This last point alone justifies the use of ultrasound, even when its intrinsic usefulness for performing the block from our present-day point of view is at least moot.

At the present time, the following is to be said here: NO PSOAS BLOCK WITHOUT ELECTRIC NERVE STIMULATION!!

The patient is positioned on his/her side as for a conventional psoas block. Starting at the level of the iliac crest, the bony structures (spinous processes, vertebrae, transverse processes) of the respective lumbar vertebra can be shown in cross-section. If the patients are not overly adipose, it is now possible to directly distinguish paravertebrally the autochthonous back muscles, and ventral to them the greater psoas muscle. The lumbar quadrate muscle is seen dorsolateral to the psoas cross-section.

 

The Technique

The block is carried out on the long axis through an ultrasound window between the transverse processes (see above). Here the needle is advanced from a puncture point ca. 4 to 5 cm lateral from the mid-line, primarily vertical to the skin (compare with a conventional block), from dorsal into the belly of the greater psoas muscle. The parts of the lumbar plexus usually lie at the transition point between the dorsal and middle third of the muscle, but are often not directly visible. For this reason, as already mentioned, this block is performed only simultaneously with electric nerve stimulation.

 

Sonoanatomic Landmarks

1 Autochthonous back muscles, 2 lumbar quadrate muscle, 3 greater psoas muscle, 4 arch of lumbar vertebra 4

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