Psoas Compartment Block Technique

Updated: Aug 07, 2014
  • Author: Bassem Asaad, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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Technique

Approach

The patient is positioned in a lateral decubitus position with a forward tilt and hip flexion (see image below). The full lower extremity should be exposed to watch for muscle contraction, especially if neurostimulation will also be used together with ultrasound guidance or with the loss of resistance technique. Monitoring of blood pressure, pulse oximetry, and EKG with 2 L of supplemental oxygen are recommended.

Patient in a lateral decubitus position. Patient in a lateral decubitus position.

With the traditional neurostimulation and loss of resistance technique, a line is drawn connecting the iliac crests, which coincide with the L4-L5 level. Another perpendicular parasagittal line parallel to the axial spine line is drawn, and this roughly coincides with the tips of the lumbar transverse processes. The intersection of the parasagittal longitudinal marking with the line marking the 2 iliac crests coincides with the area over the tip of the L4 transverse process. The area of interest is then sterilized, covered, and draped in the standard sterile fashion, and the skin is then topicalized with a 25-gauge needle.

A short bevel insulated needle is then advanced till it contacts the transverse process. It should then be directed cephalad or caudad to bypass the transverse process and advanced for 2-3 cm. Stimulation of the lumbar plexus results in a contraction of the quadriceps muscle as well as the adductor muscle group. The local anesthetic is then injected.

A catheter may be placed and advanced 3-5 cm past the needle tip. If a stimulating catheter will be placed, stimulation of the catheter should be performed before injection of the local anesthetic. A Toughy needle and loss of resistance technique may be used instead as described above. Upon entering the psoas compartment, a loss of resistance occurs. This technique can be combined with an active tip-stimulating catheter for confirmation of placement.

In a prospective, observer-blinded pilot study of 30 patients comparing the nerve stimulation with the loss of resistance technique, Danelli et al [13] concluded that the 2 techniques are comparable in terms of local anesthetic consumption, morphine requirements, and pain scores; however, the nerve stimulation allowed faster readiness for surgery than the loss of resistance technique.

In the ultrasound-guided approach, a curvilinear low-frequency probe is placed longitudinally over the sacrum, and then the scanning should advance in a cranial direction. The first spinous process seen is most likely that of the fifth lumbar vertebrae; proximal to it will be the L4/L5 intervertebral space and then the fourth lumbar vertebrae spinous process. The probe is then rotated to scan transversely at that level. The articular processes appear as hypoechoic structures bilaterally. The corresponding transverse process is seen lateral to the articular process.

The probe can then be moved more laterally until the tip of the transverse process is seen. A needle can then be advanced from medial to lateral towards a point just distal to the tip of the transverse process. The needle trajectory should then be adjusted to approach the plexus, which is located about 3 cm anterior to this point. The authors advocate using a stimulating needle in combination with the ultrasound guidance for confirmation of the placement because it is not always easy to visualize the hyperechoic plexus described above.

In a prospective observational study done on 53 patients, Ilfeld et al [14] concluded that prepuncture ultrasound imaging accurately predicts transverse process depth to within 1 cm if the lumbar plexus is estimated to be within 3 cm of the transverse process. Ultrasound allows prediction of the maximal lumbar plexus depth to within 1 cm. [14] Not advancing the needle from a lateral to a medial direction is important because this may result in inadvertent spinal canal injection. During the early stages of the scan, scanning laterally to visualize the lower pole of the kidney is recommended. This increases the safety of the procedure and decrease the risk for renal injury.

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Complications

See the list below:

  • Inadvertent spinal or epidural injection
  • Spread of the injectate toward the epidural space
  • Injury to the kidney
  • Bleeding
  • Epidural or para-vertebral hematoma
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Conclusion

Ultrasound guidance for the psoas compartment lumbar plexus block makes the approach safer and less time consuming. The technique offers an alternative to the 3-in-1 block and should be highly considered if proximal coverage of the obturator nerve and lateral cutaneous nerves are indicated. The technique may also be considered in patients with distorted anatomy that impedes the completion of the 3-in-1 approach, especially with vascular femoral procedures and in cancer patients who had inguinal area exploration and dissection.

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