Direct Lumbar Plexus Block (Psoas Compartment Block)
The psoas compartment[241]
enclosing
the lumbar plexus can be approached percutaneously with the patient in the semiprone
position, resting on the nonoperated side. The landmarks are the ipsilateral posterior
superior iliac spine, the line joining both iliac crests, and the spinous process
of L5. Two puncture sites are suitable: the midpoint between the posterior iliac
spine and the spinous process of L5[243]
(i.e.,
modified Chayen approach) and a modified site of puncture as described by Winnie
[242]
(i.e., modified Winnie approach) 1 to 2 cm
medial to the intersection of the line joining the iliac crests, with a perpendicular
line passing over the posterior iliac spine ( Fig.
45-12
). The needle is inserted perpendicular to the skin until twitches
are elicited in the ipsilateral quadriceps muscle; if the puncture site as described
by Winnie is used, the needle has to be redirected medially to reach the plexus,
thus threatening major vascular and other vital structures or organs. This technique
has elicited much research in adult patients, especially with the aim of improving
the "blind" location of the psoas compartment by seeking
Figure 45-12
Direct lumbar plexus blocks: Winnie's technique (slightly
modified) (A) and Chayen's technique (slightly modified) (B).
bone contact with the transverse process of the fifth, fourth, or even third lumbar
vertebra (i.e., performing the classic technique of lumbar paravertebral blocks that
had never gained popularity). This does not offer any advantage in pediatric patients,
and even in adults, the claimed improvement is debatable because the distance from
skin to these transverse processes is poorly correlated with the distance from skin
to the lumbar plexus.[243]
Another option is to
use an ultrasound-guided approach.[244]
Although
this technique may be very useful for academic and teaching purposes, it is rather
complicated and time consuming for routine use in clinical practice.
When long-lasting pain relief is sought, a catheter can be inserted
within the psoas compartment, using an appropriate device[243]
[245]
and a 5 mL/hour continuous infusion of 0.125%
bupivacaine or 0.2% ropivacaine in children usually provides excellent analgesia.
Suitable infusion regimens that I commonly use are displayed in Table
45-12
.
The distribution of anesthesia is usually that supplied by all
lumbar plexus nerves. Occasionally, the local anesthetic can spread to the epidural
or, rarely, the subarachnoid space. These undesirable spread complications were
rather common 15 years ago[241]
with the needles
available at that time but have become unusual with currently available insulated
block needles. However, this potential side effect must not be ignored when selecting
this block procedure, and the injected volume of local anesthetic should not exceed
20 mL (see Table 45-11
).
Because of the potential threat to intra-abdominal or pelvic contents, indications
for direct lumbar plexus blocks are usually restricted to unilateral surgery of significant
importance involving the hip, thigh (femur), and the knee.
