Ultrasound Blocks for the Anterior Abdominal Wall

92 | Ultrasound Blocks for the Anterior Abdominal Wall
this complication is important to avoid morbidity, and patients
should be informed of the transitory nature of this complication.
The incidence of inadvertent femoral nerve block ranges from
0.27% to 28% in adults and children (Lipp 2000, Lim 2002, Lipp
2004). Most reports are from pediatric patients who seem to
have an increased risk of TFNB (Erez 2002). The TFNB may be less
likely to occur in females than males because of a different
distance between the femoral nerve and the point of injection
for the IIB. The TFNB has not been reported yet after an
ultrasound-guided nerve block.
The IIB given under direct vision by surgeons appear to have a
lower incidence of TFNB. The transient femoral nerve block has
been reported also after laparoscopically guided IIB (Lange
2003).
The mechanism involved in the TFNB development may be due
to the direct instillation around the femoral nerve or the
anesthetic diffusion under the iliac fascia. The local anesthetic
may reach the plane deep to the iliac fascia and the femoral
nerve when it is deposited between the TAM and transversalis
fascia or directly under the iliac fascia around the femoral nerve
(Rosario 1994, Rosario 1997, Erez 2002). It is to be remembered
that the femoral nerve runs over the iliopsoas muscle in close
proximity to the inguinal canal (Erez 2002).
Local anesthetic introduction into the plane between the
quadratus lumborum and the psoas major muscle, blocking the
lumbar plexus roots, may be also the cause for femoral nerve
block (Winnie 1973). Moreover, the injection into the plane of
the TAM can increase the risk of this complication (Rosario
1997).
Apart from local anesthetic block, TFNB may follow femoral
nerve trauma, suture involvement, entrapment with staples,
compression or hematoma both after open or laparoscopic
hernia repair (García-Ureña 2005).