Ultrasound Blocks for the Anterior Abdominal Wall

88 | Ultrasound Blocks for the Anterior Abdominal Wall
serious consequences after an intravascular injection or if there
is rapid uptake from the tissues. Moreover, it is to be considered
that an IFB/LIA involves soft tissue infiltration. Intraperitoneal
injection may be also dangerous because of the high absorption
rate. Repeated injections may be associated with prolonged
systemic absorption and with unexpectedly high and persistent
elevations of plasma concentrations during an IFB/LIA (Mulroy
2009). Therefore, it is not recommended to repeat abdominal
blocks or supplementary anesthetic injections within the
elimination life of the local anesthetic.
Pharmacokinetic studies and the abdominal wall blocks
The plasma levels of the local anesthetics after abdominal
blocks rise gradually in a dose-proportional fashion in 15 to 60
minutes and remain near the peak levels for a 60 to 120 minute
period (Mulroy 1999, Pettersson 1998, Griffiths 2010 (2)). These
data indicate the need for caution when performing
supplemental injections of local anesthetic.
Despite the prolonged elevation of plasma levels, no signs of
local anesthetic toxicity have been reported even with 300 to
375 mg doses of ropivacaine (Mulroy 1999, Pettersson 1998, Wulf
1999, Wulf 2001, Martin 1987, Pettersson 1999). However, most
studies have used premedication with a benzodiazepine and
many are conducted under general anesthesia which may have
occulted transitory neurological effects. The TAPB performed at
the conclusion of surgery for pain relief or for brief operations,
may be potentially neurotoxic because of the elevated plasma
concentrations in conscious patients.
The ultrasound-guided IIB and TAPB have been associated with
a faster absorption and more elevated plasma concentrations in
both adults and children due to the great surface of contact
(Willschke 2005, Willschke 2006, Kettner 2009). Thus, a reduction
of the volume of local anesthetic should be considered when
using an ultrasound-guided technique for abdominal blocks in