Ultrasound Blocks for the Anterior Abdominal Wall

90 | Ultrasound Blocks for the Anterior Abdominal Wall
higher absorption of local anesthetic has been shown (Smith
1996). The cause may be the increased cardiac output/body mass
index ratio, the decreased tissue accumulation and the reduced
liver metabolism. When large doses of local anesthetic are used,
the dose per kilogram should be reduced by about 15%
(Rosenberg 2004).
Children under two years of age have been reported to have
significantly higher pain scores than those above this age
(Trotter 1995). Ropivacaine as a long-lasting agent for IIB in
children may be more effective when used with a high
concentration/small volume than when used with a high
volume/low concentration (Trifa 2009). If smaller volumes of
local anesthetic are used, ultrasounds become a necessary tool in
order to improve the chance for a successful block.
Adjuvants
Several studies have evaluated the use of adjuvants to local
anesthetics (clonidine, ketamine ecc) for improving
postoperative analgesia after the anterior abdominal blocks.
Clonidine added to intermediate or long-acting local
anesthetics for single-shot peripheral nerve or plexus blocks
prolongs the duration of analgesia and motor block by about 2 h
but at the cost of an increased risk of hypotension, fainting, and
sedation and with an unclear dose-responsiveness kinetics
(Pöpping 2009).
Clonidine used for the abdominal blocks or IFB/LIA has not
shown to give a clinically important benefit in adults and children
(Beaussier 2005, Kaabachi 2005, Dagher 2006, Elliott 1997). A
common adverse effect is orthostatic hypotension during the
first postoperative hours. In these types of block, as a
consequence of the spread into a wide zone, the accumulation of
clonidine near nerves may be decreased. Thus clonidine would
not reach the right level to affect nerve conduction or facilitate
the action of the local anesthetic (Kaabachi 2005).