Ultrasound Blocks for the Anterior Abdominal Wall

86 | Ultrasound Blocks for the Anterior Abdominal Wall
The decision to use larger volumes of a higher concentration
to achieve a longer block must be weighed against the potential
risks of higher systemic absorption. Special attention should be
posed to obese patients in which a dosing on a milligram of local
anesthetic-per-kilogram of weight basis would be dangerous. In
these patients, a dosing based on the ideal weight may be more
correct.
Maximum recommended doses are valid in relation to normal
conditions (70 kg healthy persons) and do not constitute a
maximum (Rosenberg 2004). They must be varied individually
depending on the type and site of block, the weight and the
clinical condition of the patient.
Monitoring according to the technique of administration and
to the expected plasma concentration is highly advised
(Rosenberg 2004).
Long-lasting local anesthetics
The long lasting amide anesthetics, bupivacaine,
levobupivacaine and ropivacaine, are highly lipophilic molecules
of similar properties and efficacy. Concentrations of 2.5 to
5 mg/ml of the long lasting anesthetics are generally used for
IFB/LIA, IIB and TAPB (Bay-Nielsen 1999, Mulroy 1999). The
efficacy and block duration is dose dependent (Mulroy 1999).
As reflected by clinical studies, the duration of analgesia after
IFB/LIA, IIB and TAPB after a single injection of long lasting local
anesthetics typically lasts less than 12 h. However, the benefits
on the subjective pain levels at rest and under stress, on the
postoperative amount of analgesics and on postoperative
mobilization may last for 24 hours to 10 days (Pettersson 1998,
Ding 1995, Harrison 1994).
Among the long-lasting local anesthetics, ropivacaine is
preferred for abdominal blocks because it is less cardiotoxic than
bupivacaine (Knudsen 1997). Ropivacaine (and levobupivacaine,