Diagnostic ultrasound ( PDFDrive )

CHAPTER 56 Pediatric Interventional Sonography 1951
the sedation should be increased, help should be obtained, or
the procedure should be terminated.
Our previous sedation protocol has been published, 7 although
we no longer manage our own sedation, preferring to use the
anesthesia service that is readily available in our interventional
suite. he anesthesiologists have been very lexible in accommodating
our needs. Details of radiologist-supervised sedation
are beyond the scope of this chapter. Speciic publications should
be consulted and adequate training acquired before performing
deep sedation in children. A well-organized and experienced
team that performs sedation regularly, with appropriate guidelines
and limits, is more important than which particular drugs are
used.
LOCAL ANESTHETIC TECHNIQUE
he most commonly used agent is lidocaine (Abbott Laboratories,
Chicago, IL) 1% solution. he usual maximum adult dose for
local anesthesia is 4.5 mg/kg (0.45 mL/kg of 1% solution). A
maximum dose of 3 to 4 mg/kg (0.3-0.4 mL/kg of 1% solution)
for children older than 3 years is noted in the product insert
dosage recommendations, but there is no recommendation for
younger children. We routinely use 3 to 4 mg/kg for all but
extremely premature babies. Lidocaine is chemically stable only
in a slightly acidic solution, so lidocaine is oten combined with
sodium bicarbonate 8.4% solution in a ratio of 10 : 1 immediately
before injection. his efectively neutralizes the pH and reduces
the sensation of stinging as the local anesthetic is injected. Liberal
use of topical local anesthetic creams is also useful, but they
must be applied 20 minutes before the procedure, and the entry
site for a procedure is not always known in advance.
It is a common error to inject the local anesthetic and then
immediately commence the procedure. All clinically useful local
anesthetics work by difusing across the lipid myelin and nerve
cell membrane and block the sodium channel from the intracellular
side of the sodium channel. It is therefore not surprising
that lidocaine needs 5 to 8 minutes to achieve full efect. We
usually place the local anesthetic, at least in the deep subcutaneous
tissues, before gowning and gloving and preparing equipment.
his allows time for the anesthetic to achieve maximal efect.
Dentists are well aware of the time needed for maximal local
anesthetic efect (they would lose their business if they did not
practice good local anesthetic technique), but for obscure reasons,
many physicians seem unaware of the need for waiting to achieve
good local anesthetic efect.
he pain and stretch receptors are mostly in the epidermal
layer. Discomfort associated with local anesthetic administration
arises mostly from the rapid stretching of the epidermal sensors,
before the local anesthetic agent has had time to block the axons.
hus the common practice of “raising a wheal” in the epidermis
is contraindicated. Use of 30-gauge or smaller needles for initial
slow deep subcutaneous injection minimizes the discomfort and
oten allows initial injection without the patient being aware of
the skin puncture. Initial local anesthetic application to the deep
subcutaneous layers allows the local anesthetic agent to irst
block the axons of the pain and other epidermal sensory nerve
endings. Once this has been achieved, later local anesthetic
application to the epidermis is usually painless. Care must be
taken to exclude air from the syringe and needle before injecting
the local anesthetic because even the amount of residual air in
a 30-gauge needle, injected subcutaneously, may seriously degrade
the ultrasound image.
Ultrasound-Guided Deep Local
Anesthetic Administration
One of the keys to successful percutaneous procedures in children
is adequate local anesthetic control of deep sensation. Many
practitioners anesthetize only the skin and subcutaneous tissues
and are then surprised when the patient moves or complains
vigorously as a dilator is passing through the peritoneum, deep
fascia, or the capsule of the organ. he solution is to place the
majority of the local anesthetic on the peritoneum, fascia, or
capsule. In general, it is the external covering of an organ or
muscle, the pleura, the peritoneum, the perimysium, or the deep
fascia that registers pain sensation. Subcutaneous fat, organs,
and the muscle belly have very few nerve endings. Deep local
anesthetic application is best achieved by using sonographic
guidance. Surprisingly, even 30-gauge needles can be easily
identiied close to the skin with high-quality 7-or 10-MHz
transducers. he focal zone must be adjusted appropriately, but
with optimal conditions the local anesthetic can be deposited
where it will have the most efect. his reduces the depth of
sedation required and allows some procedures to be completed
faster and without general anesthesia when it would otherwise
have been required (Fig. 56.9).
ANTIBIOTICS
Antibiotics are routinely needed only when draining an infected
collection or when the patient is immunosuppressed. We usually
use periprocedural antibiotics for liver and renal transplant
patients. he choice of antibiotics is individualized ater consultation
with the referring service, and they are usually given
intravenously at the time of sedation or anesthesia induction.
he basis for timing and duration of antibiotic prophylaxis of
interventional radiology procedure is derived from the surgical
literature. here is greatest suppression of infection when antibiotics
are administered before inoculation. he likelihood of
postprocedure infection increases with lengthening delay between
the initiation of antibiotic prophylaxis and the procedure. 8 If a
procedure is likely to be prolonged (i.e., >2 hours), a supplemental
dose of antibiotics should be considered, depending on the half-life
of the agent being administered. 9,10
THE TYPICAL PROCEDURE
Prior Consultation and Prior Studies
It is important to review previous imaging or interventional
radiology studies before the procedure. One should know what
diiculties were encountered the previous time, or if there was
a contrast reaction at a previous scan. Picture archiving and
communications systems (PACSs) with integrated radiology