Diagnostic ultrasound ( PDFDrive )

CHAPTER 17 Ultrasound-Guided Biopsy of Chest, Abdomen, and Pelvis 611
A
B
FIG. 17.15 Locking-Loop Drainage Catheter. (A) Three components of the locking-loop catheter are sharpened inner stylet (top), stiffener
(middle), and catheter with distal locking loop (bottom). (B) Assembled catheter is ready for placement using trocar technique.
chosen. In general, thicker luid is best drained with larger-caliber
catheters. A 10- to 14-French catheter provides adequate drainage
for most abscesses. Smaller (6-8 French) catheters are adequate
for less viscous collections. Catheters with retention devices,
such as a locking loop, are frequently used to prevent catheter
dislodgement (Fig. 17.15).
Patient Preparation
he procedure and risks should be explained to the patient and
informed consent obtained. he patient’s hemostatic status should
be assessed through clinical history, and recent coagulation studies
should be available. We routinely require platelets and PT for
drainage procedures. IV access is obtained in all patients for
administration of medications and for emergency access, in the
event of a complication, such as hemorrhage, sepsis, or hypotension.
Patients oten receive broad-spectrum antibiotics intravenously
to decrease the risk of sepsis. Satisfactory analgesia is
necessary throughout the procedure to provide optimal patient
comfort and cooperation. Local anesthesia is usually suicient
for needle aspiration; however, IV sedatives and analgesics such
as midazolam (Versed) or fentanyl (Sublimaze) are beneicial
for percutaneous catheter insertion; dilation of the drain tract
can be extremely painful to the patient.
Diagnostic Aspiration
Because luid collections oten have a nonspeciic appearance,
diagnostic aspiration is the irst step. A ine needle is guided
into the luid collection by the selected imaging modality. his
needle insertion deines a precise and safe route to the luid
collection. A small amount of luid is aspirated and sent for
appropriate microbiologic evaluation. he resulting culture and
sensitivity data are used to direct the antibiotic therapy. If the
luid does not appear infected (i.e., clear, colorless, and odorless),
the radiologist may elect to aspirate the cavity completely
and not perform the drainage procedure. his is important,
because a catheter placed in a sterile luid collection will eventually
serve as a nidus of infection, with subsequent infection
of the collection. If pus is aspirated, care should be taken to
aspirate only a small amount of luid, because any decrease in
the cavity size may make subsequent catheter placement more
diicult.
Catheter Placement
Catheter insertion can be performed using the trocar or the
Seldinger technique; the choice usually depends on operator
preference. In the trocar technique the catheter its over a
stifening cannula, and a sharp inner stylet is placed within the
cannula for insertion (see Fig. 17.15). he catheter assembly is
FIG. 17.16 Drain Within Deep Pelvic Abscess. With aspiration of
the abscess and subsequent luid motion within the drain, longitudinal
transperineal Doppler ultrasound image shows a color shift, allowing
good visualization of the catheter.
advanced into the luid collection. he catheter is then pushed
from the cannula, and the distal loop is formed and tightened
to secure the catheter within the luid collection. his method
works best for large and supericial luid collections.
With the Seldinger technique (guidewire exchange technique),
a guidewire is advanced through the aspiration needle and coiled
within the luid collection. he needle is then removed, and the
guidewire is used as an anchor for passage of a dilator to widen
the catheter track. he catheter-cannula assembly is placed over
the guidewire into the luid collection. he guidewire and inner
cannula are removed as the catheter is simultaneously advanced.
he distal locking loop of the catheter is re-formed to prevent
catheter dislodgement. If the catheter is diicult to see with
ultrasound, the use of CDFI may improve conspicuity. During
aspiration or irrigation, Doppler shits improve catheter visualization
(Fig. 17.16, Video 17.5).
Final positioning of the catheter is important in maximizing
the efectiveness of drainage. For this purpose, ultrasound and
CT are complementary and at times should be used together.
CT provides an anatomic road map for ideal catheter placement.
Because this ideal position seldom lies in the true axial plane,
ultrasound can be used to direct the needle, guidewire, and
catheter into the ideal position. Final placement can then be
veriied with CT.