Biomedical Engineering Reference
In-Depth Information
heparinized fluids to keep the lines patent. The intravas-
cular cannulation is also utilized in the Vascular Access
Port, a device that is typically placed and anchored
subcutaneously. This chronically indwelling device permits
multiple, nontraumatic percutaneous blood collection for
clinical pathology or plasma pharmacokinetics ( Nuchtern
et al., 2000 ) or drug administration. While such ports
facilitate blood vessel access, they also increase the risk of
infection and blood clotting.
Postsurgical Considerations
Foreign Body Reaction
Foreign body reaction may be observed in tissue encapsu-
lation of an implant as its presence impacts the local healing
process. Clinical manifestations include local inflammatory
response, soft tissue retraction away from implant, and
scattered foci of second intention healing mixed in with
patchy overgrown granulation tissue. A biopsy submitted for
histopathological examination typically reveals focal accu-
mulation of macrophages, formation of multinucleated
foreign body giant cells, migration of fibroblasts, and
angiogenesis. Local or systemic corticosteroids or antimi-
totic agents (e.g. 5 fluorouracil, see the section “Overgrown
granulation tissue” above) may facilitate management, but in
the long run explantation is often the most effective solution.
Implantable Devices for Telemetric
Transmission of Physiological Parameters
Implantable devices manufactured by DSI are designed for
intraperitoneal, subcutaneous, intrathoracic, or intracranial
placement. This technology permits remote reception of
different parameters such as heart rate, body temperature,
blood pressure, and EKG of EEG signals from conscious
and freely moving animals. The longevity of these devices
is limited by the life of a battery, although some devices can
be turned on and off remotely and can function indefinitely.
Chronic Local Peri-implant Infections
It is imperative to always adhere to performing surgeries
aseptically. If an implant, such as a recording chamber, is
attached to the cranium, neighboring muscles and subcu-
taneous tissues should be used to create a tight seal around
the implant and layers of separation between the implant
and the skin. Nonhuman primates, however, are not very
hygienic animals and their hands are soiled with fecal
matter, urine, or food. When the animal frequently touches
or manipulates the areas recently modified surgically, the
result is often an infection, even if the animal is receiving
postoperative antibiotics. A combination of the following
procedures needs to be considered in the care of chronic
percutaneous implants:
Chronic Cranio-facial Screws
These screws are placed to facilitate multiple uses of
optical markers in the studies of kinematics of chewing.
When carefully placed and protected from infection, these
screws can function for months to years ( Figure 14.12 ).
Eye-coils
Eye-coils are usually made of thin Teflon-coated stainless
steel wire and are typically placed subconjunctivally and
anchored to the sclera. The simultaneous recording of the
eyeball movement and neuronal activity through implanted
recording chambers is often used in vision research
( Figure 14.13 ).
1. Frequent (recommended daily) cleaning with antisep-
tics such as chlorhexidine, betadine, or hydrogen
peroxide.
2. Preventing the animal from interfering with infected
site
jackets, bandages, sedatives/analgesics.
3. Bacterial culture and antibiotic sensitivity to find the
best antimicrobial agent (of limited value, particularly
around implants protruding through the skin).
4. Removal of infected granulation tissue and antibiotic
therapy.
5. Excision of the infected site followed by local repair.
6. Explantation (sometimes this is the most effective
approach).
e
Maintenance of Chronic Indwelling Vascular
Cannulae
The following problems may be routinely observed:
1. Occlusion of the cannulae due to:
(a) Intravascular thrombo-embolism, which requires
frequent
FIGURE 14.12 Chronically implanted titanium screws in a rhesus
monkey mandible. One screw placed centrally in the symphysis and
two additional ones in the corpus.
flushing with
sterile
fluids with
anticoagulants.
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