XXIX. Stereotactic Surgery
A. Stereotactic surgery is often done for biopsy
of brain tumors or for the treatment of
Parkinsonism (thalamotomy). These cases are
usually done under Monitored Anesthesia Care (MAC)
with the surgeon often using a mixture of
lidocaine and bupivacaine as a local
anesthetic. Depth electrode placements are done
under general anesthesia. It is important to
review the chart for the results of coagulation
tests. Antibiotics and steroids are usually not
given until after the biopsy is taken.
B. Room Set-up
1. Routine monitors are applied. A precordial
stethoscope placed over the trachea at the
suprasternal notch is a very effective tool
in the setting of MAC.
2. Set-up of the anesthesia machine and
monitors is done with consideration of the
movement of the CT table and the fact that
it will be necessary for the
anesthesiologist to leave the room during
the CT scan.
a. CT table movement: The table will
slide the patient into the CT
doughnut. All monitor lines should be
placed with anticipation of this
movement. The best way is to arrange
the lines is down the long axis of the
patient and under the velcro bands
that hold the patient in place.
Extension tubing is placed on the
anesthesia circuit. The extension is
attached to the usual tubing by means of
rubber sleeves. The weight may cause a
disconnect at these extensions so the
tubing must be supported. The
extensions are not throw-away. The
sample tubing on the Rascal is too
short to allow the Rascal to be
anywhere except right next to the CT
table for MAC cases. If a general
anesthetic is done, placing the Rascal
next to the CT table can make the
transfer of an anesthetized patient
from the gurney to the CT table very
difficult. Therefore, an extension is
placed on the Rascal tubing. The
Rascal is placed behind the anesthesia
machine in this circumstance. For a
MAC case, a single length of tubing
for the nasal cannula is insufficient.
An extension tubing is connected,
utilizing an NG tube connecter to
attach the two lengths of tubing
together, if they are not compatible.
b. Radiation exposure: It will be
necessary to leave the room while the
pictures are exposed. The Rascal monitor
should be located high on the
Anesthesia machine to allow
visualization from the observation
room. An additional aid to patient
monitoring from a distance is to place
a dark hand towel on top of the white
velcro straps on the patient's chest.
An IV catheter may be inserted into
the nasal cannula (with the tip of the
catheter cut off at the end of the opening
of the nasal cannula - to avoid irritation
of the nose) so that the capnograph
sample line may be connected, and
a respiratory end-tidal CO2 wave form
can be generated. If a plastic tent is
used, be aware that CO2 may build up
and cause a rebreathing tracing on the
capnogram. The breath sounds may also
be monitored remotely.
3. The patient is brought into the room feet
first. The patient should be on a gurney
with a back is capable of being raised so
that the patient can be put into a sitting
position for head frame application. It is
wise to inquire of the patient whether he
has to empty his bladder. Give him any
opportunity to do so if he has to. He is
kept on the gurney until the halo is
applied and then transfered to the CT
table. If general anesthesia is used, the
patient is induced on the gurney.
C. Thalamotomy for Parkinsonism
1. Stereotactic surgery is used to ablate the
tremors of Parkinsonism. These patients
usually have a pronounced tremor on one
side of their body. Plan on placing the B/P
cuff and IV on the side that does not have
a tremor. The arm for which the brain is
being operated on should be clear so that
the surgeon can easily evaluate the
progress of the operation. The pulse ox can
also go on the good arm or (better yet) on the
toe.
2. Avoid medications that can alter or ablate
the tremors. Primarily, these are
benzodiazepines. The surgeon needs the
tremors present to guide the
surgery. Surgeons may also request that
beta-blockers be avoided.
3. The basic problem in Parkinsonism is the
dopmine receptor. Do not give these
patients medications that further block
the receptor, such as Reglan, Droperidol
or phenothiazines.
D. Stereotactic Tumor Biopsy
1. An important consideration is the use of
IV dye.
a. The administration of the dye (eg.
Conray 60%) can become a rate limiting
step for the progress of the
operation. Start it as soon as
monitors are applied, baseline
measurements have been made and nasal
O2 is going.
b. Anticipate the possibility of
anaphylaxis with dye administration.
Cardiovascular collapse and possible
bronchospasm or rash may occur. The
cardiovascular changes consist of a
drop in the blood pressure, sometimes
to unmeasureable levels, and a rise in
the heart rate. In addition to
patients with a history of iodine or
shellfish allergy, be alert for the
patient with a general history or
allergic diathesis such as hayfever or
asthma. The treatment will be fluids,
benadryl, steroids and epinephrine
appropriate to the magnitude of the
response. The dose of epinephrine can
range from 5 mcg to 1000 mcg.
(1) Non-ionic dye is used in patients
with history of allergy to regular
IV dye, patients with a history of
CHF, renal failure, elderly (>60),
and children.
(2) In my experience, I have seen a
patient who, while receiving a CAT
scan, became hypotensive. It was
initially felt to be an
anaphylactic reaction. Further
evaluation revealed an inferior wall
MI. The patient did not have the
appropriate heart rate changes for
anaphylaxis. Luckily, this patient
did not receive epinephrine before
the evaluation was complete. Don't
shoot from the hip unless you
absolutely have to.
(3) Discuss with radiology their
protocol for anaphylaxis.
c. Elderly patients with borderline renal
function, dehydrated patients or
diabetic patients may be pushed into
renal failure with contrast. These
patients should be well hydrated prior
to the administration of the dye.
Check the BUN and creatinine prior to dye
administration. The dye is also likely
to cause an osmotic diuresis that
makes the patient want to urinate.
d. A small IV is not adequate for these
patients. Also remove any constrictions in
the IV that might have been placed on the
floor. (e.g., heplocks, etc.)
E. Anesthetic considerations
1. Do not oversedate the patient for the
application of the head pins. The most
painful part of the procedure is placement
of the rubber pins in the ears. Once this is
accomplished, there is very little pain.
2. Access to the airway can become very
difficult once the halo is on, so monitor
closely and avoid heavy sedation.
3. As noted above, avoid heavy sedation in
the thalamotomy patient so that the
patient can follow the commands of the
surgeon. Benzodiazepines will ablate the
tremors and make the surgery impossible.
4. Blood pressure control may be requested by
the surgeon. Most often, this involves an upper
limit to the systolic of 150-160 mmHg.
This is accomplished most easily with
labetalol in the average patient with no
contraindications (beta blocker
contraindications include asthma and low
output heart failure). In the
thalamotomy patient, the avoidance of beta
blockers for tremor considerations will
leave vasodilators such as hydralazine.
This can be very dangerous in the fluid
restricted patient. Discuss some form of
catheterization with the surgeon that will
make fluid administration less
problematic. If both hydralazine and beta
blockers are not indicated, a remaining
option is a ganglionic blocker, Arfonad.
F. Depth Electrode Placement
1. Four sets of electrodes are placed under
general anesthesia. Virtually all of the
patient's hair is removed for this
procedure.
2. General anesthesia is induced on the CT
table. The patient is then pushed through
the CT doughnut and the head frame is
attached. The patient is then pushed back
through to the opposite side of the doughnut
to check centering of the patient. He is
then pushed back in supine position and scaned.
the patient is then pulled back out and
flipped to the prone position. He is
pushed back in though the CT machine and
depth electrodes are placed. After
placement, the patient is brought back
into the doughnut for scanning. After
scanning, he is pulled back thru for head
frame removal. Finally, the patient is
broght back thru the CT doughnut and
rolled onto the gurney. The patient is
transfered to the PACU.
3. Patients for depth electrode placement are
often on medications that greatly reduce
the half life of vecuronium.
4. The neurophysiologist monitors the raw EEG
to confirm appropriate electrode placement
and to monitor for intracranial disasters.
5. The anesthetic course is characterized by
spikes of pain as each new electrode is
placed through the scalp. After intitial
penetration, there is very little painful
stimulus.
Pediatric Neurosurgery