XVIII. Anesthetic Management of Aneurysms
A. Operative technique.
1. Temporary clips: Temporary clips are
commonly applied proximal to the aneurysm.
This obviates the need for induced hypotension
and in fact contraindicates it unless rupture
occurs. The neurosurgeon may request moderate
hypertension to ensure adequate perfusion
while the temporary clip is on. The temporary
clip is gold colored and the permanent clip is
silver. Document in the record the times of
application and removal of the temporary clip.
2. Induced hypotension may be used in those
instances where temporary clip application
is not possible.
3. Deep hypothermic arrest is used in rare
circumstances (e.g., large basilar artery
aneurysm). The patient is placed on
cardiopulmonary bypass and cooled. The
flow is then turned off and the blood is
drained out of the body. It is believed
that the brain can tolerate no perfusion
about 60 min in this setting.
B. The A-line is inserted prior to induction.
Central venous pressures are monitored.
C. Anesthesia for aneurysm surgery deals basically
with the problems of preventing rupture of the
aneurysm and minimizing the potential for
vasospasm. The peak incidence for rebleeding is
the first 24 to 48hours post hemorrhage.
Vasospasm peaks in the 5-10d (others say 6-8)
period following SAH.
D. Preventing rupture
1. There should be no excessive rises in the
systolic, mean or pulse pressure.
2. The transmural pressure across the wall of
the aneurysm should be kept constant. The
transmural pressure is the difference
between the arterial pressure and the CSF
pressure. Increaseing the transmural pressure
makes rupture more likely. Maneuvers which
decrease CSF pressure are therefore avoided
until after the dura is opened. If the
ICP is normal, the patient is not hyper-
ventilated until the dura is opened.
Mannitol may not be given, or may be given
at a different point in the procedure.
3. CSF drains are used extensively in
aneurysm surgery because of the quick and
predictable improvement in the surgical
field. Usually 30 to 50cc is removed in
10c increments, each over 3-4 minutes.
Premature removal of CSF (CSF runaway)
can be disastrous.
E. Vasospasm results in ischemia and must be prevented.
1. Vasospasm is worsened by hypovolemia,
hypocarbia, and hypotension. It is of
greatest concern in the several days
following the hemorrhage.
2. Maintain normovolemia and normocarbia,
depending on such factors as presence of
vasospasm and elevated ICP. Some texts
will quote a ml/kg goal for the initial
administration of fluid. The reality of a
neuro case with its multiple IV's is that
a great deal of fluid is given early on in
the case despite all attempts to limit
fluid. In the average case, one to two
liters of crystalloid is given not long
after induction even if the intention is
to limit fluids. This represents my limit
of crystaloid administration. I prefer to
start 5% Albumin if the CVP falls as a
result of subsequent diuretic
administration. The PaCO2 goal (not ETCO2)
is ~35. The uncomlicated aneurysm patient
is not hyperventilated unless other
methods of ICP reduction are inadequate.
The presence of elevated ICP (mass effect
from blood or hydrocephalus) will alter
the PaCO2 goal.
3. Oxygen carrying capacity is as important
as volume. The patient must not be allowed
to become anemic and RBC should be
aggresively transfused. Tune your ear to
the sound of the surgeon's suction. Heads
up when you hear a lot of blood loss. Also
arrange the suction cannisters so that you
can easily see them. Overtransfusion
carries the risk of hyperviscosity and
poor flow through vasospastic arteries.
4. If it becomes necessary to induce burst
suppression with pentothal, the resulting
hypotension shold be treated with fluids
prior to vasoactive agents.
F. Working with CSF drains
1. Inoperational if filter gets wet so keep
upright at all times, always have clamped
off in transport.
2. Keep looking for possible kinking of the
tubing of the drain.
3. When the drain and tubing is in its final
position, check to see if it is possible
for fluid to come out.
4. CSF is drained off in 10cc increments with
each increment over 2-3 min.
G. Intraop angiogram - no warming blanket.
H. BP goals for the normotensive patient.
Decisions about blood pressure goals must be
made with the degree of vasospasm in mind.
1. Before application of the temporary clip
the goal is 80-100 (mean).
2. After application of the temporary clip,
the goal is 105-110(mean).
3. The mean from the A-line will be different
from that calculated from the systolic and
diastolic pressures.
I. Fluid and Electrolyte problems with SAH
Arteriovenous Malformations