Anesthetic Management
Preprocedural anesthetic evaluation is similar to that before
neurosurgical procedures. Airway examination is important inasmuch as airway manipulation
during the procedure is not possible because of interference with head positioning
for imaging. Particularly important is a history of previous experience with radiologic
procedures and any history of contrast media reaction. Because blood pressure management
is important for these procedures, preoperative evaluation for hypertension is important,
as is good preoperative control of existing hypertension.
As in other areas outside the operative suite, communication between
anesthesiologists and interventional neuroradiologists is essential to ensure optimal
patient management. Some procedures may require awake neurologic assessment during
the procedure. Superselective injection of sodium amobarbital into a limited area
of the cerebral circulation may be used to assess functional dependence in an awake
patient.[75]
[76]
[77]
Alternatively, temporary balloon occlusion
of vessels that may be embolized may be used to assess functional dependence in an
awake patient. Clearly, management of patients during cases
involving midprocedure neurologic assessment can be particularly challenging because
the patient must remain completely immobile during all critical portions of these
long procedures, yet be awake and responsive during neurologic testing. Preoperative
training can assist in patient management. Patients who do not require neurologic
testing during anesthesia may be managed with either sedation/analgesia or general
anesthesia. General anesthesia may provide improved images (less motion artifact),
afford better airway control given the neutral head position required, and facilitate
blood pressure control.[60]
Whatever anesthetic technique is selected, standard anesthesia
monitors are established. Two intravenous catheters are placed, one for drug infusions
and one for fluid administration and drug boluses. Invasive arterial blood pressure
monitoring may be obtained through the side port of the neuroradiologist's introducer
sheath, but if postprocedural blood pressure control is considered important, placement
of a radial arterial catheter is reasonable for ongoing monitoring. A urinary catheter
is placed because of the frequent use of large amounts of radiologic contrast media
and administration of osmotic diuretic agents. Careful attention is paid to padding
all pressure points to ensure patient comfort and avoid positioning injury during
a potentially long procedure. Again, in all cases two intravenous lines are placed,
one for drug infusions and one for fluid administration and drug boluses.
Heparin is commonly administered during these procedures, with
a target activated clotting time (ACT) of 2 to 2.5 times the baseline value. Deliberate
hypotension is frequently used during AVM embolization to decrease flow to feeding
vessels, as well as during some trial balloon occlusions. Agents such as esmolol,
labetalol, or sodium nitroprusside are all useful in this situation. Deliberate
hypertension is called for during cerebral ischemia in an attempt to maximize collateral
flow. Phenylephrine is generally used, both as a bolus and as an infusion titrated
to increase systolic blood pressure 30% to 40% above baseline. Close monitoring
of ECG parameters for signs of myocardial ischemia is critical in this case. Smooth
emergence from anesthesia is important in these patients, who may be prone to device
migration or intracranial hemorrhage. Administration of antiemetics before emergence
is certainly reasonable, and precautions to avoid coughing and "bucking" should be
taken.[59]
[60]
Anesthetic management of patients undergoing interventional neuroradiologic
procedures is challenging. The anesthesiologist must remain vigilant for the occurrence
of complications and act decisively and in concert with the neuroradiology team as
complications occur to optimize patient outcome.
