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Anesthetic Management for Surgical Treat
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What research is being done on cerebral aneurysm in United States?
The National Institute of Neurological Disorders and Stroke (NINDS) recently sponsored the International Study of Unruptured Intracranial Aneurysms, which included more than 4,000 patients at 61 sites in the United States, Canada, and Europe. The findings suggest that the risk of rupture for most very small aneurysms (less than 7 millimeters in size) is low.
NINDS scientists are studying the effects of an experimental drug in treating vasospasm that occurs following rupture of a cerebral aneurysm. The drug, developed at NIH, delivers nitric oxide to the arteries and has been shown to reverse and prevent brain artery spasm in animals.
Other scientists hope to improve diagnosis and prediction of cerebral vasospasm by developing antibodies to molecules known to cause vasospasm. These molecules can be detected in the cerebrospinal fluid of subarachnoid hemorrhage patients. An additional study will compare standard treatment for subarachnoid hemorrhage to standard treatment plus transluminal balloon angioplasty immediately after severe bleeding. Transluminal balloon angioplasty involves the ion, via catheter, of a deflated balloon through the affected artery and into the clot. The balloon is inflated to widen the artery and restore blood flow (the deflated balloon and catheter are then withdrawn).
Researchers are building a new, noninvasive, high-resolution x-ray detector system that can be used to guide the placement of stents (small tube-like devices that keep blood vessels open) used to modify blood flow during treatment for brain aneurysms.
Scientists are investigating the use of intraoperative hypothermia during microclip surgery as a means to improve the rate of recovery of cognitive functions and to reduce early and postoperative complications and neurological damage. Other studies are investigating ways to improve or replace the coils used in endovascular embolization.
Cerebral Aneurysm statistics in United States
The true incidence of intracranial aneurysms is unknown but is estimated at 1-6% of the population (Wiebers, 2003). Published data vary according to the definition of what constitutes an aneurysm and whether the series is based on autopsy data or angiographic studies. In one series of patients undergoing coronary angiography, incidental intracranial aneurysms were found in 5.6% of cases, and another series found aneurysms in 1% of patients undergoing 4-vessel cerebral angiography for indications other than subarachnoid hemorrhage (SAH). Familial intracranial aneurysms have been reported (Schievink, 1997). Whether this represents a true increased incidence is unclear.
Aneurysms typically become symptomatic in people aged 40-60 years, with the peak incidence of SAH occurring in people aged 55-60 years (Greenberg, 2001). Intracranial aneurysms are uncommon in children and account for less than 2% of all cases. Aneurysms in the pediatric age group are often more posttraumatic or mycotic than degenerative and have a slight male predilection. Aneurysms found in children are also larger than those found in adults, averaging 17 mm in diameter. Aneurysms have shown a slightly more frequent in women than man.
Current diagnostic Tests for Intracranial Aneurysms
Patients with ruptured aneurysms producing SAH are usually diagnosed by CT scan. However, no test is 100 percent sensitive, and CT scans may not always detect SAH, particularly when it is mild, or if it occurred more than 24 hours before the scan. Therefore, whenever a diagnosis of SAH is being entertained, if the CT scan is negative, a lumbar puncture (spinal tap) must be performed for analyzing the spinal fluid for blood or its byproducts ("xanthochromia").
All patients with a diagnosis of SAH, or in whom an aneurysm is suspected
require 4-vessel cerebral angiography. Cerebral angiography is currently the only test sensitive enough to definitively confirm the presence of an aneurysm, and also provides critical information regarding the size, shape, and location of the aneurysm, as well as the presence of vasospasm.
For the patients without recent SAH, the initial diagnostic test is usually a Magnetic Resonance Image (MRI), a Magnetic Resonance Angiogram (MRA), or a Computed Tomographic Angiogram (CTA). These noninvasive tests have become increasingly sensitive in detecting intracranial aneurysms and the findings are generally sufficient for deciding whether the four vessel angiography is warranted. In certain situation noninvasive imaging can be used to make treatment decisions.
Current treatment Options for Intracranial Aneurysms
Aneurysms that have ruptured require treatment to prevent another rupture (rebleeding). Following the initial rupture of an aneurysm, rebleeding is very common (especially within the first two weeks after rupture), and is usually more severe than the initial rupture. Therefore, ruptured aneurysms need to be treated immediately to prevent the risk of rebleeding.
The two primary treatment methods are surgical clipping and endovascular coiling. The optimal treatment choice depends upon the patients history, physical examination, age, risk factors, and the anatomical characteristics of the aneurysm. It is estimated that 60-65% cerebral aneurysm patients in the United States have received surgical clipping, while approximately the other 30-35% of the patents have received endovascular coiling.
Optimal treatment of patients with intracranial aneurysm requires a highly experienced center that is capable of both coiling and clipping.
Anesthesia for cerebral aneurysm coiling
An interventional neuroradiologist does the aneurysm coiling in radiology suite. The procedure involves placement of small plastic tube (micro-catheter), which is threaded from the groin to the aneurysm in the brain. Then fine platinum threads (coils) are ed into the aneurysm to fill it up from the inside, much like filling a pothole. The catheter is then removed and the small groin incision covered with a Band-Aid. For an unruptured aneurysm, the patient is discharged home within 24 to 48 hours. During the coiling, general anesthesia is required at most of time. Neither SSEP nor MEP monitoring is often necessary. However, arterial BP monitoring is needed in most of the cases. There is no limitation for administering inhalation agents if patient is not on evoked potential (EP) study.
Anesthesia for cerebral aneurysm clipping
Since advanced radiological diagnostic tests have been applied to the patients, neurosurgeons are able to more precisely identify and localize cerebral aneurysm. Microscopic clipping and EP and electroencephalography (EEG) monitoring become very popular intraoperatively, which results in total intravenous anesthesia (TIVA) being required more often than before. As a trend, intentional hypotension technique and central lines are less needed since excessive introperative blood loss become less frequent. However, invasive BP mentoring still remains as pertinent requirement for the procedure. Newly designed arterial transducer (Edward-Swan) is able to calculated cardiac output. Popofol and Ramifentanyl continue infusion has provided patient with good anesthesia and analgesia with reduced time for emergence. The concept of tight control of blood glucose level is also applied, which directly affect postoperative neurological outcome. In studies published between 1966 and 1996 on clipping of unruptured aneurysms, mortality was 2.6% and morbidity was 10.9%.
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