Neurovascular Surgery Brain Aneurysm & AVM Center
Temporary Intracranial Vessel Occlusion in Aneurysm Surgery is Safe and Effective

by Christopher S. Ogilvy, M.D.

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One very useful adjunct currently employed in aneurysm surgery is to transiently occlude the vessel from which an aneurysm arises. This temporary occlusion for an interval of several minutes can soften the aneurysm, making the final microsurgical dissection safer and reduces the chance of intraoperative hemorrhage from the aneurysm. The limits of how long a vessel can be occluded without a resulting stroke are not well defined. At the MGH Aneurysm/AVM Center, we have managed over 130 patients using a regimen of mild hypothermia (32-34oC) with intravenous mannitol administered prior to temporary vessel occlusion. In addition, when the proximal vessel is occluded hypertension is induced using an intravenous pressor agent. With these techniques we have found that safe vessel occlusion can be obtained for extremes of up to 30-60 minutes without the patient developing a postoperative deficit. The usual interval of occlusion is 2-15 minutes. To further investigate this technique, a laboratory model of temporary vessel occlusion was established. In control animals (rabbits), the volume of brain infarction incurred with temporary vessel occlusion for two hours was significantly greater than when animals had blood vessels occluded with induced hypertension. Using induced hypertension in conjunction with mild hypothermia and mannitol prior to temporary vessel occlusion, only 1 out of 5 animals developed an infarction, and in this animal the infarct was tiny (Figure 1). Hypothermia lowers tissue metabolism and therefore reduces the need for cerebral glucose and oxygen during an ischemic event; mannitol improves cerebral blood flow during an ischemic event; and induced hypertension improves collateral blood flow into the area of hypoperfused tissue. Using this combination of techniques for cerebral protection during aneurysm surgery is proving to be a useful adjunct. It is through the use of such techniques that improved safety can be achieved with current aneurysm surgery.

Figure The volume of brain infarction after two hours of focal ischemia in rabbits is shown for three different experimental conditions. Control animals were normothermic and normotensive, hypertensive animals had blood pressure elevations 30% above control values using intravenous neosynephrine, and triple therapy refers to animals treated with mild hypothermia, induced hypertension, and mannitol prior to the ischemic insult. As can be seen, the volume of infarcted tissue in hypertensive animals is significantly lower than in control animals, and in rabbits treated with all three adjuncts, only one out of five animals demonstrated a brain infarction, and this was tiny.

Other Information sources on temporary occlussion

Ojemann RG, Ogilvy CS, Heros RC, Crowell RM, eds. Surgical Management of Cerebrovascular Disease, Third edition. Williams & Wilkins, Baltimore, in press.