Once symptomatic vasospasm has developed, treatment is often ineffective. Moderate hyperv-
olemia and hemodilution are commonly encouraged and instigated at the time of diagnosis of SAH, partly to reverse the usual decreased circulating blood volume associated with SAH and also in an effort to prevent or limit the development of DID. More aggressive, therapeutic "triple H" management, consisting of hypervolemia, hypertension and hemodilution, is usually commenced at the onset of symptoms of DID. The induction of hypertension pharmacologically has been shown to reverse ischemic deficits and may be necessary if hypervolaemic hemodilution is insufficient to improve symptomatology. Caution must be used in "triple H" therapy, as it may aggravate cerebral edema (reducing cerebral compliance), pulmonary edema (reducing the oxygen exchange) or dilu-tional hyponatremia and, therefore, accurate and often invasive monitoring is required. There is also an increased risk of re-hemorrhage in unsecured aneurysms, which occur in up to 50% of individuals. "Triple H" therapy was previously thought to increase CBF. It is more likely that hemodilution actually increases collateral blood flow to ischemic penumbra, minimizing the size of any infarction.
Nimodipine, a 1,4 dihydropyridine lipid-soluble calcium antagonist, has been studied in several large prospective randomized-controlled trials . It crosses the blood-brain barrier and selectively blocks the L-type voltage-dependent channels, inhibiting the calcium overload of neurons and smooth muscle cells. It has consistently been shown to improve outcome after spasm in all grades, although, in all but one trial, the incidence of symptomatic spasm was not affected. Angiographically, the calibre of the vessels remains unchanged and there appears to be no obvious effect on CBF. The mechanism by which nimodipine is effective is unclear, but a brain-protective effect is likely, possibly by limitation of calcium influx in marginally ischemic neurons or by increasing pial collateral dilatation. Although the benefit of nimodipine in prophylaxis has been clearly established, its role in the treatment of ischemia is far less clear.
Angioplasty is being increasingly used in the management of clinical vasospasm refractory to medical treatment. There is significant
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...