High blood pressure as risk factor and prognostic predictor in acute ischaemic stroke: when and how to treat it?

High blood pressure is common in the western world and is a major risk factor for the development of stroke. Lowering blood pressure reduces the risk of first and recurrent stroke. High blood pressure is also common in acute stroke and is independently associated with a poor prognosis, in part due to promoting early recurrence and the development of fatal cerebral oedema in patients with ischaemic stroke and, possibly, re-bleeding in those with haemorrhagic stroke. However, the management of blood pressure remains an enigma--its lowering could improve outcome by reducing recurrence or worsen outcome by reducing regional perfusion in the face of dysfunctional cerebral autoregulation. Conversely, raising blood pressure might improve outcome by raising regional perfusion or worsen it by inducing cerebral oedema and early recurrence. Administration of some vaso-active drugs (beta-receptor antagonists and calcium channel blockers) can worsen outcome and reduce cerebral blood flow. In contrast, other drug classes--angiotensin- converting enzyme inhibitors, angiotensin receptor antagonists and nitrates--appear to lower blood pressure without reducing measures of cerebral perfusion. In the absence of definitive trial data, which is urgently needed, blood pressure should not be routinely lowered unless it is extreme (systolic blood pressure >220 mm Hg) or associated with arterial dissection or cardiac ischaemia or failure, in which case cautious lowering (<15%), perhaps with an angiotensin-converting enzyme inhibitor, angiotensin receptor antagonist or nitrate, is appropriate.