Cerebral Haemodynamics and Orthostatic Response to Upright position in acute ischaemic Stroke (CHORUS)

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Stroke is the leading cause of adult disability and mortality in Australia, with the incidence set to rise as our population ages. The majority of strokes are ischaemic in nature and occur when a blood vessel to the brain is occluded, either by a clot or narrowing of the artery. Cerebral blood flow in acute ischaemic stroke is highly dynamic, and factors that either impair or promote cerebral blood flow during the acute phase may directly affect the infarct size and associated clinical deficit. Lowering the head of the bed in the early hours of stroke may theoretically assist flow to the ischaemic tissue, conversely, there is growing support for early mobilisation (getting up) after stroke, with a number of large clinical trials underway. Currently there is no consensus and no clinical guidelines on the safety of early upright posture when caring for acute stroke patients. We are therefore evaluating the extent and clinical relevance of orthostatic changes in cerebral blood flow in acute ischaemic stroke during position changes using transcranial Doppler ultrasound (TCD). The proposed study is a prospective, cohort study of patients with confirmed ischemic (due to a clot) stroke admitted within 24-48 hours of stroke onset to Austin Health. TCD examination is routine for people with stroke at Austin Health. It is performed flat (0 degress) of with the head slightly elevated. In this study, in recruited patients we will extend the current standard care TCD protocol to include measurement of cerebral blood flow velocity in 4 new positions: 30 degrees, 70 degrees, 90 degrees sitting (unsupported) and 90 degrees, standing (if possible). The primary outcome in this study is change in mean cerebral blood flow velocity (CBFVmean) in the middle cerebral artery on the affected stroke hemisphere with change in position from 0 degrees to 90 degrees sitting within the first 24-48 hours of stroke. The assessor of this outcome will be blinded to patient and position. This study will determine whether changing position to upright at 24-48 hours post stroke influences blood flow velocity in the affected hemisphere and whether this response modifies over the first week after stroke. A better understanding of orthostatic changes in blood flow may have significant clinical impact by providing a physiologic basis to guidelines on early head of bed elevation, positioning, and mobilisation of patients with acute anterior circulation stroke. The information from this study will therefore help inform practice and provide pilot data for a larger study that will aim to more clearly identify best practice protocols in subgroups of patients with different stroke characteristics and risk of impaired cerebral autoregulation.

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