Cerebral Hemodynamic and Metabolic Effects of Remote Ischemic Preconditioning in Patients with Subarachnoid Hemorrhage

Background: Remote ischemic preconditioning (RIPC) is a fowl of endogenous neuroprotection induced by transient, subcritical ischemia in a distant tissue. RIPC effects on cerebral hemodynamics and metabolism have not been explored in humans. This study evaluates hemodynamic and metabolic changes induced by RIPC in patients with aneurysmal subarachnoid hemorrhage (SAH). Methods: Patients underwent three or four RIPC sessions 2-12 days following SAH. Continuous vitals, intracranial pressure (ICP), and transcranial Doppler (TCD) data were collected. Brain microdialysis metabolic changes were monitored. ICP and TCD morphological clustering and analysis of intracranial pulse (MOCAIP) metrics were compared to positive and negative control groups for cerebral vasodilation. Results: Seven ICP and six TCD recordings from four patients demonstrated an increase in mean ICP (8-14.57 mmHg, p<0.05). There was a reduction in middle cerebral artery (MCA) mean velocities (111-87 cm/s, p=0.039). ICP and TCD MOCAIP metrics demonstrated variances consistent with vasodilation that returned to baseline following the RIPC. Over the duration of the RIPC, microdialysis showed reduction in the lactate/pyruvate (LIP) ratio (42.37-33.77, p=0.005) and glycerol (174.04-126 mu g/l, p<0.005), which persisted for 25-54 h after the last RIPC. Conclusions: This study demonstrated cerebrovascular effects induced by RIPC consistent with transient vasodilation. Cerebral metabolic effects suggest protection from ischemia and cell membrane preservation lasting up to 2 days following RIPC.