Abstract 2698: Immediate Cerebrovascular and Brain Metabolic Effects of Remote Ischemic Preconditioning

Objective: Remote ischemic preconditioning (RIPC) is a phenomenon by which brief periods of sublethal ischemia in one tissue confers immediate and delayed protection from ischemic injury to distant tissues. A better understanding of the effect of RIPC in the target organs in humans is necessary before this technique can be successfully translated into clinical practice. We investigated the immediate cerebral hemodynamic and metabolic effects induced by RIPC in the setting of subarachnoid hemorrhage (SAH). Methods: Patients with SAH aged 18-80 received 3 or 4 sessions of RIPC on non-consecutive days, 4-12 days after SAH. Each session consisted of four 5-minute rounds of lower limb ischemia, each followed by 5 minutes of reperfusion. During RIPC sessions, continuous ICP and transcranial Doppler (TCD) were recorded. A morphological clustering and analysis algorithm (MOCAIP) of ICP and TCD curves was used to evaluate the vascular changes. Microdialysis was used for brain metabolic assessment. Positive and negative controls for vasoreactivity and non-RIPC SAH microdialysis controls were used for comparison. Results: Seven RIPC sessions were performed in 4 patients (50% male, mean age 52, Fisher 4, H&H 2-4). During RIPC, there were no systemic changes in BP, HR or CVP. ICP increased in all but one session with a mean change of 8 to 15mmHg (p<0.001), not associated with pain or vital changes. TCD showed a tendency for ICA velocity increase (34.5 to 37cm/sec, p=0.61) and a significant MCA velocity decrease (111 to 87cm/sec, p=0.04). The MCA effect was not sustained beyond the RIPC period. ICP and TCD MOCAIP showed 20 and 3 metrics with directional variance consistent with positive controls for vasodilation. Vasodilation did not persist after the RIPC session. Microdialysis showed no significant variation in glucose, lactate or pyruvate. There were significant reductions in L/P ratio (31 to 28, p=0.002) and in glycerol (126 to 113μ g/L, p=0.009) despite TCD and angiographic evidence of vasospasm in 2 patients. Conclusions: In the setting of SAH, RIPC produces immediate, temporary hemodynamic changes characterized by vasodilation of the cerebral circulation. RIPC also reduced brain glycerol levels detected by microdialysis, indicating preservation of the integrity of cellular membranes and potentially reduction of oxidative stress.