NIRS Directed Optimal Cerebral Perfusion Pressure in Aneurysmal Subarachnoid Hemorrhage Patients: A Feasibility Study

Neurologic dysfunction is common in aneurysmal subarachnoid hemorrhage (aSAH) patients. As we know, after the initial injury, secondary insults including poor cerebral perfusion are main contributors to poor outcome and their early detection and amelioration are keystone to neurocritical care. Nonetheless, the guidelines for blood pressure management still recommend a single target blood pressure for critically ill patients: the Brain Trauma Foundation (BTF) guidelines recommend maintaining CPP between 60 and 70 mmHg; Some guidelines recognize that patients with a history of hypertension may require a higher MAP. However, these guidelines do not currently recommend cerebral autoregulation-guided therapy and leave many unanswered questions. Cerebral autoregulation is the mechanism that maintains cerebral blood supply, hence CBF approximately constant despite changes in MAP or, more precisely, despite changes in CPP. Maintaining blood pressure within the cerebral blood flow (CBF) autoregulation range (termed "optimal MAP") is associated with improved outcomes for patients. The observational data suggests that management of patients above or below CPPopt 5mmHg is associated with better outcomes and mortality than the other greater variation range. The most commonly used method for monitoring dynamic cerebrovascular reactivity is the pressure reactivity index (PRx) that uses ICP as a surrogate for CBV. However, assessing the PRx requires invasive ICP monitoring which limits its application in many clinical areas. Alternatively, in the absence of invasive intracranial pressure monitoring to determine CPP, a continuous autoregulation monitoring can be accomplished by the continuous correlation between transcranial Doppler (TCD)-measured CBF velocity of the middle cerebral artery and the mean arterial blood pressure (termed mean velocity index or Mx). Mx is a validated index of cerebral autoregulation based on measures of cerebral perfusion pressure and mean flow velocity