Introduction: Management of severe traumatic brain injury (TBI)is primarily focused on avoiding secondary ischemic events. Cerebrovascular autoregulation, the intrinsic ability of vessels to maintain constant and adequate perfusion over a wide range of cerebral perfusion pressures (CPP), is often impaired in severe TBI patients, making it difficult to determine if CPP management is sufficient. Currently, autoregulation can be assessed using intracranial pressure as a surrogate of cerebral blood volume, but this measure is indirect and not applicable to surgical patients following decompressive craniectomy. Here, we describe a novel and direct approach to continuously assess cerebrovascular autoregulation using a regional cerebral blood flow monitor (Hemedex®) that also provides absolute measures of perfusion.

Methods: In 7 patients with severe brain trauma who underwent surgical decompression, a Hemedex® rCBF probe was placed intraoperatively in peri-lesional tissue. Autoregulation was assessed as a moving Pearson correlation between CPP and rCBF (rCBFx).

Results: Composite data from all patients revealed a U-shaped autoregulation curve with intact autoregulation (<0.3) over a wide CPP range (45-90 mmHg) and maximal autoregulation (CPPopt) at 55-60 mmHg. All rCBF values fell below the ischemic threshold (<18 ml/100g/min) when CPPs were <50 mmHg compared with 11% ischemia when CPPs >50 mmHg (P<0.05). We examined the percent time during which both autoregulation was intact and rCBF exceeded the ischemic threshold. In the composite data, this variable was maximal in the CPP range of 75-80 mmHg (CPPideal). In individual patients, the range of CPPs with intact autoregulation varied widely. Individual CPPopt values ranged between 60-100 mmHg and CPPideal ranged between 65-105 mmHg.

Conclusions: These data demonstrate that autoregulatory impairment varies considerably between patients and that CPP target ranges based on consideration of autoregulation alone are significantly lower than when tissue ischemia is additionally considered. Assessment of cerebrovascular autoregulation with Hemedex® rCBF monitor could be utilized to personalize CPP management that optimizes both autoregulation and perfusion.

Patient Care: By using rCBF monitoring to provide a continuous and direct assessment of cerebrovascular autoregulation, our research will improve patient care by allowing clinicians to continuously target cerebral perfusion pressure(s) that both maximize autoregulation and avoid ischemia on a patient-to-patient basis.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of autoregulation-directed therapy as it relates to improvement in TBI outcomes, 2) Discuss the current techniques capable of continuously monitoring autoregulation, and their limitations, in the intensive care setting, 3) Identify a novel rCBF monitor-based index of autoregulation which is both feasible and could be used to guide CPP management strategies to optimize both autoregulation and perfusion

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