Nils Petersen

Pathophysiologic differences in cerebral autoregulation after subarachnoid hemorrhage

Objective: To understand the physiologic basis of impaired cerebral autoregulation in subarachnoid hemorrhage (SAH) and its relationship to neurologic outcomes. Methods: The cohort included 121 patients with nontraumatic SAH admitted to a neurointensive critical care unit from March 2010 to May 2015. Vasospasm was ascertained from digital subtraction angiography and delayed cerebral ischemia (DCI) was defined as new cerebral infarction on high-resolution CT. Cerebral blood flow and beat-by-beat pressure were recorded daily on days 2–4 after admission. Autoregulatory capacity was quantified from pressure flow relation via projection pursuit regression. The main outcome was early alterations in autoregulatory mechanisms as they relate to vasospasm and DCI. Results: Forty-three patients developed only vasospasm, 9 only DCI, and 14 both. Autoregulatory capacity correctly predicted DCI in 86% of training cohort patients, generalizing to 80% of the patients who were not included in the original model. Patients who developed DCI had a distinct autoregulatory profile compared to patients who did not develop secondary complications or those who developed only vasospasm. The rate of decrease in flow was significantly steeper in response to transient reductions in pressure. The rate of increase in flow was markedly lower, suggesting a diminished ability to increase flow despite transient increases in pressure. Conclusions: The extent and nature of impairment in autoregulation accurately predicts neurologic complications on an individual patient level, and suggests potentially differential impairments in underlying physiologic mechanisms. A better understanding of these can lead to targeted interventions to mitigate neurologic morbidity.

Proposed Standardized Neurological Endpoints for Cardiovascular Clinical TrialsAn Academic Research Consortium Initiative

&NA; Surgical and catheter‐based cardiovascular procedures and adjunctive pharmacology have an inherent risk of neurological complications. The current diversity of neurological endpoint definitions and ascertainment methods in clinical trials has led to uncertainties in the neurological risk attributable to cardiovascular procedures and inconsistent evaluation of therapies intended to prevent or mitigate neurological injury. Benefit‐risk assessment of such procedures should be on the basis of an evaluation of well‐defined neurological outcomes that are ascertained with consistent methods and capture the full spectrum of neurovascular injury and its clinical effect. The Neurologic Academic Research Consortium is an international collaboration intended to establish consensus on the definition, classification, and assessment of neurological endpoints applicable to clinical trials of a broad range of cardiovascular interventions. Systematic application of the proposed definitions and assessments will improve our ability to evaluate the risks of cardiovascular procedures and the safety and effectiveness of preventive therapies.

Autoregulation in the Neuro ICU

Purpose of reviewThe purpose of this review is to briefly describe the concept of cerebral autoregulation, to detail several bedside techniques for measuring and assessing autoregulation, and to outline the impact of impaired autoregulation on clinical and functional outcomes in acute brain injury. Furthermore, we will review several autoregulation studies in select forms of acute brain injuries, discuss the potential for its use in patient management in the ICU, and suggest further avenues for research.Recent findingsCerebral autoregulation plays a critical role in regulating cerebral blood flow, and impaired autoregulation has been associated with worse functional and clinical outcomes in various acute brain injuries. There exists a multitude of methods to assess the autoregulatory state in patients using both invasive and non-invasive modalities. Continuous monitoring of patients in the ICU has yielded autoregulatory-derived optimal perfusion pressures that may prevent secondary injury and improve outcomes.SummaryMeasuring autoregulation continuously at the bedside is now a feasible option for clinicians working in the ICU, although there exists a great need to standardize autoregulatory measurement. While the clinical benefits await prospective and randomized trials, autoregulation-derived parameters show enormous potential for creating an optimal physiological environment for the injured brain.