• Andrea Lavinio, Bogdan Ene-Iordache, Ilaria Nodari, Alan Girardini, Elena Cagnazzi, Frank Rasulo, Piotr Smielewski, Marek Czosnyka, and Nicola Latronico.
• Institute of Anaesthesiology and Intensive Care Medicine, Ospedale Civile, Pzz.le Spedali Civili, 1, 25100 Brescia, Italy. andrea.lavinio@gmail.com
• Acta Neurochir. Suppl. 2008 Jan 1;102:3-7.

IntroductionThe autonomic nervous system exerts tonic control on cerebral vessels, which in turn determine the autoregulation of cerebral blood flow. We hypothesize that the impairment of cerebral autoregulation following traumatic brain injury might be related to the acute failure of the autonomic system.MethodsThis prospective, observational study included patients with severe traumatic brain injury requiring mechanical ventilation and invasive monitoring of intracranial pressure (ICP) and arterial blood pressure (ABP). Pressure reactivity index (PRx), a validated index of cerebrovascular reactivity, was continuously monitored using bedside computers. Autonomic drive was assessed by means of heart rate variability (HRV) using frequency domain analysis.FindingsEighteen TBI patients were included in the study. Cerebrovascular reactivity impairment (PRx above 0.2) and autonomic failure (low spectral power of HRV) are significantly and independently associated with fatal outcome (P = 0.032 and P < 0.001, respectively). We observed a significant correlation between PRx and HRV spectral power (P < 0.001). The high frequency component of HRV (HF, 0.15-0.4Hz) can be used to predict impaired autoregulation (PRx > 0.2), although sensitivity and specificity are low (ROC AUC = 0.67; P = 0.001).ConclusionFollowing traumatic brain injury, autonomic failure and cerebrovascular autoregulation impairment are both associated with fatal outcome. Impairment of cerebrovascular autoregulation and autonomic drive are interdependent phenomena. With some refinements, HRV might become a tool for screening patients at risk for cerebral autoregulation derangement following TBI.

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