Cerebrovascular reactivity and autonomic drive following traumatic brain injury.
BACKGROUND
The 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.


METHODS
This 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.


RESULTS
Eighteen 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).


CONCLUSIONS
Following 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.
Lavinio
Andrea
A
Institute of Anaesthesiology and Intensive Care Medicine, Ospedale Civile, Pzz.le Spedali Civili, 1, 25100 Brescia, Italy. andrea.lavinio@gmail.com
Ene-Iordache
Bogdan
B
Nodari
Ilaria
I
Girardini
Alan
A
Cagnazzi
Elena
E
Rasulo
Frank
F
Smielewski
Piotr
P
Czosnyka
Marek
M
Latronico
Nicola
N
D000293:Adolescent; D000328:Adult; D000368:Aged; D001342:Autonomic Nervous System Diseases / Q000209:etiology*; D001794:Blood Pressure / Q000502:physiology; D001930:Brain Injuries / Q000150:complications*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004562:Electrocardiography / Q000379:methods; D006339:Heart Rate / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D019370:Observation; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D055815:Young Adult