Cerebral autoregulation following minor head injury

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✓ The purpose of this study was to determine whether patients with minor head injury experience impairments in cerebral autoregulation. Twenty-nine patients with minor head injuries defined by Glasgow Coma Scale (GCS) scores of 13 to 15 underwent testing of dynamic cerebral autoregulation within 48 hours of their injury using continuous transcranial Doppler velocity recordings and blood pressure recordings. Twenty-nine age-matched normal volunteers underwent autoregulation testing in the same manner to establish comparison values. The function of the autoregulatory response was assessed by the cerebral blood flow velocity response to induced rapid brief changes in arterial blood pressure and measured as the autoregulation index (ARI).

Eight (28%) of the 29 patients with minor head injury demonstrated poorly functioning or absent cerebral autoregulation versus none of the controls, and this difference was highly significant (p = 0.008). A significant correlation between lower blood pressure and worse autoregulation was found by regression analysis in head-injured patients (r = 0.6, p < 0.001); however, lower blood pressure did not account for the autoregulatory impairment in all patients. Within this group of head-injured patients there was no correlation between ARI and initial GCS or 1-month Glasgow Outcome Scale scores. This study indicates that a significant number of patients with minor head injury may have impaired cerebral autoregulation and may be at increased risk for secondary ischemic neuronal damage.

Article Information

Address reprint requests to: David W. Newell, M.D., Department of Neurological Surgery, Harborview Medical Center, 325 9th Avenue, Seattle, Washington 98104.Address for Dr. Jünger: University of Heidelberg, Heidelberg, Germany.

© AANS, except where prohibited by US copyright law.

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Figures

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    Histograms showing the distribution of ARI grades in head-injured patients (upper) and normal volunteers (lower). Note that in the volunteers the ARI values are normally distributed with a mean value of 4.7 ± 1. The mean ARI value is lower in the head-injured group (4 ± 2). The values in the head-injured patients appear to be distributed into two groups including a majority with intact autoregulation and a subgroup with impaired or absent autoregulation.

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    Scatterplots showing regression analysis between resting MABP and ARI. Left: Analysis in normal volunteers indicating no significant relationship between the two variables (r = −0.05, p = 0.78). Right: Analysis in head-injured patients indicating a significant association between lower blood pressure and impaired autoregulation (y = 21.8 + 0.06x, r = 0.59, p < 0.001). Several patients (asterisks) did not follow the trend and had low ARI values despite a seemingly adequate blood pressure. MHI = minor head injury.

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    Left: Computerized tomography scan demonstrating a frontal contusion in a patient with severely impaired autoregulation. Right: Graph depicting the ARI and blood pressure values over time in the same patient. The ARI values remained low on Days 2 and 4 postinjury and returned to the normal range on Day 14 despite minimal changes in blood pressure between the three evaluations. This patient's ICP was also monitored until just before the initial autoregulation testing on Day 2; the ICP was not elevated (ICP 10–12 mm Hg during a 24-hour interval prior to testing).

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    Scatterplot illustrating the relationship between initial GCS score and ARI and also showing the distribution of GCS scores within the head-injured group.

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