Cerebral autoregulation before and after blood transfusion in a child

Effects of Norepinephrine, Propofol, and Hemoglobin Concentration on Dynamic Measurements of Cerebrovascular Reactivity in Acute Brain Injury

Effects of treatment-associated variables on cerebrovascular autoregulation (CA) in acute brain injury patients remain unclear. As deficient CA is associated with worse outcomes and ideas about CA-steered management are emerging, this question is relevant. We investigated effects of norepinephrine and propofol infusion rates and hemoglobin concentration on dynamic measurements of cerebrovascular reactivity as surrogate for CA. A retrospective analysis of 91 traumatic brain injury (TBI) and 13 stroke patients admitted to the intensive care unit (ICU) of the Leuven University Hospitals was performed. Low-resolution autoregulation index (LAx) and high-frequency pressure reactivity index (PRx) were calculated as measurements of cerebrovascular reactivity. Data was binned into 5-, 15-, and 60-min intervals. Bivariate time-series analysis using lagged cross-correlations were calculated after pre-whitening and differencing. Linear mixed models evaluated effects of age, gender, cardiovascular risk, brain comorbidity, Glasgow Coma Scale (GCS), pupil reactivity, and type of injury. Median dose of norepinephrine, propofol and hemoglobin concentration was 7.8 μg/kg/h (Q1 3.6-Q3 13.8), 3 mg/kg/h (Q1 1.9-Q3 4.3), and 9.2 g·dL^-1 (Q1 8.2-Q3 10.5), respectively. Mean cross-correlations for 24 lags were close to zero and not significant for all variables. No significant differences as function of age, gender, cardiovascular risk, brain comorbidity, GCS, pupil reactivity, and type of injury were found. Dynamic intracranial pressure-based measurements of cerebrovascular reactivity in acute brain injured patients are not affected by gradually adjusted norepinephrine or propofol infusion rates or slow changes in hemoglobin concentration within the typical ranges during ICU admission. Future trials on cerebrovascular reactivity-steered management and treatment of CA impairment may not have to take these variables into account.

Change in cerebral autoregulation as a function of time in children after severe traumatic brain injury: a case series

OBJECTIVE

The objective of this study was to describe changes in cerebral autoregulation after severe pediatric traumatic brain injury (TBI).

MATERIALS AND METHODS

Two cerebral autoregulation tests were performed during the first 10 days after severe TBI in children <16 years. Cerebral autoregulation was quantified using the mean autoregulatory index (mARI).

RESULTS

Nine (five males/four females) children (10 +/- 5 years) with severe (admission Glasgow Coma Scale (GCS), 5 +/- 2) TBI were enrolled. Thirty (3/9) percent of initial exams revealed impaired cerebral autoregulation; all three had returned to intact cerebral autoregulation on second exam. However, in three of nine (33%) patients, cerebral autoregulation worsened on second exam. Of the factors examined, worsening mARI on second exam was associated with worsening head computed tomography (CT) lesion.

CONCLUSIONS

Cerebral autoregulation often changed and worsened during the first 9 days after severe pediatric TBI. Worsening cerebral autoregulation may mirror worsening TBI.

Anaemia and the brain

PURPOSE OF REVIEW

This article reviews the physiological and pathophysiological effects of anaemia on the brain, focusing on the hypothesis that anaemia-induced cerebral hypoxia contributes to anaemic cerebral dysfunction and injury. It also reviews evidence that the regulated increase in cerebral blood flow observed during anaemia represents a compensatory neuroprotective mechanism invoked to optimize cerebral oxygen delivery, thereby protecting the brain from hypoxic injury.

RECENT FINDINGS

Severe anaemia, or low haematocrit, has been associated with cognitive dysfunction, impaired cerebral vascular regulation, neurological injury, and increased mortality, which suggests that the brain is vulnerable to anaemia-induced injury. Reduced cerebral tissue oxygen tension has been measured directly at haemoglobin concentrations near 35 g/l, suggesting that hypoxia may contribute to anaemic cerebral injury. A demonstration of increased hypoxic cerebral gene expression, including neuronal nitric oxide synthase, may provide a more sensitive means of determining the minimum haemoglobin concentration at which anaemia-induced cerebral hypoxia can be detected. The measurement of increased cerebral cortical neuronal nitric oxide synthase messenger RNA and protein levels in rats, at haemoglobin concentrations between 50 and 60 g/l, suggests that cerebral hypoxia occurred at these higher haemoglobin concentrations. Mechanisms regulating anaemic cerebral vasodilation and increased cerebral oxygen delivery, including nitric oxide, require further elucidation to establish their role in protecting the brain during anaemia.

SUMMARY

Characterization of mechanisms of anaemia-induced cerebral injury will contribute to the development of optimal therapeutic strategies for anaemic patients. Such strategies would include a clearer definition of transfusion triggers based on physiological endpoints. The overall goal of these efforts would be to minimize morbidity and mortality associated with anaemia.