To Örebro University

Background: Cerebral injury may alter the autoregulation of cerebral blood flow. Pressure reactivity (PR) is considered as a surrogate measure of autoregulation. Little is known whether PR is associated with measures of brain metabolism and indicators of ischemia and cell damage. We speculate that prostacyclin may affect extracellular glycerol levels (a measure of cell membrane degradation), measured by microdialysis in the brain, and thus glycerol’s association with PR.

Material and Methods: The study is a randomized, double-blinded placebo-control study on the effect of prostacyclin treatment (0.5 ng/kg/min) in severe traumatic brain injury (sTBI). The basic treatment was an intracranial pressure (ICP) targeted therapy based on the Lund concept. Inclusion criteria were verified blunt head trauma, GCS£8, age 15 -70 yrs, and a first measured cerebral perfusion pressure of ‡10 mmHg. Multimodal monitoring was applied. Samples from a brain microdialysis catheter placed on the worst affected side, close to the penumbra zone, were analysed. Mean (glycerolmean) and maximal glycerol (glycerolmax) during the 96 hrs sampling period were calculated. The mean PR was calculated as the ICP/MAP regression coefficient based on hourly mean ICP and MAP (mean arterial blood pressure) during the first 96 hrs.

Results: 45 patients, mean age 35.5–2.2 yrs, GCS 6 (3-8) and ISS 29 (9-50) were included. In the placebo group there was a positive correlation between glycerolmean (r=0.503, p=0.01), glycerolmax (r=0.490, p=0.015) levels and PR levels. This correlation was attenuated/abolished in the prostacyclin group. Glycerol tended to be higher and PR was higher in the placebo group (p=0.0164) as compared to the prostacyclin group.

Conclusion: PR is correlated to the glycerol level in patients suffering from sTBI. Prostacyclin attenuates this correlation. Glycerol is associated with membrane degradation and may support glycerol as a biomarker for vascular endothelial breakdown. Such a breakdown may impair the regulation of cerebrovascular pressure reactivity. We suggest that prostacyclin counteracts the breakdown and beneficially affect the cerebral blood flow autoregulation measured as PR.