Background
A fluid loading and hyperosmolar solutions might modify the cortical brain microcirculation as well as the endothelial glycocalyx (EG). This study compared short-term effects of liberal fluid loading with a restrictive fluid intake followed by osmotherapy with hypertonic saline (HTS) on cerebral cortical microcirculation and EG integrity in a rabbit craniotomy model.
Methods
In the first phase, experimental rabbits were allocated randomly to receive either less than 2 ml/kg/h (group R, n = 14) or 30 ml/kg/h (group L, n = 14) of balanced isotonic fluids for one hour. In the second phase, animals were randomized to receive 5 ml/kg intravenous infusion of either 3.2% saline (group HTS, n = 14) or 0.9% saline (group NS, n = 13) in 20-min infusion. Microcirculation in the cerebral cortex using sidestream dark-field imaging, morphological index of glycocalyx damage - perfused boundary region (PBR) in sublingual and cortical brain microcirculation and syndecan-1 serum levels were evaluated. 
Results
No difference was observed in initial hemodynamic and laboratory parameters between the groups.  
After fluids, lower cortical brain perfused total vessel density (P = 0.0447), small vessel density (P = 0.0178), and perfused vessel density (P = 0.0286), were observed in group L. 
After osmotherapy, no difference was observed between the HTS and NS groups. Syndecan-1serum levels were not different between HTS and NS  (P = 0.5174) or from baseline values. Hematocrit corrected syndecan-1 serum levels were also not different between the HTS and NS groups (1.43 ± 0.60 ng/ml vs 1.36 ± 0.49 ng/ml, P = 0.7372) or from baseline values.
A nonsignificant trend toward higher cerebral PBR values (P = 0.0692) and higher hematocrit corrected syndecan-1 serum levels (1.64 ± 0.63 ng/ml vs 1.16 ± 0.31 ng/ml, P = 0.0324) were observed in L group compared to R group.
Conclusions
Liberal fluid loading was associated with altered parameters of cortical cerebral microcirculation and EG integrity. 
3.2% saline did not affect cortical cerebral microcirculation or markers of EG integrity. 

03 / Effects of fluid strategy and hypertonic saline on cortical cerebral microcirculation and markers of endothelial glycocalyx damage.