Autor: Sabrina Brunk

"The influence of different volume replacement fluids and continuous venovenous haemofiltration (CVVH) in a healthy pig model on the clinical chemistry and the histopathology of the liver" The treatment of critically ill patients poses great challenges to medicine. The often multimorbid patients are subjected to a multitude of therapy components, which, in addition to anaesthesia, medication and parenteral nutrition, also include the administration of crystalloid or colloid volume substitutes and the use of extracorporeal organ-supporting systems. In clinical studies, usually only individual therapy components are considered and different concomitant therapies such as infusion management and the associated possible biocompatibility-related interactions are disregarded, which leads to contradictory results or makes comparability almost impossible. Against this background, this animal experimental study in healthy pigs (n = 66) investigated volume replacement-specific effects of crystalloid and colloidal infusion solutions, with concomitant use of a venovenous haemofiltration circuit (CVVH) on blood chemistry and histopathological changes in the liver. The experimental animals were randomly divided into control and CVVH groups and then assigned to five volume replacement agents (NaCl, HES130, HES200, albumin (ALB), gelatin (GEL)). The CVVH animals were connected to a haemofiltration circuit for a total of 6.5 hours and received an infusion of the volume replacement agent corresponding to their group during the entire time. Extensive measurements of blood parameters (electrolytes, creatinine, urea, blood proteins, colloid osmotic pressure, lactate, liver enzymes) were carried out at five defined time points. Immediately after the end of the experiment, the animals were euthanised. The livers were evaluated for signs of altered hepatic microcirculation and possible hepatocellular damage according to a histological scoring system. Overall, the blood parameters remained largely within the physiological ranges. Higher chloride levels in the control and CVVH groups (NaCl, HES130, HES200) and higher sodium levels (NaCl, HES130, HES200, GEL) were related to the composition of the volume replacement fluid. Significantly higher creatinine values in the animals infused with GEL compared to the control and a divergent behaviour of the two HES preparations could be an indication of poorer creatinine clearance in the CVVH-GEL group. An increase in glucose concentration after bolus infusion, which was only observed in the two HES preparations, could be explained by the degradation pathway of the HES molecules to glucose. The consistently lower protein and albumin concentrations of the artificial colloids (HES130, HES200, GEL) compared to the ALB group, which were below baseline, indicated an influence on albumin homeostasis in the liver due to application of the artificial colloids. Histopathological evaluation showed a lower degree of portal field oedema in all CVVH groups compared to their controls. Furthermore, the CVVH groups of NaCl, ALB and GEL showed significantly lower scores in the widening of the spaces of Disse and sinusoidal blood stasis compared to their controls. The two HES preparations behaved divergently. However, without a measurement of intrahepatic pressures and portal flow rates, the interpretation of these results is limited. In addition to improved haemodynamics under CVVH, a biocompatibility reaction with leukocyte activation, cytokine release and subsequent vasoconstriction must also be considered in view of the higher leukocyte counts with NaCl, ALB, GEL. All CVVH groups showed a lower degree of hepatocellular vacuolisation in favour of a more pronounced oedematisation compared to their controls. This was interpreted as a lower affection of the liver cells, which was additionally reflected in blood chemistry by a lower release of AST in the animals of the HES130 and GEL group. Regrouping the experimental animals according to their mean histological score values (0-3), independent of the volume replacement fluid, showed that higher enzyme values tended to be associated with greater hepatocellular vacuolisation (AST) and greater hepatocellular oedematisation (ALT, LDH). An exclusive storage of HES molecules in the vacuoles of the liver cells could thus be disproved. Overall, this animal study was able to show that the choice of volume replacement with simultaneous use of CVVH can lead to different biocompatibility reactions. In view of the small differences in the healthy pig model, which were already evident within a few hours, it seems advisable to consider corresponding protocol aspects in the design of future preclinical studies and to include this factor in corresponding multivariate analyses for clinical studies.