Kinetic modeling of powder charcoal haemoperfusion.

The aim of this study was to achieve more understanding of the mass transfer characteristics of the filmadsorber haemoperfusion device. First, a structural model with mathematical description of the different diffusion steps was developed. Exact quantification appeared very difficult, resulting in insufficient fit of predicted and measured concentration curves. Moreover, the mathematics turned out simple, since the concentration courses could be described with one exponential power. Therefore, a formal model was developed, assuming linear isotherms and adsorption, proportional to the average concentration in the column. With this model predicted in-vitro inlet and outlet concentrations could be fitted to the measured data accurately. A relation between both models is given under the condition of high intraparticle mass transfer, which is allowed in case of powder adsorbents. It can be concluded that structural models do not yield predictive tools for optimization of device geometry. A formal model with two constants determining device performance enables device optimization with the help of some in-vitro experiments.

In vivo experiments with powder charcoal haemoperfusion (filmadsorber) in a pig model of hepatic failure.

The filmadsorber, an experimental haemoperfusion column containing activated powder charcoal embedded in a colloidal film, has been tested in pigs with ischaemicnecrosis of the liver. Haemoperfusion with a flow of 200 ml/min was performed for a duration of 4 to 6 hours. Bile acid clearances varied between +/- 52 ml/min (1st hour) and +/- 23 ml/min (6th hour). Clearances for aromatic amino acids were initially even higher (phenylalanine 115, tyrosine 112 and methionine 46 ml/min). No ammonia was removed. Side-effects were minimal, although platelets fell 24 +/- 15%. We conclude that haemoperfusion with the filmadsorber is well tolerated and associated with high clearances for bile acids and some amino acids, particularly in the first hours of treatment.

Application of computers in renal units. A question of time?

The application of computers for day-to-day patient care in renal units is still in its infancy, but the renal unit seems to be well suited for automation, because a computer may carry out functions that are often done badly or inefficiently or not at all. A data base system allows better access to information about patients and may improve the organisation of a center. Kinetic modelling can help to optimize treatment schedules and regimens. Computer-monitoring may improve the safety of dialysis, particularly home dialysis. The introduction of computers into the renal unit has been slow and hesitant. Responsible for this is the difficulty of defining exactly what data are necessary to treat renal patients. Economic benefit and improvement in patient care are also difficult to indicate. Lack of communication between computers and people still has its impact. However, those physicians and nurses who fully understand and master the area of nephrology and dialysis may appreciate the help of a computer. Finally, it can be concluded that interest for computers is more or less omnipresent. Realizing that the entire field of computer technology is continuously in motion, it can be speculated that the broad application of computers in renal units is just a question of time.

The development of a new hemoperfusion column: the filmadsorber.

A hemoperfusion system has been developed in which very small charcoal particles (average diameter 40 micrometers) are embedded and immobilized in a collodion film (Filmadsorber). In vitro studies revealed that the absorption of bile acids by these small charcoal particles is superior to that by larger ones (size: 0.5 to 5 mm) as used in commercially available adsorbers. In vivo studies confirmed these results: dogs with ligated bile ducts were subjected to hemoperfusion through different types of charcoal adsorbers. Bile acid clearances of filmadsorbers containing less charcoal than the commercials were significantly higher.