Automatic control of the extra-corporal bypass: system analysis, modelling and evaluation of different control modes.

Automatic control of the blood gas parameters during extracorporeal circulation has the potential to improve the quality of this procedure and to relieve the personnel from a time consuming task. This paper describes a model of the underlying system for a standard clinical set-up and pinpoints the major difficulties which are the variations of the process gains and the blood- and gas-flow dependent dead times and time constants. Scheduled PI-controllers both for the arterial oxygen as well as for the carbon dioxide partial pressure were designed. Scheduling was based on the blood flow rate. These controllers were tested in a simulation environment. The control systems remained stable under all tested operating condition, but if the blood flow rate was changed abruptly rather large load errors occurred. The performance was improved markedly by adding a feed-forward control path which directly influences the actuating signals based on the actual blood flow rate and the hemoglobin contents, variables which are measured anyway. The major conclusion of this study is to use such direct feed-forward compensation even if more sophisticated control algorithms are used.

[Initial clinical experiences with a plasma impermeable capillary and a radial pump as a biventricular heart replacement]. / Erste klinische Erfahrungen mit der plasmadichten Kapillare und einer Radialpumpe als biventrikulärer Herzersatz.

A 3 month old infant was treated because of acute lung failure after VSD- and ASD occlusion with an extracorporal membrane oxygenation. The system performance was monitored over a period of 21 days. A Biomedicus 540 centrifugal pump served as the drive. The HILITE 800 LT infant oxygenator was chosen for oxygenation because this product is equipped with a plasma tight fiber. An oxygenator's application with an average of 128 hours lay, as expected, relatively high. Plasma leaks were not noticed. A change of pump head though became necessary due to high hemolysis after every 51 hs.

The heater-cooler unit--a conceivable source of infection.

Even drinking water is contaminated with pathogenic microorganisms. This does not necessarily pose a risk for healthy individuals, but it may result in serious consequences in people with impaired immune systems. This is particularly valid if drinking water is used for medical purposes. The heater-cooler unit (HCU) connected to heat exchangers or blankets by tubing, the connection is closed water circuit that contains microorganisms and algae. While connecting the tubing to the heat exchanger, spilling of water cannot be avoided. Microbiological examinations showed that germs and particles pollute the units. Exposure to the patient and the OR equipment has the potential to increase the risk of infection should the HCU water come in contact with the patient. As a result of the high incidence of particle and algae in the HCU, malfunction occurs. Sampling shows >1000/mL CFU (colony forming units) at 36 degrees C and 55/mL CFU at 20 degrees C on average. The specific findings include Pseudomonas and Legionella. Disinfecting HCU is very difficult. Often HCUs do not provide any technology to reduce bacterial or other contamination. The instructions for use of oxygenators often exclude the use of disinfectants. Maintenance instructions for the HCU advocate the use of disinfectants that carry the risk of oxygenator damage and of heat exchanger leakage. The effect of chemical disinfectants and heat exchanger membranes have not been examined, they may impair heat exchanger permeability and function. As an alternative to chemical and thermal disinfection, we used the alternative method of filtration. Using a membrane filter element, we noticed a decreasing number of CFUs from 55 to sterile conditions at 20 degrees C and from >1000 CFUs to 100 CFUs at 36 degrees C (Figure 1). In addition, we noticed a removal of other particles and algae. In conclusion, we have demonstrated a technique that is simple to implement and effectively reduces the microbiological load of the water in the heater-cooler unit.