The Heater–Cooler Unit—A Conceivable Source of Infection

Heartcenter of North Rhine-Westphalia, F. R. Germany

^* Address communication to: H.H. Weitkemper, Heartcenter of North Rhine-Westphalia, Georg-Str.11, 32545 Bad Oeynhausen, F. R. Germany. E-mail: hweitkemper@t-online.de

Received: March 2002
Accepted: October 2002

Abstract

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°C and 55/mL CFU at 20°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°C and from >1000 CFUs to 100 CFUs at 36°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.