Evidence against Airborne Bacterial Transmission from Contaminated Heater Cooler Devices in Cardiac Surgery

Heater-cooler devices (HCD) are an integral component of cardiac surgery using cardiopulmonary bypass. Recently, they have been implicated in an airborne contamination scenario potentially causing prosthetic valve endocarditis (Sax et al.).

Hypothesis: We reasoned that such a mechanism is unlikely in an operating room with laminar airflow and new HCD.

Methods: We obtained three new HCD (FlexTherm) and assessed the occurrence as well as the source and speed of bacterial contamination. In parallel, we collected repeated microbiological samples from different sites in the operating room either by swab sticks or by exposing agar plates to room air. We also reviewed microbiological results from all cardiosurgical wound infections within the past 4 years and endocarditis cases. Finally, we simulated cardio-surgical conditions and assessed the devices' ability to expel air reaching the operative field.

Results: There was no bacterial growth in any of the sites sampled on the new heater cooler devices before first use. Despite application of newly introduced extensive decontamination procedures as expected by the authorities, bacterial growth could be identified after 12 weeks with the following organisms: Fusarium solani, Sphingomonas paucimobilis, Pseudomonas aeruginosa, and one time with both Mycobacterium chelonae and Mycobacterium goronae. Tap water samples contained a mix of organisms (incl. some of those found on the new HCD), but all below official German limits. However, while we found bacterial growth on 28% of swab sticks and agar plates taken from the room (incl. the operating table area), the identified organism were not the same as those isolated from the HCD. Importantly, none of the HCD organisms was found in patients with surgical wound infections or endocarditis. Using dry ice fog in a simulated operative scenario revealed that the HCD fans expelled air not above knee level with a maximum radius of 40 cm.

Conclusion: Heater cooler devices cannot be expected to remain sterile despite extensive decontamination procedures. However, the suggested airborne contamination mechanism by ventilating the pathogens into the operative field is highly unlikely when laminar airflow is present in the operating room. Thus, heater cooler devices appear safe for routine use in cardiac surgery independent of the high likelihood of external surface contamination.

No conflict of interest has been declared by the author(s).