FDA continues to monitor water-based heater-cooler devices for role in infections

June 15, 2022

The Food and Drug Administration (FDA) is presently evaluating and monitoring reports of Nontuberculous Mycobacteria Infections (NMI) associated with water-based heater-cooler devices.

Heater-cooler devices are used during cardiothoracic surgeries, as well as other medical and surgical procedures, to warm or cool a patient to optimize medical care and improve patient outcomes. Heater-cooler devices include tanks that provide temperature-controlled fluid (usually water) to external heat exchangers or warming/cooling blankets through closed circuits.

Although the fluid in the circuits does not come into direct contact with the patient, there is the potential for contaminated fluid to enter other parts of the device or transmit bacteria through the air (aerosolize) through the device's exhaust vent, or other unsealed openings, into the environment and to the patient.

Through the FDA's analysis of adverse event reports, medical literature, and information from national and international public health agencies, the FDA is aware that the use of water-based heater-cooler devices has been associated with Nontuberculous Mycobacteria (NTM) infections, primarily in patients undergoing cardiothoracic surgical procedures. NTM organisms are widespread in nature and can be found in soil and water, including tap water sources. They are typically not harmful, but in rare cases may cause infections in some patients.

The FDA is collaborating with professional societies, public health partners, heater-cooler manufacturers, and experts to evaluate additional strategies to mitigate infections associated with heater-cooler devices. This includes working with:

Health care facilities and professional medical societies to understand their experiences using water-based heater-cooler units and to become more informed about challenges in diverse hospital environments, as well as their capabilities for implementing potential risk mitigation measures.

Infectious disease specialists, health care providers, members of academia, aerosolization science and public health experts to better understand the causes and risk factors for transmission of microbial agents associated with water-based heater-cooler devices and to develop strategies to minimize patient exposure.

The Centers for Disease Control and Prevention and state public health departments to evaluate documented events of heater-cooler contamination and subsequent patient infection.

International public heath regulatory agencies to increase awareness of infections associated with water-based heater-cooler units and to discuss activities to reduce the risks of infection.

The FDA's current analysis has identified potential root causes of contamination from water-based heater-cooler devices, which include:

NTM bacteria transmitted through the air (aerosolization):

There is the potential for NTM bacteria to grow in a water tank in the heater-cooler units. Although the water in the heater-cooler unit does not come into direct contact with the patient, there is the potential for contaminated water to enter other parts of the device or disperse the NTM through the device's vent(s) or other small openings between the inside and outside of the water tanks into the operating room environment and the patient's open surgical cavity. Water agitation (bubbling) inside the water tanks via pumps, mixing components, return circuit water, etc., may increase the potential for aerosolization of NTM bacteria.

For example, mycobacteria are found in much higher concentrations in water droplets emitted into the air from air bubbles rising and bursting in the tank, as compared to the concentration of mycobacteria found in the water in the tank. The water tanks are not airtight, so these aerosolized NTM in the water droplets can escape from the inside of the heater-cooler unit possibly facilitated by the unit's fans and out the vent(s) and into the surgical suite. In addition, these water droplets containing NTM bacteria may remain suspended in the air, which may increase the chances of entering the patient's open surgical cavity or contaminating a sterile implant such as a heart valve.

Laminar flow disruption:

Laminar air flow is an engineering control, which in this case, describes the operating room environment that is intended to add a level of protection by reducing airborne contaminants during surgery. One study, utilizing a single water-based heater-cooler unit, suggests that the device's exhaust fan, depending on the distance and direction of the exhaust, may disrupt the protective nature of the laminar air flow above the patient. The authors of this study hypothesized NTM that is airborne may then be carried into the surgical field.

Water-Based Heater-cooler design:

The designs of most heater-cooler devices are similar since they contain between one and three large tanks filled with water that are either heated or cooled for delivery to heat exchanger(s) or blankets. While the heater-cooler device is running, the water in these tanks is agitated during normal circulation through the circuits.

Some heater-cooler devices contain air filters and water filters; others do not. Water filters (0.22 micron) should be able to remove most NTM from tap water that is used in filling/refilling, topping off, rinsing, making ice and cleaning the heater cooler units. However, the air filters located on some units are not sufficient enough to capture NTM bacteria. An air filter that has the capability of capturing NTM bacteria may alter device safety or performance and would therefore need to be evaluated by the manufacturer as a possible mitigation technique before implementation.

Fans are found on most units and are usually used to cool the unit or aid in the cooling efficiency of a compressor. These fans may facilitate the movement of aerosolized NTM from the inside of the unit into the operating room, and possibly into the sterile surgical field.

In 2015, the FDA issued a final guidance, Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling; Appendix E of the guidance was updated on June 9, 2017 to include water-based heater-cooler devices. The guidance document reflects the scientific advances in knowledge and technology involved in reprocessing reusable medical devices and the FDA’s current thinking on submissions associated with reprocessed medical devices.

Because water-based heater-cooler devices pose a risk of microbial transmission and patient infection through aerosolization if not adequately cleaned and disinfected, the guidance notes 510(k) submissions for these devices should include data to validate cleaning and disinfection instructions. Due to the knowledge gained since the FDA started its evaluation, the FDA is requesting methods to reduce aerosolization when applicable.

·        Data to validate cleaning and disinfection instructions includes protocols and test reports demonstrating the procedures reliably and consistently achieve the specified endpoints and the instructions can be followed as intended.

·         Data to reduce aerosolization includes protocols and test reports measuring the extent of aerosolization and demonstrating methods to reduce aerosolization (if occurring) are successful.

In the United States, there are currently three companies manufacturing and distributing water-based heater-cooler devices. The table below lists the manufacturers, device models, and the status of the cleaning and disinfection validation and aerosolization testing. The FDA continues to work with heater-cooler manufacturers to ensure they provide testing results, and the FDA will update the table to notify the public when test results are complete and adequate.

FDA release