Through the FDA’s analysis of adverse event reports, the medical literature, and information from national and international public health agencies, we are aware that the use of heater-cooler devices has been associated with Nontuberculous Mycobacteria (NTM) infections. On October 15, 2015, the FDA issued Nontuberculous Mycobacterium Infections Associated with Heater-Cooler Devices – Safety Communication to provide recommendations to minimize patient exposure. On June 1, 2016, the FDA issued Mycobacterium chimaera Infections Associated with Sorin Group Deutschland GmbH Stöckert 3T Heater-Cooler System - Safety Communication to provide new information and recommendations about Mycobacterium chimaera infections (a type of NTM), associated with the use of the Stöckert 3T Heater-Cooler System in patients who have undergone cardiothoracic surgeries.
On October 13, 2016, the FDA updated its June 1, 2016 Safety Communication to provide new information about Mycobacterium chimaera infections associated with the use of the LivaNova (formerly Sorin Group Deutschland GmBH) Stockert 3T Heater-Cooler System. Specifically, the FDA has received reports of patients in distinct geographic regions within the U.S. being infected with M. chimaera after undergoing cardiothoracic surgery that involved the use of the 3T. Whole genome sequencing was completed on clinical isolates taken from infected patients and samples taken from 3T heater-cooler devices in hospitals where clusters of patient infections were identified. Samples of the water drained from the 3T devices and air samples collected while the devices were in operation were tested. The results strongly suggest the 3T heater-cooler units are the source of M. chimaera contamination.
The FDA continues to evaluate Nontuberculous Mycobacteria (NTM) infections associated with heater-cooler devices, primarily in patients undergoing cardiothoracic surgical procedures. This includes reviewing adverse event reports, medical literature, and information from state, national and international public health agencies. Our current analyses have identified potential root causes of contamination from heater-cooler devices, which we are evaluating to determine whether they definitively contribute to patient infection. Potential root causes 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 transmit 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.), during heater-cooler operation, may increase the potential for aerosolization of NTM bacteria present inside the water tank.
For example, mycobacteria are found in much higher concentrations on water droplets ejected into the air from air bubbles rising and bursting in the tank as compared to the concentration of mycobacteria found in the water. The water tanks are not air tight, so these aerosolized NTM can escape from the inside of the heater-cooler unit and out the vent(s) and into the surgical suite, possibly facilitated by the unit’s fans. 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 refers to an engineering control within the operating room environment that intends to provide protection by reducing the risk of airborne exposure to bacteria or other contamination during surgery. One study2, utilizing a single 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 that NTM that is airborne may then be carried into the surgical field.
- 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 the device’s heat exchanger(s) or to 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 (0.2 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. Air filters located on some units are not efficient enough to capture NTM bacteria. An air filter that has the capability to capture NTM bacteria may alter device safety or performance and would therefore need to be evaluated by each manufacturer as a possible mitigation technique before implementation.
Fans are found on most units and are usually used to cool the unit and/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.
2 Sommerstein R, Rϋegg. Kohler P, Bloemberg G, Kuster SP, Sax H. Transmission of Mycobacterium chimaera from Heater-Cooler Units during Cardiac Surgery despite an Ultraclean Air Ventilation System. Emerg Infect Dis. 2016 June;22(6):1008-13.).