Heater–cooler units: contamination of crucial devices in cardiothoracic surgery

doi:10.1016/j.jhin.2016.02.006

Journal of Hospital Infection

Volume 93, Issue 3, July 2016, Pages 223-228

https://doi.org/10.1016/j.jhin.2016.02.006 Get rights and content

Summary

Background

Several cases of Mycobacterium chimaera infection have recently been reported in cardiosurgical patients. So-called heater–cooler units (HCUs) used in cardiosurgical procedures are suspected to be the reservoir for pathogen growth and dissemination.

Aim

To assess the contamination status of HCUs at our facility.

Methods

Air sampling for mycobacteria was conducted at different distances from the machines and in the area around the operating table. Air sampling was also conducted for non-fermenters as a surrogate parameter for water-associated pathogens.

Findings

Mycobacterium chimaera was detected in the water tanks of the HCUs. When the devices were operating, M. chimaera was also found in their exhaust air, as well as in the area around the operating table. Non-fermenters were identified at different distances from the running HCU and the area around the operating table. Cultures remained negative when the devices were switched off.

Conclusions

Exhaust air from HCUs may be a pathway of pathogen transmission to patients undergoing open chest heart surgery. Although, for technical reasons, relocation of HCUs is difficult to achieve, only strict separation of the HCU from the operating room appears to enhance patient safety. Using non-fermenters as a surrogate parameter may be considered a viable option for a timely risk assessment. The design of HCUs should be modified to keep susceptibility to contamination at a minimum.

Introduction

Several cases of severe infection with Mycobacterium chimaera, e.g. endocarditis and prosthetic graft infection have recently been reported from Switzerland, The Netherlands, Germany and Great Britain.1, 2, 3, 4, 5 These infections occurred after a latency period of between a few months and several years in patients having previously undergone open chest heart surgery.1, 3

Following a detailed outbreak investigation conducted by University Hospital Zürich, so-called heater–cooler units (HCUs) manufactured by the Sorin Group (Milan, Italy) were identified as the probable source of pathogen contamination.3, 6 HCUs are used during open chest heart surgery to regulate the temperature of the blood during extracorporeal circulation, and contain tanks filled with sterile filtered tap water as a temperature exchange medium. They are connected by tubing to the membrane oxygenator of the heart–lung machine and are therefore usually placed inside the operating room. Regarding the possible transmission path during surgery, direct leakage between HCU circuits and extracorporeal circulation does not appear probable. Mycobacterium chimaera was, however, identified in the machines' exhaust air, which is propelled into the operating room by the HCU cooling fan and then disseminated. This was therefore identified as a potential transmission pathway.³

In this context, the Swiss Federal Health Office (BAG: Bundesamt für Gesundheit) launched a public alert in July 2014. In Germany, the Federal Institute for Drugs and Medical Devices (BfArM: Bundesinstitut für Arzneimittel und Medizinprodukte) adopted the theme, as did the European Centre for Disease Prevention and Control (ECDC), which communicated the problem at European level.6, 7

As several Sorin HCUs are in use at our facility, their contamination status with M. chimaera was assessed. To develop recommendations for greater patient safety we aimed to confirm dissemination of the pathogens in air. As the scope of the problem was previously unknown, a series of exploratory and systematic investigations was launched.

Section snippets

Setting

The University Heart Center Freiburg–Bad Krozingen is affiliated to University Hospital Freiburg, a tertiary care university hospital located in south-west Germany. The Center's Department of Cardiac and Vascular Surgery conducts about 4650 surgical procedures annually at two separate locations in Freiburg and nearby Bad Krozingen. The survey focused on five HCUs (A, B, C, D, E) located at University Hospital Freiburg. During the investigation, HCU C was replaced by HCU D.

Four of the HCUs were

Air sampling for non-fermenters (August 2014)

Non-fermenters were identified at different distances from the running HCU C (Table I).

As long as HCU B was not in use, cultures taken from the area around the operating table remained negative for non-fermenters. Once the HCU was started, cultures showed considerable growth of non-fermenters (Table II). Other organisms such as coagulase-negative staphylococci, micrococci, and Gram-positive rods were identified independent of the operational status of the HCU.

Contamination of tanks and circuits (January 2015)

Mycobacterium chimaera was detected

Discussion

The investigation presented here demonstrates that M. chimaera was found in the water tanks of HCUs; we postulate that exhaust air may be a pathway of transmission to patients undergoing open chest heart surgery. These findings confirm results of previous research conducted in Switzerland. Sax et al. hypothesized that contaminated droplets from inner tubes or connections of an HCU could have reached the turbulent airflow produced by a fan in the lower part of the machine.³ Our examinations

Acknowledgements

We thank Ms D. Lawrie-Blum for language assistance.

References (9)

Y. Achermann et al.
Prosthetic valve endocarditis and bloodstream infection due to Mycobacterium chimaera
J Clin Microbiol
(2013)
P. Kohler et al.
Healthcare-associated prosthetic heart valve, aortic vascular graft, and disseminated Mycobacterium chimaera infections subsequent to open heart surgery
Eur Heart J
(2015)
H. Sax et al.
Prolonged outbreak of Mycobacterium chimaera infection after open-chest heart surgery
Clin Infect Dis
(2015)
Public Health England
Mycobacterial infections associated with cardiopulmonary bypass surgery
(10 June 2015)

There are more references available in the full text version of this article.

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Cardiopulmonary bypass in neonates and infants
2022, Cardiopulmonary Bypass: Advances in Extracorporeal Life Support
Using cardiopulmonary bypass (CPB), congenital cardiac surgeons have the ability to intervene earlier on complex lesions. As a result, definitive and palliative surgical options can be offered to neonates and infants. These populations have higher overall mortality than older children who undergo cardiac surgery. However, this measurement does not consider case-mix. Subsequently, means of mortality risk-adjustment have emerged, which allow for comparison of different surgical groups, quality improvement, and enhanced research. Another common finding postoperatively is vital organ injury, including acute kidney injury, cerebral injury, and myocardial injury. These morbidities have been associated with poor long-term outcomes as the patients age; neural injury is especially tied to poor development, suggesting the need for further neuroprotection in the intraoperative setting through multimodality neuromonitoring. Another major complication that neonates are especially susceptible to is severe inflammatory response secondary to hemodilution and transfusion due to relative circuit size. Using oxygenators with integrated arterial filters, smaller inner diameter tubing, shorter tubing length, mast-mounted pump heads, and lower venous reservoir levels are all ways to reduce priming volumes. However, the safety and hemodynamics of each component must be assessed through in vitro/in vivo evaluations as drastic miniaturization of the circuit could pose more risks than benefits. Additionally, utilizing modified ultrafiltration and optimizing each component of the CPB circuit may help reduce morbidity/mortality for the most fragile patient population.
Prophylaxis and prevention of infective endocarditis
2022, Infective Endocarditis: A Multidisciplinary Approach
Infective endocarditis is a rare disease but with very severe consequences. The difficulty of treatment and high mortality and morbidity mandates the institution of effective preventive measures. Antibiotic prophylaxis for high-risk procedures such as invasive dental procedures has been used as a preventive measure for more than 60 years. However, the efficacy of antibiotics in preventing infective endocarditis is not well established. Daily oral hygiene activities such as brushing, flossing, and even chewing are associated with some level of bacteremia. Bacteremia associated with routine daily activities might be causing a higher cumulative burden than sporadic single tooth extractions. Widespread antibiotic prophylaxis has risks such as adverse events like anaphylaxis and the potential of antibiotic resistance. Therefore, guidelines of the past 10–15 years have restricted antibiotic prophylaxis of infective endocarditis to the patients who are at the highest risk of suffering from a poor outcome. Although more than 10 years have passed from these recommendations, controversies remain unresolved. The most effective preventive measures continue to be nonspecific ones like good oral and cutaneous hygiene practices.
Failure to eradicate non-tuberculous mycobacteria upon disinfection of heater–cooler units: results of a microbiological investigation in northwestern Italy
2020, Journal of Hospital Infection
Citation Excerpt :
HCUs are closed, non-sterile circuits placed outside the sterile field, where no contact with the patient's blood or body fluids occurs. Nonetheless, NTM species, chiefly Mycobacterium chimaera, can spread throughout the operating room via HCU-mediated aerosolization (particle size <1 μm) of colonized water [1,5,6]. The M. chimaera-containing aerosol can then fall on to the patient's open surgical wound, leading to surgical site infections [5].
Heater–cooler units (HCUs) used during cardiopulmonary bypass may become colonized with non-tuberculous mycobacteria (NTM), including Mycobacterium chimaera. Recently, a worldwide investigation conducted in hospitalized infected patients has detected M. chimaera in several Stockert 3T HCUs manufactured by LivaNova.
Microbiological surveillance on Stockert 3T (LivaNova) and Maquet HCU40 (Getinge) devices as well as an evaluation of the efficacy of their recommended decontamination protocols.
A total of 308 water samples were collected from 29 HCUs: 264 samples were collected from 17 Stockert 3T HCUs and 44 samples from 12 Maquet HCU40 devices. Samples were tested for total viable counts (TVCs) at both 22 and 36°C, Pseudomonas aeruginosa, coliform bacteria, and NTM. The microbiological surveillance began in June 2017 and ran until October 2019.
A total of 308 HCU water samples were analysed, 65.5% of which yielded NTM. The most frequently colonized device with NTM was the Stockert 3T (88.2%), with a frequency of positive samples of 59.5% (157/264). The Maquet HCU40 devices less frequently yielded NTM (33.3%), with a frequency of positive water samples of 13.6% (6/44). Disinfection procedures were effective in reducing TVCs of bacteria with the exception of NTM species. NTM were detected in both pre-disinfection (50.1%) and post-disinfection (55.7%) samples, and no significant association was found between disinfection and NTM results both in Stockert 3T and Maquet HCU40 devices.
This study suggests that manufacturers' procedures for disinfection are ineffective and/or inadequate. Until effective disinfection protocols become available, the only way to minimize the risk of NTM contamination is to closely monitor the water quality in the HCU, keep it as clean as possible, and treat it like any other biohazardous material.
The effect of sodium thiosulfate on the recovery of Mycobacterium chimaera from heater–cooler unit water samples
2020, Journal of Hospital Infection
Heater–cooler units (HCUs) have been implicated in the recent global outbreak of invasive Mycobacterium chimaera infection among patients following cardiothoracic surgery. Because infected patients tend to remain asymptomatic for extended periods, detection of M. chimaera from HCUs in real time is essential to halting the ongoing M. chimaera HCU-associated outbreak. Sample collection protocols to evaluate the presence of M. chimaera offer conflicting recommendations regarding the addition of sodium thiosulfate (NaT) during the collection process.
To study the effect of NaT on M. chimaera recovery and culture contamination.
Seventy-six paired HCU water samples (with and without NaT) were collected, processed and cultured simultaneously into Lowenstein–Jensen slants, Middlebrook 7H10 agar plates, and mycobacterial growth indicator tubes (MGITs), and incubated at 37°C. A subset of 31 paired samples was additionally cultured on MGITs and incubated at 30°C.
Of 76 samples incubated at 37°C in each of the three media, with and without NaT, M. chimaera was identified in at least one aliquot of 21 samples.
The presence of NaT did not significantly increase the probability of recovering M. chimaera in a multi-variable conditional logistic model and culture contamination rates were similar between aliquots with and without NaT. In the subset of samples cultured on MGITs at both 30°C and 37°C, the presence of NaT again was not associated with M. chimaera recovery, but was significantly associated with reduced culture contamination.
Mycobacterium chimaera infections: An update
2020, Journal of Infection and Chemotherapy
Citation Excerpt :
If not promptly diagnosed and properly treated, M. chimaera infections my become life-threatening [10,11]. The primary mode of transmission has been identified in the water tanks of heater-cooler units (HCUs), thermoregulatory components of ECMOs, which produce a contaminated aerosol [12–14] (Fig. 1). Stagnation of water and high temperature (up to 40 °C) promote the formation of biofilms, creating a more favourable environment for M. chimaera [15,16].
Mycobacterium chimaera is a non-tuberculous mycobacterium belonging to the Mycobacterium avium complex, described for the first time in 2004. It acts as an opportunistic pathogen, with infections, usually respiratory illnesses, occurring more frequently in immunocompromised patients or in patients with underlying respiratory diseases. During the last decade Mycobacterium chimaera disseminated infections following cardiothoracic surgery, especially open-heart surgery, have been increasingly reported worldwide. From a pathogenic standpoint, Mycobacterium chimaera is acquired during cardiopulmonary bypass via bioaerosols emitted from contaminated heater-cooler units water systems. Due to non-specific symptoms and long latency, postoperative Mycobacterium chimaera infections may not be promptly diagnosed and treated, and may become life-threatening. The indication for revision surgery needs to be carefully evaluated on a case-by-case basis, and antibiotic therapy should be based on drug susceptibility testing results. Our review aims to provide an updated account of microbiological characteristics, clinical presentation, diagnosis, and management of Mycobacterium chimaera infections, with a special focus on those developing after cardiothoracic surgery.

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Journal of Hospital Infection

Summary

Background

Aim

Methods

Findings

Conclusions

Introduction

Section snippets

Setting

Air sampling for non-fermenters (August 2014)

Contamination of tanks and circuits (January 2015)

Discussion

Acknowledgements

References (9)

Prosthetic valve endocarditis and bloodstream infection due to Mycobacterium chimaera

J Clin Microbiol

Healthcare-associated prosthetic heart valve, aortic vascular graft, and disseminated Mycobacterium chimaera infections subsequent to open heart surgery

Eur Heart J

Prolonged outbreak of Mycobacterium chimaera infection after open-chest heart surgery

Clin Infect Dis

Mycobacterial infections associated with cardiopulmonary bypass surgery

Cited by (60)

Infectional protection and antimicrobial support for cardiopulmonary bypass

Cardiopulmonary bypass in neonates and infants

Prophylaxis and prevention of infective endocarditis

Failure to eradicate non-tuberculous mycobacteria upon disinfection of heater–cooler units: results of a microbiological investigation in northwestern Italy

The effect of sodium thiosulfate on the recovery of Mycobacterium chimaera from heater–cooler unit water samples

Mycobacterium chimaera infections: An update