Heater-Cooler Unit- an overview about a preventive method to decrease the bioburden- Aydogdu F. et al.

1. 1
University hospital of Ulm
2
Hochschule Furtwangen University
Point Source Infections Related with Heater Cooler Units (HCU)
- an overview about a preventive method to decrease the bioburden
Albrecht G.1
, Aydogdu F. 1
, Sajgo S. 1
, Hildebrandt U. 2
University clinic of Ulm, August 2017, Department of Cardiothoracic and Vascular surgery-
Cardiovascular perfusion technologies,
Ulm, Germany
Abstract
According to the safety prescriptions of the FDA and the
manufacturer of HCU, Liva Nova PLC (formerly Sorin Group
Germany GmbH), the Heater- Cooler- Units were identified as
a source of Mycobacterium chimaera (1), (2). In Switzerland,
two patients were infected with NTM (Non- Tuberculosis-
Mycobacteria) by cardio-thoracic surgery receiving a
prosthetic valve implantation and with lethal ending (3).
By this observation special awareness was taken into
consideration as well as for the manufacturer as for health care
providers, surgeons, hospital staff and last but not least for the
patient.
Key words: Heater-Cooler- Unit (HCU), P. aeruginosa, M.
chimaera, disinfection and cleaning of HCU, micro PES filter
I. INTRODUCTION
An essential part of extracorporeal circuits is a Heater-Cooler-
Unit (HCU), which either cools or warms the blood
temperature during Cardiopulmonary Bypass surgeries. The
HCU from the manufacturer Sorin 3 T includes three water
tanks, which are filled with disinfected water and pass via
external hose system through an oxygenator by a heat
exchanger. By this way it is possible to cool or warm the
blood temperature during cardiothoracic surgeries (4).
While the use of HCU in extracorporeal circuits is unalterable,
they were reported 5 incidents with infections alone Europe,
since 2008 (5). In Switzerland for the first timing in 2011 an
infection was observed with M. chimaera by a contaminated
Heater Cooler- Unit (HCU). Also earlier investigations on a
national level revealed contamination of HCU in 16 out of 78
cardio-thoracic treatment centers (5). Besides of M. chimaera
there were additionally detected P. aeruginosa, L.
pneumophilae, S. maltophilia and mushrooms. The trigger of
this slow growing incident is referable to the responsible
germ, called mycobacteria chymaera. Whereas the germ is
benign in normal environment, it is in a clinical context
getting a potential risk for infections, especially in patients
with immunosupressed status, who were undergone a
cardiothoracic surgery (6).
The purpose of this current work was to detect the source of
the infections associated with Heater-Cooler-Units during
Cardiopulmonary bypass. Furthermore, this current work will
present preventive methods, like disinfection and cleaning of
the Heater- Cooler- Units, including a filter with a pore size of
0.2 µm, which can reduce or in the best case eliminate the
transmission of Mycobacteria into the chirurgical field.
II. MATERIAL AND METHOD
Referring to the safety notices of Liva Nova from July 2014,
which was firstly reported of infections with the germ M.
chimaera, strongly disinfection methods were implemented.
For minimizing a potential risk for possibly contamination of
HCU with M. chymaera there should be observed the
guidelines for product care and maintenance. Health care
providers should take care for additional sources of infection
risk.
The task of this current work was thereby to determine the
efficacy of an additional component- a micro pore size filter,
certified in 2009, which retains the contamination in 3 T HCU
circuits as soon as the quality of disinfection procedures.
Besides of mentioned prophylactic recommendations like
product care and maintenance, an onset of a MicroPES filter
was applicated as an extra precaution. The evaluated filter
consists of a hydrophil polyethersulfon- a polymermembrane
with a permeability of 0.2 µm and a surface area of 0.6 m². The
maximum operating pressure accounts to 1 bar and the
maximum operating temperature to 45 degrees (7). The filter
was installed in HCU between the outlet circuit 1 and outlet
circuit 2 (4).
To come up to the standard of the university clinic of Ulm:
Routine tests of sampling tests from the tanks were checked
and performed by the microbiology laboratory institute of the
university of Ulm. The protocol unit includes an investigation
of the sampling tests, which were obtained from the tanks of
the heater cooler unit – pre filter and post filter. By this way it
is possible to identify the bioburden in each Heater Cooler
Unit. In addition to the effortful disinfection procedure at
Heater- Cooler- Units (HCU) the chief aim is to integrate an
additional component, which eliminates in the best case the
bioburden.

2. III. RESULTS
To get real specifications of the efficacy from integrated filter,
this retrospective investigation was separated in three phases
(8).
Stage 1: As a starting point screening the efficacy of the filter,
for usage of 3T Heater Cooler Units in the university hospital
must be considered regarding to the quantity of
microorganisms. The sampling for tests are taken from the
tanks for determination of the involved microorganisms. An
examination in the microbiological institute of Ulm confirmed
the detection of P. aeruginosa. The results are shown in chart
1.
chart1: Results of detected microorganisms, examined in the
Institute for Microbiology at the University hospital of Ulm
Stage 2: At this stage of assignment for elimination the
bioburden, cleaning and disinfection methods were performed
all 7 days. Additionally new PVC (polyvinyl chloride) hoses
were replaced, the Micro PES 2F PH was integrated and hansa
clutches were disinfected for 24 hours with disinfectant
solution.
According to the operating instructions for disinfection and
cleaning of Heater Cooler Units of Liva Nova, the Heater
Cooler Units were filled with 20 liters filtered, potable water
and swilled with 80 ml Peresal for 10 minutes. After chemical
flushing twice repeated flushing cycles were realised (10
minutes per Heater Cooler Unit).
Finally, as predefined from the manufacturer, 250 ml
hydrogen peroxide was stuffed in the water tank and 20 l
filtered water. An additional component, a micro pore size
filter, which should guarantee an effective retention of
microorganisms, was applicated at this stage of investigation.
The results from the effectiveness of the integrated filter are
shown in chart 2: The retention of P. aeruginosa is
considerably larger as in the case of absence of the filter.
chart 2: Results of remained P. aeruginosa with integrated
filter, examined in the Institut for Microbiology at the
University hospital of Ulm
Stage 3: The procedure for disinfection and cleaning of HCU
was conducted again as described by stage 2. For safety
precaution of colonization with microorganisms, the operating
temperature of HCU was adjust to 20° degree. In accordance
with DIN 16266 there were no qualitative and quantitative
detection of Mycobacteria or P. aeruginosa- naccording to the
inspection report from the Institute for Microbiology in the
university hospital of Ulm (9).
IV. DISCUSSION
After customer safety advisor notices from the manufacturer
LivaNova, firstly reported in 2014, a new origin of potential
risk of infection for immunosupressed patients were identified.
The chief aim of this current work was, ideally, to degerm all
three HCU, which are employed in our university clinic.
In this way it was necessary for an implementation of
optimized procedures for product care and maintenance in
HCU to decrease the bioburden. The manufacturer published
since 2014 safety arrangements continuously and
measurements for decreasing the bioburden. In our
investigation we have tested the efficacy of the conventional
Laboratory
number
source of sample-
taking (OR-
operating room)
microbiological
findings
[CFU/100 ml]
operating room 6
2726 HCU OR 6 - tank >106
P. aeruginosa
2727 HCU OR 6- post
hose system
>106
P. aeruginosa
operating room 5
2728 HCU OR 5- tank >106
P. aeruginosa
2729 HCU OR 5- post
hose system
>106
P. aeruginosa
3002 HCU OR 5- post
filter
>106
P. aeruginosa
3003 HCU OR 6- post
filter
>106
P. aeruginosa
Laboratory
number
source of sample-
taking
microbiological
findings
[CFU/100 ml]
2726 HCU 1 -tank 100 CFU
P. aeruginosa
2727 HCU 1- post filter 20 CFU
P. aeruginosa
2728 HCU 2 - tank no quantitative and
qualitative detection
of P. aeruginosa
2729 HCU 2 – post filter no quantitative and
qualitative detection
of P. aeruginosa
3002 HCU 3 - tank >106
P. aeruginosa
3003 HCU 3 – post filter no quantitative and
qualitative detection
of P. aeruginosa

3. disinfection method and an additional component, a micro
pore size filter, which have passed in an in vitro evaluation
from the producer Membrana GmbH the bacterial challenge
test (10). At the stage 1 of our investigation, all three Heater
Cooler Units were generously contaminated with
P.aeruginosa. Same results were obtained in spite of
application the filter. This was primarily due to contaminated
external hose systems, which were replaced at the stage 2. In
the second phase of our investigation, at stage 2, adjusted heat
transfer fluids were obtained with a 100 CFU per 100 ml. This
quantity is equivalent to drinking water ordinance.
Consequently, our research confirmed the clinical efficacy of
the applied filter.
Currently there are no opportunities given, which retain the
contamination without any external components (10). The
extensive disinfection method is a good basis for cleaning the
water tanks, but based on our investigation at the stage 1 of
our evaluation, it is not clearly effective to eliminate
microorganisms. Especially, P. aeruginosa couldn’t retained
with the disinfection and cleaning methods of HCU.
Considering that the structural conditions in water tanks of
HCU there is not a planar area (12). Therefore, the problem of
germ load is preexisting and generate an appropriate
disinfection procedure. Whereas the attempt in stage 2 of our
evaluation, the implementation of the micro pore size filter
presented a high retention power of microorganisms. For safe
and reliable operation of the Membrana micro pore size PES-
filter, the time interval of 7 days should be observed.
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