The residual heparin concentration in the autotransfusion system product in cardiothoracic surgery: A pilot study

The clinical perfusionist in the MCL is responsible for the use of the ATS
during CTS. Sometimes, a potential detrimental effect on hemostasis is seen
after retransfusion of the ATS product. Possible residual heparin concentration
after washing is considered. This pilot study aims to explore the residual
heparin concentration in ATS product.

Besides, the optimal intraoperative washing regimen (Popt) is defined by the
perfusion protocol in the MCL. However, variation in practice exists causing
uncertainty regarding the extent (efficiency) to which heparin is eliminated
during the ATS washing process. Therefore, also the relationship between the
washing quantity and the residual heparin concentration in the ATS product will
be examined.

Sometimes, after washing around 700 ml, a message is displayed: minimum quality
reached. This message is based on the transparency of the waste liquid and the
contaminant removal algorithm. The Xtra ATS indicates that at a wash volume of
700 ml, the wash quality may possibly be acceptable. The transparence is
detected by the waste line color indicator, an optical sensor. However, the
wash out of heparin is not mentioned in the Xtra manual or literature (Sorin,
2021). Administration of an ATS product containing heparin could potentially
result in increased bleeding tendency and transfusion requirements.

1.3 Hypothesis
The ATS is very often used during CTS procedures, but only sometimes additional
measures of coagulation are necessary. Besides the experience, the residual
heparin in washed blood in the study of Vieira et al. is <0.1 IU/ml (Vieira et
al., 2021). The study of Overdevest et al. reported the elimination rate of
heparin in the ATS product (98.8%) for the Popt regimen (Overdevest et al.,
2012). In this pilot study, a residual heparin concentration <0.5 IU/ml is
expected with the standard washing quantities (1000 ml), as required by the
AABB guidelines (American Association of Blood Banks, 2013; Buys et al., 2017;
Vieira et al., 2021) .

Sometimes, the Xtra ATS indicates that at a wash volume of 700 ml, the wash
quality may possibly be acceptable. However, the wash out of heparin is not
mentioned in the Xtra manual or literature (Sorin, 2021). For comparison, the
aim is to examine whether there is a difference in residual fraction of heparin
in the ATS product in case of more than the standard volume washing (1000 ml).
Therefore, besides the wash quantity of 700 ml, also 1300 ml is added.

The study of Overdevest et al. compared the Popt and Pstd_P regimens of the
Xtra with regard to residual heparin concentration (Overdevest et al., 2012).
The Pstd_P regimen used a wash quantity of 600, compared with the 1000 ml of
the Popt regimen of the Xtra. Besides the wash quantity in Pstd_P, other
parameters also varied in the study of Overdevest et al. such as prime speed,
wash speed and empty speed (Overdevest et al., 2012). These other parameters
were detrimental to the residual fraction of heparin. Nevertheless, the Popt
and Pstd_P were almost equal in the elimination rate of heparin: 98.8% and 99%,
respectively (Overdevest et al., 2012).

Based on these data and the experience of perfusionists, the null hypothesis is
expected as an outcome, showing no difference in residual concentration of
heparin in the ATS product at the various washing quantities.

The ACT, APTT and anti-Xa determination are all measurements to monitor the
efficacy of UFH (Eikenboom, 2021; Hoffmann et al., 2007; Nguyen et al., 2021).
The ACT is measured on the intrinsic pathway in whole blood and has a higher
measurement range than APTT. Besides UFH, the ACT is prolonged by multiple
factors, such as thrombocytopenia. The APTT is prolonged when there is a
deficiency of at least one CF from the intrinsic pathway, such as UFH
(Eikenboom, 2021; Hammami & Staros, 2021; Hoffmann et al., 2007; Winter et al.,
2017). The current gold standard to measure UFH in citrated human plasma is the
chromogenic anti-Xa assay. Color development is inversely proportional to the
amount of heparin or anti-Xa activity. Hyperbilirubinemia, hyperlipidemia and
hemolysis due to the free hemoglobin can be interfering factors for this test
(Eikenboom, 2021). Therefore, the research hypothesis is that higher residual
heparin concentration (anti-Xa) in the ATS product leads to prolonged APTT and
ACT measurements.

Primary Objective: What is the residual heparin concentration in
autotransfusion system product in cardiothoracic surgery?

Secondary Objective(s):
1. What is the outcome of the anti Xa determination?
2. How much residual heparin concentration does autotransfusion system product
contain after washing with different wash quantities (700 ml, 1000 ml and 1300
ml)?
3. What is the correlation between the APTT and ACT and the concentration of
residual heparin (=anti-Xa) in the autotransfusion system product?

A prospective, single-center, pilot clinical study is performed, with the
primary outcome assessing the residual heparin fraction in the erythrocyte
concentrate obtained by the ATS. The study is executed at the CTS of the MCL.

3.4.1 Collection and processing blood
The study population can be divided into three groups of 15 patients. This sub
population has a certain wash volume of the ATS (700 ml, 1000 ml and 1300 ml).
The standard setting of 1000 ml washing quantity in Popt will be compared with
700 ml and 1300 ml washing quantity. The researcher decides the washing
quantity of the ATS prior to the procedure by randomization. A container
contains 15 tickets with 700 ml, 15 tickets with 1000 ml and 15 tickets with
1300 ml. If the ATS is not used during the procedure, the corresponding ticket
will be returned to the container. The examiner will adjust this quantity on
the ATS. The washing quantity will be taped during the procedure. The
randomization is blind to the surgeon and anesthesiologist.

All measurements will be performed with an ATS from the company LivaNova:
Xtra®. The ATS will be performed according to the program Popt. This regimen
includes two different filling flow rates (400ml/min and 250ml/min) and an
automatic standby mode. This does not require any adjustments to the settings
of the ATS for the measurements, except for the different washing volumes. The
Xtra bowl (225ml) is used for measurements (LivaNova, 2020).

3.4.2 CTS procedure
During the CTS procedure, the Xtra ATS system is connected via a drip chamber
(Aspiration and Anticoagulation line - AAL) with one liter of saline including
50 000 IU heparin. The filter (40µm) of the reservoir (Xres T) is wetted with
saline containing heparin (approximately 100 ml), after which the liquid is
administered dropwise (approximately 1 drop per second) into the reservoir. The
ATS is set to the Popt regimen and Xvac is set to -100 mmHg.

The perioperative heparin administration was standardized. The perfusionist
routinely added 7500 IU of heparin to the CPB circuit prime. The
cardio-anesthesiologist administers 300-350 units/kg of unfractionated heparin
(UFH) as the initial dose at the start CPB, as outlined in the CTS anesthesia
protocol of the MCL (Loos, 2021). Dripping heparinizing saline is stopped by
the perfusionist at complete heparinization (ACT>480 seconds). During the CTS
procedure, ACT values are recorded on the appendix form. The ATS is initiated
when the collection reservoir contains sufficient blood from which
approximately 225 ml of ATS product can be obtained (approximately 500 ml blood
loss excluding saline, depending on the patient*s Hct). During CPB, the
perfusion protocol of the MCL will be followed (Broek, 2021). Study information
will be obtained from each patient, represented in a form in the Appendix. The
ATS washing quantity is filled in later.

After weaning CPB, the ATS is connected to the 3L saline for washing. Then the
ATS product is formed from the aspirated blood in the ATS reservoir. The
perfusionist restarts the dripping heparinizing saline when protamine sulfate
is initiated by the cardio-anesthesiologist (1:1 with initial heparin dose).
After 10 minutes the protamine is administered 2.7 mL of blood will be
collected in a citrate tube for ROTEM measurement and an ACT measurement is
initiated. This ACT value may deviate no more than 10% from the ACT value
before heparin was administered. In case the ACT varies, further correction is
made with protamine. Before the ATS product is infused to the patient, a sample
(4ml) is taken to determine the residual fraction of heparin. Again, after
administering the ATS product, 2.7 ml of blood is collected in a citrate tube
for a ROTEM measurement. Close monitoring of the coagulation and possible
correction with blood products reduces the impact of the possible coagulation
problem. Blood products may be administered even if the patient does not
participate in this study. When a sample is taken from the patient in the ICU,
an APTT value will also be determined in the laboratory.

3.4.3 Anti Xa assay
The MCL Certe will perform the chromogenic anti-Xa test. The results of the
residual heparin fraction will not be displayed in the electronic patient
record (EPD). The measurement will be performed in research setting, with
patient approval.

3.4.4 Standard of care and research
Waste blood, e.g. from wound area, is collected and processed by the ATS. This
allows to produce an erythrocyte concentrate, also called ATS product. This
study differs slightly compared to standard care, because a 4 ml sample of the
ATS product is taken for the anti-Xa test. After the sample is taken, the ATS
product is administered to the patient. In other words, patients receive 4 ml
less ATS product that has collected and processed the waste blood. In addition,
the ATS does not use a standard wash volume of 1000 ml. Patients are randomly
assigned to a wash volume of 700, 1000 or 1300 ml.

Blood (4ml) from the erythrocyte concentrate is sampled during the operation.
The surgical procedure will not take longer when the patient participates in
the study. In addition, the patient does not need to visit the MCL additionally
for this study.

The blood sample (4 ml) of erythrocyte concentrate (minimum 225 ml) does not
cause any side effects. Another wash volume set of the cellsaver may not cause
any urgent side effects. Blood (products) might be administered after surgery
to correct the coagulation. This may be administered even if the patient does
not participate in this study.

Coagulation factors may not be returned to the patient due to centrifugation of
the ATS. Due to the fact that the patient only receives erythrocytes back from
the wasted blood, it is thought that the ATS may affect coagulation after
surgery. Blood (products) might be needed postoperatively because heparin might
still have been present in the erythrocyte concentrate.