Thrombocyte function and the relationship to blood loss and need for transfusion during coronary artery bypass surgery.

Cardiothoracal surgical procedures as coronary artery bypass grafting (CABG)
are frequently accompanied by transfusions. Several studies have shown that
extensive transfusion during and after the procedure is associated with a
reduced prognosis of the patient. Risk factors that attribute to this are
transfusion reactions, infections and immune suppression.

Several procedural issues (use of extracorporal circulation, hypothermia,
haemodilution etc) reduce the thrombocyte function during the operation.
Moreover, use of aspirin and clopidogrel result in an acquired
thrombocytopathy, additionally reducing the functionality of the thrombocytes.
To prevent bleeding events thrombocyte concentrates are frequently transfused,
predominantly in patients using clopidogrel. The transfusion is based on
estimated and expected blood loss and not on laboratory testing of thrombocyte
function. As the response of thrombocyte function on clopidogrel is highly
variable, it is expected that many patiënt are transfused without adequate
indication.

Nowadays several laboratory techniques are available that can be employed to
estimate the thrombocyte function during the CABG-procedure. Established
techniques are Light Transmission Aggregometry (LTA), thromboelastografy (TEG)
and Multiple Electrode Aggregrometrie (MEA). Also, a new application has
recently been launched for the Platelet Function Analyzer (PFA100) to
specifically determine the effect of clopidogrel on platelet function. These
techniques can potentially be used to measure thrombocyte function during the
CABG-procedure and to base an effective thrombocyte transfusion decisions on,
for an optimal patient care.

The analysis is performed of thrombocyte function before, during and and after
CABG surgery with dedicated tests as Light Transmission Aggregometry(LTA),
thromboelastography (TEG), Multiple Electrode Aggregrometry (MEA) en Platelet
Function Analyzer (PFA100) . De predictive value is determined of the separate
testing procedures for peri- en post-operative blood loss and the number of
transfused blood products. Calculations are performed in a patient group that
has been treated with clopidogrel until the day of the procedure (in
combination with aspirin) and in a patient group that has not been treated with
clopidogrel for at least 5 days before the procedure and has only been treated
with aspirin.

Monocenter, prospective, observational investigation

The burden during the study exists of blood sampling from mostly an arterial
line on tree time points:
1. Before start of the surgical procedure.
2. Meteen Immediately after the surgical procedure after antagonisation of
heparin
3. Later after the surgical procedure after arrival at the ICU