| Study Summary: |
|
Background:
Cardiopulmonary bypass (CPB) consists of an extracorporeal (outside of the body) circuit
which allows the circulation and oxygenation of blood during cardiac surgery. The circuit
includes an oxygenator, a reservoir and tubing, all of which needs to be primed with a
balanced electrolyte solution. Prior to initiating CPB, the venous and arterial ends of the
CPB circuit are appropriately attached to the patient. The volume of the circuit is usually
1.5 liters which is equivalent to 30-38% of a typical patient's total blood volume that is
generally between 4 and 5 liters.
When CPB is initiated, the patient's blood is mixed and diluted by the CPB priming fluid.
Consequently, when the operation is completed and the CPB is discontinued, the content of
the CPB circuit consists of the patient's diluted whole blood. The standard practice is to
return as much of this hemodiluted CPB contents as the patient will accommodate and process
the rest of the contents of the circuit with a cell washer and return packed red blood cells
to the patient.
When the cell washer is used, plasma proteins, clotting factors and platelets are not
returned to the patient. An alternate approach would be to use an ultrafiltration device to
remove this non-cellular water and preserve proteins,
clotting factors and platelets as well as red blood cells that can then be returned to the
patient. This alternate approach is the basic principle of the Hemobag®, an ultrafiltration
technology and method.
Ultrafiltration is a well documented technique usually used in-line (interposed in the
circuit) during CPB. The Hemobag® is a collection reservoir used to facilitate
ultrafiltration of the CPB circuit after the patient has been disconnected from CPB). It
represents a novel and safe modification of the modified ultrafiltration system (MUF). MUF
is a technique commonly used in cardiac surgery for many years, especially with smaller
hemodiluted patients, and mainly in the pediatric population.
The focus of the Hemobag® system is on whole blood volume recovery as opposed to red cell
volume recovery only, and helping to satisfy the requirements of the patient after CPB has
been discontinued: hemostasis, reversal of dilutional effects, and returning back to
homeostasis, which is the normal physiologic and metabolic status of the patient.
The investigators hypothesize that the Hemobag® method of returning residual CPB blood is
superior to the current practice of cell washing and concentration. This hypothesis is
based on previous studies that have shown that the ultrafiltrated whole blood product is
superior to the cell-washed RBC product. The main purpose of this study is to discover the
differences in outcome measures when, at the end of CPB, the residual diluted pump blood is
processed by either cell washing or by the Hemobag® method. The null hypothesis states that
there would be no difference in post-operative patient outcomes when residual pump blood is
processed by either a cell washing method or the Hemobag® protocol.
Pilot Study:
The investigators did an Maine Medical Center (MMC) Institutional Review Board
(IRB)-approved pilot study in March 2011 which consisted of ten (10) cases in order to
confirm the significant treatment effect shown in other studies and to familiarize the team
with the Hemobag® system. Outcome metrics included chest catheter drainage in the first 24
hours post-operative, allogeneic blood component requirements (red blood cells (RBC's),
platelets, plasma), platelet counts, evidence of acute kidney injury by the Acute Kidney
Injury Network (AKIN) definition, mortality, stroke, and requirements for inotropic support
on the second post-operative day. The results of the pilot study showed a promising trend
with regard to less chest catheter drainage and higher platelet counts.
Materials and Methods and Analysis:
The investigators propose to do a randomized, controlled trial comparing the two methods as
described above: The standard method of returning the residual pump volume to the patient
as washed, centrifuged cells (control group) and the Hemobag® method of returning residual
CPB blood (study group).
Outcome metrics will be the same as they were for the pilot study:
(1) Chest catheter drainage in the first 24 hours post-operative; (2) Allogeneic blood
component requirements (RBC's, platelets, plasma); (3) Pre and post operative platelet
counts; (4) Evidence of acute kidney injury by AKIN definition; (5) Mortality; (6) Stroke;
(7) Requirements for inotropic support on the 2nd post-operative day.
The investigators propose to enroll 100 patients, 50 in the control group and 50 in the
study group. The study will be limited to adults (18 years and older) who have heart
surgery (valve and /or coronary) using CPB who do not have anemia or coagulation disorders
preoperatively.
An interim analysis will be performed by an independent, unblended analyst to determine
efficacy and safety half way through the study (50 patients). Terminating the study early
would be a consideration if one group were clearly superior to the other or if there were
safety issues. In the event that there are no concerns regarding superiority or safety, the
study would continue until the entire sample size has been studied. The results of the
interim analysis will be submitted to the IRB.
Conclusion:
There are a number of intra-operative blood management strategies in cardiac surgery and the
salvage of post-CPB whole blood using ultrafiltration from the CPB circuit is emerging as
one of the most significant contributors to reducing allogeneic blood component use in
cardiovascular surgery. The investigators hypothesize that the Hemobag® method of returning
residual CPB blood is superior to the current practice of cell washing and concentration and
more expeditious than modified ultrafiltration (MUF).
|