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A. Dabbagh et al. (eds.), Postoperative Critical Care for Cardiac Surgical Patients,
DOI 10.1007/978-3-642-40418-4_12, © Springer-Verlag Berlin Heidelberg 2014
Abstract
Development of the cardiopulmonary bypass (CPB) technology in the second
half of the twentieth century was one of the most important medical events and
was responsible of cardiac surgery basis and provided the condition to operate on
a completely motionless, bloodless heart. It fulfi lls the role of the heart (and
M. Foroughi , MD
Cardiovascular Research Center , Shahid Beheshti University
of Medical Sciences , Tehran , Iran
e-mail: mahnoosh.foroughi@gmail.com, m_foroughi@sbmu.ac.ir
1 2
Postoperative Considerations
of Cardiopulmonary Bypass in Adult
Cardiac Surgery
Mahnoosh Foroughi
Contents
12.1 Cardiopulmonary Bypass Circuit Structure .................................................................. 296
12.1.1 History ............................................................................................................. 296
12.1.2 Blood Circuit ................................................................................................... 297
12.1.3 Cardiotomy ..................................................................................................... 298
12.1.4 Membrane Oxygenator ................................................................................... 298
12.1.5 Anticoagulation ............................................................................................... 299
12.1.6 Cannulation ..................................................................................................... 299
12.1.7 Cardioplegia .................................................................................................... 299
12.1.8 Heat Exchanger ............................................................................................... 300
12.1.9 Arterial Filter .................................................................................................. 300
12.1.10 Minimized Extracorporeal Circulation ......................................................... 300
12.1.11 Ultrafi ltration ................................................................................................. 301
12.2 Cardiopulmonary Bypass-Related Complications ........................................................ 301
12.2.1 Infl ammation ................................................................................................... 301
12.2.2 CPB and Hematologic Effect .......................................................................... 302
12.2.3 CPB and Kidney.............................................................................................. 302
12.2.4 CPB and Lung ................................................................................................. 303
12.2.5 CPB and CNS ................................................................................................. 304
12.2.6 Off-Pump Coronary Artery Bypass ................................................................ 305
References ................................................................................................................................ 306
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lungs) by preserving the systemic circulation. Since the fi rst initial machine, evo-
lution from cross-sectional technique till to minimal extracorporeal circulation
continues. From there CPB has been the main part of heart surgery. As improved
knowledge in pathophysiology of cardiopulmonary machine effects, efforts led
to make new extracorporeal technology. Although it simplifi es cardiac surgery,
CPB by itself induces a systemic infl ammatory response syndrome, mostly due
to blood contact with artifi cial surfaces. It causes activation of coagulation, fi bri-
nolytic cascade, complement, leukocyte, upregulation of proinfl ammatory cyto-
kines, and production of oxygen free radicals and alters nitric oxide metabolism.
Nearly all organs can be affected by these changes. The fi rst section describes the
parts of cardiopulmonary machine. The issues of most organs involvement dur-
ing CPB are addressed in the second section.
12.1 Cardiopulmonary Bypass Circuit Structure
12.1.1 History
In spite of other fi elds of surgery, cardiac surgery was suspended for centuries due
to lack of knowledge and technology. What was the cause of this slow and delayed
evolution?
The lack of its requirements:
1. Inability to preserve systemic circulation independent to heart contraction
2. Need to preserve adequate systemic anticoagulation that could be reversed at the
end of the operation
3. Need a method to exchange and correct blood gases during the operation, inde-
pendent to lung function
The introduction of the heart–lung machine in 1953 and development of cardio-
pulmonary bypass allowed the surgical treatment of intracardiac diseases possible
and become a standard part of cardiac operation; its development has a prolonged
evolution way from concept of extracorporeal circulation (Le Gallois in 1812) to the
Theodor Billroth opinion in 1881 “No surgeon who wished to preserve the respect of
his colleagues would ever attempt to suture a wound of the heart,” to the fi rst heart
surgery using CPB by John Gibbon in 1953, signifi cant refi nement since then till to
the present trend of minimal extracorporeal circulation. Pump structure: the cardio-
pulmonary bypass machine is equipment that provides mechanical circulatory sup-
port of the heart and lungs. The machine consists of pumps, membrane oxygenator,
venous and arterial cannula, polyvinyl chloride (or silicone tubing), reservoir cardi-
otomy, and heat exchanger. This section discusses in brief the ingredients of cardio-
pulmonary bypass system for better understanding for postoperative care of cardiac
surgery patients considering the related different viewpoints regarding the issue
(Galletti 1993 ; Evora et al. 1995 ; Moen et al. 1996 ; Nolan et al. 1997 ; Stammers
1997 ; Shigeta et al. 1999 ; Edmunds 2002 ; Paparella et al. 2002 ; Litwak 2003 ;
McLaughlin and Dunning 2003 ; Raymond et al. 2003 ; Chew 2004 ; Teoh et al. 2004 ;
Thanikachalam et al. 2004 ; Daly et al. 2005 ; Raja and Dreyfus 2005 ; Salzberg et al.
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2005 ; Boodhwani et al. 2006 ; Martens et al. 2006 ; Skinner et al. 2006 ; Apostolakis
and Akinosoglou 2008 ; Campos and Paniagua 2008 ; Hirleman and Larson 2008 ;
Spiess 2008 ; Boodhwani et al. 2009 ; Halkos and Puskas 2009 ; Vohra et al. 2009 ;
Apostolakis et al. 2010 ; Sellke et al. 2010 ; Sobel 2010 ; Buffolo et al. 2011 ; Chauhan
and Subin 2011 ; El-Essawi et al. 2011 ; Krane et al. 2011 ; Weisse 2011 ; Beckmann
et al. 2012 ; Hausenloy et al. 2012 ; Papadopoulos et al. 2013 ).
12.1.2 Blood Circuit
In normal condition, blood enters the heart in the right atrium and passes through
the right ventricle. From there the blood leaves the heart into the lungs where carbon
dioxide is extracted from the blood and substituted by oxygen. Then the blood is
sent back into the left atrium, enters into the left ventricle, and injected into the aorta
where it transfers to the systemic circulation. The cardiopulmonary bypass acts
nearly the same performance outside of the body. At the beginning of the operation,
CPB tubing is primed by crystalloid solution. Colloid solutions, mannitol, sodium
bicarbonate, heparin, and sometimes blood are prime additives. Venous line removes
blood by means of gravity or siphonage from right side of the heart and returned it
in oxygenated form to the systemic circulation via arterial line by pump. Pump acts
like a ventricle. There is two type of pump: roller and centrifugal.
12.1.2.1 Roller Pump
This pump consists of two rollers placed on the ends of a rotating arm, opposite to each
other. It has occlusive nature. The rollers rotate and engage the tubing which is then
compressed against the pump’s housing, propelling blood ahead and forward fl ow is
induced (Fig. 12.1 ). The fl ow rate is determined by the diameter of the tubing and the
rotation rate of the rollers. It is not dependent to preload and afterload. The fl ow rate of
2–2.4 L/m
2
/min is suffi cient for adequate systemic perfusion, with consideration of
patient’s temperature. Optimal perfusion targets remain to be in controversy, but it is
recommended to preserve mean arterial pressure 50–70 mmHg, CVP < 5 mmHg,
hematocrit more than 20 %, and mixed venous saturation >65 % during CPB.
Fig. 12.1 Roller pump
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12.1.2.2 Centrifugal Pump
In plastic housing, a complex of plastic cones coupled magnetically to an electric
motor. They rotate rapidly; by creating a pressure gradient between the inlet and
outlet of the pump, kinetic energy is transferred to blood and resulting forward
blood fl ow (Fig. 12.2 ). In spite of roller pump, centrifugal pump is non-occlusive;
therefore fl ow rate is dependent to preload and afterload too.
12.1.3 Cardiotomy
A fi ltered reservoir collects blood drained from the venous circulation. It is for stor-
age, defoaming, and fi ltration before added directly to arterial circuit. Other fl uid
such as blood products and medication may also be added.
Reservoir designs include open or closed systems. The open system (hard shell)
has graduated lines that shows amount of blood volume in the container. The design
is open to atmosphere, allowing blood interface with atmospheric gases possible. In
the closed system, the soft pliable bag eliminates the air–blood interface. Volume is
measured by weight or by change in radius of the container.
12.1.4 Membrane Oxygenator
A fl at sheet of hollow fi bers imitates the pulmonary capillary function, by interpos-
ing a thin membrane between blood and gases, and creates gas–blood interface gas
without blood passing. Gas fl ows through the hollow fi ber and blood fl ow is around
Fig. 12.2 Centrifugal pump
M. Foroughi
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the fi ber. In spite of carbon dioxide, oxygen is not diffusible in plasma well, so the
blood is spread very thin to facilitate the transfer of oxygen by increased gradient
pressure.
12.1.5 Anticoagulation
Unfractionated heparin is used to achieve adequate systemic anticoagulation, by
measuring activated clotting time (ACT) ≥400 s. It remains the absolute choice of
anticoagulant in cardiac surgery. Heparin is obtained from lung beef and or porcine
intestinal mucosa. It isn’t an anticoagulant itself but could potentiate the antithrom-
bin III (AT), a potent endogenous anticoagulant of body.
Heparin is given in the bolus dose of 2.5–4 mg/kg to aim an ACT of 400–480 s,
before aortic and venous cannulation. Additional heparin is repeated to maintain
ACT above 400 s during CPB, for adequate anticoagulation state.
An inadequate response to heparin (heparin resistance) may be seen in patients
with long preoperative heparin use; this condition is corrected by FFP or recombi-
nant AT administration.
At the end of operation, after CPB weaning it is reversed by protamine (isolated
from fi sh sperm) to establish normal hemostasis condition after surgery. There are
some ways to determine the protamine dose: protamine titration, fi xed dose of prot-
amine (in the ratio of 1.2–1.5 mg for 100 unit of heparin previously administered),
ACT/heparin dose response curve, and heparin concentration. Protamine has mild anti-
coagulant effect too and inhibits platelet-induced aggregation. Although it has short
half-life, but care should be taken not to infuse protamine too fast as it can induce sys-
temic hypotension due to systemic vasodilation and pulmonary vasoconstriction.
Heparin rebound, a state of recurrent anticoagulant activity of heparin after ade-
quate protamine administration, contributes in postoperative bleeding. Because not
all of heparin is bounded to protamine, some of it binds to other plasma proteins and
vascular cells, reappearance in circulation gradually.
12.1.6 Cannulation
Arterial and venous cannulation sites are infl uenced by the planned operation. In rou-
tine valve and coronary surgeries, the ascending aorta and right atrium are selected.
Alternative sites of arterial cannulation are the femoral artery, axillary artery, and left
ventricular apex. Cannulation site for venous access can be the inferior and superior
vena cava, femoral vein, and internal jugular vein. Cannula is made from clear poly-
vinyl chloride, the oxygenator casing and connections are from polycarbonate.
12.1.7 Cardioplegia
A blood-free and motionless operative fi eld is obtained by potassium-based car-
dioplegic solution that causes diastolic electromechanical arrest. In addition to stop
12 Postoperative Considerations of Cardiopulmonary Bypass
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electrical and consequently mechanical activation, preserving myocardial function
and attenuating ischemic–reperfusion injury are other main goals of it. Cardioplegic
solution can be categorized according to the type of solution (crystalloid vs. bloody),
temperature (cold vs. warm), infusion type (antegrade into aortic root vs. retrograde
through coronary sinus), and infusion interval (continuous vs. intermittent).
12.1.8 Heat Exchanger
The heat exchanger is used in combination with the oxygenator. This device is typi-
cally placed just before the oxygenator, because it helps to prevent bubble forming
in the blood too. Heat exchanger controls the body temperature by heating or cool-
ing blood passing through the circuit, at the beginning and end of CPB, respectively.
In heat exchanger, the blood and water lines are separated by a metallic barrier. As
the water temperature is changed, the blood temperature which enters the body
circulation and the tissue temperature change. There is a consensus on protective
effect of hypothermia for organ function during ischemic period. Hypothermia
reduces oxygen consumption and metabolic rate. Even mild hypothermic condition
can increase brain tolerance against ischemic injury. Although it is associated with
side effects such as induced coagulopathy and leftward shift of oxygen–hemoglobin
dissociation curve. Acid–base balance is affected by hypothermia, too. Depending
on the type of operation, the patient’s temperature may be kept normothermic to less
than 20 °C. Monitoring the blood temperature during the operation and the speed
and temperature of rewarming is mandatory. Rewarming too great or too quickly
may affect important problems. Hyperthermia during rewarming period is known to
intensify ischemic damages especially in the brain and kidney.
12.1.9 Arterial Filter
Inclusion of arterial fi lter in CPB circuit is used to reduce microembolic events. It
holds air bubble, particles of platelet aggregation, and thrombus during CPB.
12.1.10 Minimized Extracorporeal Circulation
Minimized extracorporeal circulation (MECC) is an alternative to conventional
CPB. It consists of a membrane oxygenator, centrifugal pump, and arterial fi lter. It
includes short heparin-coated circuit, less prime volume, and no cardiotomy suction
and venous reservoir, thus the blood–air interface is limited, while conventional
CPB circuit is an open circuit because of free contact of blood–air. The shed blood
is washed through cell-saving device before return to arterial line. It seems that
these differences lead to attenuate the adverse effect of conventional CPB: less
infl ammatory response, reduced hemodilution (and therefore less need to blood
transfusion), and less changes in hemostasis system; some studies showed cardiac
M. Foroughi
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surgery with MECC is associated with less postoperative neurologic defi cit, less
need for blood transfusion, and less postoperative bleeding.
12.1.11 Ultrafiltration
Ultrafi ltration removes water and low molecular weight materials from blood to a
fi ltrate part under hydrostatic pressure through hollow-fi ber semipermeable mem-
brane. Ultrafi ltration is used during cardiac surgery to reduce total body water,
attenuate hemodilution during pump and need to transfusion, and remove infl am-
matory mediators. Hemodilution is inevitable at the beginning of CPB. There is a
mixture of patients’ blood with prime content of CPB tube at the beginning of CPB,
inducing acute hemodilution. Although hemodilution decreases blood viscosity and
facilitates tissue perfusion in hypothermic setting, studies have shown that intraop-
erative hematocrit less than 23 % is associated with interstitial edema (decreased
oncotic pressure) in vital organs and increased mortality; it decreases blood transfu-
sion requirement. There are two main types of ultrafi ltration. Conventional ultrafi l-
tration is done only during CPB, and modifi ed ultrafi ltration is performed after CPB
weaning to concentrate plasma volume.
12.2 Cardiopulmonary Bypass-Related Complications
12.2.1 Inflammation
Cardiopulmonary bypass and blood contact with synthetic surface of CPB circuit
can promote whole-body systemic infl ammatory response that plays a role in mul-
tiorgan failure. Continuous exposure of heparinized blood to foreign surfaces in the
perfusion circuit and nonendothelial cells in the wound provoke complement ana-
phylatoxins, adhesion molecules, proinfl ammatory cytokines, vasoactive sub-
stances, coagulation, and fi brinolytic activation. In addition, ischemic–reperfusion
injury (due to aortic clamp and declamping), endotoxemia (due to splanchnic hypo-
perfusion), hypothermia, surgical trauma, blood loss, and transfusion may contrib-
ute in activation of infl ammatory cascade. Leukocyte activation, especially
neutrophil, is responsible to initiate the release of infl ammatory mediators that have
negative impact in all organs. The severity of this exaggerated response can range
from being barely clinically detectable to respiratory failure, coagulopathy, and
multiorgan dysfunction. There are suggested strategies to attenuate infl ammatory
response, though there is not a consensus regarding their clinical outcome and ben-
efi ts; these include heparin-coated circuit, corticosteroids, hemofi ltration, leukocyte
depletion, minimized extracorporeal circulation, aprotinin, complement inhibitors,
free radical scavengers, and antioxidants (Miller and Levy 1997 ; Paparella et al.
2002 ; El Kebir et al. 2005 ; Raja and Dreyfus 2005 ; Patel and Ghatak 2008 ; Warren
et al. 2009a , b ; Rimmele et al. 2010 ; Augoustides 2012 ; Dieleman et al. 2012 ;
Hausenloy et al. 2012 ).
12 Postoperative Considerations of Cardiopulmonary Bypass
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