Lupine Publishers | LOJ Medical Sciences
Opinion
Heart-lung machine
(HLM), also called oxygenator pump or cardiopulmonary bypass (CPB) pump (Figure
1), aims to provide extracorporeal circulation (ECC) with maintenance of
oxygenated blood flow to the body organs when the device is connected to the
arteriovenous system. The HLM is an essential component of openheart surgery to
bypass the circulatory system of the heart and lungs, termed CPB. The main
principle is to draw the blood from the major veins (venae cavae) to an
oxygenator in the HLM where it is re-oxygenated, and then pumped into the
arterial system (ascending aorta). Additionally, the myocardial contractility
during CPB can be halted by running a cardioplegic solution containing
potassium citrate. The initial concept to constitute an artificial circulation
and hence CPB was stated in the 19th century on the basis that the
contractility of muscle could be restored by perfusion of an oxygenated blood
under pressure to enable better perfusion of isolated organs. Therefore, there
was a need to develop an artificial heart-lung system to perfuse an oxygenated
solution without interruption of blood flow, which became a real in the
beginning of the 20th century after discovery of the ABO blood group system to
reduce inconveniences of incompatibility, in addition to discovery of heparin
to inhibit coagulation [1].
Nowadays, no one can
ignore the great clinical role of heartlung machine (HLM) in the development
and progress of cardiac surgery, since the first successful clinical use of CPB
by John Gibbon Jr on 1953. The practical routine uses of CPB for open heart surgery
began in 1955, thanking to the efforts of John Kirklin and Walton Lillehei [2].
Thereafter, many technical and practical advances occurred in HLM and perfusion
science in line with advancements in anesthesia and cardiac surgery, to reach
about seven decades after its first clinical application with contemporary
important developments and promising future. Since its incorporation for
cardiac surgery, subsequent important developments have been driven to HLM and
CPB. The improvements allowed an increase in the operative time, better
myocardial protection, and extension of open-heart surgery to include patients
at extreme age or those who have inoperable conditions [3]. The oxygenators of
HLM have passed by many transitions from disposable biologic oxygenators in
1960s, to microporous polypropylene oxygenators in 1970s, hollow-fiber
oxygenators in 1980s and 1990s, nonporous true diffusion membrane in 2000s, and
more recently screen microfilters to eliminate the need for a separate arterial
line. The initial Sigmamotor finger pumps arterial pumps were replaced by
roller pumps, centrifugal pumps, and pulsatile mode pumps. In addition, the
technical advances in HLM and CPB include improvements in arterial cannulation,
venous drainage and cannulation, temperature management, anticoagulation
therapy, hemofiltartion, organ preservation, brain protection, and monitoring
[4].
The developments in the
ECC technology, particularly the use of centrifugal pumps and nonporous true
diffusion membrane, lead to development of partial CPB termed extracorporeal
membrane oxygenator (ECMO) to prolong life-support systems for patients with
heart and/or lung failure [5]. Currently, ECMO is used as a technique to treat
critically ill patients with cardiogenic shock and cardiac arrest, to obtain
worldwide use of ECMO further improvements in circuit design, oxygenator
technology, and portability are required [6]. Despite seven decades of
continuous improvements in ECC and HLM, the device was not without its faults
because of the possible complications related to inflammatory response,
hemodilution, coagulation abnormalities, cerebral dysfunction, and endothelial
damage. Multiple strategies have been introduced to reduce the severity of the
associated systemic inflammation and organ dysfunction, including
anti-inflammatory drugs, novel pharmacologic components of the CPB, and
modified surgical techniques, but the efficacy of these strategies is
controversial [7,8]. To avoid the unfavorable consequences during coronary
artery bypass grafting (CABG), exclusion of CPB namely off-pump coronary artery
bypass (OPCAB) have been advocated and widely used since its introduction on
1990s [3,9].
Despite the theoretical
benefits of OPCAB in reduction of myocardial injury, stroke, neurocognitive
impairment, and cardiac mortality, comparisons of OPCAB with on-pump CABG
showed favorable short-term and doubtful long-term outcomes. In comparison to
on-pump CABG, the benefits of OPCAB regarding reduced need for blood
transfusion and reduced postoperative hospital stay may be outweighed by the
risk of incomplete ineffective revascularization, with current decline in the
worldwide rates of OPCAB [9]. A debate remains regarding the use of HLM as it
is an essential element of cardiac surgery, but its use is still faced by some
limitations which may constitute more challenges for future investigations. In
other words, CPB has a rapid evolution since the clinical introduction of HLM
until the current remarkable safety but its perfection is still pending.
In conclusion, invent of
HLC with development of CPB constitute the real breakthrough for cardiac
surgery. Through approximately seven decades, the clinical evolution of HLM and
CPB with a reduction of its early complications encouraged the performance of
more cardiac procedures and the involvement of more population in open heart
surgery including those with comorbidities and advanced age. However, the
complications of CPB remain possible in relation to the associated hemolysis
and inflammatory response which indicates more future work to eliminate any
intricacy.
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