Episode Transcript
Hello Anesthesia colleagues,
My name is Dr. Victor Moulin, I am a cardiac anesthesiologist practicing in Houston, Texas. I
was invited by the Anesthesia Toolbox project to put together this podcast on the history of
cardiopulmonary bypass and cardiac surgery.
I volunteered for this topic because it is a really fascinating intersection of technology and
medicine. The historical information provides context to understanding the current technology
and its applications. I really wish someone had given me the historical framework to learn how
it developed while I was going through training. Everything I’ve learned about the history since
has made me more fluent in the operating room when I interact with perfusionists or ECMO
technicians. It also has led me to a better understanding of perfusion physiology. This is such a
critical technology in our current practice environment. It is abundantly clear to me that if we,
meaning humanity, had not developed this technology, we would not be able to support
thousands of patients suffering from influenza and COVID-19 in addition to all the patients
needing cardiac surgery.
In the early part of the twentieth century, which is considered the era when modern surgery
developed, the heart was thought to be too dangerous to operate on by almost all surgeons.
There were a few case reports here and there of good outcomes with daring heart surgeries.
Perhaps one of the most famous examples were the first ever attempted pulmonary
embolectomies, by a German surgeon known as Friedrich Trendelenburg. These surgeries were
unsuccessful, but one of his students reported the first patient to have a full recovery in 1924.
This procedure became known as the Trendelenburg operation. I’ll come back to it later since it
played an important role in the development of cardiopulmonary bypass.
A few decades later, in the 1940s, surgeries for congenital heart lesions, including patent ductus
arteriosus, coarctation of the aorta, Blalock-Taussig shunts, and valvulotomies for valvular
disease were slowly becoming more common Johns Hopkins and the University of Minnesota in
Minneapolis were leading the way. One of the earliest cardiac surgeries was called a mitral
commissurotomy. This involved a surgeon cutting a hole in the left atrium and using a blade or
finger to open a stenotic mitral valve. There were also aortic valvulotomies and pulmonary
valvulotomies either with instruments or manual dilation but results of all these surgeries were
poor. One surgical technique for aortic insufficiency in the pre-bypass era involved sewing a
ball-valve in the descending aorta. A patient that had a left coronary artery that communicated
with the pulmonary artery had a successful repair in 1946. To get around the lack of a bypass
machine, hypothermic cooling of the patient with ice in the chest was used at the time. It
became clear that a machine to replace the heart would be necessary to achieve good and
reproducible outcomes. Replacing the heart and lungs with a machine was a complex
engineering puzzle to be solved. There were three main problems that needed a solution to
create an artificial heart and lungs for cardiac surgery.
The first problem to be solved involved controlling the clotting cascade. Since blood clots when
it stops flowing, an anticoagulant of some kind was needed to use the pump safely. That
anticoagulation would need to be reversed before the patient left the operating room, or else
fatal bleeding would occur. Fortunately, protamine was isolated from salmon sperm in 1874
and heparin was isolated from canine liver tissue in 1916, making this issue manageable.
A reliable pump mechanism for circulating fluid was the second element. Believe it or not, it
was actually the dairy and food industry that provided an inspiration for the technology. In
industrial milk production, they use centrifugal pumps to pump milk from point A to point B.
Inspiration can come from unlikely sources! The most challenging and most essential problem
was that you needed to create a method to replace the human lung, which removes CO2 easily
but has a harder time oxygenating the blood, without a large surface area and hemoglobin.
These three problems and the general principles guided the early inventors and innovators.
Michael DeBakey, the famous heart surgeon, developed a rolling pump mechanism (also known
as a roller pump) while in medical school at Tulane in 1932. Another innovative solution to
creating a reliable pump was using an adult human! This was given the subtle name of “Cross
Circulation”. The idea was to use a parent as a bypass machine for their child needing cardiac
surgery. The child’s deoxygenated blood was given to the parent who then returned
oxygenated blood to their baby. The blood going to the baby was not under high pressure
unfortunately. Dr. Lillehei at the University of Minnesota performed 45 of these operations
with a 40% mortality in 1954. As a parent I can understand why someone would go to that
extreme to help their child, but we are very lucky that real bypass technology now exists and
has become so reliable since that time.
Another method which was tried was called autologous lung bypass, where a right-sided circuit
pumped blood through the lungs and a left side circuit took the outflow from the lungs and
circulated it systemically.
The methods I just described have faded into history, but they taught us what the machine
needed to do to truly support the operation. Luckily Dr. John Gibbon, aka the “father of
modern bypass” at the University of Minnesota invented the world’s first reliable cardiac
bypass machine. The story of how he got there is very interesting.
John Gibbon was a young surgeon who obtained a research fellowship with the Chief of Surgery
at the Massachusetts General Hospital in 1930. In October of that year he had a case of a
patient who needed an open pulmonary embolectomy, also known as the Trendelenburg
procedure I mentioned earlier. The patient was having a massive pulmonary embolus after a
general surgical operation. Dr. Gibbon wrote the following:
"My job that night was to take the patient's blood pressure and pulse every 15 minutes and plot
it on a chart. During the 17 hours by the patient's side, the thought constantly recurred that the
patient's hazardous condition could be improved if some of the blue blood in the patient's
distended veins could be continuously withdrawn into an apparatus where the blood could pick
up oxygen and discharge carbon dioxide and then pump this blood into the patient's arteries. At
8 A.M. the patient's blood pressure could not be measured. Dr. Edward Churchill, the chief of
surgery, immediately opened the chest through an anterior left thoracotomy, then occluded
both the pulmonary artery and the aorta as they exited from the heart. He opened the
pulmonary artery and removed massive blood clots. The patient did not survive"
This terrible experience started his lifelong research. He began experimenting and making
pumps at Mass General for several years, then moved to Philadelphia where he continued his
work. Dr. Gibbon reported in 1937 that only 9 of 142 patients who had undergone the
Trendelenburg operation survived. He served in World War II and afterwards joined the faculty
at Jefferson University. He worked tirelessly in his free time from clinical duties. His wife Mary
Hopkinson was a huge support.
One of his medical students was friends with the IBM chairman of the board in the 1940s. Dr.
Gibbon began collaborating with IBM engineers. They eventually developed the machine they
called the Model 1. It worked well in small animals but could not move volumes large enough
to support a human bypass. Finally, after much trial and error, they developed the machine
they called the Model 2. It had six cylindrical screen oxygenators, with blood interfacing with
both sides. This provided 8 square meters of surface area. It also used three roller pumps that
modified DeBakey’s original roller pump design. It was also 2000 pounds and required 2-3
technicians to operate.
After the machine had reasonable success in dogs, Dr. Gibbon attempted to operate on a 15-
month-old infant, thought to have an ASD. At the time Cardiac Catheterization could not be
done prior to surgery. Unfortunately, the patient died on the table because there no was no
ASD, but rather a large left to right shunt through a patent ductus arteriosus. However, Dr.
Gibbon did not lose resolve, and eventually performed the first successful open-heart surgery
on bypass, which was an ASD Closure of an 18-year-old patient in 1953. The arterial cannula
went into the left subclavian artery, and the venous cannulas were in both vena cavae. The
patient went on bypass for 26 minutes and survived with a good long-term outcome. There
were operations on bypass attempted before this landmark surgery, however those patients
did not survive. Tragically, the same year in 1953 Gibbon attempted ASD repairs in two fiveyear-old girls on bypass. Both of them died intraoperatively, leading Gibbon to declare a
moratorium until his machine could be perfected. On a general note, it took extraordinary
resilience on his part to continue the work to develop the machines when he experienced so
many poor outcomes in children. When physicians are involved in poor outcomes and adverse
events, they can become what is known as “second victims”. Our response as individuals to
these traumas can ultimately decide the trajectory of our entire careers. Dr. Gibbon was clearly
one individual who used adversity to push forward and thrive.
After Dr. Gibbon’s experience others modified and improved the design; the first commercially
used machine was the Mayo-Gibbon machine. It was developed by John Kirklin at Mayo Clinic
and was said to be an improved version of the Gibbon Model II. It used wire mesh screens to
oxygenate.
Another machine which is considered to have greatly contributed to cardiac surgery is the
Lillehei pump with a bubbling oxygenation mechanism. Denton Cooley, another legendary
cardiac surgeon called this machine “the can opener at the cardiac surgery picnic”. Cardiac
Surgery continued on with these technologies, and many of the pioneers of heart surgery
including Michael DeBakey, Denton Cooley, Christian Barnard and others performed thousands
of operations with these machines in the subsequent decades, driving the field forward.
A major step up in terms of mimicking human pulmonary function occurred in the 1980s, when
bubble oxygenators and cylindrical oxygenators were replaced by hollow microfiber membrane
oxygenators. These consist of a very fine mesh with a large surface area in a PVC container.
Gas is delivered through the large surface area of the hollow fiber mesh, and when blood is
moving through it, oxygen gets delivered into the blood. This high efficiency gas exchange
design allows reliably oxygenated outflow, and blood warming and cooling thru a heat
exchange wiring and cooling system. These modern oxygenators greatly enhance the safety of
the pump, and also make it feasible to deliver anesthetic gas through the pump. The anesthetic
for cardiac surgery in the early years was often a mixture of high amounts of narcotics and
paralytics, and so there were numerous issues with recall. This is less of an issue now and the
pump can be trusted to maintain the anesthetic. However, some modern practitioners still use
IV anesthesia to supplement the anesthetic during bypass runs.
Let’s switch gears for a minute and talk a little bit about ECMO. ECMO or extracorporeal
membrane oxygenation, is in widespread use today. It evolved as an extension of
cardiopulmonary bypass. Initially bypass was never longer than six hours. Two patients were
supported for prolonged periods with a bypass machine in the late sixties/early 1970s, leading
to the first NIH randomized controlled study of ECMO from 1972-1975, which showed no
difference in outcomes between adults supported by ECMO vs. conventional ventilation.
However, Dr. Robert Bartlett in Michigan reported the first series of neonates treated for
persistent fetal circulation with ECMO in 1976. ECMO is still used today with good outcomes in
children. The extracorporeal life support organization, or ELSO for short, keeps a national
registry of both adult and pediatric patients receiving ECMO in the USA.
There are functional differences between ECMO Circuits and surgical bypass circuits. Many
people think they are the same, but they are not. Full bypass pumps used in operating rooms
contain a venous reservoir, which allows for volume addition and prevention of air suction by
the pump. They tend to be large and contain other components like anesthetic vaporizers.
They can also support surgery with various suction mechanisms. ECMO circuits, on the other
hand are different from bypass circuits because they are compact, have no additional
components besides the main flow, and do not have pre-pump reservoirs. Both are a
significant improvement over the initial prototypes of the 1950s.
Both ECMO and Surgical Bypass pumps use centrifugal pumps, which have a plastic cone or
impeller mounted inside plastic housing. The impeller runs by magnetic coupling to the motor
directly underneath. The pressure gradient of blood moving at different velocities creates the
driving pressure. It works faster when the afterload is low, and slower when afterload is high;
therefore, it can be described as afterload sensitive. The short-term circuits such as
cardioplegia pumps used in surgical bypass use roller pumps. These pumps contain a rolling pin
mechanism that pushes the blood forward regardless of the afterload.
The increase in complexity and sophistication of the machinery, combined with improved
surgical techniques has almost certainly translated to better patient outcomes. Of the four
bypass cardiac operations I described performed by Dr. Gibbon from 1952-1953, only one
patient survived. In 2014, a retrospective review of 18000 cardiac operations found a total
mortality of 3.4%. Furthermore, surgery for mitral, pulmonary and tricuspid valve repair has
become much safer thanks to improved surgical techniques and the ability to go on bypass.
Aortic valvular and vascular repairs were made possible by bypass, although aortic valve
replacement surgery is now moving in the general direction of transcatheter replacement
across the board. Even the transcatheter replacement cannot be performed without a bypass
machine on backup. The story of the creation of cardiopulmonary bypass is a great
achievement of engineering and medicine.
You can find a copy of this script and some other supporting materials on the website. Other
items from the Toolbox which may be of interest to complete your understanding of bypass
include CV Podcast 12 and Online modules 8.1, 8.2, 26, and 29. Thank you for listening to this
Anesthesia Toolbox Podcast on the history of Cardiopulmonary Bypass.
