Heart-Lung Machine
• What is a Heart-Lung Machine?
• Cardiopulmonary bypass (CPB)?
• Pump-oxygenator?
• It is a technique that temporarily takes over
the function of the heart and lungs during
surgery.
• It maintains the circulation of blood (blood
flow) and the oxygen content of the body
(respiration) for the patient while the heart is
stopped.
When We Use Heart-Lung Machine?
• It is commonly used in operations requiring
the opening of the chambers of the heart to
support the circulation during the heart
surgery period because of the difficulty of
operating on the beating heart.
• Cardiac valve repair and/or replacement.
• Repair of heart defects.
• Transplantation (heart transplantation, lung
transplantation, heart–lung transplantation).
Heart-Lung Machine History
• The first known operation involving open
heart with temporary mechanical takeover of
both heart and lung functions on April 5, 1951
at the University of Minnesota Hospital. The
patient did not survive due to an unexpected
complex heart defect.
• The first successful open heart procedure on
a human utilizing the heart lung machine was
performed on May 6, 1953 at Thomas
Jefferson University Hospital in Philadelphia.
Basic look
Main Components
• The Heart-Lung machine consists of two main
functional units, the pump and the
oxygenator which remove oxygen-deprived
blood from a patient's body and replace it
with oxygen-rich blood through series of
hoses.
Pumps:
• It typically includes up to five pumps
assemblies. A pump can be used for
circulation of the blood. The four remaining
pumps provide fluid and gas for delivery or
removal to the heart chambers and surgical
field.
• An additional pump is available for emergency
backup of the arterial pump in case of
mechanical failure.
1- Roller Pump:
The pump console usually comprises several
rotating motor-driven pumps that "massage"
tubing. This action gently propels the blood
through the tubing.
2- Centrifugal Pump:
By altering the speed of revolution (RPM) of
the pump head, blood flow is produced by
centrifugal force. Centrifugal Pumps are
considered to be superior to roller pumps
because it is thought to produce less blood
damage and for the maintenance and control
of blood flow during CPB
• Both pumps can provide pulsed, as from a
heartbeat, or non-pulsed blood flow to the
systemic circulation.
Oxygenator (The artificial lung):
• The oxygenator is designed to transfer oxygen
to infused blood and remove carbon dioxide
from the venous blood.
1- Bubble Oxygenator:
• The venous blood is passed up a vertical
column through which bubbles of oxygen are
rising. Oxygen enters the blood and carbon
dioxide is released.
2- Membrane Oxygenator:
• Uses a thin semi-permeable membrane to
separate the blood and gas phases.
• Membrane oxygenators have supplanted
bubble oxygenators since the 1980s.
A- Heparin-coated Membrane Oxygenator:
• It is a new type which is believed to produce
less inflammation and decrease the
propensity for blood to clot in the CPB circuit.
Other Components
Tubing:
• The components of the CPB circuit are
interconnected by a series of tubes made of
silicone rubber or PVC (Polyvinyl chloride is
the third most widely produced plastic).
Cannulae:
• A cannula (plural cannulae) or canula is a tube
that can be inserted into the body.
• Multiple cannulae are sewn into the patient's
body in a variety of locations, depending on
the type of surgery.
• A venous cannula removes oxygen deprived
blood from a patient's body. An arterial
cannula is sewn into a patient's body and is
used to infuse oxygen-rich blood.
Cardioplegia:
• It is a separate circuit for infusing a solution
into the heart itself to produce cardioplegia
(i.e. to stop the heart from beating), and to
provide myocardial protection (i.e. to prevent
death of heart tissue).
Venous reservoir :
• Buffer (atrium)
• Air trap
• Defoaming
• Air filtering
• Suction blood
• Fluids
• Medication
• Emptying patient
• Reaction time!
Components
The machine may consist of:
• 1. venous and arterial cannula (tubes),
• 2. polyvinyl chloride (PVC) or silicone tubing,
• 3. reservoir (to hold blood),
• 4. membrane oxygenator,
• 5. cardiotomy (filtered reservoir),
• 6. heat exchanger(s), tubes are placed in a water bath,
• 7. pump(s), typically includes up to five pump assemblies.
• 8. flow meter,
• 9. inline blood gas and electrolyte analyzer,
• 10. pressure-monitoring devices.
Operational Aspects
Blood Loss Reduction:
• Any blood which escapes the circulation and spills
into the operating field around the heart can be
suctioned and returned to the pump.
• This feature is made possible because the blood has
been rendered incapable of clotting by large doses of
heparin.
• Returning blood into the heart-lung machine greatly
preserves the patients own blood stores throughout
the operation.
Control Body Temperature:
• The patient body temperature can be
controlled by selectively cooling or heating the
blood as it moves through the heart-lung
machine.
• Thus the surgeon can use low body
temperatures as a tool to preserve the
function of the heart and other vital organs
during the period of artificial circulation.
Medications during surgery:
• The bypass pump has connectors into which
medications and anesthetic drugs can be
given.
• In this way, medications arrive to the patient
almost instantly by simply adding them to the
blood within the heart-lung reservoir.
Specialized Technicians (The Perfusionist):
• The machine is attended to at all times by a
specialized technician, called the perfusionist.
• Each heart operation requires a dedicated and
trained perfusionist to manage all aspects of the
heart-lung machine during the time period of
artificial circulation.
• The perfusionist maintains the function of the pump
and also monitors the delivery of blood back to the
patient, the blood oxygen content, and other vital
parameters.
• During this time, the surgeon is then freed up
to concentrate on the technical aspects of the
heart operation itself.
• Operating a heart-lung machine is an excellent
example of team work in action.