2. IntroductionThe Heart-lung machine is a device which is used to
provide blood circulation and oxygenation while
the heart is stopped during the open heart surgery.
Heart-lung machine consists of three main functional
units, the pump, the oxygenator and heat exchanger.
To function, the heart-lung machine must be connected to
the patient in a way that allows blood to be removed,
processed, and returned to the body.
3. HistoryThe researchers searched mainly for a means to provide
oxygenated blood to organ preparations. They filtered the
blood through various screens and membranes and even
pumped it through the lungs of dogs or monkeys, but their
problem was not to be solved, though this may be
considered the beginning of research into a heart-lung
device.
The first successful open heart procedure on a human
utilizing the heart lung machine was performed by John
Gibbon in 1953. He repaired an atrial septal defect in an
18-year-old woman.
4. Purpose of Heart-lung machine:-
The heart-lung machine provides the benefit of a
motionless heart during open heart surgery.
The heart-lung machine is valuable during this time since
the patient is unable to maintain blood flow to the lungs or
the body.
5. Surgical procedures in which
Heart-lung machine is used:-
Coronary artery bypasses surgery.
Cardiac valve repair and/or replacement (aortic
valve, mitral valve, tricuspid valve, pulmonic valve)
Repair of large septum defects (atrial septum defect,
ventricular septum defect, atrioventricular septum
defect)
Transplantation (heart transplantation, lung
transplantation, heart–lung transplantation)
Implantation of heart.
8. Cardioplegia
Heart-lung machine circuit consists of a separate circuit
for infusing a solution into the heart itself to
produce cardioplegia to stop the heart from beating, and to
provide myocardial protection (to prevent death of heart
tissue).
9. Cannula
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.
A cardioplegia cannula is sewn into the heart to deliver
a cardioplegia solution to cause the heart to stop
beating
10. Blood reservoir
The blood reservoir serves as a receiving chamber for
venous return, facilitates a venous bubble trap, provides a
convenient place to add drugs, fluids, or blood, and adds
storage capacity for the perfusion system.
Reservoirs may be rigid (hard) plastic or soft, collapsible
plastic bags.
11. Heparin Pump
Once using a heart-lung machine during open-heart surgery,
A powerful anticoagulant, Heparin should be given to the
patient in order to reduce the blood's ability to clot, reducing
the risk of clots forming in the heart-lung machine.
12. Pumping system
1. Roller pumps
Roller pumps compress a segment of the
blood filled tubing. Blood is then pushed
ahead of the moving roller.
Roller pumps consist tubing, which is
compressed by two rollers 180° apart. Forward
flow is generated by roller compression and
flow rate depends upon the diameter of the
tubing, rate of rotation.
Excessive compression of the tubing in a roller
pump increases the risk of hemolysis.
13. Conti
Fig: Diagrams of blood pumps. (A) Roller
pumps with two rollers, 180 degrees apart. The
compression of the rollers against the raceway
is adjustable. Blood is propelled in the
direction of rotation. (B) The impeller pump
uses vanes mounted on a rotating central
shaft. (C) The centrifugal pump uses three
rapidly rotated, concentric cones to propel
blood forward by centrifugal force
14. 2 Centrifugal pump
Centrifugal pump have replaced roller pumps at many
institutions; mainly because they cannot over pressurize
the heart-lung machine system.
It consists of smooth plastic cones, which when rotated
rapidly, propel blood by centrifugal force. An arterial flow
meter is required to determine forward blood flow, which
varies with the speed of rotation and the after load of the
arterial line.
15. Oxygenators
Oxygenators not only supply vital oxygen for the blood,
but also transport carbon dioxide, anaesthetics and other
gases into and out of the circulation.
There are three types of oxygenator
1. Membrane oxygenators
2. Bubble oxygenator
3. Film oxygenator
16. 1.Membrane oxygenators Membrane oxygenators imitate the natural lung by a thin
membrane of either micro porous polypropylene or silicone
rubber between the gas and blood phases.
Diagram of a hollow fiber membrane oxygenator and heat exchanger
unit. Oxygen enters one end of the bundles of hollow fibers and exits at
the opposite end. The hollow fiber bundles are potted at each end to
separate the blood and gas compartments. Oxygen and carbon dioxide
diffuse in opposite directions across the aggregate large surface of the
hollow fibers.
17. 2.Bubble oxygenator
In bubble oxygenators, venous blood drains directly into a
chamberinto which oxygen is infused through a diffusion
plate. The diffusion plate produces thousands of small
oxygen bubbles within blood. Gas exchange occurs across a
thinfilm at the blood-gas interface around each bubble.
Carbon dioxidediffuses into the bubble and oxygen diffuses
outward into blood.
18. Heat Exchanger
Control body temperature by heating or
cooling blood passing through the perfusion
circuit.
In heat exchanger, blood flows through spiralling coils
made of stainless steel. The inner walls of the coils are
coated with polymers to limit blood-surface
interactions. The circulating water is chilled to nearly
0 0C in an ice bath and heated by an electric resistance
coil to an absolute maximum of 42 0C.
19. Stopping of Heart-lung machine
Once operation is completed, The surgeongradually
occludes the arterial pressure and pulse, and central
venous pressure are monitored and adjusted. When
cardiac performance is satisfactoryand stable,
protamineis given to reverse cardioplegia and blood
return from the surgical field is discontinued.
20. Complications
Haemolysis
Capillary leak syndrome
Clotting of blood in the circuit – can block the
circuit or send a clot into the patient.
Air embolism
Leakage – lose blood perfusion of tissue if a line
becomes disconnected.
1.5% of patients that undergo Heart-lung machine
are at risk of developing Acute Respiratory
Distress Syndrome.
21. Why Automation in the Heart-lung
Machine needed?
During open heart surgery, Per fusionists take care of the
connection procedures and maintain the performance of
machine as per requirement at the time of surgeries; sometimes
there occur faults due to carelessness. To overcome that
Automation of Heart-Lung machine is a need.
During surgery, Pressure in the arterial line is monitored
continuously to instantly detect any increased resistance to
arterial inflow into the patient.
22. Computerized CPB System
The computerized CPB system consists of an 80286
microcomputer. a reservoir blood level sensor,
acollapse sensor, and temperature sensor.
23. Safety mechanisms
The computer regularly verifies all samples with their
priorvalues and detects not only artifacts but also hardware
failures.
On detecting the improper sensor output, the computer
maintainsboth the flow rates constant and displays a
warning messagewith estimated locations of the trouble.
The pump rotationspeeds are also monitored and matched
with the computer's command.
In case the computer breaks down, a perfusionist can take
overthe pump control by turning an automatic/manual
switch to themanual mode.
