BLOOD PUMP FOR CARDIOPULMONARY BYPASS

1. BLOOD PUMPS
AKSHAY KATOCH
PERFUSIONIST

2. Key Points:-Four types of blood pumps are
currently available for CPB:
• ROLLER PUMPS
• CENTRIFUGAL PUMPS
• PULSATILE PUMPS
• NONOCCLUSIVE ROLLER PUMP

3. Various types of blood pumps are available for cardiopulmonary bypass (CPB). The ideal pump
for CPB should have the following characteristics:
•Able to pump blood at a flow rate of 7 L/min against a pressure of 500 mmHg.
•Should not damage the cellular or acellular components of blood.
•All parts in contact with the bloodstream should have a smooth continuous surface with no dead
space to cause stagnation or turbulence, should be disposable, and should not
contaminate the permanent parts of the pump.
•Calibration of pump flow should be exact and reproducible so that blood flow can be accurately
monitored.
•In the event of a power failure, the pump should be manually operable.

4. Roller pump is One type of the positive
displacement pump
Mostly commonly used type for CPB
In 1934, DeBakey designed the pump for CPB
In 1959, Melrose proposed a more advanced design, in
which the roller run along the tubing held in place by a
grooved backplate. The tube guides prevented lateral
motion of the tubing during operation.

5. Pumps are classified as single, double, and multiple roller pumps
1.Single-roller pump consists of a circular raceway in which a 360-
degree loop of tubing is inserted. Single-roller pumps were used for
CPB in the 1950s which is produded more pulsatility
2.Double-roller pump, which has been the most commonly used
pump for CPB, consists of a 210-degree semicircular backing plate
and two rollers with the rotating arms set 180 degrees apart.
• When one roller ends its occlusive phase, the other has
already begun its occlusive phase. Because one of the two
rollers is always compressing the tubing.
• Double-roller pump generates a relatively non-pulsatile flow
3. Multiple-roller pump has been proposed for extracorporeal blood
handling, it is not clinically available because it causes more
hemolysis.

6. Original DeBakey roller pump. Note dual rollers and knob for
rotating roller assembly. This pump required specially edged
tubing (D, right) for securing it between plates in the roller
mechanism

7. structure
 Roller pumps contain a length of tubing located inside a curved raceway.
These arms are arranged in such a manner that one roller is compressing
the tubing at all times. By compressing a segment of the blood-filled
resilient tubing, blood is pushed ahead of the moving roller, thereby
producing continuous blood flow.
 The output of the rotary pump is determined by the revolutions per
minute (rpm) of the pump and the volume displaced with each revolution.
 The volume depends on the size of tubing and length of the track.

8. Double-roller pump module, showing a large knob that
controls revolutions per minute, which are displayed
digitally on the front of the console.

9. TUBING
 Three basic materials currently used for tubing: silicone rubber, latex
rubber, and polyvinyl chloride (PVC)
 PVC is most widely used for roller pumps because of its durability and
acceptable hemolysis rates
 Latex rubber generates more hemolysis than PVC
 Silicone rubber produces less hemolysis when the pump is completely
occluded
 PVC tubing stiffens during hypothermic CPB and tends to induce spallation,
which refers to the release of plastic microparticles from the inner wall of
tubing as a result of roller pump compression
 Silicone rubber tubing releases more particles than PVC

10. How to check Occlusion
 Occlusion can be adjusted by either increasing or decreasing the
compression of the tubing by the rollers
 Excessive compression induces hemolysis and tubing wear, whereas too
little occlusion may also cause hemolysis but, more important,
compromises forward output
 The exact output of the roller pump may vary during CPB, and it is difficult
to determine the exact flow rate due to occlusion variance throughout
the bypass
 At nonocclusive settings, roller pump output can be sharply decreased,
resulting in hypoperfusion
 The occlusion is set by holding the outflow line vertically so the top
of the fluid is about 60 to 75 cm above the pump and then gradually
decreasing occlusiveness until the fluid level falls at a rate between 1

11. COMPLICATIONS
 Roller pumps include
1. Malocclusion (over- or under occlusion)
2. Miscalibration
3. Fracture of tubing
4. Runway pumping
5. Loss of power
6. Spallation
7. If out flow become occluded, pressure increased, tubing or connector disconnect or
break
8. If the inflow become occluded or limited,develop excessive negative pressure can
cause cavitation (microscopic air bubbles)
 Roller pumps may also develop pinhole leaks, which may lead to pushing microscopic
air bubbles toward the patient

12. CENTRIFUGAL BLOOD PUMPS

13. • Centrifugal pumps for CPB have been commercially available since
1976. At many institutions, the centrifugal pump has replaced roller
pumps for routine CPB for cardiovascular surgery.
• They are also used for mechanical circulatory support, including
ventricular assistance, percutaneous cardiopulmonary support, and
extracorporeal membrane oxygenation
• Centrifugal pump consists of an impeller arranged with either vanes or
a nest of smooth plastic cones inside a plastic housing
• Magnet inside the disposable pump head spins in conjunction with
another magnet spinning in the drive console
• Magnetic coupling means that the speed (rpm) of the driver magnet
inside the console equals the rotational speed of the pump

14. When the impeller rotates rapidly, it generates a pressure differential causing
blood flow (a negative pressure at the inlet port of the pump pulling blood into the
pump housing and a positive pressure at the outlet port expelling blood).
Excessive rotational speed can cause de-coupling, in which the impellers or cones
cannot spin as fast as the driver motor.

15. COMPARISON BETWEEN ROLLER PUMPS AND CENTRIFUGAL PUMPS
 Nonocclusive pump
 CENTIFUGAL PUMP ARE
DISPOSABLE AND COST
EFFECTIVE
 Negligible chance of circuit rupture,
cannot over pressurize (maximum
limit 700-900mmHg
 Generates negative pressure(-400
to -500 mmHg
 Reduce the risk of cavitation and
microembolus
 Retrograde flow can occur with loss
or severe reduction of forward flow
 Actively sucking blood from open
venous reservoir
 Occlusive pump
 REQUIRED PIECE OF TUBING
 HIGH CHANCE OF CIRCUIT
RUPTURE, pump (outlet side) is
accidentally kinked or clamped
 pump (inlet side) is accidentally
kinked or clamp generate
dangerously low negative
pressures that could result in
blood cavitation, hemolysis, and
suction of room air through
loose stopcocks or tubing
connectors.

16.  Priming of centrifugal pump
done with gravity
 Preload and after load sensitive
 No need to play the knob of
centrifugal pump if SVR dec or
increase
 Flow meter is required
(electromagnetic or ultrasonic
flow meter)
 Cenrtifugal pump trap the 32-52
ml of air,more then mention
volume , need prime
 Air colume can damage the
cone due to heat generate,can
damage the cell as well
 Positive and negative pressure
control in occlusive roller pumps
is typically accomplished with
additional electronic equipment
such as pressure control
modules or with a mechanical
bladder that shuts off the pump
if dangerous pressures are
generated
 Actively sucking blood from
open venous reservoir
 Easy to prime
 If SVR decrease,lead to
increase rpm to maintain the
constant pressrure

17. Complications
 Centrifugal pumps are generally safe, and the overwhelming majority of cardiac operations are
completed without incident. Although these pumps will not pass large quantities of air, centrifugal
pumps are nonocclusive, and therefore retrograde flow can occur whenever the pump
malfunctions, stops, or when the pump slows enough so that the pressure produced is less than
that needed to maintain forward flow.
 Retrograde flow can create a hemodynamic siphon that can exsanguinate the patient and can
draw air into the arterial line at the cannulation site.
Retrograde flow could commence after power to the pump is shut off.
 The reverse flow occurs if RPM is to low (as per company recommendation).
 The only way to prevent retrograde flow is for the perfusionist to clamp the arterial line when the
pump slows or stops. To sustain a pressure adequate to maintain forward flow, the perfusionist
should partially occlude the arterial inflow line when low flows are requested, as when the patient
is weaned from CPB. However, incidents have occurred where the perfusionist has forgotten to
clamp the arterial line

18. Specific clinically available centrifugal pumps
 BioMedicus pump, In 1976, the first centrifugal pump was used for CPB.
 Delphin pump, The Sarns 3M Delphin centrifugal pump has a vaned
magnetically coupled impeller within an acrylic housing. As with the
BioMedicus pump, the inflow and outflow ports are oriented at right angles
to each other, and the priming volume is 40 mL. Blood flow is measured by
an ultrasonic flowmeter along the outlet tubing and is proportional to the
rotational speed.
 Life stream centrifugal pump, was introduced clinically in 1988. The
impeller is composed of curved vanes to minimize eddies and cavitation and
to optimize overall flow patterns . The shaft, seal, and bearings have been
modified to reduce the risk of blood contact and potential pump failure. The
shaft is magnetically coupled to the driver console with integrated battery
backup. An electromagnetic flowmeter measures blood flow.

19. Capiox centrifugal pump, consists of a rotor with a unique
straight-path design to reduce pump rotational speed without
decreasing hydraulic efficiency. The straight-path design with a
constant cross-sectional area minimizes the change of blood
flow velocity and direction. Demonstrates the pump's
performance, which is note worthy for less afterload sensitivity at
higher flows when compared with other centrifugal pumps. The
small priming volume of approximately 46 mL may reduce
stagnant flow within the rotor.

20. PULSATILE PUMPS
Even conventional roller pumps produce some
pulsatile flow. However, one of the methods to
generate more pulsatile blood flow during CPB is to
use intra aortic balloon pumping.
A dramatic increase in post operative ejection
fraction was observed in the pulsatile perfusion
group with intra aortic balloon pumping

21. NONOCCLUSIVE ROLLER PUMP
 The Metaplus pump is a new type of blood pump that appears to incorporate some
advantages of a centrifugal pump while minimizing some disadvantages of a
conventional roller pump. This pump will not drain the venous reservoir, will not
create negative pressure and cavitation, will not over pressurize, and will not allow
retrograde flow.
 Forward fluid flow is accomplished by a passive-filling tapered pumping chamber
fabricated of two sheets of flat polyurethane tubing bonded at the edges. This pump
chamber segment is stretched under tension over three rollers. Unlike a conventional
roller pump, the Metaplus pump is considered nonocclusive because there is no
backing plate against which the tubing can be compressed with rollers. The rollers
are mounted on a rotor that spins to impart a peristaltic action on the fluid within the
pump chamber. The priming volume is 120 mL.

22. Metaplus pump rotor and motor assembly (right) and
membrane oxygenator (left). Pump position is fixed in
relationship to the hard-shell venous reservoir to
supply the inlet of the pump. Note requirement for
large-bore, semirigid, U-shaped tubing connecting the
outlet of the venous reservoir to the inlet of the pump.

23. The pump chamber fills passively as a function of the height of the fluid column within the
reservoir. Reservoir volume changes will have little effect on pump flow rate until the volume
drops to a minimum level. Once that level is reached, there is insufficient hydrostatic pressure
to fill the pump chamber and flow ceases, demonstrating the preload sensitivity of the pump.
When venous return is reestablished, blood flow resumes gradually. As a result, air is not
entrained nor does a potentially cavitating vortex form at the outlet of the CPB reservoir.
As stated earlier, the potential for retrograde flow is a key safety concern with nonocclusive
pumps. With the Metaplus pump, the pump chamber flattens and becomes occlusive as it
wraps around the individual rollers to prevent retrograde flow from the patient. The pump is also
afterload sensitive, because the pressure it generates is limited. If the arterial line occludes, the
flat segment of the pump chamber becomes distended and the pump then becomes
nonocclusive. This occurs at pressures lower than those required to induce failure of tubing
connections. Because the system is both preload and afterload sensitive, a noninvasive
electronic flow probe must be used to accurately measure blood flow, and a separate modular
pump console must be used to control the pump.

24. Schematic drawing of nonocclusive roller pump.
A, Operating principle of the triple-roller pump and pumping chamber. Polyurethane pumping chamber is
stretched over the rollers, and roller rotation is counter clockwise. E-E: Cross-sectional view of pumping
distended when blood is supplied at a pressure above ambient. B: Pumping chamber inlet collapsed when
blood is not supplied at a pressure above ambient. F-F: Cross-sectional view of the collapsed pumping

25. •Key points:-
• The ideal pump for CPB would be able to deliver physiologic blood flows against high
resistance without damaging blood, should provide flows that are exact and easily monitored,
should create no turbulence or stagnation, and should be manually operable in the event of a
power failure.
• The two pumps used most commonly for CPB are roller pumps and centrifugal pumps.
• Roller pumps have the advantages of simplicity, low cost, ease and reliability of flow calculation,
and the ability to pump against high resistance without reducing flow. Disadvantages include the
need to assess occlusiveness, spallation of the inner tubing surface that potentially produces
particulate arterial emboli, capability for pumping large volumes of air, and ability to create large
positive and negative pressures.
• Compared with roller pumps, centrifugal pumps offer the advantages of lesser air pumping
capabilities, lesser abilities to create large positive and negative pressures, less blood trauma, and
virtually no spallation. Disadvantages include higher cost, the lack of occlusiveness (creating the
possibility of accidental patient exsanguination), and afterload-dependent flow requiring constant
flow measurement.

26. • Four commercially available centrifugal pumps demonstrate some
differences in hydraulic performance, afterload sensitivity, priming
volumes, ability to transmit air, and possibly blood trauma.
• A nonocclusive roller pump has been recently introduced. This pump
appears to be incapable of generating dangerously high positive or
negative pressures or of permitting retrograde flow. This pump is
undergoing clinical evaluations to establish its appropriate clinical
applications.
• In the setting of short-term CPB for cardiac surgery, it remains uncertain
whether the selection of a roller pump over a centrifugal pump or of any
specific centrifugal pump over another has clinical significance.