PUMPS AND OXYGENATORS

1. Pumps, Oxygenators and Priming
Solutions

2. Pumps in Cardiopulmonary Bypass

3. Ideal pump
• Move large volumes against significant pressure
(7 l/min against 500 mmHg)
• Minimize flow velocity- limit damage to blood
• Inert pump components – no activation of coagulation and inflammation
• Minimal dead space – avoid stagnation and turbulence
• Calibration - easy, reliable, and reproducible
• Manual operations possible

4. Positive displacement pump
• Periodic volumetric change of a working space
• Low volume but high pressure flow
Centrifugal pump
• Energy transfer due to velocity deflection
• High volume low pressure flow
Pumps - Classification

5. Roller pump – Working principle
 Contain a length of tubing inside a curved
raceway placed at the travel perimeter of
rollers mounted on the ends of rotating
arms
 “Rolls” blood through piece of tubing.
 Generates both negative and positive
pressures.
 Independent of resistance (afterload)
hydrostatic pressure head (preload)

6. Stroke volume and blood flow
Roller pump – Working principle
TUBING DIAMETER(IN) STROKE VOLUME(ML) BLOOD FLOW(L/MIN) AT 150
RPM
3/16 7 1050
1/4 13 1950
3/8 27 4050
1/2 54 8100

7. Advantages
Simple to use.
Low cost.
Preload and Afterload independent

8. Disadvantages
Spallation
Tube material fatigue
Blood cell damage
Pump air
Cavitation
Potential pressurisation of arterial line.

9. Non occlusive roller pumps
 Rhone – Poulenc in France.
 MC 3 Pump.
 Passive filling peristaltic pump.
 Combines advantages of centrifugal and roller pumps.
 Two sheets of flat polyurethane tubing bonded at edges which are
stretched under tension over three rollers.
 Completely flat pump chamber.
 No backing plate against which the tubing can be compressed.
 Priming volume 120 ml.

10. Non occlusive roller pumps – Working Principle

11. Non occlusive roller pumps – Working Principle

12. METAPLUS PUMP
•Pump position is fixed in relation to the hard shell venous reservoir.
•Large bore, semi-rigid, U-shaped tubing connects the outlet of venous reservoir to inlet of pump
PUMP ROTOR AND MOTOR
ASSEMBLY
VENOUS RESERVOIR AND
MEMBRANE OXYGENATOR

13. Advantages
Preload dependent – cannot suck air.
No retrograde flow when pump stopped.
Blood damage and microbubble generation is reduced as no negative
pressure generated.
Non occlusive nature – tubing wear reduced.

14. Centrifugal pump
• In early 1970s, research related to the development of an
artificial heart was basis of the development of centrifugal
pumps for CPB.
• Boimedicus 600 - 1973.
•In the United States, the centrifugal pump is extensively used.

15. Centrifugal Pump – Working Principle
 Creating pressure gradient between inlet and oulet of pump.
 This pressure gradient results from the creation of a vortex by the
rotation of the pump head.
 The vortex can be created by using cones that impart motion to the
blood by viscous shear or by rotating impellers.
 The rotating motion creates an area of low pressure in the center
and an area of high pressure on the sides.

16. Centrifugal Pump – Working Principle

17. Centrifugal Pump – Working Principle
• Resultant blood flow-
•The resistance at the outlet is a function of two components: the CPB circuit
and SVR.
•Centrifugal pumps are afterload dependent and flow is influenced by
changes in resistance in both the circuit and the patient
•Flow meter necessary.

18. Centrifugal force
Centrifugal Pump – Working Principle

19. Centrifugal Pump – Working Principle
•HEAT GENERATION: All centrifugal pumps will generate heat
depending on the amount of energy that is impaired into the
blood.
•Combination with the low flow in the center of the pump head -
may create blood clots and blood cell activation in the pump.

20. SPECIFIC CLINICALLY AVAILABLE CENTRIFUGAL PUMPS
•BIOMEDICUS PUMP
• In 1976, the first centrifugal pump was used for CPB.
• The pump head is acrylic, with inlet and outlet ports oriented at right angles to each other, and its
priming volume is 80 ml.
• Cones driven by magnetic coupling to external console.

21. CENTRIFUGAL PUMPS - Capiox pump
Rotor with unique straight path
design to reduce pump
rotational speed without
decreasing hydraulic efficiency
Small priming volume – 46 ml
reduces stagnant flow within
the rotor

22. CENTRIFUGAL PUMPS – Nikkiso Pump
•Smallest commercially available pump
•Priming volume of 25 ml.
•Made of polycarbonate, with a V shaped ring seal that
separates the pump housing and the actuator chamber.
•Seal – made of fluororubber, suppresses heat generation and
prevents blood leakage.
•Six washout holes are incorporated into impeller to generate
blood flow from the back to front surface of the impeller.
•These holes prevent thrombus formation in areas behind the
impeller and around the sealing part.

23. Problems associated with centrifugal pumps
Flow rate affected by preload and after load.
Retrograde flows down the arterial line.
Potential air entrapment if inadequate aferload.
For forward flow pressure in the pump head (PP) must be greater than the
combined patient pressure (PPT) and the pressure head (PH) {hydrostatic
pressure}.
--PP > PPT + PH forward flow

24. Centrifugal Pump vs Roller Pump
Expensive Inexpensive
Pump flow function of SVR Flow predictable based on pump speed
Cannot pump large amount of air Can pump large amount of air
Pump stalls on occlusion without generating
high suction or outlet pressure.
Potential to overpressurize circuit if
inadvertently clamped.
Retrograde flow when pump slows / stops No retrograde flow.
Does not require continous monitoring Continuous strict monitoring of blood level
Hemolysis and damage to formed blood
elements is less
More hemolysis and damage to formed blood
elements.
Less wear and tear of pump. No spallation More wear and tear of tubing in pump head.
Spallation.

25. Oxygenator
 Blood gas exchange device.

26. Oxygenator
Oxygenate venous blood.
Remove CO2
Represent the largest surface area to which circulating blood is exposed.
Components -
Membrane module
Heat exchanger
Reservoir

27. AN IDEAL OXYGENATOR
Oxygenation of venous blood: device must have sufficient capacity to
provide oxygenation over a wide range of venous flow rate.
Carbon dioxide elimination to avoid hypercarbia or hypocarbia.
Minimum trauma to the blood
Small priming volume - to limit the deleterious effects of hemodilution
Safety

28. CLASSIFICATION
Bubble oxygenator:
The earliest oxygenators.
Exchange gases through direct interaction of gas and blood.
These devices were used during early advent of CPB.
Membrane oxygenator
Semi-permeable barrier that separates fluid from gas.
Diffusive qualities of the membrane material determine the
transfer of oxygen and carbon dioxide between phases.

29. BUBBLE OXYGENATORS
• First widely available commercial oxygenators
• Structure : 3 sections of operation
Bubble column
Defoaming area
Arterial reservoir
• Desaturated blood passively enters mixing chamber, where 100%
oxygen flows across a disparager plate into the stream of blood,
which forms small bubbles

30. BUBBLE OXYGENATORS
Blood becomes oxygenated and carbon dioxide is reduced
as stream of gas percolates through blood.
Blood is defoamed by the presence of silicone antifoam-A,
which consist of the liquid polymer dimethylpolysiloxane
(96%) and particulate silica (4%), which destabilizes the
bubbles, causing them to implode.

31. BUBBLE OXYGENATORS
The arterialized blood is collected in an arterial reservoir that is
then actively pumped.
The simple design of bubble oxygenators relies on the
hydrostatic pressure head from the patient to the mixing
chamber connected by the venous line.
The pressure drop through bubble oxygenator is <30 cm of
water, in contrast to the 100 cm of water pressure drop
typically found in membrane oxygenators.

32. BUBBLE OXYGENATORS
Bubble size is critical to adequate gas
transfer.
The bubble size selected must be a
compromise between optimal surface
area for oxygenation and volume for
carbon dioxide transfer.
Decreasing size of bubbles increases total
surface area of blood gas interface with
better oxygenation but limiting total CO2
transfer.
Bubble sizes of 3 to 7 mm are used to
optimize both O2 and CO2 transfer.

33. MEMBRANE OXYGENATORS
• Complete barrier between the gas and blood phases and diffusion is through membrane
material
• Costly to manufacture and require large priming volume
• Most membrane lungs used for CPB have micropores

34. Willem J. Kolff
During dialysis in 1943 noticed that the
blue blood in the rotating-drum
artificial kidney became red
Clowes and Neville(1958) Poineers in
using membrane oxygenators (teflon
flat membranes)

35. MEMBRANE OXYGENATORS – Materials
Historically – Cellulose.
Polytetrafluoroethylene
Polyethylene
Currently -
Silicon rubber (homogeneous, nonporous membrane).
Polypropylene (heterogeneous, microporous, hydrophobic
membrane).

36. Silicone Vs Polypropylene Membrane
Silicone membrane
Long term support
Without a diminution in gas transfer capacity
Avoid plasma leakage and membrane wet out
Microporous polypropylene membrane
Cheap
Good for short periods
New generation membranes that incorporates benefits of
silicone with polypropylene have been developed.

37. MEMBRANE OXYGENATORS – Designs
Membrane materials are organized in three configurations:
Scrolled envelope
Parallel plate
Hollow fiber

38. Types of Membrane Oxygenators
Plaque oxygenators
-microporous expanded polypropylene
-folded Z shape
-blood & gas flow opposite direction
-Cobel Excel, Cobe VPCML,Shirley M2000
Spiral oxygenators
-silicon membranes
-rolled around central axis
-Kolobow oxygenator.

39. Types of Membrane Oxygenators
Hollow fibre oxygenator
1970 Benlips introduced
Capillary fibers of microporous polypropylene

40. Spiral Membrane Oxygenators
Kolobow
Silicon membrane in shape of an envelope that is coiled on
itself.
Used primarily in ECMO
Ability to maintain stable CO2 and O2 for long periods
(weeks).
Available in gas exchange surface area sizes from 0.5 to 4.5
m2.

41. Hollow Membrane Oxygenators
Blood flow inside the capillaries
Gas flow inside the capillaries
Blood flow through the fiber was abandoned -
High trans membrane pressure
Activation of platelets
Increased haemolysis
Blood flow either perpendicular or in the direction of fiber bundle
In latter case, blood will flow in a counter current direction to the gas
flow - Optimized gas gradients during the dwell time

42. Membrane oxygenators &
lung
MEMB OXYGN LUNG
SURFACE AREA(M2) 0.5-4 70
Blood path width (µm) 200 8
Blood path length (µm) 250000 200
Memrane thickness (µm) 150 0.5
Max O2 transfer(ml/min) 400-600 2000

43. ADVANCES IN OXYGENATORS
Biocompatibility
Heparin coating – 1980's
Surface Modifying Additive—
Polydimethylsiloxane polycaprolactone oligomer
Phosphorylcholine
Bioline
X Coating
Trillium Biopassive Surface—polyethylene oxide.
Cost-effectiveness'????

44. Priming Solutions

45. Priming solutions for CPB Circuit
 Need of prime – to achieve adequate flow rates on initiation of
CPB without air embolism.
 Ideal prime -
Similar electrolyte content, osmolarity and pH as
that of plasma.
On mixing with blood maintains oxygen delivery, CO2 removal and
physiological homeostasis.

46. Historical perspective of prime solutions

47. Homologous blood syndrome
 Blood borne infection
 Severe pulmonary insufficiency
 Impaired immunity – wound infection, sepsis
 Impaired resistance to Malignant cell transformation
 Graft versus host disease

48. Impetus for nonhemic prime
Severe strain on hospital blood bank
Increased access to the emergency surgery
Increased exposure to O2 in polycythemics
Refusal of hemic prime from Jehovah’s witness faith
Experimental success of hemodilution in CPB

49. Glucose in priming solution
1962, Cooley – 5% dextrose in addition to blood - improves outcome
Solution with glucose as major component – isotonic but after
metabolisation of glucose become severely hypotonic
Fluid shift from Extracellular to Intracellular compartment -
Red blood cell lysis
Pulmonary edema
Cerebral edema
Hyperglycemia – poor neurological outcome
Priming solution – Normotonic, near physiologic sodium concentration.

50. Colloidal Priming solution
 Hemodilution – decreased colloid oncotic pressure – fluid
shift into intracellular compartment – cellular edema and
dysfunction.
 Colloid solution - counteract reduction in colloid oncotic
pressure – prevent fluid shift.
 CPB – systemic inflammatory response – tight junctions at
endothelial lining "permeable" to high molecular weight
proteins – high molecular weight protein trapped in ECF –
paradoxical increase in cellular edema.

51. Common priming solutions

52. Additives to priming solution

53. Experimental prime solutions
Perfluoro carbons
- 0.118 microns, half the viscocity of blood
-O2 release even at low po2 environments
-O2 relase is not related to pH/ temp
- can perfuse distal capillareis
- still at experimental stage
Stroma free Hb
-natural O2 carrying capacity &osmotic activity
-lower viscocity than blood
-do not cause immunosuppression
-still in preclinical testing

54. Priming Solution (AIIMS)
Ringer lactate – 20 ml/kg.
Hydroxy Ethyl Starch – 10 ml/kg.
Mannitol – 5 ml/kg.
Soda bicarbonate – 1 ml/kg.
Heparin – on the basis of circuit used.
If blood is added to prime – additional soda bicarbonate 10ml/300ml blood
is added.

55. Mannitol
 Potent osmotic diuretic.
 Maintain urine output during CPB and in immediate
post bypass period.
 Preserves renal function.
 Free radical scavenger.

56. Oxygenator-heat exchanger
Heat exchanger
Membrane oxygenator

57. Pump tubings
Internal diameter
(inch)
Volume
(ml/feet)
Used as
1/4 8.6 Suction / vent
<6kg – art./venous line
3/8 21.6 <10 kg – venous line.
>11 kg – arterial line
1/2 37.0 > 20 kgVenous line

58. CPB circuit according to age
Weight
(kg)
Oxygenator Prime vol
(ml)
Art. line Venous line Circuit
Priming
vol. (ml)
Heparin
(mg)
Max. Flow
(lt/min)
< 6 Baby Rx 35 1/4 1/4 400 - 500 25 1.2
6 - 10 Minimax 109 1/4 1/4 or 3/8 400 –600 25 - 30 2.3
11 - 20 Sx 10 135 3/8 3/8 1000 - 1100 50 3.5
>20 Affinity NT 290 3/8 1/2 1500 - 1700 75 7

59. Priming volume
 Volume required to fill the arterial and venous limbs, adequate
voulme in reservoir to prevent air entering the arterial line on
initiation of CPB.
 Acceptable hemodilution??

60. Calculation of Blood Volume to be added
Pts estimated blood volume x Hct
Predicted Hct= ____________________________
Pts estimated blood vol +CPB prime+
pre CPB iv fluid volume (TCV)
RBC Vol. To be added = TCV (Hct Desired – Hct Predicted)
Bank Blood volume to be added = RBC Vol to be added / 0.7

61. Blood preservation techniques
Pre CPB – Retrograde circulation
Adult
Hct > 32%
CVP > 8 mm hg.
SBP > 80 mm hg
On CPB – Hemofilter.
Cell Saver.
Post CPB – Chase prime with crystalloid.
Completely reverse and pack

62. Thank you