The document discusses the history and components of cardiopulmonary bypass (CPB) and extracorporeal life support (ECLS). It describes the evolution of heart-lung machines from early models that combined pumping and oxygenation functions to separate pump and oxygenator units. The key components of modern CPB circuits are described including roller pumps, centrifugal pumps, membrane oxygenators, heat exchangers, and cannulae. The document also reviews priming solutions, temperature regulation, and applications of CPB beyond cardiac surgery such as ECLS and ventricular assist devices.

1. OXYGENATORS

2. Heart-Lung Machine
• Machine for cardiopulmonary bypass
– For open cardiac surgery
– For supporting cardiac function, pulmonary function, or
cardiopulmonary function
• In the past
– One unit
• Recently
– Separate units
• Pump system (Heart)
• Oxygenator (Lung)

3. History
• First open cardiotomy (Apr 5, 1951)
– Temporary mechanical takeover of both heart and lung function
– Not survive due to unexpected complex congenital defect
– 4-yr experimentation of dogs followed
• First successful OHS (Sep 2, 1952)
– Dr. F John Lewis
– ASD closure using general hypothermia and inflow occlusion
• First successful OHS using CPB (by John Gibbon May 6, 1953)
– ASD closure
– High mortality rate
• VSD closure by azygos flow concept (controlled cross-
circulation) (Dr Walton Lillehei Mar 26, 1954)

4. • DeWall-Lillehei helix bubble oxygenator (May 1955)
– Beginning in a large series of patients
– Method of choice worldwide for OHS
• Rotating Disk oxygenator
– Developed by Drs Fredrick Cross and Earl Kay
– Used for early OHS in USA
• Membrane oxygenator
– Developed in 1950s-1970s; but clinically not frequently used
– In the mid-1980s, microporous designs; frequently used.
• Hemodilution
– Major technologic advance in CPB

5. Cardiopulmonary Bypass
• Goals
1. Still, bloodless heart for cardiac surgery
2. Replacement of cardiac and pulmonary function

6. Functions of CPB
• Respiration
• Ventilation
• Oxygenation
• Circulation
• Venous drainage (by gravity, centrifugal pump, or negative
pressure)
• Arterial inflow
• Temperature regulation (hypothermia)
• Low blood flow -> decreased blood trauma
• Decreased body metabolism

7. Components of CPB
• Total CPB
• Partial CPB
• Integral Components of Extracorporeal Circuit
– Pumps
– Oxygenator
– Heat exchanger
– Arterial filter
– Cardioplegic delivery system
– Cannulae (aortic; arterial; vena caval)
– Suction and vent

8. Basic CPB circuit with oxygenator and
centrifugal pump

9. Typical CPB Circuit

10. Pumps
• Two principle types
– Displacement pumps
• Roller pump
• Non occlusive roller pumps
– Rotatory pumps
• Radial (centrifugal) pumps
• Axial pumps (Archimedes’ screw)
• Diagonal pumps

11. Roller Pumps
• Most commonly used
• Volume Displacement
• Non pulsatile blood flow
• Used for
• Forward flow
• Cardioplegic delivery
• LV vent suction

12. Roller Pumps
• Flow determined
– Tubing diameter, roller RPM, length of tubing in contact with rollers
• Proper set occlusion for minimal hemolysis
• 100% occlusion in cardioplegia and vent pumps
– Full occlusion -> hemolysis
• Larger tubing and lesser rotations cause minimal hemolysis.
– High RPM and fully occlusive setting -> hemolysis
• Tubing spallation cause microemboli
• Easily pump air
• Resistance = resistance of tubing + oxygenator + heat exchanger
+ filter + aortic cannula + SVR
• Line pressure depends on SVR and pump flow rate
• Pressure limit = 150-350 mmHg ( >250 mmHg seldom accepted)

13. Nonocclusive Roller Pumps
• Flat compliant tubing placed over the rollers
• Positive pressure at the inlet to fill the tubing
• Unlikely microair emboli
• Require use of an in-line flowmeter

14. Radial (Centrifugal) Pumps
• Impeller spinning within a rigid housing
– Creates regions of lower and higher pressure
– Blood moved from inlet to outlet
• No spallation with rigid housing
• Very dependent on afterload
• Nonocclusive
– Permit back-bleeding
– Require occlusive device
• Reqiure use of in-line flow meter

15. Axial / Diagonal Pumps
• Axial pumps
– Low internal volume, high-velocity axial impeller
– Currently best suited for ventricular assist application
• Diagonal pumps
– Very similar to centrifugal pump in design and application

16. Differences of Rotatory Pumps

17. Alternate Classification of Pumps
a. Roller pumps
b. Impeller pumps (Impeller >)
c. Centrifugal pumps (Cone >)

18. Centrifugal pumps > Roller pumps
• Long-term CPB
• In high-risk angioplasty patients
• Ventricular assistance
• Neonatal ECMO
• Centrifugal pumps
– Biomedicus Biopump (Medtronic Inc)
– Sarns/3M centrifugal pump (Terumo)
– Levitronix CentriMag blood pump
• LVAD, RVAD, Bi VAD
• BiVAD + oxygenator in RVAD = ECMO

19. Pulsatile Perfusion
• Significant physiologic advantages
• Diastolic run-off
• Stimulation of the endothelium
• Problem
• Noncompliant high resistance CPB circuit
• High flow with resultant shear stress
• Hemolysis
• Possible with roller pump and diagonal pump, but not with
centrifugal pump
• Requires larger bore arterial cannulas
• Alternative method for generating pulsatile flow in high-risk
patients
• Use of IABP during CPB
• Additional cost and invasiveness

20. Oxygenator
• Limited reserve for gas transfer vs. natural lung
• Much smaller surface
• Limited by diffusion
• Types of oxygenator
• Disk oxygenator
• Bubble oxygenator
• Membrane oxygenator
• Maximum oxygen transfer
• Less than 25% that of normal lung
• Proportional to partial pressure difference and surface area,
inversely to diffusion distance

21. Disk or bubble oxygenator
• Direct contact oxygenators
• Bubbles in direct contact with blood
• Increasing cellular trauma

22. Bubble oxygenator
• Bubble oxygenator
• Larger bubbles improve removal of CO2
• Smaller bubbles are very efficient at oxygenation but poor in CO2
removal
• Larger the No. of bubbles, Greater the efficiency of the oxygenator

26. Deforming Chamber of Bubble Oxygenator
• Deforming the frothy blood
• Large surface area coated with silicone
– Increased surface tension of bubbles -> causing them to burst

27. Bubble Oxygenator
• Advantage
– Easy to assemble
– Relatively small priming volume
– Deforming the frothy blood
– Low cost
• Disadvantages
– Micro emboli
– Blood cell trauma
– Destruction of plasma protein
– Excessive removal of CO2
– Deforming capacity exhausted

28. Membrane Oxygenator
• Charateristics
– Gas exchange across a thin membrane
– No need in direct contact with blood and no need for
deformer; so more physiologic
– Minimal blood damage
• Two types
– Solid type (Silicone)
– Microporous type (polypropylene)
• 0.3-0.8-um pores
• Most popular design = hollow fibers (120-200 um)

29. Membrane Oxygenator
• Microporous / Hollow fibers

30. Microporous (Polypropylene) Membrane
Oxygenator
• Currently predominant design used for CPB
• Micropores
– Less than 1.0 um in diameter
– Initially porous, but plasma protein coating the membrane-gas
interface
– Surface tension of blood prevent gas leakage into the blood
phase
– Conduit for O2 and CO2 exchange
• Problems
– Plasma leakage and membrane wet at use of period > 24
hours

31. Silicone Membrane Oxygenator
• True membrane oxygenator
• Silicone polymer
– Improved biocompatibility -> long-term support
– The 1980s-the mid-1990s
– Still the membrane of choice for long-term procedures
• ECLS/ECMO
• Problems
– Gas exchnage inferior to that of polypropylene (microporous)
oxygenator
• Need greater surface area and larger prime volume
– Difficult in manufacturing and quality control

32. New Generation Membrane Oxygenator
• Silicone polymer
• A continuous sheet of silicone membrane rolled into a
coil
– Manufactured by Medtronic Cardiopulmonary Inc.
– Membrane surface area + 0.6-4.5 M2
– Most common use for ECLS/ECMO

33. Heat Exchanger
• Intergrated into oxygenator for warming and cooling of the blood
stream
• Exchange surface made of
– Stainless steel, aluminium, or polypropylene
• Counter-current mechanism
• Temperature difference between waterside and blood side
– Historic reports : maximum difference of 10 °C
– Recent recommendation : 6 °C and longer rewarming times
• To improve neurocognitive outcome
• Hyperthermic circulatory temperature
– Blood damage (protein denaturation
– Limit absolute maximum temperature (42 °C) in blood

34. Circuits
• Venous drainage by gravity into oxygenator
– Height difference between venae cavae and oxygenator > 20-30 cm
• Mechanical suction Not desirable
– Entrain air
– Suck the vena cava walls against the cannula orifices
• Arterial blood return to the systemic circulation under pressure

35. Size of cannula
Adult Children
• SVC (1/3 of total flow) 28 24
• IVC (2/3 of total flow) 36 28
• Example: 1.8 m2 patient
– Total flow 5.4 l/min
– SVC 1.8 l/min, IVC 3.6 l/min
– SVC > 30 Fr, IVC > 34 Fr : Single cannula > 38 Fr
– 36-51 Fr cannula required.

36. Arterial Return
• Ascending aorta just proximal to inniminate artery
• Femoral artery access in
• Dissecting aortic aneurysm (0.2-3%)
• Reoperation
• Emergency
• Problems of femoral cannulation (more than ascending aorta
cannulation)
• Sepsis
• Formation of false aneurysm
• Development of lymphatic fistula
• Arterial cannula
• The narrowest part of CPB circuit
• Should be as short as possible
• As large as the diameter of vessel permits
• < 100 mmHg in full CBP flow

37. Arterial Cannula
• Long or diffuse-tipped cannula
• Minimize risk of dislodgement of atheroma in the ascending or transverse
aorta
• Axillary –subclavian artery, innimonate artery, LV apex
• In special circumstances
• Limitations and more complications
• Dissection of aorta
• All sites of arterial cannulation
• Prompt recognition and surgical correction
• TEE helpful for diagnosis

38. Other circuits
• Tubing sizes and lengths and connectors
• Should minmize blood velocity and priming volume
• Search for better biomaterials
• Cardiotomy suction
• Major source of microemboli and activated blood (humeral and cellular)
• Minimize amount, substition by cell salvage
• Cell processed blood may pose hazards
• Hemoconcentrator
• During and after CPB
• Removal of plasma and raising of Hct
• More cost effective than cell salvage and washing devices

39. Prime Fluid
• Ideally close to ECF
• Whole blood not used
• Homologous blood syndrome
• Postperfusion bleeding diathesis
• Incompatibility reaction
• Demand on blood banks
• Advantages of hemodilution
• Lower blood viscosity
• Improve microcirculation
• Counteract the increased viscosity by hypothermia
• Risk of hemodilution
• Decreased viscosity : SVR decreased
• Low oncotic pressure
• O2 carrying
• Coagulation factor

40. Composition of Prime
• Average 1,500-2,000ml
• Hct 20- 25%
• Example
• Balanced salt sol. RL 1250 ml
• Osmotically active agent (Mannitol, Dextran 40, Hexastarch)
100 ml
• NaHCO3 50 ml
• KCL 10 ml
• Heparin 1 ml

41. • CPB for cardiac surgery
• ECMO for ECLS
• ECMO for supporting cardio/pulmonary function
• VAD for supporting cardiac function
– RVAD; LVAD; Bi VAD
– BiVAD + oxygenator in RVAD = ECMO