CPB Class by me.

1. DR DHANESH KUMAR
19-03-2016
PRINCIPLES OF CPB

2. What is It ?
 Temporary mechanical circulatory support to
the stationary heart and lungs
 Heart and Lungs are made “functionless
temporarily” , in order to perform surgeries

3. History
 First open cardiotomy (Apr 5, 1951)
 First successfulOHS (Sep 2, 1952)
 Dr. F John Lewis
 ASD closure using hypothermia and inflow occlusion
 First successfulOHS using CPB (by JohnGibbon May 6, 1953)
 ASD closure
 High mortality rate
 VSD closure by azygos flow concept (controlled cross-
circulation) (Dr C.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 Dr Fredrick Cross and Earl Kay in 1962
 Used for early OHS in USA
 Membrane oxygenator
 Developed in 1950s-1970s; but initially 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 principal types
 Displacement pumps
 Roller pump
 Non occlusive roller pumps
 Rotatory pumps
 Radial (centrifugal) pumps
 Axial pumps (Archimedes’ screw)
 Diagonal pumps

11. Impeller PumpRoller Pump Centrifugal Pump
Pumps

12. Centrifugal pumps > Roller pumps
 Long-term CPB
 Ventricular assistance
 Neonatal ECMO
 Centrifugal pumps
 Biomedicus Biopump (Medtronic Inc)
 Sarns/3M centrifugal pump (Terumo)
 Levitronix CentriMag blood pump
 LVAD, RVAD, BiVAD
 BiVAD + oxygenator in RVAD = ECMO

13. 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

14. 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 pO2 difference and surface area,
inversely to diffusion distance

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

16. 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

17. 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

18. Membrane Oxygenator
 Characteristics
 Gas exchange across a thin membrane
 No direct contact with blood and no defoamer; more physiologic
 Minimal blood damage
 Two types
 Solid type (Silicone)
 Microporous type (polypropylene)
 0.3-0.8-micron pores
 Most popular design = hollow fibers (120-200 microns)

19. Membrane Oxygenator
 Microporous / Hollow fibers

20. Microporous (Polypropylene) Membrane
Oxygenator
 Currently predominant design used forCPB
 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

21. Silicone Membrane Oxygenator
 True membrane oxygenator
 Silicone polymer
 Improved biocompatibility -> long-term support
 1980s to mid-1990s
 Still the membrane of choice for long-term procedures
 ECMO
 Problems
 Gas exchange inferior to polypropylene (microporous) oxygenator
 Need greater surface area and larger prime volume
 Difficult in manufacturing and quality control

22. 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 sq.m
 Most common use for ECLS/ECMO

23. Heat Exchanger
 Integrated into oxygenator for warming and cooling
 Exchange surface made of
 Stainless steel, aluminum, 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

24. Filters and Bubble Traps
 In the circuit, micro emboli are monitored by
arterial line ultrasound or monitoring screen
filtration pressure.
 Depth filters consist of porous foam, have a
large, wetted surface and remove micro
emboli by impaction and absorption
 Screen filters are usually made of woven
polyester or nylon thread.

25. Tubing
 Medical grade Polyvinyl Chloride (PVC)
tubing
 It is flexible, compatible with blood, inert,
nontoxic, smooth, nonwettable, tough,
transparent, resistant to kinking and collapse
 Can be heat sterilized
 The Duraflo II heparin coating ionically
attaches heparin to a quaternary ammonium
carrier (alkylbenzyl dimethyl - ammonium
chloride), which binds to plastic surfaces.

26. Perfusion Monitors and
Sensors
 A sensor with alarms on the venous reservoir and
a bubble detector on the arterial line are
desirable safety devices.
 Flow-through devices are available to
continuously measure blood gases,
hemoglobin/hematocrit , and some electrolytes
 Temperatures of the water entering heat
exchangers

27. 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

29. Arterial Return
 Ascending aorta just proximal to innominate A
 Femoral artery access in
• Dissecting aortic aneurysm (0.2-3%)
• Reoperation
• Emergency
• MICS
 Problems of femoral cannulation (more than ascending aorta
cannulation)
• Sepsis
• Pseudoaneurysm
• lymphatic fistula
 Arterial cannula
• The narrowest part of CPB circuit
• As short as possible
• As large as the diameter of vessel permits
 < 100 mmHg in full flow

30. Arterial Cannula
 Straight/Angled cannula
• Minimize risk of dislodgement of atheroma in the
ascending Aorta or Arch
 Axillary –subclavian artery, innominate artery, LV
apex
• In special circumstances
• Limitations and more complications
 Complication: Dissection of aorta
• All sites of arterial cannulation
• Prompt recognition and surgical correction
• TEE helpful for diagnosis

31. Size of venous 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.

32. 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