Cardiopulmonary bypass development and history Indication of cpb Hardware in cpb Arterial and venous cannulation Oxygenator Heat exchanger Filter How to conduct cpb and problems in cpb Cardioplegia

1. BASICS OF
CARDIOPULMONARY BYPASS
DR DAVID IDOWU

2. OUTLINE
• INTRODUCTION
• INDICATION
• CARDIOPULMONARY BYPASS CIRCUIT
• CONDUCT OF CPB
• COMPLICATIONS OF CPB
• CONCLUSION

3. INTRODUCTION
• Cardiopulmonary bypass (CPB) and Extracorporeal circulation are two
synonymous terms.
• CPB was coined out by Denton Cooley
• Breakthru and advancement in cardiac surgery has been possible due
to development of CPB
• CPB function is circulatory & respiratory support along with
temperature management to facilitate surgery on the heart and great
vessels
• Blood returning to the heart is temporarily drained venous cannula
• Diverted blood passes via a reservoir into a pump, which propel blood thru
oxygenator into arterial circulation

4. Introduction….
• 1930s- Develop CPB and use in
animals
• 1953- 1st successful human cardiac
surgery using CPB (6th May 1953)
• Repair ASD, (Cecilia Bavolek, 18yr)
• High mortality
• Temporarily abandoned
• Walton Lillehei- Controlled cross
circulation
• 1965- John Kirklin modified Gibbon
CPB
• Great biomedical inventions in health
care, rivaling development of
roentgenography & hemodiadialysis.

6. INDICATIONS FOR CPB
• Cardiac surgery
• Open heart surgery.
• Empty the heart. Drain blood out
• Oxygenate it
• Adjust chemical & electrolyte content
• Adjust its temperature
• Return it to patient
Other roles
• Salvage lost blood
• Prevent distension of heart during
surgery via cardiac vent
• Myocardial protection- deliver CP
Noncardiac use of CPB
• Removal of intracranial masses
• Where profound hypothermia/ low flow/
circulatory arrest is used
• Thoracic tumour/ major airway
resection
• Pulmonary embolectomy
• Lung transplant
• Venovenous bypass for liver resection
• Caval reconstruction for renal tumour
• Resuscitation of hypothermic accident
victims

7. CPB circuit

8. CARDIOPULMONARY BYPASS CIRCUIT

9. CARDIOPULMONARY BYPASS CIRCUIT…
• Pump
• Cannulae
• Tubing
• Reservoir
• Oxygenator
• Heat exchanger
• Arterial line filter
• Cardioplegia system
• Monitoring system in modern CPB
• Pressures
• Temperature
• Oxygen saturation
• Haemoglobin
• Blood gases
• Electrolytes
• Safety devices
• Bubble detector
• Oxygen sensor
• Reservoir low-level detector alarm

10. CPB CIRCUIT- Pump
• Sigma motor pump- Historical interest
• Roller pump
• Has 2 rollers positioned on rotating arm,
• Compresses a length of tubing to produce forward flow
• Mechanism can produce hemolysis & tubing debris, which increases over time
• Centrifugal pump
• Consists of impellers/stacked cones within housing
• When rotated rapidly, -ve pressure is created one inlet, +ve pressure at the other,
thus propelling the blood forward
• Afterload dependent, cardiac out drops if SVR increases
• Improves platelet preservation, renal function, neurological outcomes

12. Typical set up of Roller pump

13. Centrifugal Pump

15. CPB CIRCUIT- CANNULAE
• Cannulae connects patient to the CPB circuit
• Made of polyvinylchloride (PVC) and are wire reinforced to prevent
obstruction due to kinking
• Made of flexible plastics
• Tip made of thin plastic or metal (for better id/od ratio)
• 1/3rd of total flow by SVC, 2/3rd by IVC
• Venous cannula
• Arterial cannula
• Cannulation
• Central or peripheral
• Open or percutaneous

16. Venous cannula
• Single stage cannulae
• Used during most open-heart
surgery
• 2 cannulae are inserted into IVC &
SVC, joined by Y-piece
• Dual stage cannulae
• Used for most closed procedure
• A single cannula is inserted into RA
• Cannula tip hole drain IVC
• Body side holes drain SVC /RA
• Cavo-atrial
Mechanism:
• Gravity siphonage
• Venous reservoir- 40-70cm below
Patient
• Lines must be filled with blood or
fluid
• Vacuum assisted venous
drainage
• Allows use of smaller cannulae &
tubing

17. Venous cannula….
• Amount of blood drained is determined by
• Central venous pressure
• Intravascular volume
• Venous compliance
• Sympathetic tone
• Height differential
• Resistance within the tubing system (cannulae, tubing, connectors)
• Inadequate blood volume or excessive siphon pressure cause
compliant venous or atrial walls to collapse against cannula intake
opening to produce chattering or fluttering

18. Venous cannula….
Other cannulation site
• Femoral/ Iliac vein
• Minimally invasive or redo surgery
• Open or percutaneous
• Special cannula- long, ultrathin,
wire reinforced

20. Venous cannula- Complications
• Atrial dysrhythmias
• Bleeding of the atrium
• Air embolism
• Malposition of tip (inserting the tip into azygous, innominate or
hepatic vein, or across an ASD into Lt heart
• Caval tape may occlude venous line

21. Causes of low venous return
• Inadequate height
• Malposition of venous cannula
• Obstruction or excess resistance
• Inadequate venous pressure (venodilation or hypovolemia)
• Kink, air-lock, insertion of PA balloon catheter into a cannula
• During rewarming tendency for kinking is more (softening of tubes)
• Surgical manipulation
• Drug induced venous dilation
• Small cannula

22. Arterial Cannula
• Provides oxygenated blood systemically during CPB
• Sites
• Distal Ascending aorta
• Standard cannulation site
• Brachiocephalic trunk ( and LCCA)
• LV Apex
• Distal arch aorta
• Femoral artery
• External iliac artery
• Subclavian or axillary artery

23. Arterial Cannula- choice of sites
• Procedure being performed
• Fresh vs redo surgery
• Emergency surgery
• Minimally invasive surgery
• Anatomic anomaly
• Robotic cardiac surgery
• Anterograde vs retrograde flow
• Patient body habitus
• Degree of atherosclerotic
disease present

24. Aortic Cannula- potential complications
• Bleeding
• Difficult insertion
• Tear in aortic wall
• Malposition of cannular tip
• Atheromatous emboli
• Failure remove all air from arterial line
• Injury to aortic back wall
• Inadequate or excessive cerebral blood flow
• Inadvertent decannulation
• Aortic dissection

25. CPB CIRCUIT- Oxygenator
• Gives respiratory support
• Types-
• Film oxygenator used by Dr John gibbon
• Bubble & Disk oxygenators are of historical interest
• Membrane oxygenator
• True membrane oxygenator- made of silicon
• Microporous membrane oxygenator- made of polypropylene
• Polypropylene fibre (100-200 µm internal diameter)
• Blood flow outside the fibre, while gas passes inside the fibre
• Low risk for air embolism
• Better control of gas
• Newer design has integrated filter to manage emboli (making arterial filter
unnecessary)

26. Oxygenators....
• A heat exchanger is integrated
with the oxygenator and placed
proximal to it to reduce the
release of gaseous emboli due to
alterations in the temperature of
saturated blood.

27. CPB CIRCUIT- Tubing and Connectors
• Polyvinyl tubing & fluted polycarbonate connectors connects various
components of CPB
• Medical grade polyvinyl chloride tubing is universally used
• Flexible, inert, smooth, nontoxic, tough, nonwettable, transparent
• Compatible with blood
• Resistant to kinking/ collapse
• Can be heat sterilized
• Internal diameter (1/2- 5/8 inch) is used in most adults
• Loose tubing connections can be sources of air intake & blood leakage
• For convenience & safety most tubing & connectors are prepacked

28. CPB CIRCUIT- Reservoir
• Placed immediately before arterial pump when oxygenator is used
• A high capacitance (low-pressure) receiving chamber for venous
return.
• Facilitates gravity drainage
• Venous bubble trap
• Provides access for drugs, fluids, blood & increase storage capacity of
perfusion system
• Types includes
• Rigid (hard) plastic canister vs soft, collapsible plastic bag
• Open vs closed

29. Venous Reservoir
• Rigid plastic canister
• Facilitates volume measurement & management of venous air
• Often has larger capacity, easier to prime
• Permit suction for VAVD (vacuum assist venous drainage)
• Less expensive
• Disadvantage-
• Includes use of silicon antifoam compound, which may provide microemboli, and
increase activation of blood element
• Soft plastic reservoir
• Eliminates blood gas interface
• By collapsing reduces risk of pumping massive air emboli if venous return is
suddenly interrupted

30. CPB CIRCUIT- Cardioplegia System
• Intracardiac repair requires AXC, causes myocardial ischemia
• Cardioplegia is a strategy for myocardial protection
• Potassium rich solution with additional factors-
• HCO3, Mannitol, Mg, Ca, procaine, glucose, adenosine, glutamate
• Causes electromechanical arrest of the heart (Diastolic arrest)
• Crystalloid (cold) vs Blood (warm, cold)
• Cannula inserted proximal to AXC
• A separate CPB pump delivers cardioplegia
• Anterograde (aortic root/ coronary ostial) vs Retrograde (coronary sinus)
• Continuous vs intermittent
•

31. CPB CIRCUIT- Filter
• Surgical wound & CPB circuit generate gaseous, biological &
nonbiological microemboli (<500µm)
• Microemboli produces most of morbidity associated with cardiac surgery
using CPB
• Gaseous emboli contains O2 & Nitrogen, & can enter the circuit thru different
sources e.g. stopcocks, sampling & injection sites, priming solution….
• Blood also produce large no of particulate emboli related to thrombus, fibrin,
platelet & platelet-leucocyte aggregation, hemolyzed RBC…
• Other biological emboli are atherosclerotic debris, cholesterol crystal, Ca
particles dislodged by cannulation, manipulation for exposure

32. Major Sources of
Microemboli

33. CPB CIRCUIT- Filter….
• Evaluation of microemboli
• In vivo, microemboli >100µm done with TEE, retina inspection, fluorescence
angiography
• CPB microemboli- arterial line USS, monitoring screen filtration pressure
• Prevention & control of Microemboli
• Use of membrane oxygenator & cardiotomy filter
• Minimizing & washing blood aspirated from the field
• Prevent air entry into the circuit
• Use of LV vent when the heart is opened
• Strategies to selectively reduce microemboli to Brain (receives 14% of CO)
• Reducing PaCO2 to cause cerebral vasoconstriction; hypothermia; placing aortic cannula
downstream to cerebral vessels; using special aortic cannulas

34. CPB CIRCUIT- Filter…
• Depth filter
• Consists of packed fibres or porous
foam
• No define pore size
• Remove microemboli by impaction &
absorption
• Dacron wool depth filter is most
effective
• Screen filter
• Made of woven polyester or nylon
thread
• Has defined pore size
• Filter by interception
• Pressure difference across filter
varies from 24-36mmHg @ 5L/min
flow
• Cause slight hemolysis & platelet
trapping
• Also activates complements
• CPB filter sites
• Cardiotomy reservoir
• Arterial line microfilter

35. CPB CIRCUIT- Heat Exchanger
• Controls the body temperature by heating or cooling the blood
passing thru perfusion circuit
• Hypothermia is used during cardiac surgery to reduce O2 demand or
facilitates operative exposure with brief period of circulatory arrest
• Gases are more soluble in cold than in warm blood-
• Hence rapid rewarming of cold blood within the circuit or body generates
bubble emboli
• Recent membrane oxygenator is integrated with heat exchanger
• Blood should not be heated above 400C to prevent denaturation of plasma
protein
• Temperature gradient between body & perfusion circuit gradient remains
within 10oC to prevent bubble emboli

36. CPB CIRCUIT- Other components
• Gas line and Blender-
• Delivers fresh gas to the oxygenator in a controlled mixture.
• Set FiO2 determines PaO2 while total flow determines PaCO2 on the bypass.

37. CONDUCT OF CPB
• Perfusion Team
• Priming
• Initiation of CPB
• Anticoagulation
• Anaesthesia & Monitoring of CPB
• Temperature Management
• Acid-base management
• Ultrafiltration
• Weaning

38. CONDUCT OF CPB- Perfusion Team
• Team
• Cardiac surgeon
• Determines planned operation, target perfusion temperature, method of cardioplegia,
cannulations
• Communicates procedure steps involved in connecting & disconnecting patient from CPB
• Anaesthesiologist
• Perfusionist
• Set CPB, perform safety checks, operates CPB machines, monitor conduct od CPB &
anticoagulation, adding prescribed drugs, maintain perfusion record
• Written protocol for different operations & emergencies
• For proficiency, and speed during emergency
• Multidisciplinary conferences

39. CONDUCT OF CPB- Priming
• Traditional adult CPB requires 1.5-2.0L of balanced crystalloids (Ringer’s
solution, Plasma-Lyte)
• About 30-35% of total blood volume, reduces Hematocrit to 2/3rd
• Small patient or PreOp anemia, bank blood can be added.
• Optimal hematocrit 21-25% (28-30% - children) @ moderate hypothermia (25-32oC)
• Viscosity is reduced, promote flow but O2 carrying capacity is reduced
• Mannitol may be added to promote diuresis
• Autologous blood priming
• Reduces perfusate volume, may need vasopressors for hemodynamics stability
• Use of colloids (albumin, gelatins, dextran, heterstarch)
• Minimizes decrease in colloid osmotic pressure

40. Priming equations
• Total circulating volume (TCV) = Patient’s blood volume + priming
volume
• Target haematocrit (Hct) on CPB = Patient’s blood volume (PBV) ×
Hct/TCV
• Blood required on prime = (Target Hct × TCV) – (Pt. Hct × PBV)/Hct of
donor blood
• Cardiac index of a 70 kg adult with normal metabolism at 37°C is 2.2–
2.4 L/m2 /min.
• For each 1°C decrease in temperature, the required CO reduces by
7%, and the pump flow can be reduced by an equivalent factor
• Pump flow rate = BSA x Cardiac index

41. CONDUCT OF CPB- Initiation of CPB
• Heparin 300U/kg iv is administered before Aortic cannulation
• Target ACT (measured after 3min) is 480s
• B.P. for aortic cannulation- 90-100mmHg to reduce risk of dissection
• This is done 1st to provide volume resuscitation in case of hypotension
associated with venous cannulation
• Check line pressure once aortic cannula is connected to tubing to rule out
dissection
• After venous cannulation, venous clamp is gradually released to
establish full CPB
• Discontinue ventilation

42. CONDUCT OF CPB- Anticoagulation
• Clotting on CPB is life-threatening (body or CPB circuit)
• Heparin most common agent used
• Lung-beef type from bovine (most preferred since 1980s)
• Has reduced risk of thrombocytopenia & production of heparin antibody
• Porcine mucosal type from swine
• Activated clotting time (ACT) is a point-of-care test to assess
heparinization.
• Normal value of ACT ranges from 80-120seconds
• It can be affected by hemodilution, hypothermia
• Monitor ACT every 30-40min
• Automated devices to measure ACT- Hemochron℗ and HemoTec℗

43. Anticoagulation…
• Other methods to titrate anticoagulation –
• Heparin dose-response curve
• Hepcon device, which measures plasma heparin concentration
• Heparin resistance, failure to achieve target ACT despite high dosage (800-
1000U/kg)
• Causes- elderly age, recent exposure to heparin, NTG infusion, thrombocytosis,
antithrombin lll deficiency (congenital/ acquired)
• Treatment- Antithrombin lll concentrate (1000units) or fresh frozen plasma (2-
4units)
• Alternative anticoagulants are
• Lepirudin, Argatroban, Danaparoid, Bivalirudin
• All have no reversal. Bivalirudin has half-life of 24min

44. Anticoagulation…
• Reversal of Anticoagulation is with protamine (sperm of salmon)
• A macromolecule compound
• Dosage: 1.0:1.3 (heparin : protamine)
• S/E- bronchoconstriction & hypotension, hence test dose should be given and
check for reaction
• Diabetic patient are occasionally sensitive to protamine

45. Anaesthesia & Monitoring of CPB
• Perfusion pressure is used as surrogate marker for organ perfusion.
• Maintain between 50-70 mmHg (pulseless perfusion)
• Higher pressure required in Hypertensive, risk of stroke (Carotid Arterial Dx), CKD
• Cerebral oximetry, transcranial doppler- monitor cerebral blood flow
• Mixed venous O2 saturation monitoring
• Provides an estimate of the balance between global O2 delivery & demand
• 70% or greater is maintained
• Bolus of IVF and vasoconstrictors are used to manage drop in pressure
• Blood level in the reservoir should be monitored to prevent air embolism
• Central venous pressure (CVP)-
• High CVP is indicated poor venous return

46. Anaesthesia & Monitoring of CPB….
• Arterial line pressure
• Temperature
• ABG
• Integrity of gas delivered to oxygenator
• Blood glucose maintained between @ 120-180 mg/dL
• Maintenance of anaesthesia
• Inhalational or TIVA
• Hypothermia reduced the need for anaesthesia requirement
• Hemodilution alter pharmacokinetics of drugs

47. Temperature Management
• Hypothermia is commonly used with CPB because of its protective
effects (decrease O2 demand of body tissues)
• Blood viscosity increases with hypothermia, this enables higher perfusion
pressure despite hemodilution
• Hypothermia reversibly inhibits platelet & clotting factors.
• Core temperature monitoring sites-
• Rectum, urinary bladder, oesophagus, pulmonary artery
• Nasopharyngeal temperature gives estimate of cerebral temperature
• Temperature grades
• Normal (35.5 – 37oC); mild hypothermia (32 – 35oC); moderate hypothermia
(28-32oC); deep or profound hypothermia (< 20oC)

48. Acid-base Management
• Two strategies to manage acid-base during hypothermia, pH & Alpha stat.
• CO2 becomes more soluble as temperature drops, ↓PaCO2, causing alkalosis.
• “Alpha” in alpha-stat refers to alpha-imidazole ring in histidine which is an
important intracellular buffer
• pH is not correct, PaCO2 is allowed to fall with hypothermia
• Maintains cerebral autoregulation, limits microembolism, beneficial in adult
• Disadvantage is inhomogeneous cooling
• pH stat maintain a constant pH & PaCO2 with hypothermia
• CO2 added to oxygenator cause increase cerebral flow & cooling
• If prolonged, can cause severe acidosis
• Beneficial in infants prone to neurological injury

49. CONDUCT OF CPB- Ultrafiltration
• Ultrafiltration during & after CPB removes inflammatory mediators &
excess fluid thereby producing hemoconcentration
• Conventional ultrafiltration uses hemofilter inserted into the circuit
• Naik et al 1991 introduced modified ultrafiltration (MUF)
• Used after completion of surgical repair before protamine administration
• Blood is removed from arterial line & returned to venous line after passing
thru hemofilter
• Reduced blood loss & transfusion

50. CONDUCT OF CPB- Weaning
• Weaning is the process where extracorporeal support is gradually
withdrawn as the heart takes over the circulation.
• Several steps are involved
• Gradual rewarming to normothermic state, temperature gradient between venous
blood & heater should not exceed 10oC
• Supplemental doses of anaesthetics are given
• Ensure acid-base balance, electrolytes, PaO2, PaCO2, sugar, hematocrit are within
normal range. K (4.5-5mmol/L) is target to prevent arrhythmias
• Deairing (open heart surgery), TEE used to assess adequacy
• Air embolism frequently involve RCA due to its anterior location causing ST-changes,
arrhythmias & Ventricular dysfunction
• Rx- increase perfusion pressure & maintain pulsatile perfusion by partially clamping venous
line

51. CONDUCT OF CPB- Weaning….
• Heart rate, rhythm & contractility are assessed
• Sinus bradycardia is treated with atropine or B-adrenergic agonist
• Epicardial pacing for persistent A-V block
• Removal of AXC can cause VF
• Defibrillation is done using internal paddles with biphasic energy 5-20J
• Antiarrhythmics (amiodarone, lidocaine, Mg) for persistent dysrhymias
• Mechanical ventilation is started
• Perfusionist gradually occlude the venous return & fill the heart while
incrementally reducing pump flow
• Protamine administration
• Aortic decannulation is final step of weaning

52. CONDUCT OF CPB- Weaning…
• Difficulties in weaning manifested by systemic hypotension
• May be due to either hypovolaemia, ventricular dysfunction or low SVR.
• Hypovolaemia is treated by giving controlled boluses of blood from the
circuit.
• Low SVR is treated with vasopressors such as phenylephrine, noradrenaline or
vasopressin
• Inotrope is used to manage ventricular dysfunction
• Inodilators such as milrinone, dobutamine and levosimendan can be used in
the setting of ventricular dysfunction with increased afterload.
• Use of levosimendan may be associated with a reduction in mortality
• Mechanical support (IABP, LVAD) for persistent cases

53. COMPLICATIONS OF CPB- Mechanical
• Aortic cannulation-
• Bleeding,
• Cannula malposition cause selective cerebral perfusion
• Plaque dislodgement & dissection- Dissection presents with
• Low arterial BP, high arterial line BP (>300 mmHg)
• Loss of venous return & bluish discoloration of vessels
• Repair is necessary under DHCA
• Venous cannulation
• Bleeding,
• Cannula malposition/ air-lock: cause inadequate venous return, leading to
cerebral & splanchnic congestion

54. COMPLICATIONS OF CPB….
• Massive air embolism
• Caused by pumping from empty reservoir
• Rx- cessation of pumping, commencing retrograde cerebral perfusion
• Oxygenator failure
• Pump malfunction
• Clotting in circuit
• Tubing rupture or disconnection
• Gas supply failure
• Electrical failure

55. COMPLICATIONS OF CPB- Systemic
• Platelet dysfunction (qualitative & quantitative)
• Concentration of procoagulants decrease with hemodilution
• Inflammatory, coagulation, complements, fibrinolytic pathways are activated
• Thromboelastplasty can assist in knowing cause of bleeding diathesis
• Prolong CPB time, redo-surgery, preoperative use of anticoagulant cause bleeding
• IV tranexamic acid 10 mg/kg
• Acute kidney injury
• From inflammatory response & hypotension
• Risk factors- prolong bypass time, sepsis, DM
• Rx- high perfusion pressure

56. Systemic Complication…
• Cerebral injury ranges from cognitive dysfunction to stroke.
• High perfusion pressure, adequate hematocrit, alpha stat management
• Epiaortic USS of Ascending aorta for plaque/ calcification
• Systemic inflammatory response
• Causes- contact of blood with artificial surfaces, ischemia-reperfusion injury,
endotoxaemia, operative trauma
• Acute phase reaction due to release of completements, cytokines, endotoxin,
NO cause increased capillary permeability
• Subclinical myocardial injury
• Stunning, Hibernation

57. Systemic Complication…
• Acute respiratory distress syndrome follows use of CPB
• Anesthesia induced atelectasis & reduced mucociliary clearance worsens
acute lung injury.
• Rx- use of respiratory protective strategies
• Vasoplegia
• Characterised by severe, vasopressor-resistant vasodilation due to activation
of nitric oxide synthase, vascular smooth muscle ATP-sensitive K-channels and
relative deficiency of vasopressin.
• Treatment includes fluid resuscitation and vasopressors such as
phenylephrine, norepinephrine and vasopressin.

58. CONCLUSION
• CPB has made increasingly complex cardiac surgeries possible in the
current era.
• Since inception, CPB has undergone immense modifications in the
form of novel defoaming agents, heparin coated circuitry,
ultrafiltration, miniaturised circuit design, integrated arterial filter
with oxygenator
• However, it still has its significant adverse effects

59. •THANK YOU