Cardiopulmonary bypass

1. Cardiopulmonary bypass: Basic circuit,
Anticoagulation, Blood conservation,
Myocardial protection in cardiac surgery
Presenter: Dr. Kushal Ranjit
Moderator: Assist. Prof. Dr. Sanish Gurung

2. Objectives
• To know about the basic CPB circuit
• To know about anticoagulation in CPB
• To know about blood conservation
• To know about methods of myocardial protection in cardiac surgery

3. History
• The birth of CPB for cardiac surgery is attributed to its first successful
clinical use by John Gibbon Jr, 61 years ago.
• Practical clinical use really began in 1955 when 2 groups led by John
Kirklin at the Mayo Clinic and C Walton Lillehei at the University of
Minnesota, initiated the routine use of CPB for open heart surgery.

4. Cardiopulmonary Bypass (CPB)
• CPB is a form of extracorporeal circulation
• Blood is rerouted outside the vascular system and the functions of
the heart and lungs is temporarily assumed by surrogate technology

5. Goals
• Circulation of blood
• Oxygenation and elimination of carbon dioxide
• Systemic cooling and rewarming of the blood
• Providing a bloodless and motionless surgical field

6. Indications
• CABG
• Cardiac valve repair/replacement
• Large septal defects
• Congenital heart defects
• Repair of some large aneurysm (cerebral or aortic aneurysm)
• Pulmonary thrombectomy
• When oxygenation or perfusion of organs cannot be maintained by other means
(e.g., local anesthetic systemic toxicity, anterior mediastinal mass).

7. • Components of CPB
• Venous canula
• Blood tubing
• Venous reservoir
• Perfusion pump
• Heat exchanger
• Oxygenator
• Arterial line filter
• Arterial cannula
• Cardiotomy suction
pump
• Vent
• Cardioplegia

8. Arterial Cannula
• Generally established before venous cannula
• Preferred site: Ascending aorta
• Alternate sites:
• Femoral artery
• Axillary artery
• Innominate artery

9. Venous Cannula
• Cannula connect the patient to the CPB circuit
• Polyvinyl chloride (PVC) wire reinforced
• Single-stage
• most open-heart surgeries
• two cannula- one each into the superior
and inferior vena cava

10. • Dual-stage
• most closed-heart procedures
• single cannula is inserted into the right
atrium
• Alternative site for venous cannulation
• Femoral vein : minimally invasive, redo
surgeries

11. Blood tubing
• Connects various components of the CPB
• Composed of medical grade PVC
• Newer generation PVC:
• Surface coatings
• Reduces plasma levels of markers of subclinical coagulation
• Attenuates the increase of inflammatory markers

12. Venous reservoirs
• Displacement of large volume of blood out of the
circulation
• Positioned between the venous line and arterial
pump
• Collapsible plastic bags
• Hard shelled containers:
• Integral filtration mechanism
• Vaccum assisted venous drainage possible

13. Perfusion pump
• Replaces the function of the heart
• Types in CPB
• Positive displacement pump • Centrifugal Pump

15. Heat exchanger
• External source of heat to regulate body
temperature
• Function: warm or cool the patient’s blood
• Made up of aluminum, stainless steel,
polypropylene

16. Oxygenator
• Substitutes for the patient’s native lungs
• Function: Gas exchange
• Consists of a gas space and a blood space separated
by a microporous polypropylene membrane
• Driven by passive diffusion gradients
• Capable of arterializing 7 L/ min of typical venous
blood

17. Arterial line filter
• Placed in the arterial line as the last
component
• Pore sizes of 20 to 40 μm
• Removes particulate and gaseous micro-
emboli
• Have been shown to reduce the rate of
neurocognitive dysfunction.
• Integrated into oxygenator

18. Cardiotomy Suction Pump
• Allows blood to be salvaged from the operative field
• Returns to the circuit via the reservoir

19. Vent
• Return of blood through thebessian and bronchial veins --- distension of LV
• Venting prevents distension of left ventricle, provides bloodless field and aids
visualization.
• Potential sites :
• Right superior pulmonary vein
• Pulmonary artery
• Aortic root
• Ventricular apex
• Major complication: air embolism

21. Anticoagulation
• Aim: To prevent thrombosis in both the patient and extracorporeal
circuit
• Before cannulation
• Heparin based on the patient’s weight (300-400 units/kg) as IV bolus
• Desired level of anticoagulation achieved using Activated Coagulation
Test (ACT)

22. • Heparin:
• Binds to Anti thrombin III forming heparin-AT complex which effects
procoagulant effect of thrombin.
• Heparin-AT complex affects several coagulation factors but thrombin
and factor Xa are most sensitive to heparin. (thrombin>>Xa)

23. Monitoring anticoagulation
• Activated clotting time (ATT)
• High dose thrombin time (HiTT)

24. • ACT > 300 sec is safe for cannulation
• ACT > 400 sec is safe for going on bypass
• ACT > 480 sec is safe for going on DHCA
• Issues: Heparin resistance, altered heparin responsiveness, heparin
rebound, heparin induced thrombocytopenia

25. Heparin Resistance, Altered Heparin
Responsiveness
• Heparin resistance: ACT of less than the target (400-480 seconds) after 600
to 800 units/kg of intravenous heparin are administered.
• Can result from a congenital deficiency or abnormality of AT.
• Altered heparin responsiveness can result from an acquired AT deficiency,
increased levels of heparin-binding proteins, activated platelets, sepsis.
• Treatment: Supplemental heparin. In refractory cases, treatment with AT
concentrate or recombinant AT.

26. Heparin rebound
• Clinical bleeding that occurs within approximately 1 hour of
protamine neutralization.
• Accompanied by partial thromboplastin time (PTT) or thrombin time
and increased anti-factor Xa activity.
• Mechanisms:
• Slow dissociation of protein-bound heparin after protamine clearance
• More rapid clearance of protamine than of heparin
• Lymphatic return of extracellular sequestered heparin
• Management: Low dose protamine infusion (25 mg/h) for up to 6
hours after the end of CPB

27. Heparin-Induced Thrombocytopenia
• Immune-mediated prothrombotic disorder that occurs in patients
exposed to heparin.
• Antibodies form against PF4-heparin complex.
• Specific immunoglobulin G (IgG), binds to the complex and leads to
immunologically mediated platelet activation and hyperaggreggation
of the activated platelets occurs. (Hallmark)
• Platelet count less than 100,000/μL or to less than 50% of the
baseline count.

29. Reversal of anticoagulation
• Protamine remains the heparin reversal drug of choice in cardiac
surgery.
• Protamine/heparin ratio is limited to less than 2.6 mg protamine/100
Units of heparin.

30. Protamine reactions
• Classified as:
• Type I: type I protamine reaction involves isolated hypotension, with normal
to low filling pressures and normal airway pressures.
• Type II: moderate to severe hypotension and features of anaphylactoid
reactions, such as bronchoconstriction.
• Type III: severe hypotension and elevated PA pressures that may lead to acute
RV failure.
• Explanations for protamine reactions:
• Endothelial nitric oxide release
• Mast cell degranulation
• Histamine release associated with rapid infusion

31. Treatment options for protamine reaction
• Protamine should be administered slowly (i.e., over ≥5minutes). Limit
protamine dose to less than 2.6 mg protamine/100 units of heparin.
• Protamine should not be given to patients with documented
protamine reaction.
• Vasoactive medications, such as phenylephrine or ephedrine, use of
calcium chloride, or increased inotropic support may be necessary.
• In severe cases planning for return to CPB should be done.

32. Blood conservation
• The Task Force gave specific recommendations on blood conservation that
included the following five points:
1. Consideration should be given to the use of drugs that either increase
preoperative blood volume (e.g., erythropoietin) or decrease
postoperative bleeding (e.g., antifibrinolytic drugs).
2. Techniques of conserving blood, including cell saver sequestration and
retrograde priming of the pump, should be included in the operative plan.
3. To spare the patient’s blood from the insult of CPB, normovolemic
hemodilution or platelet-rich plasmapheresis can be considered.

33. 4. Institutions should implement transfusion algorithms supported with
POC testing.
5. A multimodal application of all of the previously mentioned
guidelines is the best way to conserve blood.

34. Intraoperative autologous hemodilution
• Removing blood from a patient prior to systemic heparinization and
CPB.
• Returning this blood following the separation from CPB.
• Contraindications
• Preoperative anemia
• Unstable angina/high-grade left main coronary artery disease
• Aortic stenosis.

35. Blood salvage (cell saver)
• Reinfusion of shed blood
• Units of shed blood may have hematocrits of 70%.
• Contraindications
• Infection
• Malignancy

36. Antifibrinolytic
• Standard in most cardiac centers
• Aminocaproic acid and Tranexamic acid
• Prevents the lysis of fibrin clots.
• Decreases bleeding after CPB
• Reduces the risk of blood transfusion.

37. Retrograde autologous priming (RAP)
• Crystalloid prime contained within the CPB circuit is displaced prior to
the initiation of CPB and replaced by blood drained retrograde via the
arterial and venous cannulae.
• Care must be taken to avoid acute hypovolemic hypotension.
• Benefits
• reduces hemodilution
• reduce the need for blood transfusion

38. Ultrafiltration (hemoconcentration)
• Plasma water is separated from low–molecular-weight solutes,
intravascular cell components, and plasma proteins with a
semipermeable membrane, using a hydrostatic pressure differential
created by external suction.
• Advantages
• Reduction in free water
• Increase in hemoglobin and hematocrit
• Preservation of hemostasis
• Decrease in levels of circulating inflammatory mediators

39. Myocardial protection
• Set of pharmacological and physiological strategies aimed at
attenuating the intensity of myocardial ischemia-reperfusion injury
during cardiac surgery and its consequences on myocardial function

40. Phases of myocardial injury during CPB
• Antecedent ischemia
• Also called unprotected ischemia
• Occur prior to start of CPB
• Protected ischemia
• Occur during CPB
• Reperfusion injury
• Occur during intermittent infusion of cardioplegic solution
• After removal of cross clamping
• After discontinuing CPB

41. Measures against antecedent ischemia
• Continue all preoperative CVS drugs like B-blocker, antiarrhythmic, CCB,
digoxin
• Intubation response suppression
• Adequate hydration to enable heart to tolerate hypotension.
• Anesthetic preconditioning

42. Measures against protected ischemia
• Asystole with chemical cardioplegia
• Hypothermia
• Buffering
• Intermittent cross clamping with brief periods of reperfusion
• Left ventricular venting

43. Measures against reperfusion
• Oxygen free radical scavenging
• IV sedation with propofol
• Anti-ischemic agents
• ATP sensitive potassium channel openers
• Cromokalim
• nicorandil
• Agents which increase intravascular adenosine

44. • Cessation of myocardial electromechanical activity
• Reduction of cardiac metabolism.
• Potassium enriched cardioplegia reduces the myocardial oxygen consumption by
90%.
• Augmented with hypothermia by administering cold cardioplegia
• 97% reduction in myocardial oxygen consumption
• Enables the tissue to withstand a complete interruption of blood flow for 20 to 40
minutes.
• Reversed by reperfusing warm normokalemic blood.

45. Cardioplegia
• Arrest of heart in diastole to provide a motionless surgical field
• Composition:
• Crystalloid cardioplegia
• Blood cardioplegia
• Potassium enriched solution arrest the heart in depolarized state
• Del Nido, St. Thomas I and II, Bretschneider’s HTK solution (Custodiol)

46. • Del Nido cardioplegia
• Four parts crystalloid to one part whole blood
• Crystalloid base contains plasmalyte
• In one liter of plasmalyte, addition of:

47. Cardioplegia- Route
Antegrade Retrograde
Cardioplegia delivered within the
ascending aorta or directly into the
coronary ostia
Mimics the natural mechanisms of
coronary flow
Not appropriate in:
Severe coronary artery disease
Presence of aortic insufficiency
Densely calcified ostia
Cardioplegia delivered through coronary
sinus.
Provides distribution of cardioplegia
independent of coronary artery disease
Difficult to place
The septum and RV are often under-
perfused

48. Anesthetic Management Pre bypass
• Induction and maintenance of anesthesia
• Antibiotic prophylaxis
• Positioning
• Anti-fibrinolytics
• Incision and sternotomy
• Treat hypertension and tachycardia due to painful stimuli
• “Lungs down” : Brief interruption of ventilation during sternotomy to
avoid lung injury

49. Sequence of events in CPB
• Priming of circuit
• Anticoagulation
• Cannulation
• Initiation and maintenance of CPB
• Myocardial protection
• Weaning and termination from CPB.

50. Take home message
• Communication between the anesthesiologist, surgeon and the
perfusionist is the key to conduct safe cardiac surgery with CPB.
• Anesthesiologists must be aware about the basic CPB circuit, the
sequences that takes place and their role in it.
• Heparin is given at the dose of 300-400 units/kg before cannulation.
• ACT value should be 400-480 for cannulation.
• Del nido cardioplegic solution ceases electromechanical activity of the
heart and provides motionless surgical field with myocardial
protection

51. Reference
• Miller’s Anesthesia, 9th edition
• Barash et al. Clinical Anesthesia, 8th ed

52. THANK YOU!