Basics of cpb

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- 1 st successful human cardiac surgery using CPB (6 th 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 .

5. 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

6. CPB circuit

7. CARDIOPULMONARY BYPASS CIRCUIT

8. 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

9. 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

10. Typical set up of Roller pump

11. Centrifugal Pump

12. 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) 1/3 rd of total flow by SVC, 2/3 rd by IVC Venous cannula Arterial cannula Cannulation Central or peripheral Open or percutaneous

13. 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

14. 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

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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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)

22. 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.

23. 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

24. 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

25. 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

26. 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

27. 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

28. Major Sources of Microemboli

29. 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

30. 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

31. 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 O 2 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 40 C to prevent denaturation of plasma protein Temperature gradient between body & perfusion circuit gradient remains within 10 o C to prevent bubble emboli

32. 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.

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

34. 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

35. 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 2/3 rd Small patient or PreOp anemia, bank blood can be added. Optimal hematocrit 21-25% (28-30% - children) @ moderate hypothermia (25-32 o C) 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

36. 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

37. 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 1 st 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

38. 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 ℗

39. 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

40. 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

41. 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

42. 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

43. 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 – 37 o C); mild hypothermia (32 – 35 o C); moderate hypothermia (28-32 o C); deep or profound hypothermia (< 20 o C)

44. Acid-base Management Two strategies to manage acid-base during hypothermia, pH & Alpha stat. CO2 becomes more soluble as temperature drops, ↓PaCO 2 , causing alkalosis. “Alpha” in alpha-stat refers to alpha-imidazole ring in histidine which is an important intracellular buffer pH is not correct, PaCO 2 is allowed to fall with hypothermia Maintains cerebral autoregulation, limits microembolism, beneficial in adult Disadvantage is inhomogeneous cooling pH stat maintain a constant pH & PaCO 2 with hypothermia CO 2 added to oxygenator cause increase cerebral flow & cooling If prolonged, can cause severe acidosis Beneficial in infants prone to neurological injury

45. 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

46. 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 10 o C Supplemental doses of anaesthetics are given Ensure acid-base balance, electrolytes, PaO 2 , PaCO 2 , 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

47. 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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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.

54. 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

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