심폐기의 발달과 구성

1. 심폐기의 발달과 구성 전북대학교 의학전문대학원 흉부외과학교실 최종범

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 • Still, bloodless heart for cardiac surgery • 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 • Roller pumps • Impeller pumps (Impeller >) • 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