심폐기의 발달과 구성
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심폐기의 발달과 구성. 전북대학교 의학전문대학원 흉부외과학교실 최종범. 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) - PowerPoint PPT PresentationTRANSCRIPT
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심폐기의 발달과 구성
전북대학교 의학전문대학원 흉부외과학교실최종범
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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)
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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)
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• 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
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Cardiopulmonary Bypass
• Goals1. Still, bloodless heart for cardiac surgery2. Replacement of cardiac and pulmonary function
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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
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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
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Basic CPB circuit with oxygenator and centrifugal pump
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Typical CPB Circuit
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Pumps
• Two principle types– Displacement pumps
• Roller pump• Non occlusive roller pumps
– Rotatory pumps• Radial (centrifugal) pumps• Axial pumps (Archimedes’ screw)• Diagonal pumps
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Roller Pumps
• Most commonly used• Volume Displacement • Non pulsatile blood flow
• Used for • Forward flow• Cardioplegic delivery• LV vent suction
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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)
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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
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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
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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
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Differences of Rotatory Pumps
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Alternate Classification of Pumps
a. Roller pumpsb. Impeller pumps (Impeller >)c. Centrifugal pumps (Cone >)
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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
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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
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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
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Disk or bubble oxygenator
• Direct contact oxygenators• Bubbles in direct contact with blood • Increasing cellular trauma
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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
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Deforming Chamber of Bubble Oxygenator
• Deforming the frothy blood• Large surface area coated with silicone
– Increased surface tension of bubbles -> causing them to burst
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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
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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)
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Membrane Oxygenator
• Microporous / Hollow fibers
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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• 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