심폐기의 발달과 구성

전북대학교 의학전문대학원 흉부외과학교실최종범

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)

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)

• 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

Cardiopulmonary Bypass

• Goals1. Still, bloodless heart for cardiac surgery2. Replacement of cardiac and pulmonary function

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

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

Basic CPB circuit with oxygenator and centrifugal pump

Typical CPB Circuit

Pumps

• Two principle types– Displacement pumps

• Roller pump• Non occlusive roller pumps

– Rotatory pumps• Radial (centrifugal) pumps• Axial pumps (Archimedes’ screw)• Diagonal pumps

Roller Pumps

• Most commonly used• Volume Displacement • Non pulsatile blood flow

• Used for • Forward flow• Cardioplegic delivery• LV vent suction

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)

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

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

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

Differences of Rotatory Pumps

Alternate Classification of Pumps

a. Roller pumpsb. Impeller pumps (Impeller >)c. Centrifugal pumps (Cone >)

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

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

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

Disk or bubble oxygenator

• Direct contact oxygenators• Bubbles in direct contact with blood • Increasing cellular trauma

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

Deforming Chamber of Bubble Oxygenator

• Deforming the frothy blood• Large surface area coated with silicone

– Increased surface tension of bubbles -> causing them to burst

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

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)

Membrane Oxygenator

• Microporous / Hollow fibers

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

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

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

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

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

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.

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

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

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

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

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

• 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