EQUIPMENTS FOR EXTRACORPOREAL MEMBRANE OXYGENATION AN INTRODUCTION TO PERFUSION TECHNOLOGY

1. EQUIPMENTS FOR EXTRACORPOREAL MEMBRANE OXYGENATION –AN INTRODUCTION TO PERFUSION TECHNOLOGY Dr. Chan King-chung Pamela Youde Nethersole Eastern Hospital

2. What is Perfusion Technology? Perfusion Technology is the study of physiology, pathology and associated equipment used to support and/or assume the function of the heart and/or lungs during medical procedures. The perfusionist measures various blood and other parameters to identify appropriate mechanical, pharmacological and thermal manipulation to maintain tissue viability, as directed by physicians. Operation of cardiopulmonary bypass machine

3. Brief History of Perfusion 1813 – Le Gallois First proposed extracorporeal circulation to preserve viability of tissue 1858 – Brown-Sequard Draw his own venous blood Beating venous blood vigorously For oxygenation & defibrination Perfusing an animal limb with syringe ? able to restore local reflexes 1882 – Waldemar von Schroder Bubbling of blood for oxygenation Problem with foaming / gas embolism

4. History 1885 – Max von Frey & Max Gruber “Filming” of blood for oxygenation Dispersing the blood as a thin film inside a rotating slanted cylinder filled with oxygen Very limited oxygenating capacity (small animal) Improved design in 1933 ?

5. History 1895 – Jacobj Use of animal lung as oxygenator for organ perfusion

6. History 1916 – McLean Discovery for heparin for anticoagulation (1870 – Miescher discovered protamine) 1929 – Brukhonenko & Tchetchuline Perfusion of guillotined head of a dog by cross-perfusion

7. History 1934 – DeBakey Invented roller pump for transfusion 1935 – Lindbergh & Carrel Sterile mechanical heart pump

8. History 1944 – Kolff Extracorporeal circuit for dialysis 1951 – Dennis First (failed) attempt of CPB for adult heart surgery 1952 – Lewis First successful ASD closure with open heart under direct vision, with blood inflow stasis and hypothermia only

9. John Gibbon 1937 – First successful CPB on cats 1951 – Screen oxygenator 1953 – First successful CPB for ASD repair

10. Gibbon-IBM Machine

11. History 1955 – Lillehei Repaired intracardiac defects in 32 infants & young children, using a donor adult to provide oxygenation (with cross circulation) 1955 – Mustard Animal lungs used as oxygenator during human cardiac surgery

12. Bubble Oxygenator 1956 – Dewall Bubbling thought to be dangerous Overcome by reservoir, bubble traps and defoaming agents coated chamber Efficient, cheap, easy to assemble, and reusable Explosive development of cardiac surgery

13. History 1960 – Kay & Cross Rotating disc oxygenator 1963 – Bodell Explored use of tubular capillary membrane oxygenator 1965 – Bramson First commercially available membrane oxygenator (silicone rubber sheets)

14. Components of Perfusion Equipments Pump Roller Centrifugal Oxygenator Hollow fibre Silicone membrane Cannulae Arterial Venous Circuit tubing Coating Gas source Haemofilter Temperature control Pressure/Gas Monitors Filter for emboli Anticoagulation / Monitor Priming fluid

16. Much Simpler ECMO Circuit Venous outflow (1x or 2x) ? Pump ? Oxygenator ? Return cannula (± backflow cannula) Gas blender ? Oxygenator Water bath ? Oxygenator

17. Roller Pump Positive displacement pump Commonest pump for CPB A length of resilient tubing located inside a curved raceway Rollers mounted on the ends of rotating arms One roller is compressing the tubing at all times Blood is pushed ahead of the moving roller, thereby producing continuous blood flow Flow determined by Revolutions per minute (rpm) of the pump Volume displaced with each revolution Size of tubing Length of the track

18. Types of Roller Pump Single-roller pump Used for CPB in the 1950s and early 1960s Produce more pulsatility Double-roller pump Most commonly used pump 210-degree semicircular backing plate 2 rollers with the rotating arms set 180 degrees apart one of the two rollers is always compressing the tubing ? a relatively nonpulsatile flow Multiple-roller pump Not clinically available because it causes more haemolysis

19. Tubing of Roller Pump Polyvinyl chloride (PVC) Most widely used Durable Some spallation (release of plastic microparticles) Latex rubber More haemolysis than PVC Silicone rubber Less haemolysis than PVC More spallation then PVC

20. Occlusiveness Adjustable in CPB machine Excessive occlusion Haemolysis and tubing wear Inadequate Compromises forward flow Target “barely nonocclusive” Holding the outflow line with fluid level 60 to 75 cm above the pump Adjust occlusiveness until the fluid level falls at a rate between 1 and 12 cm/min Cause less haemolysis than centrifugal pump in some study

21. Complication Malocclusion (over- or under-occlusion) Miscalibration Fracture of the tubing Loss of power Spallation Capacity to pump grossly visible air Tubing or connectors break with outflow obstruction Microscopic air bubbles ("cavitation") with inflow obstruction Pinhole leaks from fracture in tubing, leading to microscopic air embolism

22. Centrifugal Pump (Kinetic Pump) Mainstay for ECMO Impeller with either vanes or a nest of smooth plastic cones inside a plastic housing Couples magnetically with an electric motor either directly or through a tether When the impeller rotates rapidly, it generates a pressure differential causing blood flow

23. Characteristics

24. Roller vs. Centrifugal Pump

25. Complications Generally safe Allows retrograde flow Exsanguinate a patient by siphon into reservoir Draw air into the arterial line at the cannulation site

26. Oxygenator Separate blood from gas and allow exchange 2 main types in current use Hollow Fibre Silicone membrane (non-porous) Kolobow spiral coil membrane lung Medtronic / Avecor Primarily for ECMO Ability to maintain stable CO2 & O2 for weeks

27. Membrane Lung vs. Natural Lung

28. Achieving Good Gas Exchange Increasing driving gradient of gas (oxygen) Increased blood path length ? Increase surface area ? Increase priming volume Decreasing diffusion path Minimizing blood path thickness placing membranes as close as possible ? Increase resistance Secondary flows (induced eddies) to promote mixing Increasing dwell time of blood in oxygenator ? Increase priming volume

29. Membrane Design Microporous membranes (<1um) Increases efficiency by enhancing diffusion Fluid leakage prevented mainly by surface tension Hydrophobic membrane + coating of pores can produce plasma-proof membrane

30. Other Considerations Blood may flow inside or outside the fiber Inside: fixed thickness of blood, clotting Outside: lower resistance, easier de-airing CO2 transfer depends mainly on membrane material (silicon poorest) Long duration of use reduce efficiency by Coating of platelets/fibrin on membrane surface Water vapour collected in gas pathway Low priming volume reduce haemodilution

31. Oxygenator Design

32. Medtronic Affinity NT

33. Quadrox PLS

34. Specification of Some Oxygenators

35. Specification of Some Oxygenators

36. Cannulae Peripheral vs. Central ECMO Wire-reinforced to prevent collapse Wider, Shorter ? higher flow Side port available in arterial cannula For back flow cannula More side holes preferable for femoral drainage cannula Appropriate length for femoral vs. jugular placement Long femoral return cannula without side holes Coated cannulae available

38. Tubing Standard tubing of 3/8 inch or ½ inch for adult application 3/8 inch was be used mostly in HK for ECMO Coating available

39. Bioline coating form Maquet Covalently bonded heparin to an albumin layer on PVC surface Reduced clotting activity Reduction of platelet adhesion and of thrombi creation Less complement activation & neutrophil activation

40. Carmeda coating from Medtronic End-point attached heparin Decreased thrombus formation Reduced loss of platelets Attenuated inflammatory response

41. Gas Source Usually a simple oxygen blender for ECMO O2 flowmeter may suffice during transport

42. Hemofilter Used in operation to remove fluid CRRT machine for ICU patient on ECMO Attachment to post-pump, pre-oxygenator preferable Avoid shunting Avoid risk of air embolism Cannot tolerate a positive A-pressure for Prisma machine (Meaning of A & V are different in CRRT & ECMO circuit)

43. Temperature Control Thermo-controlled water bath necessary Avoid a high water bath temperature if possible Bubble formation with heating of blood Not more than 4C compared with blood

44. Pressure Monitors Venous pressure Detect insucking Arterial pressure Detect obstruction to outflow Pressure drop across oxygenator Detect oxygenator clotting Risk of thrombosis / infection as a segment of stagnant blood is introduced Integrated senor in the Cardiohelp system (cannot recalibrate)

45. Gas Monitor FiO2 monitor Detects hypoxic sweep gas Venous O2 saturation Detects recirculation Arterial O2 saturation Detects failure of oxygenator Inline pH/pCO2/pO2 monitor Provide continuous ABG data Haemoglobin concentration Detects change in blood volume Bubble detector Prevent gas embolism

46. Others Filter / bubble trapper Anticoagulation / Monitor Heparin ? Lower dose than recommendation by manufacture Higher need for anticoagulation when flow is low Monitor with ACT/APTT/Thromboelastography Priming fluid Colloid / Blood prime in children / infants