Pumps, oxygenators and priming solution

PUMPS AND OXYGENATORS

1. Pumps, Oxygenators and Priming Solutions

2. Pumps in Cardiopulmonary Bypass

3. Ideal pump Move large volumes against significant pressure (7 l/min against 500 mmHg ) Minimize flow velocity- limit damage to blood Inert pump components – no activation of coagulation and inflammation Minimal dead space – avoid stagnation and turbulence Calibration - easy, reliable, and reproducible Manual operations possible

4. Positive displacement pump Periodic volumetric change of a working space Low volume but high pressure flow Centrifugal pump Energy transfer due to velocity deflection High volume low pressure flow Pumps - Classification

5. Roller pump – Working principle Contain a length of tubing inside a curved raceway placed at the travel perimeter of rollers mounted on the ends of rotating arms “Rolls” blood through piece of tubing. Generates both negative and positive pressures. Independent of resistance ( afterload ) hydrostatic pressure head (preload)

6. Stroke volume and blood flow Roller pump – Working principle TUBING DIAMETER(IN) STROKE VOLUME(ML) BLOOD FLOW(L/MIN) AT 150 RPM 3/16 7 1050 1/4 13 1950 3/8 27 4050 1/2 54 8100

7. Advantages Simple to use. Low cost. Preload and Afterload independent

8. Disadvantages Spallation Tube material fatigue Blood cell damage Pump air Cavitation Potential pressurisation of arterial line.

9. Non occlusive roller pumps Rhone – Poulenc in France. MC 3 Pump. Passive filling peristaltic pump. Combines advantages of centrifugal and roller pumps. Two sheets of flat polyurethane tubing bonded at edges which are stretched under tension over three rollers. Completely flat pump chamber. No backing plate against which the tubing can be compressed. Priming volume 120 ml.

10. Non occlusive roller pumps – Working Principle

11. Non occlusive roller pumps – Working Principle

12. METAPLUS PUMP Pump position is fixed in relation to the hard shell venous reservoir. Large bore, semi-rigid, U-shaped tubing connects the outlet of venous reservoir to inlet of pump PUMP ROTOR AND MOTOR ASSEMBLY VENOUS RESERVOIR AND MEMBRANE OXYGENATOR

13. Advantages Preload dependent – cannot suck air. No retrograde flow when pump stopped. Blood damage and microbubble generation is reduced as no negative pressure generated. Non occlusive nature – tubing wear reduced.

14. Centrifugal pump In early 1970s, research related to the development of an artificial heart was basis of the development of centrifugal pumps for CPB. Boimedicus 600 - 1973. In the United States, the centrifugal pump is extensively used.

15. Centrifugal Pump – Working Principle Creating pressure gradient between inlet and oulet of pump. This pressure gradient results from the creation of a vortex by the rotation of the pump head. The vortex can be created by using cones that impart motion to the blood by viscous shear or by rotating impellers. The rotating motion creates an area of low pressure in the center and an area of high pressure on the sides.

16. Centrifugal Pump – Working Principle

17. Centrifugal Pump – Working Principle Resultant blood flow- The resistance at the outlet is a function of two components: the CPB circuit and SVR. Centrifugal pumps are afterload dependent and flow is influenced by changes in resistance in both the circuit and the patient Flow meter necessary.

18. Centrifugal force Centrifugal Pump – Working Principle

19. Centrifugal Pump – Working Principle HEAT GENERATION: All centrifugal pumps will generate heat depending on the amount of energy that is impaired into the blood. Combination with the low flow in the center of the pump head - may create blood clots and blood cell activation in the pump.

20. SPECIFIC CLINICALLY AVAILABLE CENTRIFUGAL PUMPS BIOMEDICUS PUMP In 1976, the first centrifugal pump was used for CPB. The pump head is acrylic, with inlet and outlet ports oriented at right angles to each other, and its priming volume is 80 ml. Cones driven by magnetic coupling to external console.

21. CENTRIFUGAL PUMPS - Capiox pump Rotor with unique straight path design to reduce pump rotational speed without decreasing hydraulic efficiency Small priming volume – 46 ml reduces stagnant flow within the rotor

22. CENTRIFUGAL PUMPS – Nikkiso Pump Smallest commercially available pump Priming volume of 25 ml. Made of polycarbonate, with a V shaped ring seal that separates the pump housing and the actuator chamber. Seal – made of fluororubber , suppresses heat generation and prevents blood leakage. Six washout holes are incorporated into impeller to generate blood flow from the back to front surface of the impeller. These holes prevent thrombus formation in areas behind the impeller and around the sealing part.

23. Problems associated with centrifugal pumps Flow rate affected by preload and after load. Retrograde flows down the arterial line. Potential air entrapment if inadequate aferload . For forward flow pressure in the pump head (PP) must be greater than the combined patient pressure (PPT) and the pressure head (PH) {hydrostatic pressure}.   --PP > PPT + PH  forward flow

24. Centrifugal Pump vs Roller Pump Expensive Inexpensive Pump flow function of SVR Flow predictable based on pump speed Cannot pump large amount of air Can pump large amount of air Pump stalls on occlusion without generating high suction or outlet pressure. Potential to overpressurize circuit if inadvertently clamped. Retrograde flow when pump slows / stops No retrograde flow. Does not require continous monitoring Continuous strict monitoring of blood level Hemolysis and damage to formed blood elements is less More hemolysis and damage to formed blood elements. Less wear and tear of pump. No spallation More wear and tear of tubing in pump head. Spallation.

25. Oxygenator Blood gas exchange device.

26. Oxygenator Oxygenate venous blood. Remove CO2 Represent the largest surface area to which circulating blood is exposed. Components - Membrane module Heat exchanger Reservoir

27. AN IDEAL OXYGENATOR Oxygenation of venous blood : device must have sufficient capacity to provide oxygenation over a wide range of venous flow rate. Carbon dioxide elimination to avoid hypercarbia or hypocarbia . Minimum trauma to the blood Small priming volume - to limit the deleterious effects of hemodilution Safety

28. CLASSIFICATION Bubble oxygenator: The earliest oxygenators. Exchange gases through direct interaction of gas and blood. These devices were used during early advent of CPB. Membrane oxygenator Semi-permeable barrier that separates fluid from gas. Diffusive qualities of the membrane material determine the transfer of oxygen and carbon dioxide between phases.

29. BUBBLE OXYGENATORS First widely available commercial oxygenators Structure : 3 sections of operation Bubble column Defoaming area Arterial reservoir Desaturated blood passively enters mixing chamber, where 100% oxygen flows across a disparager plate into the stream of blood, which forms small bubbles

30. BUBBLE OXYGENATORS Blood becomes oxygenated and carbon dioxide is reduced as stream of gas percolates through blood. Blood is defoamed by the presence of silicone antifoam-A, which consist of the liquid polymer dimethylpolysiloxane (96%) and particulate silica (4%), which destabilizes the bubbles, causing them to implode.

31. BUBBLE OXYGENATORS The arterialized blood is collected in an arterial reservoir that is then actively pumped. The simple design of bubble oxygenators relies on the hydrostatic pressure head from the patient to the mixing chamber connected by the venous line. The pressure drop through bubble oxygenator is <30 cm of water, in contrast to the 100 cm of water pressure drop typically found in membrane oxygenators.

32. BUBBLE OXYGENATORS Bubble size is critical to adequate gas transfer. The bubble size selected must be a compromise between optimal surface area for oxygenation and volume for carbon dioxide transfer. Decreasing size of bubbles increases total surface area of blood gas interface with better oxygenation but limiting total CO2 transfer. Bubble sizes of 3 to 7 mm are used to optimize both O2 and CO2 transfer.

33. MEMBRANE OXYGENATORS Complete barrier between the gas and blood phases and diffusion is through membrane material Costly to manufacture and require large priming volume Most membrane lungs used for CPB have micropores

34. Willem J. Kolff During dialysis in 1943 noticed that the blue blood in the rotating-drum artificial kidney became red Clowes and Neville(1958) Poineers in using membrane oxygenators ( teflon flat membranes)

35. MEMBRANE OXYGENATORS – Materials Historically – Cellulose. Polytetrafluoroethylene Polyethylene Currently - Silicon rubber (homogeneous, nonporous membrane). Polypropylene (heterogeneous, microporous, hydrophobic membrane).

36. Silicone Vs Polypropylene Membrane Silicone membrane Long term support Without a diminution in gas transfer capacity Avoid plasma leakage and membrane wet out Microporous polypropylene membrane Cheap Good for short periods New generation membranes that incorporates benefits of silicone with polypropylene have been developed.

37. MEMBRANE OXYGENATORS – Designs Membrane materials are organized in three configurations: Scrolled envelope Parallel plate Hollow fiber

38. Types of Membrane Oxygenators Plaque oxygenators - microporous expanded polypropylene - folded Z shape - blood & gas flow opposite direction - Cobel Excel, Cobe VPCML,Shirley M2000 Spiral oxygenators - silicon membranes - rolled around central axis - Kolobow oxygenator.

39. Types of Membrane Oxygenators Hollow fibre oxygenator 1970 Benlips introduced Capillary fibers of microporous polypropylene

40. Spiral Membrane Oxygenators Kolobow Silicon membrane in shape of an envelope that is coiled on itself. Used primarily in ECMO Ability to maintain stable CO2 and O2 for long periods (weeks). Available in gas exchange surface area sizes from 0.5 to 4.5 m2.

41. Hollow Membrane Oxygenators Blood flow inside the capillaries Gas flow inside the capillaries Blood flow through the fiber was abandoned - High trans membrane pressure Activation of platelets Increased haemolysis Blood flow either perpendicular or in the direction of fiber bundle In latter case, blood will flow in a counter current direction to the gas flow - Optimized gas gradients during the dwell time

42. Membrane oxygenators & lung MEMB OXYGN LUNG SURFACE AREA(M 2 ) 0.5-4 70 Blood path width (µm) 200 8 Blood path length (µm) 250000 200 Memrane thickness (µm) 150 0.5 Max O2 transfer(ml/min) 400-600 2000

43. ADVANCES IN OXYGENATORS Biocompatibility Heparin coating – 1980's Surface Modifying Additive— Polydimethylsiloxane polycaprolactone oligomer Phosphorylcholine Bioline X Coating Trillium Biopassive Surface—polyethylene oxide. Cost-effectiveness'????

44. Priming Solutions

45. Priming solutions for CPB Circuit Need of prime – to achieve adequate flow rates on initiation of CPB without air embolism. Ideal prime - Similar electrolyte content, osmolarity and pH as that of plasma. On mixing with blood maintains oxygen delivery, CO2 removal and physiological homeostasis.

46. Historical perspective of prime solutions

47. Homologous blood syndrome Blood borne infection Severe pulmonary insufficiency Impaired immunity – wound infection, sepsis Impaired resistance to Malignant cell transformation Graft versus host disease

48. Impetus for nonhemic prime Severe strain on hospital blood bank Increased access to the emergency surgery Increased exposure to O 2 in polycythemics Refusal of hemic prime from Jehovah’s witness faith Experimental success of hemodilution in CPB

49. Glucose in priming solution 1962, Cooley – 5% dextrose in addition to blood - improves outcome Solution with glucose as major component – isotonic but after metabolisation of glucose become severely hypotonic Fluid shift from Extracellular to Intracellular compartment - Red blood cell lysis Pulmonary edema Cerebral edema Hyperglycemia – poor neurological outcome Priming solution – N ormotonic , near physiologic sodium concentration.

50. Colloidal Priming solution Hemodilution – decreased colloid oncotic pressure – fluid shift into intracellular compartment – cellular edema and dysfunction. Colloid solution - counteract reduction in colloid oncotic pressure – prevent fluid shift. CPB – systemic inflammatory response – tight junctions at endothelial lining "permeable" to high molecular weight proteins – high molecular weight protein trapped in ECF – paradoxical increase in cellular edema.

51. Common priming solutions

52. Additives to priming solution

53. Experimental prime solutions Perfluoro carbons - 0.118 microns, half the viscocity of blood -O2 release even at low po2 environments -O2 relase is not related to pH/ temp - can perfuse distal capillareis - still at experimental stage Stroma free Hb -natural O2 carrying capacity &osmotic activity -lower viscocity than blood -do not cause immunosuppression -still in preclinical testing

54. Priming Solution (AIIMS) Ringer lactate – 20 ml/kg. Hydroxy Ethyl Starch – 10 ml/kg. Mannitol – 5 ml/kg. Soda bicarbonate – 1 ml/kg. Heparin – on the basis of circuit used. If blood is added to prime – additional soda bicarbonate 10ml/300ml blood is added.

55. Mannitol Potent osmotic diuretic. Maintain urine output during CPB and in immediate post bypass period. Preserves renal function. Free radical scavenger.

56. Oxygenator-heat exchanger Heat exchanger Membrane oxygenator

57. Pump tubings Internal diameter (inch) Volume (ml/feet) Used as 1/4 8.6 Suction / vent <6kg – art./venous line 3/8 21.6 <10 kg – venous line. >11 kg – arterial line 1/2 37.0 > 20 kgVenous line

58. CPB circuit according to age Weight (kg) Oxygenator Prime vol (ml) Art. line Venous line Circuit Priming vol. (ml) Heparin (mg) Max. Flow (lt/min) < 6 Baby Rx 35 1/4 1/4 400 - 500 25 1.2 6 - 10 Minimax 109 1/4 1/4 or 3/8 400 –600 25 - 30 2.3 11 - 20 Sx 10 135 3/8 3/8 1000 - 1100 50 3.5 >20 Affinity NT 290 3/8 1/2 1500 - 1700 75 7

59. Priming volume Volume required to fill the arterial and venous limbs, adequate voulme in reservoir to prevent air entering the arterial line on initiation of CPB. Acceptable hemodilution ??

60. Calculation of Blood Volume to be added Pts estimated blood volume x Hct Predicted Hct = ____________________________ Pts estimated blood vol +CPB prime+ pre CPB iv fluid volume (TCV) RBC Vol. To be added = TCV ( Hct Desired – Hct Predicted) Bank Blood volume to be added = RBC Vol to be added / 0.7

61. Blood preservation techniques Pre CPB – Retrograde circulation Adult Hct > 32% CVP > 8 mm hg. SBP > 80 mm hg On CPB – Hemofilter . Cell Saver. Post CPB – Chase prime with crystalloid. Completely reverse and pack

62. Thank you