7 unit 4 Foundations of Perfusion Technology and Techniques.pdf

Perfusion Program Foundations of Perfusion Technology & Techniques What we will cover: Unit 4 - Describe the different types of filtering technology used during CPB - Discuss the characteristics of individual filter types used during CPB Filters in the Extracorporeal Circuit Depth Filter • Hig...

Perfusion Program Foundations of Perfusion Technology & Techniques What we will cover: Unit 4 - Describe the different types of filtering technology used during CPB - Discuss the characteristics of individual filter types used during CPB Filters in the Extracorporeal Circuit Depth Filter • High-efficiency polyester depth filter • Polyurethane defoamer • Depth filters create a tortuous path between fibers and retain particles mechanically • Designed to remove debris and gross air, some models may contain a defoamer to reduce bubbles from incoming suction or ports Filters in the Extracorporeal Circuit Screen Filters • most common type and are typically made of a woven polyester mesh • They are usually pleated to allow for a larger surface area in a confined space and trap particulates or emboli that are larger than their particular pore size • Filters come in a size range from 0.2 μm for gas line filters to 40μm for arterial line filters Cardiotomy reservoir, available in 20-120 microns filter Brand: Liva Nova Filters in the Extracorporeal Circuit Screen Filters 0.02 microns (ALF) Arterial Line Filter : 20-40 microns High flow blood filter – commonly referred to ask “Pall Filter” (Pall is one of the original manufacturers of this filter, but many do so now) *40 microns, but 20-30 micron available Pre-bypass Filter 0.2 micron filter <- Integrated ALF Gas line filter Syringe Filters Variable micron size 0.2-20 microns (typically green) 0.2 micron Cardioplegia deliver set with screen filter (circled) 150 micron Brand: Medtronic Filters in the Extracorporeal Circuit Screen filter animation Filters in the Extracorporeal Circuit But what do we do with the bubbles? • Defoaming Agents • All cardiotomy reservoirs and hard shell venous reservoirs have antifoam material • many antifoaming agents are commercially available, but the ones of concern to cardiac surgery are Antifoam A and Antifoam C. • there is little information about the composition of these antifoaming agents that is provided by the manufacturers • Because of this, composition and biological effects poorly understood “Air is bad, ummkay?” Filters in the Extracorporeal Circuit Anti-foam A • pharmaceutical/medical grade antifoams used in extracorporeal devices are silicone oil-based antifoams with silica particles • most widely used silicone oil in extracorporeal devices is Polydimethylsiloxane (PDMS), better known as Simethicone, which consists of 95.1% Polydimethylsiloxane and 4.8% silicone dioxide (hydrophobic silica gel particles) • Simethicone might sound familiar. . . • most well-known type of this pharmaceutical grade antifoam used for extracorporeal devices is Antifoam A Filters in the Extracorporeal Circuit Simethicone • Antacid and anti-gas medication • Ex. Gas-X, Beano, Mylanta • Simethicone is used to relieve the painful symptoms of gas in the stomach and intestines • Oral use obviously has different implications than those associated with use intravascularly. Filters in the Extracorporeal Circuit Anti-foam A (continued) • PDMS-treated hydrophobic silica gel is one of the most hydrophobic dewetting surfaces available and significantly enhances the effectiveness of this antifoam agent • enhancement may result from dewetting of the hydrophobic silica particles by the bubble film which then causes the bubble to collapse due to direct ‘pin like’ mechanical shock, which subsequently disrupts other bubbles nearby • components contained in antifoam A may include heavy metals (<10 ppm), emulsifiers, thickeners and preservatives • first mention of the use of Antifoam A in cardiac surgery goes back to 1955 when DeWall developed a bubble oxygenator made out of 22 gauge needles and polyvinyl tubing arranged in a helix manner Filters in the Extracorporeal Circuit Anti-Foam C • In an attempt to improve biocompatibility and further reduce blood contact with PDMS oil and silica particles, some manufacturers have stopped using of Antifoam A (100% Simethicone) in their cardiotomy filters and replaced it with another silicone based defoamer called Antifoam C (30% Simethicone) • Due to the lower Simethicone content of this antifoam, concentrations of around 50 ppm are needed to suppress foaming in most systems, and its ability to disrupt foam bubbles is more of an oil based dispersant than a mechanical silica based dispersant. Filters in the Extracorporeal Circuit Anti-Foam C • Antifoam C is still a combination of PDMS and silicon dioxide (Simethicone), but contains only 30% Simethicone by weight of the Dow Corning Antifoam A compound • • Antifoam C also contains methylcellulose, sorbic acid and water Antifoam C appears to be as effective as Antifoam A in addressing blood foam, an also provides further reduction in blood exposure to silica during extracorporeal circulation <- Blood enters Leukocyte reducing filter (Leuko Guard) <- Blood Exits Filters in the Extracorporeal Circuit • Air entrainment through the venous return line, fluid, drug and blood administration through the cardiotomy reservoir, as well as ingress of air and particulate matter from cardiotomy suckers and vents, all contribute to the embolic load patients may be exposed to. • While it is not possible to eliminate the embolic load in its entirety, the use of arterial filters and bubble traps can reduce this significantly. Filters in the Extracorporeal Circuit Bubble Point Pressure • bubble point pressure is known as the pressure at which the first bubble of gas comes out from the liquid at a given temperature • The gas that has less density can quickly move from the liquid • Therefore, increasing the gas density or gas specific gravity decreases the bubble point pressure • Theoretically this will lead to bubbles escaping liquid exponentially faster after the initial “bubble point pressure” is reached Filters in the Extracorporeal Circuit Bubble point vs Dew Point • Isn’t dew point for meteorologists’ reporting the weather? • Well, kinda • The limits in the case of gas-liquid phase changes are called the bubble point and the dew point • The names imply which one is which: • The bubble point is the point at which the first drop of a liquid mixture begins to vaporize. • The dew point is the point at which the first drop of a gaseous mixture begins to condense. Filters in the Extracorporeal Circuit Bubble Point Pressure. . . Just a little bit more • Below bubble point pressure, the liquid composition is changing as pressure decreases *This is why an “Insta Pot” works so quickly – it has temperature and pressure! • Below the bubble point pressure, the solution gas is liberated with decreasing reservoir pressure or redissolved with increasing the pressure • This is part of the reason there are manufacturer listed reservoir minimums while actively pumping blood (on bypass) • Theory: the lower the reservoir level, the higher the chance for liberated gas from solution (micro-air). • But don’t forget – temperature has an effect of this action as well. . . The bubble point is the same as the boiling point for a pure liquid But for a mixture, the bubble point occurs when enough energy is supplied for the mixture to first change phase (evaporate, or release vapor) Filters in the Extracorporeal Circuit Arterial Line Filter • arterial-line conventional microfilters are used in nearly all adult and pediatric CPB cases in the United States. (now an AmSect standard) • Heparin-coated arterial-line micropore filters have been introduced to reduce platelet aggregation and loss, and to facilitate debubbling and priming • Available filter size ranges from 20-40 microns, with 38-40 microns being the most commonly used ALF size. • Smaller micron pore size results in greater GME removal, but higher platelet damage, hemolysis, and compliment activation, and potentially higher pressure drop at the same flow (in LPM). • STS: Class I, level of evidence A: and the 2013 AmSECT Standards and Guidelines for Perfusion Practice state that “[a]n arterial-line filter shall be used during CPB procedures” (Standard 6.5) (7) A: Conventional adult arterial-line microfilter and bubble trap. Blood enters tangentially at the top (A), which encourages any possibly entrained bubbles to rise to the top where they are vented out through a continuous purge line connecting the threeway stopcock to the cardiotomy or venous reservoir. Blood then passes through a screen microfilter (20–40-μm pore size), which also serves as a barrier to the passage of gaseous microemboli Filters in the Extracorporeal Circuit AngioVac B: Arterial-line bubble trap. The design and flow dynamics are similar to the arterial filter, but blood only passes through a coarse screen strainer (approximately 170-μm pore size). Filters in the Extracorporeal Circuit Leukocyte-Depleting Filters Leuko Guard • Activation of leukocytes and release of cytokines are thought to be major contributors to the systemic inflammatory response syndrome (SIRS) and organ injury that may follow CPB, especially in organs subject to ischemia/reperfusion (e.g., heart and lungs). • *** LD Filters commonly used in Lung transplant surgery • These contain nonwoven polyester fibers that have been surfacemodified to remove leukocytes. • LD filters may be placed in many different locations in the ECC, including the arterial line, venous line, and cardioplegia line, and leukofiltration may be performed on cardiotomy suction blood, cell saver blood, residual pump blood, and transfused blood products (RBCs, platelets, fresh frozen plasma [FFP]) • The effects of LD filters are probably influenced by both pressure and flow passing through them, and they probably become saturated and less efficient over time. • They appear to be more selective at removing activated than nonactivated WBCs LD Filter specific for cardioplegia inline insertion Filters in the Extracorporeal Circuit Depth filters Screen Filters • Consists of packed fibers of Dacron wool or polyurethane foam • Composed of a woven mesh of polyester fibers • NO defined pore size • Defined pore sizes • Sizes 20-40 microns • These filters have large wetted surface areas to • All of the arterial line filters used in filter the blood by absorption, and they are modern times are screen filters effective in trapping gross bubbles