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A comparative study of adult arterial line filters / Matthew P. Tittl.

by Tittl, Matthew P.

Cardiopulmonary bypass -- Adverse effects

Extracorporeal Circulation -- methods

Blood -- Circulation, Artificial -- Complications.

Commercial products -- Testing

Assorted pagination : ill. ; 29 cm.

Committee members: Dr. Larry Fennigkoh, Dr. Charles Tritt, Dr. Vincent Canino

Clinical advisors: Charles Alterbern, Matthew Hietpas

Introduction -- Experimental materials and methods -- Statistical and analytical methods -- Results -- Discussion -- Conclusion -- References -- Arterial line filter and experimental equipment manufacturers -- Appendix A) The Coulter Z series counter - Principles of operation B) The Hatteland instrumenting CMD20 cardiovascular microbubble detector C) The manual platelet count - Unopette method D) Sigma diagnostics test for plasma hemoglobin E) Bovine blood preparation protocol F) The Hemochron 401 whole blood coagulation system - Principles of operation G) Arterial line filter connection schedule H) Exact tubing measurements for the arterial line filter test circuits -- Publishing information -- Supplement table of contents.

This experiment is titled "A Comparative Study of Adult Arterial Line Filters". The arterial line filter is considered one of the most important devices in the cardiopulmonary bypass (CPB) circuit since it represents the final filtering mechanism for the bloodstream before it returns to the patient. Considering both the significance and the limited amount of literature or standards available concerning this subject, a definite need existed for an independent, unbiased, and updated comparison of arterial line filter performance.

This project examined the performance characteristics of some prominent adult arterial line filters currently available on the market. Areas of evaluation included particle filtration efficiency, pressure drop (resistance), air filtration efficiency, platelet depletion, plasma-free hemoglobin generation (hemolysis), and priming ease. These are the most critical factors for positive patient outcomes when CPB is employed.

Presently, the primary adult arterial line filter manufacturers include C.R. Bard, Baxter (Bentley), Cobe, Gish, Jostra, Medtronic (Acevor), Pall, Sorin (Dideco), and Terumo. To request comparable product samples and explain the objectives and testing protocol of the study, representatives from each of these corporations were contacted. Eight samples of eleven filter brands and six samples of two filter brands were then obtained. Miscellaneous tubing, connectors, and supplies were also acquired.

The testing protocol was divided into three distinct phases. Phase I investigated particle filtration using a normal saline perfusate. Phase II studied air filtration efficiency using a normal saline perfusate. Finally, Phase III examined air filtration efficiency, platelet depletion, and plasma-free hemoglobin generation using a fresh bovine blood perfusate. In all phases, priming ease and pressure drop characteristics were recorded.

To accurately determine particulate filtration efficiency, the Beckman-Coulter Z2 particle counting device (Beckman-Coulter Incorporated, Hialeah, Florida) was utilized. Flows and pressures were maintained at constant levels. A mixture of polymer spheres was used to represent foreign particulate in the CPB circuit. These contaminants were injected into the circuit prior to each filter, and the resulting number of spheres remaining downstream were measured and recorded.

Pressure drop was measured by attaching a DLP-60000 digital pressure monitor (DLP Incorporated, Grand Rapids, Michigan) near the inlet and outlet of each filter. Flow was then varied from 1 LPM to 6 LPM, with the purge line opened for one measurement set and closed for the other. The difference between the two pressure monitor readings represented the pressure drop.

Air removal efficiency was measured with the Hatteland Instrumentering CMD-20 microbubble detection device (Hatteland Instrumentering, Reyken, Norway). Flows and pressures were maintained at constant levels. Small and large air boluses were injected into the circuit prior to each filter, with the purge line open for one measurement set and closed for the other. The number of all downstream bubbles, with their respective sizes, was then measured and recorded.

Platelet depletion and plasma-free hemoglobin generation were measured over a two-hour CPB duration by drawing periodic blood samples from the CPB circuit. Flows, pressures, and hematocrits were maintained at constant levels. Platlets were isolated from other blood cells using a prepared chemical solution and counted manually under a microscope. Plasma-free hemoglobin levels were found using a specific chemical assay available from SIGMA Diagnostics (SIGMA-Aldrich Corporation, St. Louis, Missouri).

Priming ease was measured in all three phases by observing the time taken from beginning of filter priming to the total absence of air bubbles downstream, as verified by the Hatteland Instrumentering CMD-20 microbubble detection device. An identical flow rate and priming procedure was utilized for each filter. Average priming times were then calculated from the results of the three phases.

Whenever appropriate, control trials were performed to determine what influence the arterial line filter actually had on the performance variables tested. In addition, some controls were necessary to validate the Phase III testing protocol. Using these controls, various measurements of arterial line filter performance were adjusted accordingly.

The arterial line filters removed particles greater than their respective pore sizes (20 ιm to 43ιm) in an 86.6% to 100% range. At a maximum flow rate, arterial line filter resistances (which were calculated using pressure drop data) ranged betwen 5.7 PRU and 8.1 PRU using a normal saline perfusate and 5.7 PRU and 8.2 PRU using a bovine blood perfusate. The arterial line filters passed air bubbles greater than their respective pore sizes in a 0 to 5 count range. After 120 minutes of operation with the bovine blood perfusate, platelets were depleted in a 5.20% to 17.85% range with respect to the initial counts, and a plasma-free hemoglobin (a blood cell hemolysis indicator) was generated in an 85.0% ro 177.2% range with respect to the initial levels. Finally the arterial line filters were completely primed and debubbled in a 57 sec to 120 sec range. Control values are not included in these results, but they are included with the adjusted performance values in the report.

Statistical analyses were performed using the one-way and two-way analysis of variance, pairwise comparisons, and correlations. The tables and graphs necessary for effectively presenting the information were also developed. Finally, three overall rating systems were devised to serve as ultimate comparisons of these arterial line filters.

Significant differences in performance, for both better and worse, were identified among arterial line filters in most of the evaluation areas (p <0.05). Significances were also observed in specific performance variables, regardless of arterial line filter brand, as they were adjusted according to protocol (p <0.05). Finally, excluding platelet depletion and plasma-free hemoglobin generation, significantly different results were evident when comparing control circuits to those including arterial line filters (p <0.05). This supports the initial premise that the use of arterial line filters in CPB circuits provides satisfactory protection against particulate contaminants and air emboli.

Altogether, 532 statistically significant correlations were identified and quantified (p <0.05). However, only twenty-three of these correlations were considered applicable using a +/-0.7 correlation coefficient (r) standard. The number of significant relationships was lower than anticiplated, and those identified oftentimes did not occur in the expected areas of performance. This may be the result of the particular data recorded during this experiment, which was subject to fluctuations considering the possible circumstances for relativity. Therefore, the relationships identified and unidentified in this experiment might not be indicative of the arterial line filter population as a whole.

Each filter was ranked in six categories according to the results, and three overall performance indices were developed. A variety of best performers was observed, which suggested an effort by individual manufacturers to produce arterial line filters excelling in specific performance areas. While designing and fabricating an arterial filter to perform the best in all of these categories may be an impossible assignment, the Baxter-Bentley AF1025D Duraflo II appeared to achieve the superior balance throughout the six primary performance areas.

Emphasized throughout the experiment, the arterial line filter is regarded as the most important safety device of the CPB circuit and the last line of defense for removing dangerous microemboli from the blood before it returns to the patient. Considering this significance, frequent and through arterial line filter assessments are essential now and in the future. The ultimate values of this project, therefore, are ease of repeatability and flexibility for future evaluation of new and additional arterial line filters, including pediatric varieties. A continual pursuit toward filtration perfection will enhance CPB outcomes and ultimately improve the entire profession of cardiac surgery.

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