Gaseous Microemboli Research Articles

Extracorporeal bubbles: a word of caution

Gaseous microemboli (GME) are a cause of neurocognitive deficit postcardiac surgery with cardiopulmonary bypass. However, the measurement of microbubbles during cardiopulmonary bypass is not easy, because blood is an opaque fluid and contains microparticles. Recently, two new microbubble counters, the Gampt BC200 and the emboli detection and classification (EDAC) quantifier, were developed for use during cardiac surgery. The accuracy of both devices was validated against industrial standards. A clear blood analogue (30%/70% glycerol-water) was pumped, by means of a rollerpump out of a partially filled arterial line screen filter with a nominal pore size of 20 microm. Downstream the pump, all test sensors and an optical cuvette, were inserted in a vertically mounted 3/8 inch tubing. Measurements were taken at flows of 405, 1080, 3000 and 6000 ml/min. Backlight shadowgraphy and optical counting were used as industrial reference techniques for measuring size and counts. On average the EDAC quantifier underestimates average bubble diameter by 35+/-1%, 13+/-8%, 71+/-7% and 33+/-4% at 405, 1080, 3000 and 6000 ml/min, respectively. The Gampt BC200 has good sizing agreement at 1080 ml/min (+5+/-17%) and 3000 ml/min (+33+/-6%) but overestimates average diameter by 220+/-40% and 295+/-49% at 405 and 6000 ml/min, respectively. Both devices only partially count the number of microbubbles at higher flows. At 3 l/min the EDAC counts 38%, the Gampt 18% of total counts and at 6 l/min both the EDAC and Gampt only count 3% of total counts. Both the EDAC and Gampt can be used in a clinical setting for monitoring basal GME production. However, both devices have some major limitations when used for studying 'worst case' scenarios. One should take great caution when correlating measured data with neurocognitive outcome. Finally, results obtained by one device in a first study cannot be compared nor exchanged with results from the other device in a second study.

Clinical Real‐Time Monitoring of Gaseous Microemboli in Pediatric Cardiopulmonary Bypass

We describe the occurrence and distribution of gaseous microemboli with real-time monitoring in a pediatric cardiopulmonary bypass (CPB) circuit and in the cerebral circulation of patients using the Emboli Detection and Classification (EDAC) system and transcranial Doppler (TCD). Four patients (weights 3.2-13.8 kg) were studied. EDAC monitors were located on the venous line and on the postfilter arterial line to measure gaseous microemboli in the CPB circuit. TCD was used to measure high-intensity transient signals (HITS) in the middle cerebral artery. Before the initiation of CPB, EDAC detected gaseous microemboli in two cases when giving volume through the arterial line. At the initiation of CPB, gross air appeared in the venous line and gaseous microemboli were detected in the arterial line in all patients. EDAC detected a total of 3192-14 699 gaseous microemboli in the arterial line during the whole CPB period, more than 99% of which were smaller than 40 microns. After cessation of CPB, EDAC detected gaseous microemboli in the arterial line in all cases. The TCD detected HITS in two cases (25 and 315), and detected no HITS in two cases. We observed that the venous line acted as a principal source of gaseous microemboli, particularly when using vacuum-assisted venous drainage, and that a significant number of these gaseous microemboli smaller than 40 microns were subsequently transferred to the patient. Using EDAC and TCD together could strengthen the monitoring of gaseous microemboli in the extracorporeal circuit and cerebral circulation.

Evaluation of Membrane Oxygenators and Reservoirs in Terms of Capturing Gaseous Microemboli and Pressure Drops

An increasing amount of evidence points to cerebral embolization during cardiopulmonary bypass (CPB) as the principal etiologic factor of neurologic complications. In this study, the capability of capturing and classification of gaseous emboli and pressure drop of three different membrane oxygenators (Sorin Apex, Terumo Capiox SX25, Maquet QUADROX) were measured in a simulated adult model of CPB using a novel ultrasound detection and classification quantifier system. The circuit was primed with 1000 mL heparinized human packed red blood cells and 1000 mL lactated Ringer's solution (total volume 2000 mL, corrected hematocrit 26-28%). After the injection of 5 mL air into the venous line, an Emboli Detection and Classification Quantifier was used to simultaneously record microemboli counts at post-pump, post-oxygenator, and post-arterial filter sites. Trials were conducted at normothermic (35 degrees C) and hypothermic (25 degrees C) conditions. Pre-oxygenator and post-oxygenator pressure were recorded in real time and pressure drop was calculated. Maquet QUADROX membrane oxygenator has the lowest pressure drops compared to the other two oxygenators (P < 0.001). The comparison among the three oxygenators indicated better capability of capturing gaseous emboli with the Maquet QUADROX and Terumo Capiox SX25 membrane oxygenator and more emboli may pass through the Sorin Apex membrane oxygenator. Microemboli counts uniformly increased with hypothermic perfusion (25 degrees C). Different types of oxygenators and reservoirs have different capability of capturing gaseous emboli and transmembrane pressure drop. Based on this investigation, Maquet QUADROX membrane oxygenator has the lowest pressure drop and better capability for capturing gaseous microemboli.

An In Vitro Study of the Effectiveness of Carbon Dioxide Flushing of Arterial Line Filters

Gaseous microemboli (GMEs) have been connected to neurologic impairment and other ischemic complications after surgery. The components of the extracorporeal circuit (ECC) have a large influence on GME production. This in vitro study investigates the use of carbon dioxide flushing of the 38-μm Medtronic Affinity CB351 and 38-μm Medtronic Affinity 351 arterial line filters (ALFs) to decrease GMEs and time for air to clear the ALF. An adult circuit was implemented with a silicone oxygenator for vacuum-assisted gas removal and to reduce air before ALF. The 48 filters were separated into four equal groups: flushed coated and non-coated and non-flushed coated and non-coated. Carbon dioxide flushing was performed at 6 L/min for 3 minutes. ALFs were retrograde primed at 200 mL/min. An Emboli Detection and Classification Quantifier (EDAC) was used to gather data. The average total emboli and time to clear (seconds) for flush coated were 20.25 ± 16.78 and 142.17 ± 174.80 seconds, respectively, flushed non-coated were 30.5 ± 34.65 and 124.17 ± 131.40 seconds, non-flushed coated were 162.08 ± 79.90 and 390.42 ± 84.36 seconds, and non-flushed non-coated were 163.67 ± 212.67 and 305.92 ± 179.36 seconds. Flushed filters had an average total emboli count of 25.375 ± 27.14 and an average time to clear of 133.167 ± 151.51 seconds. Non-flushed filters had an average total emboli count of 162.875 ± 157.11 and an average time to clear of 348.167 ± 143.70 seconds. Coated and non-coated filters for total emboli and time to clear had p values of .86 and .24, respectively. Flushed and non-flushed filters had total emboli and time to clear p values of &lt;.001 and &lt;.001, respectively. No significant difference was found between coated and non-coated filters involving total embolic count and time to clear. A significant difference was found in total embolic count and time to clear between flushed and non-flushed filters. This study shows that fewer emboli and faster embolic clearance time correlate with carbon dioxide flushing of the ALF.

Gaseous Microemboli in a Pediatric Bypass Circuit with an Unprimed Venous Line: An In Vitro Study

Miniaturizing cardiopulmonary bypass (CPB) circuits to reduce hemodilution and allogenic blood product administration is common in cardiac surgery. One major concern associated with smaller CPB circuits is a possible increase in gaseous micro-emboli (GME) sent to the cerebral vasculature, which is exacerbated by vacuum-assisted venous drainage (VAVD). The use of VAVD has increased with smaller venous line diameter and venous cannulae. This study examines the effects of CPB initiation with an unprimed venous line and VAVD in a pediatric circuit. A CPB circuit was set up with reservoir, oxygenator, and arterial filter with a bag reservoir to simulate the patient. All trials were done in vitro, and GME were measured using the EDAC Quantifier by Luna Innovations. EDAC sensors were placed proximal and distal to the oxygenator and distal to the arterial filter. Group 1 was the control group with no VAVD and a primed venous line. Groups 2, 3, and 4 used an unprimed venous line and VAVD of −40, −20, and −10 mmHg, respectively. Total microemboli counts and total embolic load in micrometers were measured at each sensor. Groups 2 (12,379.00 ± 3180.37) and 3 (8296.67 ± 2818.76) had significantly more microemboli than group 1 (923.33 ± 796.08,p&lt; .05) at the pre-oxygenator sensor. Group 2 (57.33 ± 25.01,p&lt; .05) had significantly more microemboli than group 1 (5.33 ± 3.21) at the post-oxygenator sensor. No other findings were statistically significant. The results suggest that, if an oxygenator and arterial filter with sufficient air handling capabilities are used, this method to reduce prime volume may not increase GME in the arterial line distal to the arterial filter.

Clinical Gaseous Microemboli Assessment of an Oxygenator with Integral Arterial Filter in the Pediatric Population

The use of an arterial line filter (ALF) within the pediatric cardiopulmonary bypass (CPB) circuit is not a new concept. It has always presented the perfusionist with a circuit component that while valuable, increased prime volume. The purpose of this study was to evaluate the change in prime volume and emboli between a conventional oxygenator with separate ALF and a new generation oxygenator with integral arterial filter (AF). We performed a clinical, non-randomized retrospective evaluation of the Terumo Capiox® RX15 (Terumo Cardiovascular Systems Corporation, Ann Arbor, MI) (n= 10) in conjunction with the Terumo Capiox® AF125X ALF or the Capiox ® AF02 vs. the Terumo Capiox® FX15 oxygenator with integral AF (n= 10). The above circuit components, in combination with the LUNA EDAC® (emboli detection and classification) Quantifier (LUNA Innovations, Blacksburg, VA) were placed at various locations within each patient’s CPB circuit to establish and quantify the presence and volume of gaseous emboli during all phases of cardiopulmonary bypass. The EDAC® system is available/used for all patients undergoing CPB at this institution. When compared to a more conventional CPB circuit, the Capiox® FX15 primes more easily as it does not require a carbon dioxide flush while still providing a 32 μ AF. There was no statistical difference in air handling between the tested oxygenators and their associated circuits. During this review it was determined that use of the Capiox® FX15 simplifies the arterial limb of the pediatric CPB circuit. Removal of the separate ALF led to the removal of several, now unnecessary, arterial connectors and additional tubing (arterial line filter bypass). Removal of these components led to a reduction in prime volume and decreased the hemodilutional effect. The FX15 provided a safe, simplified pediatric CPB circuit and was as effective in gaseous microemboli removal as was the more traditional RX15 with separate ALF during this review.

Post-Arterial Filter Gaseous Microemboli Activity of Five Integral Cardiotomy Reservoirs during Venting: An In Vitro Study

During a previously published study on gaseous micro-emboli (GMEs) and perfusionist interventions, it was noted that emboli could be detected after the arterial filter when blood/air challenges entered the membrane oxygenator’s integral cardiotomy. The findings indicated that further study into the oxygenator’s integral cardiotomy reservoir was warranted. This is the first know published report that connects the vent return to GME activity after the arterial filter. To study the air handling ability of the membranes integral cardiotomy, an in vitro study was conducted on five hard shell coated membrane oxygenators (Terumo Capiox SX25, X coated; Sorin Synthesis, phosphorylcholine coated; Gish Vision, GBS coated; Medtronic Affinity NT, trillium coated; Maquet Quadrox, bioline coated). The oxygenators were matched with their own manufacturer’s coated arterial filters (Medtronic 351T Arterial Filter, Sorin Synthesis Integrated Arterial Filter, Terumo CXAF200X Arterial Filter, Gish GAF40GBS-2 Arterial Filter, and Maquet Quart HBF140 Arterial Filter). There were three arms to the study, and three separate oxygenator/filter combinations were used in each arm. The first arm consisted of a pump flow of 4.0 L/min with only the filter purge blood entering the integral cardiotomy. In the second arm, 500 mL/min of simulated vent blood was added to the filter purge blood entering the integral cardiotomy. During the final arm, 200 mL/min of air was added to the vent blood as it entered the integral cardiotomy, to more closely simulate vent return during cardiopulmonary bypass. All GME activity in the oxygenator/filter combinations was examined using the Hatteland CMD20 Microemboli Counter. Placement of the Hatteland probes was 4 in after the hard shell reservoir outlet (PRO) and 12 in after the arterial filter (PAF). When vent blood flow was turned on, there was a significant increase in the PRO microemboli activity detected in all reservoirs. In the PAF position, three of the oxygenator/filter combinations were able to remove 98–99% of the GME, one removed 84.3%, and another removed only 55.5% of the GMEs coming out of the oxygenator’s reservoir. All oxygenators were found to have a dramatic increase in reservoir GME activity when the vent was turned on. Depending on the oxygenator/filter combination, vent return into the oxygenator’s integral cardiotomy resulted in the presence of significant amounts of GMEs after the arterial filter.

Vacuum-assisted Venous Drainage and Gaseous Microemboli in Cardiopulmonary Bypass

When conventional gravity siphon venous drainage cannot achieve satisfactory venous drainage during minimally invasive cardiac and neonatal surgeries, assisted venous drainage techniques are needed to ensure adequate flow. One assisted venous drainage technique, vacuum-assisted venous drainage (VAVD), the aid of a vacuum in the venous reservoir, is now widely used to augment venous drainage during cardiopulmonary bypass (CPB) procedures. VAVD permits the use of smaller venous cannulae, shorter circuit tubing, and lower priming and blood transfusion volumes, but increases risk of arterial gaseous microemboli and blood trauma. The vacuum should be set as low as possible to facilitate full venous return, and realtime monitoring of gaseous microemboli in the arterial and venous line should be used to achieve the safest conditions. With current ultrasound technology, it is possible to simultaneously detect and classify gaseous microemboli in the CPB circuit. In this article, we summarize the components, setup, operation, advantages, and disadvantages of VAVD techniques and clinical applications and describe the basic principles of microemboli detectors, such as the Emboli Detection and Classification (EDAC) Quantifier (Luna Innovations, Roanoke, VA) and Bubble Counter Clinical 200 (GAMPT, Zappendorf, Germany). These novel gaseous microemboli detection devices could help perfusionists locate the sources of entrained air, eliminate hidden troubles, and minimize the postoperative neurologic impairments attributed to gaseous microemboli in clinical practice.

Cerebral Microemboli and Brain Injury During Carotid Artery Endarterectomy and Stenting

Cerebral microembolic signals detected by transcranial Doppler are frequent during carotid angioplasty with stenting and carotid endarterectomy (CEA). Their potential harmful effects on the brain are, however, unclear. The aim of this study was to relate the frequency and type of per-procedural microembolic signals to procedure-related ipsilateral ischemic strokes and new ipsilateral ischemic lesions on diffusion-weighted cerebral MRI. Eighty-five patients who were prospectively treated with CEA (61) or carotid angioplasty with stenting (30) for high-grade (>/=70%) internal carotid artery stenoses were monitored during the procedures using multifrequency transcranial Doppler with embolus detection and differentiation. Pre- and postprocedural cerebral diffusion-weighted cerebral MRIs were performed on a subset of patients. Solid and gaseous microemboli were independently associated with procedure-related ipsilateral ischemic strokes (solid: P=0.027, gaseous: P=0.037) or new ipsilateral diffusion-weighted cerebral MRI lesions (solid: P=0.043, gaseous: P=0.026). Microembolic signals were detected during all procedures except one (CEA); 17% and 21% of all emboli were solid during carotid angioplasty with stenting and CEA, respectively. Patients undergoing carotid angioplasty with stenting had more solid (P<0.001) and gaseous (P<0.001) emboli and more new ipsilateral ischemic strokes (P=0.033) compared with patients undergoing CEA. Echolucent plaques (P=0.020) and preprocedural diffusion-weighted cerebral MRI ischemic lesions (P=0.002) were associated with increased numbers of solid emboli. Solid and gaseous microemboli were increased in patients with procedure-related ipsilateral ischemic strokes or new diffusion-weighted cerebral MRI lesions, which suggests that both solid and gaseous emboli may be harmful to the brain during CEA and carotid angioplasty with stenting.

The Capability of Trapping Gaseous Microemboli of Two Pediatric Arterial Filters With Pulsatile and NonPulsatile Flow in a Simulated Infant CPB Model

The study objective was to test the capability of Medtronic Affinity and Terumo Capiox pediatric arterial filters to trap gaseous microemboli in a simulated infant cardiopulmonary bypass (CPB) model. The filters were used in parallel pattern. The circuit was primed with lactated ringer's solution (700 ml) and postfilter pressure was maintained at 100 mm Hg using a Hoffman clamp. Trials were conducted at flow rates ranging from 500 to 1,250 ml/min. After introducing 20 ml air into the venous line via an 18-G needle, 2-minute segments of data were recorded. This entire process was repeated 6 times for each unique combination of arterial filter, flow rate and perfusion mode, yielding a total of 96 experiments. More than 80% of gaseous microemboli were trapped by the two pediatric arterial filters. With increased flow rates and pulsatile mode, more gaseous microemboli passed through the arterial filters. There were no differences in terms of the percentage of gaseous microemboli trapped and pressure drops between Medtronic Affinity and Terumo Capiox pediatric arterial filters. Results demonstrated that Medtronic Affinity and Terumo Capiox pediatric arterial filters could trap the majority of gaseous microemboli in this particular setting of an open arterial filter purge line in a simulated infant CPB circuit with pulsatile and nonpulsatile flow.

Gaseous Microemboli Detection in a Simulated Pediatric CPB Circuit Using a Novel Ultrasound System

The objective of this study was to evaluate the effect of flow rate and perfusion mode on the delivery of gaseous microemboli in a simulated pediatric cardiopulmonary bypass (CPB) circuit with an open arterial filter purge line using a novel ultrasound detection system. The circuit was primed with 450 ml fresh, heparinized bovine blood plus 200 ml Lactated Ringer's solution (total volume 650 ml, corrected Hct 25%). After the injection of 5 ml air into the venous line, an Emboli Detection and Classification (EDAC) Quantifier (Luna Innovations, Inc., Roanoke, VA) was used to simultaneously record microemboli counts at postpump, postoxygenator, and postarterial filter sites. Trials were conducted at four different flow rates (500, 750, 1,000, 1,250 ml/min) and two perfusion modes (pulsatile, nonpulsatile). Microemboli counts uniformly increased with increasing pump flow rates. In all trials, the majority of gaseous microemboli detected in the simulated pediatric CPB circuit were <20 microm in diameter. At the lowest flow rate tested (500 ml/min), all microemboli (>10 microm) were cleared from the circuit by the oxygenator and arterial filter. Clearance efficiency was decreased at higher flow rates (750-1,250 ml/min). Over 98% of microemboli detected at the postoxygenator site were <40 microm in diameter. In general, pulsatile flow delivered more microemboli to the circuit at postpump and postoxygenator sites than nonpulsatile flow. The results of this study confirmed that entrained air from the venous line could be delivered to the systemic circulation (as represented by our pediatric pseudo patient) at flow rates from 750 to 1,250 ml/min, despite the presence of an arterial filter and open arterial filter purge line. All of the microemboli distal to the arterial filter were smaller than the conventional detectable level of 40 microm.

Comparison of Two Different Blood Pumps on Delivery of Gaseous Microemboli During Pulsatile and NonPulsatile Perfusion in a Simulated Infant CPB Model

The purpose of this study was to compare two different blood pumps (Jostra roller pump vs. Medos deltastream DP1 rotary pump) on delivery of gaseous microemboli during pulsatile and nonpulsatile perfusion in a simulated infant cardiopulmonary bypass (CPB) model. The Jostra and Medos pump were used in parallel pattern. The circuit was primed with lactated ringer's solution (700 ml) and the postfilter pressure was maintained at 100 mm Hg. Three transducers (postpump, postoxygenator and postfilter sites) of the Emboli Detection and Classification (EDAC) Quantifier were inserted into the CPB circuit to detect and classify gaseous microemboli. Trials were conducted at flow rates ranging from 500 to 1250 ml/min (250 ml/min increments). The arterial filter purge line was kept open during all trials. After injecting 20 ml air into the venous line, 2-minute segments of data were recorded simultaneously through three transducers. This entire process was repeated six times for each unique combination of blood pump, flow rate and perfusion mode, yielding a total of 96 experiments. Independent of perfusion mode and flow rate, Medos pump delivered less gaseous microemboli than Jostra pump at the postpump site, but only at 1,250 ml/min of pump flow rate the differences reached statistical significance (p < 0.01). There was no difference in delivery at the postfilter site. Compared with nonpulsatile flow, pulsatile flow transferred significantly more gaseous microemboli at the postpump site at 1,250 ml/min of pump flow rate in both groups (p < 0.01). The majority of gaseous microemboli were trapped by the membrane oxygenator. The results of this study confirm that rotary pump could deliver less gaseous microemboli than roller pump at the postpump site when a fixed volume air was introduced into the venous line. Pulsatile flow could transfer more gaseous microemboli at the postpump site, no matter which blood pump was used. Only few gaseous microemboli appeared at the postfilter site at high flow rates with an open arterial filter purge line.

Delivery of Gaseous Microemboli With Vacuum-Assisted Venous Drainage During Pulsatile and Nonpulsatile Perfusion in a Simulated Neonatal Cardiopulmonary Bypass Model

This study investigated delivery of gaseous microemboli (GME) with vacuum-assisted venous drainage (VAVD) at various flow rates and perfusion modes in a simulated neonatal cardiopulmonary bypass (CPB) model. Four transducers (postpump, postoxygenator, postfilter, and venous line) of the emboli detection and classification (EDAC) quantifier were inserted into the CPB circuit to detect and classify GME. Four negative pressures (0, -15, -30, and -45 mm Hg), 3 flow rates (750, 1,000, and 1,250 ml/min), and 2 perfusion modes (pulsatile and nonpulsatile) were tested. After injecting 10 ml air into the venous line via an 18G needle, 2-minute segments of data were recorded simultaneously through 4 transducers. This entire process was repeated 6 times for each unique combination of pressure, flow rate, and perfusion mode, yielding a total of 144 experiments. Independent of perfusion mode and flow rate, the use of VAVD with higher negative pressures delivered significantly more GME at the postpump site. There was no difference in delivery at the postfilter site. The majority of GME were trapped by the Capiox Baby-RX hollow-fiber membrane oxygenator. Compared with nonpulsatile flow, pulsatile flow transferred more GME at the postpump site at all 3 flow rates. Our results suggest that VAVD with higher negative pressures, increased flow rates, and pulsatile flow could deliver more GME at the postpump site when a fixed volume air is introduced into the venous line. The Emboli Detection and Classification Quantifier is a sensitive tool for the detection and classification of GME as small as 10 microns in this simulated neonatal model.

Solid and gaseous cerebral microembolization after biologic and mechanical aortic valve replacement: Investigation with multirange and multifrequency transcranial Doppler ultrasound

Cerebral microembolization is a well-recognized phenomenon after cardiac valve replacement, but the relative proportion of solid and gaseous emboli is uncertain. Particulate microemboli are thought to be the most damaging. With the use of multifrequency transcranial Doppler ultrasound, we compared the number and nature of microemboli in recipients of biologic and mechanical aortic valve prostheses. The middle cerebral arteries of 60 patients were monitored bilaterally with a new-generation transcranial Doppler ultrasound (Embo-Dop, DWL Elektronische Systeme GmbH, Singen, Germany) that rejects artefacts online and automatically discriminates between solid and gaseous microemboli. All recordings were performed during a 30-minute period 1 day before and at a mean of 5 days and 3 months after isolated aortic valve replacement with a biologic (30, group B) or mechanical (30, group M) prosthesis. The patients in group B were older, with a mean age of 70.6 +/- 9.7 years versus 55.4 +/- 9.4 years (P < .005) in the patients in group M. Biologic prosthesis recipients were all taking aspirin (no warfarin); patients with mechanical valves were well anticoagulated with warfarin both 5 days and 3 months after surgery. None of the patients had solid microemboli preoperatively. Five days postoperatively, the absolute number of cerebral microemboli was 145 and 594 for total microemboli (P = .001) and 41 and 182 for solid microemboli (P = .002) in groups B and M, respectively. At 3 months, the absolute number was 65 and 608 for total microemboli (P < .001) and 10 and 188 for solid microemboli (P < .001) in groups B and M, respectively. Solid microemboli accounted for 16% of the total microembolic load in group B compared with 31% in group M (P = .05) at 3 months. Solid cerebral microemboli represent approximately one third of the total cerebral microembolic load after mechanical aortic valve replacement and are detectable in the majority of such patients both 5 days and 3 months after surgery. The neurofunctional consequences of this phenomenon should be carefully assessed.

Arterial Line Filters Ranked for Gaseous Micro-Emboli Separation Performance: An In Vitro Study

Arterial line filters (ALFs) are arguably the most important component in the cardiopulmonary bypass circuit to protect the patient from gaseous macro-and micro-emboli (GME) originating in the perfusion circuit. The GME separating ability of 10 ALFs was ranked according to seven performance criteria. Ten ALFs rated between 20 and 43 μm were evaluated for flow resistance, the count, size, and volume of GME passed after a 10-mL room air bolus, and the ability to separate a high-count, 10-to 200-μm flowing distribution of GME. The Luna Innovations EDAC™ emboli detector was used to size, count, and sort GME. Three test trials were conducted for 3 each of the 10 filters. Performance criteria were correlated by regression analysis, statistically compared using analysis of variance, or ranked using non-parametric tests. Significance was set at 0.05. Weighting all seven test parameters equally, the most effective ALFs were the Cobe 21 and Gish 25-μm filters. The Pall LG-6 ranked more efficient than the Medtronic 20 and Dideco 27-μm filters. The Cobe 43, Terumo 40, Medtronic 38, Terumo 37, and Gish 40-μm filters were less effective as a group compared with the other filters. For the 10 filters, blood flow resistance was not correlated to rated pore size. Generally, the smaller the pore rating, the higher the GME separation ability rank, except for the leuko-reduction filter, which performed more effectively than other large pore filters.

Microemboli detection on extracorporeal bypass circuitsa

Numerous authors have associated gaseous microembolization with adverse cerebral outcomes during cardiopulmonary bypass (CPB). The introduction to this review provides background on the connection between microemboli and adverse cerebral outcomes. This connection is often difficult to quantify, as outcomes depend on a number of factors, including the size of the bubble, where it passes through the patient, patient comorbidities and other factors. Nonetheless, numerous studies have shown statistically significant differences in the mean number of cerebral emboli detected in patients that stroked and those that did not, as well as for patients with major cardiac complications and patients with a longer length of hospital stay. Our introduction is followed by case reports and laboratory studies showing how monitoring for gaseous microemboli (GME) can be used to reduce the embolic load delivered to the patient through the bypass circuit. These methods include improved qualification of bypass circuit design prior to surgery, modification of priming procedures to reduce air in the circuit at the start of surgery, new methods for injecting drugs into the circuit during surgery, and better detection of removal of sources of air during surgery. The review concludes with background on the ultrasonic detection of GME, comparing through-transmission gross air detectors and Doppler ultrasound technology with fixed-beam ultrasonic imaging of emboli, a new ultrasonic technique that images moving emboli in the blood using a single ultrasound transducer element in a fixed position. This overview is meant to shed light on why different ultrasonic detection technologies report widely varying counts and emboli loads, and why fixed-beam ultrasonic imaging represents an improvement in the ability to monitor, measure and quantitate embolic load during CPB.

Microembolic signal characterization by transcranial Doppler imaging

Transcranial Doppler detection and monitoring of cerebral microemboli have provided a new and useful method to diagnose, and potentially to foresee, increased risk of stroke. Until now, however, the assessment of this method in routine clinical practice has been limited by the lack of a reliable automatic differentiation between solid and gaseous microemboli. The aim of this work is the definition of a clinical diagnostic support procedure for the automatic recognition of emboli of different composition. The proposed method makes use of image processing techniques and neural algorithms for data interpretation and performs a feature-based analysis of the ultrasonographic images showing the microembolic events. Application to clinical cases selected by expert neurologists for their clinical relevance and experimental results have showed effective operability of the developed procedure.

Acoustical Bubble Trapper Applied to Hemodialysis

Gaseous microemboli can arise in extracorporeal lines and devices such as dialysis machines. They are associated with severe pulmonary side effects in patients undergoing chronic hemodialysis sessions. The goal of this study was to develop a gaseous emboli trapper using ultrasound waves to remove any air bubble from the tubing system before they reach the patient. A homemade bubble trapper, developed in the laboratory, consists of a Perspex block containing a main channel connected to the tubing of a hemodialysis machine and a second subchannel positioned perpendicularly to the main one, used to trap the air microemboli. The microemboli flowing in the main channel were insonified through an acoustic window with an ultrasound wave, at a frequency of 500 kHz and with a maximal acoustic pressure of 500 kPa, generated by a single-element transducer positioned 3 cm away from the main flow. The radiation force induced by the ultrasound beam acts directly on the flowing air emboli, by pushing them into the subchannel. Two Doppler probes operating both at 2 MHz, connected to a DWL Doppler machine were placed before and after the bubble trapper to count sequentially the number of embolic events. The flow of the machine was varied between 200 mL/min and 500 mL/min. Depending on the flow velocity, the number of microembolic signals (MES) detected by the Doppler probes before and after the trapping system was identical and ranged from 5 to 150 MES/min in absence of the ultrasound irradiation. When the air bubble trapper was activated, a reduction of the number of MES, up to 70%, was achieved. Doppler recordings suggest that the circulating bubbles were either fragmented into smaller bubble fragments or directly got pushed into the second subchannel where they were collected. This simple approach using an ultrasound-based trapping system was shown to operate adequately with the current settings and can be used to filter air microemboli. (E-mail: palanchon@med.univ-tours.fr)

Detection and Classification of Gaseous Microemboli During Pulsatile and Nonpulsatile Perfusion in a Simulated Neonatal CPB Model

We compared the effects of perfusion modes (pulsatile vs. nonpulsatile) on gaseous microemboli delivery using the Emboli Detection and Classification (EDAC) Quantifier at postpump, postoxygenator, and postarterial filter sites in a simulated pediatric cardiopulmonary bypass (CPB) model. The mock loop was subjected to five different pump flow rates of equal 100 ml/min intervals, ranging from 400 to 800 ml/min. When the target pump flow rate was achieved, 5 cc air was introduced into the venous line. The EDAC system recorded gaseous microemboli counts simultaneously at three locations in 5-minute intervals. Regardless of the type of perfusion mode, when the pump flow rate was increased, more gaseous microemboli were generated at postpump site. Compared with nonpulsatile flow, pulsatile flow did deliver significantly more gaseous microemboli at postpump site, but there was no difference between two groups at postoxygenator and postarterial filter sites. Capiox Baby-RX hollow-fiber membrane oxygenator significantly reduced the gaseous microemboli counts in both groups at all five pump flow rates with either pulsatile flow or nonpulsatile flow in this model. Our results suggest that using this novel EDAC system, we could detect the size of gaseous microemboli, as small as 10 microm, and the percentage of detected gaseous microemboli, <40 microm, was about 90% in total gaseous microemboli counts at any flow rate with pulsatile or nonpulsatile flow.

Preventing Gaseous Microemboli During Blood Sampling and Drug Administration: An In Vitro Investigation

The detection and prevention of gaseous microemboli (GMEs) during cardiopulmonary bypass has generated considerable interest within the cardiac surgical community. There have been several landmark papers that have used transcranial Doppler devices during cardiopulmonary bypass to detect gaseous microemboli activity in the patients’ middle cerebral artery during perfusionist interventions. To determine if this source of emboli could be prevented, a shunt was developed between the oxygenator’s sampling manifold and the oxygenator’s venous line. This shunt bypassed the venous line and emptied into the oxygenator’s integral cardiotomy. An in vitro experiment was performed using three open system oxygenators (Sorin Synthesis, Sorin PrimeOx2, and Terumo Capiox SX25) to compare post-arterial filter emboli detection using the Hatteland CMD20 Microbubble Detector under tightly controlled conditions. After injection of air through the sampling manifold, the PrimeOx2 and the Synthesis oxygenators had statistically significant fewer GMEs with the shunt used than when the shunt was not used. Using a shunt in the sampling manifold during perfusionist interventions will dramatically reduce or eliminate gaseous microemboli transmission to the patient during bypass with both the PrimeOx2 and Synthesis oxygenators. However, results indicate that further study of GME handling with all oxygenator’s integral cardiotomies is warranted.