The effect of air-free administration of intravenous drugs on microemboli during cardiopulmonary bypass

OBJECTIVE

During cardiopulmonary bypass (CPB), gaseous microemboli (GME) that originate from the extracorporeal circuit are released into the arterial blood stream of the patient. Gaseous microemboli may contribute to adverse outcome after cardiac surgery with CPB. Possibly, air may be collected in the right atrium during induction of anesthesia and released during CPB start. The aim of this study was to assess if the GME load entering the venous line of the CPB circuit could be reduced by training of anesthesia personal in avoiding air introduction during administration of intravenous medication.

METHODS

In 94 patients undergoing coronary artery bypass grafting with CPB, GME number and volume were measured intraoperatively with a bubble counter (BCC300). The quantity and the relationship between GME number and volume in the venous and arterial line were determined in 2 periods before and after education of the anesthesiologists and nurses.

RESULTS

In the venous line no significant differences were observed between numbers and volumes of GME between groups. Comparing patients with low versus high GME load, showed significantly more patients from the intervention group in the low GME-load group, namely 29 versus 18. Administration of medication by anesthesia was confirmed as a clear cause of GME/air-introduction into the venous circulation. Scavenging properties of the CPB circuit including the oxygenator showed a 99.9% reduction of GME.

CONCLUSIONS

A wide spread of GME generation during perfusion was present with no difference in generation of GME between groups. Lower GME load observed in patients (intervention group) and examples of air introduction during drug administration suggest that air introduced by anesthesia contributes to the GME load during CPB. Scavenging properties of the CPB circuit contribute very much to patient safety regarding reduction of venous air. Awareness and education create the possibilities for further reduction of GME during cardiopulmonary bypass.

Hypobaric type oxygenators - physics and physiology

Brain injury is still a serious complication after cardiac surgery. Gaseous microemboli (GME) are known to contribute to both short and longer-term brain injury after cardiac surgery. Hypobaric and novel dual-chamber oxygenators use the physical behaviors and properties of gases to reduce GME. The aim of this review was to present the basic physics of the gases, the mechanism in which the hypobaric and dual-chamber oxygenators reduce GME, their technical performance, the preclinical studies, and future directions. The gas laws are reviewed as an aid to understanding the mechanisms of action of oxygenators. Hypobaric-type oxygenators employ a high oxygen, no nitrogen environment creating a steep concentration gradient of nitrogen out of the blood and into the oxygenator, reducing the risk of GMEs forming. Adequately powered clinical studies have never been carried out with a hypobaric or dual-chamber oxygenator. These are required before such technology can be recommended for widespread clinical use.

The effects of pulsatile versus nonpulsatile flow on cerebral pulsatility index, mean flow velocity at the middle cerebral artery, regional cerebral oxygen saturation, cerebral gaseous microemboli counts, and short-term clinical outcomes in patients undergoing congenital heart surgery

Objective

The objective of this retrospective review was to evaluate whether or not pulsatile flow improves cerebral hemodynamics and clinical outcomes in pediatric congenital cardiac surgery patients.

Methods

This retrospective study included 284 pediatric patients undergoing congenital cardiac surgery with cardiopulmonary bypass support utilizing nonpulsatile (n = 152) or pulsatile (n = 132) flow. Intraoperative cerebral gaseous microemboli counts, pulsatility index, and mean blood flow velocity at the right middle cerebral artery were assessed using transcranial Doppler ultrasound. Clinical outcomes were compared between groups.

Results

Patient demographics and cardiopulmonary bypass characteristics between groups were similar. Although the pulsatility index during aortic crossclamping was consistently higher in the pulsatile group (P < .05), a significant degree of pulsatility was also observed in the nonpulsatile group. No significant differences in mean cerebral blood flow velocity, regional cerebral oxygen saturation, or gaseous microemboli counts were observed between the perfusion modality groups. Clinical outcomes, including intubation duration, intensive care unit and hospital length of stay, and mortality within 180 days were similar between groups.

Conclusions

Although the pulsatility index was greater in the pulsatile group, other measures of intraoperative cerebral perfusion and short-term outcomes were similar to the nonpulsatile group. These findings suggest that while pulsatile perfusion represents a safe modality for cardiopulmonary bypass support, its use may not translate into detectably superior clinical outcomes.

Hematic Antegrade Repriming Reduces Emboli on Cardiopulmonary Bypass: A Randomized Controlled Trial

Particulate and gaseous microemboli (GME) are side effects of cardiac surgery that interfere with postoperative recovery by causing endothelial dysfunction and vascular blockages. GME sources during surgery are multiple, and cardiopulmonary bypass (CPB) is contributory to this embolic load. Hematic antegrade repriming (HAR) is a novel procedure that combines the benefits of repriming techniques with additional measures, by following a standardized procedure to provide a reproducible hemodilution of 300 ml. To clarify the safety of HAR in terms of embolic load delivery, a prospective and controlled study was conducted, by applying Doppler probes to the extracorporeal circuit, to determine the number and volume of GME released during CPB. A sample of 115 patients (n = 115) was considered for assessment. Both groups were managed under strict normothermia, and similar clinical conditions and protocols, receiving the same open and minimized circuit. Significant differences in GME volume delivery (control group [CG] = 0.28 ml vs. HAR = 0.08 ml; p = 0.004) and high embolic volume exposure (>1 ml) were found between the groups (CG = 30.36% vs. HAR = 4.26%; p = 0.001). The application of HAR did not represent an additional embolic risk and provided a four-fold reduction in the embolic volume delivered to the patient (coefficient, 0.24; 95% CI, 0.08-0.72; p = 0.01), which appears to enhance GME clearance of the oxygenator before CPB initiation.

Dynamics of appearance and decay of gaseous microemboli during in vitro extracorporeal circulation

INTRODUCTION

Extracorporeal life support (ECLS) patients are at risk for complications caused by gaseous microemboli (GME). GMEs can cause hypoxia, inflammation, coagulation, and end-organ damage. The objective of this in vitro study was to assess dynamics of GME formation during circulation of whole blood or a glycerol blood surrogate. We hypothesized that there is no difference in GME counts and sizes between whole blood and the glycerol blood surrogate and that the membrane lung reduces GME counts over time.

METHODS

A circulation platform was developed using the Cardiohelp ECLS system to run either donor blood or glycerol solution. We conducted 10 repetitions consisting of three phases of ultrasound GME detection using the EDAC^™ Quantifier (Luna Innovations, Charlottesville, VA, USA) for each group. Phases were 3-minute recordings at the initiation of 2 L/min flow (Phase 1), post-injection of a GME suspension (Phase 2), and 10 minutes after injection (Phase 3). The number and size of GME pre- and post-ML were recorded separately and binned based on diameter ranges.

RESULTS

In Phase 1, GME count in blood was higher than in glycerol. In Phase 2, there was a large increase in GME counts; however, most GME were reduced post-membrane in both groups. In Phase 3, there was a significant decrease in GME counts compared to Phase 2. GME > 100 μm in glycerol decreased post membrane.

CONCLUSIONS

We demonstrated GME formation and decay dynamics during in vitro circulation in an ECLS system with blood and glycerol. GME counts were higher in blood, likely due to varying rheological properties. There were decreases in GME levels post membrane in both groups after GME injection, with the membrane lung effectively trapping the GME, and additional reduction 10 minutes after GME injection.

To Purge or Not to Purge

To remove gaseous microemboli (GME) using an oxygenator with an integrated arterial filter, it is recommended by some manufacturers to purge the oxygenator as an additional safety feature while on bypass. In this in vitro study, we evaluated whether purging of oxygenators with an integrated arterial filter is efficient in reducing GME. Five different types of commercially available contemporary oxygenators with an integrated arterial filter based on progressive filter filtration (1), cascade filtration (1), screen filtration (2), or self-venting (1) were tested for their efficiency in removing GME while keeping the purge line open or closed. A bubble counter was used for pre- and post-oxygenator GME signaling, from which the filter efficiency was computed. Freshly drawn heparinized porcine blood was used at blood flow rates of 3 and 5 L/min. Three units of each oxygenator were tested with its specific reservoir at a fixed volume level of 1,500 mL. GME load was introduced into the venous line at 1,000 mL air/min. Measurements started as soon as GME were detected by the pre-oxygenator probe and then continued for 1 minute. There was no statistically significant difference in filter efficiency between the purged and non-purged groups for specific oxygenators. At a blood flow of 3 L/min, the average filter efficiency stayed approximately invariable when comparing the non-purged and purged groups, where 89.1-88.2% indicated the largest difference between the groups. At a blood flow rate of 5 L/min, the filter efficiency changed in one screen filter group from an average of 55.7% in the non-purged group to 42.4% in the purged group. Other filter efficiencies at the blood flow rate of 5 L/min for non-purged compared with purged groups were, respectively, 98.0 vs. 98.0% (screen filtration), 88.6 vs. 85.8% (self-venting filtration), 82.8 vs. 75.5% (progressive filter filtration), and 65.4 vs. 65.1% (cascade filtration). Based on these results, purging while confronted with continuous GME challenge did not result in an increased filter efficiency.

Lack of Association Between Gaseous Microembolisms Assessed by a Single Detection Device and Cerebral Complications in Cardiac Surgery Patients

OBJECTIVE

To assess the association between total volume and number of gaseous microemboli (GME) in the cardiopulmonary bypass (CPB) circuit and the occurrence of new postoperative cerebral infarctions and postoperative cognitive dysfunction (POCD) in patients undergoing cardiac surgery.

DESIGN

Predefined subanalyses of the randomized controlled Perfusion Pressure Cerebral Infarcts (PPCI) trial.

SETTING

Primary heart center in a university hospital.

PARTICIPANTS

A total of 143 adult patients undergoing cardiac surgery with CPB.

INTERVENTIONS

Patients were allocated 1:1 to a low-target mean arterial pressure (MAP) of 40 to 50 mmHg or a high-target MAP of 70 to 80 mmHg during CPB with a fixed pump flow of 2.4 liters per minute per square meter body surface area plus 10% to 20%.

MEASUREMENTS AND MAIN RESULTS

The total volume and number of GME in the CPB circuit were assessed by the Bubble Counter Clinical 200® (GAMPT GmbH). New cerebral infarcts were identified by diffusion-weighted magnetic resonance imaging (DWI) 3 to 6 days after surgery. The median number of GME per patient was 8069 (range 1,523-204,095) with a median total volume of 1.2 μL (range 0.07-48 μL). A total of 66 (46%) patients had DWI detected cerebral infarcts postoperatively, and 36 (28%) patients had POCD after 7 days. The authors found no significant association between volume or number of GME with MAP target allocation, presence of cerebral infarction, or POCD.

CONCLUSIONS

The authors found no significant associations between volume or number of GME with the occurrence of cerebral infarction or cognitive dysfunction in cardiac surgery patients.

Air removal capacity of two different minimal invasive ECC systems: an in vitro comparison

Minimally invasive extracorporeal circulation systems are developed to decrease the deleterious effects of cardiopulmonary bypass. For instance, prime volume and foreign surface area are decreased in these systems. However, because of the lack of a venous reservoir in minimized systems, air handling properties of these minimally invasive extracorporeal circulation systems may be decreased as compared to conventional cardiopulmonary bypass systems. The aim of this in vitro study is to compare the air handling properties of two complete minimized cardiopulmonary bypass systems of two manufacturers, of which one system is provided with the air purge control. In an in vitro study, two minimally invasive extracorporeal circulation systems, Inspire Min.I manufactured by Sorin Group Italia, Mirandola, Italy (LivaNova, London, United Kingdom) and minimized extracorporeal circulation manufactured by Maquet, Rastatt, Germany (Getinge, Germany), were challenged with two types of air challenges; a bolus air challenge and a gaseous microemboli challenge. The air removal characteristics of the venous bubble traps and of the complete minimally invasive extracorporeal circulation systems were assessed by measuring the gaseous microemboli volume and number downstream of the venous bubble traps in the arterial line with a bubble counter. No significant differences were observed in air reduction between the venous bubble traps of Getinge (venous bubble traps) and LivaNova (Inspire venous bubble traps 8 in conjunction with the air purge control). Similarly, no significant differences were observed in volume and number of gaseous microemboli in the arterial line of both complete minimally invasive extracorporeal circulation systems. However, the gaseous microemboli load of the Inspire Min.I system was marginally lower after both the bolus air and the gaseous microemboli challenges. Both minimally invasive extracorporeal circulation systems assessed in this study, the LivaNova Inspire Min.I and the Getinge minimized extracorporeal circulation, showed comparable air removal properties, after both bolus and gaseous microemboli air challenges. Besides, air purge control automatic air removal system provided with the LivaNova Inspire Min.I. system may enhance patient's safety with the use of a minimally invasive extracorporeal circulation system. We consider both systems equally safe for clinical use.

Retrospective Analysis of Air Handling by Contemporary Oxygenators in the Setting of Cardiac Surgery

Purpose: Cardiac surgery with the use of extracorporeal circulation is associated with a significant risk for gaseous microemboli (GME) despite excellent surgical techniques and highest operative standards. GME are associated with postoperative neurocognitive dysfunction and negative clinical outcome. This study determines whether oxygenator design has influence on perioperative outcome after cardiac surgery.

Methods: Three different oxygenator models with integrated arterial filter (HiliteAF 7000, Fusion Affinity, and Synthesis) were retrospectively evaluated in 55 patients undergoing elective cardiac surgery with the use of extracorporeal circulation. The two-channel ultrasound bubble counter BCC200 was used to detect GME in real time.

Results: All three oxygenators differ in terms of structural specifications and have different rates of number and volume GME reduction. The Fusion Affinity had the lowest arterial GME volume (1.81 µL ± 0.23 µL), which was statistically significant compared to the Synthesis (3.37 µL ± 0.71 µL, p = 0.014). However, the Synthesis had lower absolute numbers at the venous GME count (31771 µL ± 6579 µL) versus the Fusion Affinity (49304 µL ± 8196 µL). However, with regard to clinical outcome after cardiac surgery (duration of invasive and non-invasive mechanical ventilation, incidence of delirium, stroke, acute renal failure, or new myocardial infarction), we found no differences between groups.

Conclusion: Despite significant differences in the design specifications, all oxygenators eliminated relevant GME volumes safely.

Effect of Normobaric versus Hypobaric Oxygenation on Gaseous Microemboli Removal in a Diffusion Membrane Oxygenator: An In Vitro Comparison

Gaseous microemboli (GME) are an abnormal physiological occurrence during cardiopulmonary bypass and extracorporeal membrane oxygenation (ECMO). Several studies have correlated negative sequelae with exposure to increased amounts of GME. Hypobaric oxygenation is effective at eliminating GME in hollow-fiber microporous membrane oxygenators. However, hollow-fiber diffusion membrane oxygenators, which are commonly used for ECMO, have yet to be validated. The purpose of this study was to determine if hypobaric oxygenation, compared against normobaric oxygenation, can reduce introduced GME when used on diffusion membrane oxygenators. Comparison of a sealed Quadrox-iD with hypobaric sweep gas (.67 atm) vs. an unmodified Quadrox-iD with normal atmospheric sweep gas (1 atm) in terms of GME transmission during continuous air introduction (50 mL/min) in a recirculating in vitro circuit, over a range of flow rates (3.5, 5 L/min) and crystalloid prime temperatures (37°C, 28°C, and 18°C). GME were measured using three EDAC Doppler probes positioned pre-oxygenator, post-oxygenator, and at the arterial cannula. Hypobaric oxygenation vs. normobaric oxygenation significantly reduced hollow-fiber diffusion membrane oxygenator GME transmission at all combination of pump flows and temperatures. There was further significant reduction in GME count between the oxygenator outlet and at the arterial cannula. Hypobaric oxygenation used on hollow-fiber diffusion membrane oxygenators can further reduce GME compared to normobaric oxygenation. This technique may be a safe approach to eliminate GME during ECMO.

Clinical evaluation of the air-handling properties of contemporary oxygenators with integrated arterial filter

Gaseous microemboli (GME) may originate from the extracorporeal circuit and enter the arterial circulation of the patient. GME are thought to contribute to cerebral deficit and to adverse outcome after cardiac surgery. The arterial filter is a specially designed component for removing both gaseous and solid microemboli. Integration of an arterial filter with an oxygenator is a contemporary concept, reducing both prime volume and foreign surface area. This study aims to determine the air-handling properties of four contemporary oxygenator devices with an integrated arterial filter. Two oxygenator devices, the Capiox FX25 and the Fusion, showed significant increased volume of GME reduction rates (95.03 ± 3.13% and 95.74 ± 2.69%, respectively) compared with both the Quadrox-IF (85.23 ± 5.84%) and the Inspire 6F M (84.41 ± 12.93%). Notably, both the Quadrox-IF and the Inspire 6F M as well as the Capiox FX 25 and the Fusion showed very similar characteristics in volume and number reduction rates and in detailed distribution properties. The Capiox FX25 and the Fusion devices showed significantly increased number and volume reduction rates compared with the Quadrox-IF and the Inspire 6F M devices. Despite the large differences in design of all four devices, our study results suggest that the oxygenator devices can be subdivided into two groups based on their fibre design, which results in screen filter (Quadrox-IF and Inspire 6F M) and depth filter (Capiox FX25 and Fusion) properties. Depth filter properties, as present in the Capiox FX25 and Fusion devices, reduced fractionation of air and may ameliorate GME removal.

In vitro elimination of gaseous microemboli utilizing hypobaric oxygenation in the Terumo® FX15 oxygenator

BACKGROUND

This study examines the efficacy of hypobaric oxygenation as it relates to the elimination of gaseous microemboli (GME) at designated flow, pressure and temperature combinations.

METHODS

Hypobaric oxygenation was employed for experimental trials (n=60), but not for control trials (n=60), while circuit design, data measurements and testing conditions were maintained for both settings. Hypobaric oxygenation conditions were created by applying 100% oxygen at sub-atmospheric sweep gas pressures of 0.67 atmospheres to the gas phase of an integrated hollow-fiber microporous membrane oxygenator. GME were quantified using an Emboli Detection and Classification system (EDAC), while a continuous air infusion, at a rate of 100 ml/min, was applied to the circuit. Trials were conducted at 37°C, 28°C, and 18°C and at two flow and line pressure combinations of: 3.5 L/min & 150 mmHg and 5 L/min & 200 mmHg.

RESULTS

Sub-atmospheric sweep gas pressures allowed adequate oxygenation independent of carbon dioxide removal while significantly reducing the potential entrance of nitrogen into the blood. GME was reduced significantly across all temperatures and flows when compared to control trials; GME counts were reduced by 99.7% post-oxygenator and 99.99% at the arterial cannula.

CONCLUSION

Correlation between the use of hypobaric oxygenation and GME counts suggests hypobaric oxygenation could play a significant role in the reduction of GME.

Arterial Limb Microemboli during Cardiopulmonary Bypass: Observations from a Congenital Cardiac Surgery Practice

Gaseous microemboli (GME) are known to be delivered to the arterial circulation of patients during cardiopulmonary bypass (CPB). An increased number of GME delivered during adult CPB has been associated with brain injury and postoperative cognitive dysfunction. The GME load in children exposed to CPB and its consequences are not well characterized. We sought to establish a baseline of arterial limb emboli counts during the conduct of CPB for our population of patients requiring surgery for congenital heart disease. We used the emboli detection and counting (EDAC) device to measure GME activity in 103 consecutive patients for which an EDAC machine was available. Emboli counts for GME <40 μ and >40 μ were quantified and indexed to CPB time (minutes) and body surface area (BSA) to account for the variation in patient size and CPB times. Patients of all sizes had a similar embolic burden when indexed to bypass time and BSA. Furthermore, patients of all sizes saw a three-fold increase in the <40 μ embolic burden and a five-fold increase in the >40 μ embolic burden when regular air was noted in the venous line. The use of kinetic venous-assisted drainage did not significantly increase arterial limb GME. Efforts for early identification and mitigation of venous line air are warranted to minimize GME transmission to congenital cardiac surgery patients during CPB.

Clinical evaluation of emboli removal by integrated versus non-integrated arterial filters in new generation oxygenators

OBJECTIVE

To compare the emboli filtration efficiency of five integrated or non-integrated oxygenator-filter combinations in cardiopulmonary bypass circuits.

METHODS

Fifty-one adult patients underwent surgery using a circuit with an integrated filtration oxygenator or non-integrated oxygenator with a separate 20 µm arterial line filter (Sorin Dideco Avant D903 + Pall AL20 (n=12), Sorin Inspire 6 M + Pall AL20 (n=10), Sorin Inspire 6M F (n=9), Terumo FX25 (n=10), Medtronic Fusion (n=10)). The Emboli Detection and Classification quantifier was used to count emboli upstream and downstream of the primary filter throughout cardiopulmonary bypass. The primary outcome measure was to compare the devices in respect of the median proportion of emboli removed.

RESULTS

One device (Sorin Inspire 6 M + Pall AL20) exhibited a significantly greater median percentage reduction (96.77%, IQR=95.48 - 98.45) in total emboli counts compared to all other devices tested (p=0.0062 - 0.0002). In comparisons between the other units, they all removed a greater percentage of emboli than one device (Medtronic Fusion), but there were no other significant differences.

CONCLUSION

The new generation Sorin Inspire 6 M, with a stand-alone 20 µm arterial filter, appeared most efficient at removing incoming emboli from the circuit. No firm conclusions can be drawn about the relative efficacy of emboli removal by units categorised by class (integrated vs non-integrated); however, the stand-alone 20 µm arterial filter presently sets a contemporary standard against which other configurations of equipment can be judged.

Perspective on Cerebral Microemboli in Cardiac Surgery: Significant Problem or Much Ado About Nothing?

From the time an association was perceived between cardiac surgery and post-operative cognitive dysfunction (POCD), there has been interest in arterial microemboli as one explanation. A succession of studies in the mid-1990s reported a correlation between microemboli exposure and POCD and there followed a focus on microemboli reduction (along with other strategies) in pursuit of peri-operative neuroprotection. There is some evidence that the initiatives developed during this period were successful in reducing neurologic morbidity in cardiac surgery. More recently, however, there is increasing awareness of similar rates of POCD following on and off pump cardiac operations, and following many other types of surgery in elderly patients. This has led some to suggest that cardiopulmonary bypass (CPB) and microemboli exposure by implication are non-contributory. Although the risk factors for POCD may be more patient-centered and multifactorial than previously appreciated, it would be unwise to assume that CPB and exposure to microemboli are unimportant. Improvements in CPB safety (including emboli reduction) achieved over the last 20 years may be partly responsible for difficulty demonstrating higher rates of POCD after cardiac surgery involving CPB in contemporary comparisons with other operations. Moreover, microemboli (including bubbles) have been proven harmful in experimental and clinical situations uncontaminated by other confounding factors. It remains important to continue to minimize patient exposure to microemboli as far as is practicable.

Understanding Off-Label Use and Reference Blood Flows in Modern Membrane Oxygenators

This editorial will address two issues that are still a source of global controversy and confusion in present day perfusion practice. Membrane oxygenators are designed and tested to a set of stringent flow standards prior to their release from every manufacturer. But how well do we know the iatrogenic consequences of pushing these devices beyond their maximum rated limits? In addition, how well do we know the meaning of the term 'AAMI Reference Flow' as it relates to the Manufacturers Maximum Rated Flow?

Centrifugal pump performance during low-flow extracorporeal CO2 removal; safety considerations

AIM

The aim of this study was to examine the hydrodynamic performance and gaseous microemboli (GME) activity of two centrifugal pumps for possible use in low-flow extracorporeal CO2 removal.

MATERIALS & METHODS

The performance of a Rotassist 2.8 and a Rotaflow 32 centrifugal pump (Maquet Cardiopulmonary AG, Hirrlingen, Germany) was evaluated in a water-glycerine mixture-filled in vitro circuit that enabled measurement of pressures and GME at the pump inlet and pump outlet. Pressure-flow curves were acquired in a 1,000 to 5,000 rpm range while increasing drainage resistance in one series and outlet resistance in another.

RESULTS

Respective minimum pump inlet and maximum pump outlet pressures were -539 mmHg and 754 mmHg for the Rotassist 2.8 and -606 mmHg and 806 mmHg for the Rotaflow 32. Maximum standard deviations on pump pressures and flow amounted to 3.0 mmHg and 0.03 L/min, respectively, regardless of pump type and drainage or outlet resistance. The GME at the pump outlet were detectable at pump inlet pressures below -156 mmHg at 0.2 L/min and 2,500 rpm for the Rotassist 2.8 and below -224 mmHg at 0.9 L/min and 3,000 rpm for the Rotaflow 32.

CONCLUSION

Both the Rotassist 2.8 and Rotaflow 32 centrifugal pumps show a comparably high hydrodynamic stability, but potential GME formation with decreasing pump inlet pressures should be taken into account to ensure safe centrifugal pump-based low-flow extracorporeal CO2 removal.

Can the oxygenator screen filter reduce gaseous microemboli?

Gaseous microemboli (GME) define small bubbles as < 200 microm in size. GME are reported to increase morbidity after cardiopulmonary bypass (CPB) and cardiac surgery. To prevent intrusion of GME into the systemic circulation during CPB, arterial line filtration is generally recommended. New trends in oxygenator design promote location of arterial filtration as an integral part of the oxygenator housing. The present experimental study aimed to evaluate the GME removal properties of an integrated arterial screen filter in a standard microporous oxygenator. The GME properties of Terumo Capiox FX25 with an integrated arterial screen filter was assessed in an experimental setup and compared with Capiox RX25, in which no arterial screen filter is present. A blood analog prime solution was recirculated using a roller pump at 4 and 6 L per minute flow rate, respectively, through a customized CPB circuit comprising oxygenator, reservoir, and connecting tubing. A controlled volume of air was introduced into the circuit. The GME activity was measured and computed using a Gampt BCC200 ultrasonic device placing one probe at the venous inlet and one other at the arterial outlet of the oxygenator. Transmembrane delta values of GME activity were used to calculate the removal efficacy based on counts and volume of GME. Use of screen filtration reduced the GME volume by 99.1% +/- .1% compared with 98.0% +/- .1% for controls at 4 L/min flow rate (p < .001). At 6 L/min, the reduction was 97.9% +/- .1% compared with 97.0% +/- .1% (p < .001). In contrast, the reduction of GME counts was less effective after screen filtration compared with controls: 89.6 +/- .6% versus 91.4 +/- .4% at 4 L/min and 55.6% +/- 1.6% versus 76.0% +/- 1.4% at 6 L/min, respectively (p < .001). The tested oxygenator with incorporated arterial screen filter reduced GME activity based on the calculated volume at the same time as counts of GME increased.

Clinical experience with Affinity Pixie oxygenation system in paediatric and infant patients

INTRODUCTION

Great Ormond Street Children's Hospital undertakes over 500 open heart cardiothoracic procedures requiring cardiopulmonary bypass per year. Data from our centre show that many of our neonatal/paediatric patients require higher cardiac indexes than previously thought. We evaluated the new Pixie oxygenation system, rated from 0.1 L/min to 2 L/min, to determine if it could be used for these patients.

METHODS

Between 2010 and 2012, 250 Pixie oxygenators were used on consecutive patients requiring correction of congenital cardiac defects. Data were collected on FiO2 requirements, oxygenator pressure drop and gaseous microemboli handling. Retrospective analysis was also undertaken on the procedures and demographics of all patients during 2011-2012 to determine the percentage of patients on whom the Pixie could be used.

RESULTS

Analysis of the procedures undertaken at Great Ormond Street Hospital (GOSH) showed that 89% were in patients under 20 kg, requiring a flow rate of <2 L/min (at a base cardiac index of 2.8 L/min/m2). The maximum FiO2 required at 2.5 L/min was 85%. Gaseous microemboli were reduced by 82.5±9.9% and bubble volume was decreased by 94.3±8.4% from the 'venous' pre-oxygenator to the 'arterial' post-oxygenator.

DISCUSSION

The Pixie oxygenator proved effective at flows up to 2.5 L/min, with air-handling capabilities comparable with other oxygenators. This represents a single oxygenator that could potentially be used to cover 89% of our surgical procedures. However, we believe that, for the smallest patients (i.e., < 2 kg), a smaller priming oxygenator should be used in order to limit unnecessary haemodilution in this vulnerable group.

Mini cardiopulmonary bypass: Anesthetic considerations

This review article is going to elaborate on the description, components, and advantages of mini-cardiopulmonary bypass (mini-CPB), with special reference to the anesthetic management and fast track anesthesia with mini-CPB. There are several clinical advantages of mini-CPB like, reduced inflammatory reaction to the pump, reduced need for allogenic blood transfusion and lower incidence of postoperative neurological complications. There are certainly important points that have to be considered by anesthesiologists to avoid sever perturbation in the cardiac output and blood pressure during mini-CPB. Fast-track anesthesia provides advantages regarding fast postoperative recovery from anesthesia, and reduction of postoperative ventilation time. Mini bypass offers a sound alternative to conventional CPB, and has definite advantages. It has its limitations, but even with that it has a definite place in the current practice of cardiac surgery.

In-vitro quantification of gaseous microemboli in two extracorporeal life support circuits

During the course of extracorporeal membrane oxygenation, patients are at constant risk of exposure to air emboli. Air emboli may enter the circuit during routine lab sampling, medication administration, air entrainment through the venous cannula, or via a circuit disruption. Circuit components have been designed and positioned to minimize the quantity of air that travels through the arterial line to the patient. The purpose of this study was to assess the air handling of a newer generation extracorporeal life support circuit. The extracorporeal life support circuit consisted of an open hard-shell venous reservoir, Better Bladder (BB14) or silicone bladder (R-14), and Quadrox D oxygenator or 0800 silicone oxygenator. Air emboli detection sensors were placed in the extracorporeal life support circuit: post bladder, post oxygenator, and post heat exchanger if applicable.Air was injected as a 1 mL/min for 5 minutes injection or as a single 5 mL bolus. Emboli detection was recorded continuously during and for 3 minutes post air injection at two blood flow rates (Qb) (.5 and 1.2 L/min). All tests were performed in triplicate with each condition. All tested components reduced the embolic volume transmitted through the circuit. The quantity of this reduction was dependent on both the Qb and the air injection condition. During this in-vitro testing, air emboli passing through any of the components tested was decreased. Furthermore, the emboli delivery was reduced post component with the slower Qb (.5 L/min).

Blood temperature management and gaseous microemboli creation: an in-vitro analysis

Gaseous microemboli have been associated with post operative neurological deficits in patients undergoing cardiopulmonary bypass. Creating an optimal perfusion system that minimizes microemboli production and has enhanced abilities to sequester entrained air during the bypass procedure has been an important focus. This study examines the air-handling capabilities of a cardiopulmonary bypass circuit and correlates blood temperatures with microemboli loads proximal and distal to the arterial line filter within the circuit. Utilizing a Capiox RX25R oxygenator, Capiox 37 micron arterial filter, vacuum assisted venous return, and emboli detectors, 30 mL of air were injected into the venous line of a bypass circuit at eight different temperatures. Emboli were counted distal to the arterial line filter by the EDAQ Quantifier (Emboli Detection and Classification). The average number of emboli detected distal to the arterial filter progressively increased as the perfusate temperature was dropped. At 37.0 degrees C an average of 1.4 emboli was observed distal to the arterial filter within 90 seconds of the air injection. At 23.0 degrees C an average of 49.8 emboli was detected. Air introduced into the venous side of the bypass circuit resulted in showers of microemboli being sent past the arterial line filter. In addition, as the bovine blood was cooled, the air handling capability of the circuit was diminished.

Is the air handling capability of the quadrox D pump dependent within an ECMO circuit? An in vitro study

The occurrence of gaseous microemboli (GME) within the extracorporeal membrane oxygenation circuit is largely overlooked, as are methods to ameliorate this occurrence. We aimed to determine if the air handling capability of the Quadrox D oxygenator was dependent upon whether it was used in conjunction with a centrifugal or roller pump; and if application of a Pall air eliminating filter (AEF) would prevent circuit air introduction from intravenous infusions. Using a blood primed circuit 1 mL of air was infused pre pump. GME were quantified post pump and post oxygenator using the EDAC Quantifier. Trials were conducted at 1 and 2 L/min flow. To prevent GME recirculation a Capiox SX18 was used in circuit with negative pressure applied to its oxygenator; an EDAC cuvette distal to this device quantified GME recirculation. Following air infusion, 3-5 minute data recordings were carried out for each trial. Separate trials were carried out for centrifugal and roller pumps, and for each flow rate. The process was then repeated following the application of the AEF to the air infusion line. More GME were detected post Quadrox D when the centrifugal pump was used in comparison to the roller pump at 1 L/min (p < .05), and 2 L/min (p = .05). A greater volume of air was detected post Quadrox D when used in conjunction with the centrifugal device at 1 L/min (p < or = .05), and 2 L/min (p < or = .05). Application of the AEF resulted in zero GME detected at any circuit location. The results of this study confirm that a greater total count and volume of GME are detected distal to the Quadrox D when used in conjunction with a Rotaflow centrifugal pump. Application of a Pall AEF to infusion and drug lines can prevent air introduction from this source.

Monitoring microemboli during cardiopulmonary bypass with the EDAC quantifier

Gaseous emboli may be introduced into the bypass circuit both from the surgical field and during perfusionist interventions. While circuits provide good protection against massive air embolism, they do not remove gaseous microemboli (GME) from the bypass circuit. The purpose of this preliminary study is to assess the incidence of GME during bypass surgery and determine if increased GME counts were associated with specific events during bypass surgery. In 30 cases divided between 15 coronary artery bypass grafts and 15 valve repairs, GME were counted and sizedt the three locations on the bypass circuit using the EDAC" Quantifier (Luna Innovations, Roanoke, VA). A mean of 45,276 GME were detected after the arterial line filter during these 30 cases, with significantly more detected (p = .04) post filter during valve cases (mean = 72,137 +/- 22,113) than coronary artery bypass graft cases (mean = 18,416 +/- 7831). GME detected post filter were significantly correlated in time with counts detected in the venous line (p < .001). Specific events associated with high counts included the initiation of cardiopulmonary bypass, heart manipulations, insertion and removal of clamps, and the administration of drugs. Global factors associated with increased counts post filter included higher venous line counts and higher post reservoir/bubble trap counts. The mean number of microemboli detected during bypass surgery was much higher than reported in other studies of emboli incidence, most likely due to the increased sensitivity of the EDAC Quantifier compared to other detection modalities. The results furthermore suggest the need for further study of the clinical significance of these microemboli and what practices may be used to reduce GME incidence. Increased in vitro testing of the air handling capability of different circuit designs, along with more clinical studies assessing best clinical practices for reducing GME activity, is recommended.

Evaluation of Quadrox-i adult hollow fiber oxygenator with integrated arterial filter

Gaseous microemboli (GME) remain a challenge for cardiopulmonary bypass procedures in adult as well as pediatric cardiac surgery patients. The present study tested the effectiveness of a new adult membrane oxygenator in models both with and without an integrated arterial filter to evaluate GME trapping capability and determine membrane pressure drops at various flow rates and temperatures. The experimental circuit included a RotaFlow centrifugal blood pump, Quadrox-i (n = 8) or Quadrox (n = 8) adult microporous membrane oxygenator, and Sorin adult tubing package. A Sorin Cardiovascular VVR 4000i venous reservoir served as pseudo-patient. The circuit was primed with 900 mL heparinized human red blood cells and 300 mL Lactated Ringer's solution. The final hematocrit was 36%. Tests were performed at different flow rates (4 L/min, 5 L/min, and 6 L/min) and temperatures (35 degrees and 30 degrees). Five mL of bolus air was injected into the venous line over 15 seconds using a syringe connected to a 3/8 x 1/2 luer connector. The Quadrox-i adult microporous membrane oxygenator with integrated arterial filter had a similar pressure drop at 4 L/min and 35 degrees C compared with Quadrox membrane oxygenator whereas it had higher pressure drops at 5 L/min and 6 L/min (p < .001). Quadrox-i adult microporous membrane oxygenator reduced the total emboli count and total emboli volume delivered to the pseudo-patient at all flow rates (p < .001).The emboli handling of Quadrox-i adult microporous membrane oxygenator was not affected by flow rate and temperature. Compared with the traditional Quadrox oxygenator, Quadrox-i adult microporous membrane oxygenator with integrated arterial filter and Softline coating has improved GME handling capacity.

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 microm 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.

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 microemboli (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 < .05) at the pre-oxygenator sensor. Group 2 (57.33 +/- 25.01, p < .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.

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 microm 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-microm 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-microm filters. The Pall LG-6 ranked more efficient than the Medtronic 20 and Dideco 27-microm filters. The Cobe 43, Terumo 40, Medtronic 38, Terumo 37, and Gish 40-microm 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.

KEYWORDS

arterial line filter, gaseous microemboli, in vitro test.

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.

In vitro evaluation of the air separation ability of four cardiovascular manufacturer extracorporeal circuit designs

Neurologic impairment is a common complication of adult cardiac surgery. Cerebral gaseous microemboli (GME) detected during cardiopulmonary bypass has been associated with cognitive impairment after adult cardiac surgery. Several previous studies have shown that components comprising the extracorporeal circuit (ECC) can affect the ability of the ECC to eliminate air. The differences in the air separation ability of four manufacturer's commonly used ECCs were studied. The air-separating ability of Cobe Cardiovascular, Gish Biomedical, Medtronic, and Terumo Cardiovascular Systems Corp. ECCs were studied in vitro under clinically relevant conditions. Bolus and continuous venous air were introduced and output GME patterns by size, time, and count were measured (using an embolus detection device) and statistically analyzed. Graphic representations depicting elapsed time, GME size, and bubble count helped to visually rank the air-handling performance of the ECCs. There are significant air-handling differences between the ECCs tested. Overall, the blinded results reveal that ECC A and ECC C removed significantly (p < 0.001) more suspended GME than ECC B and ECC D. In the 50-mL venous room-air bolus and the 100 mL/min pulsed air challenges, ECC B and ECC D allowed significantly more GME to pass (p < 0.001) compared with ECC A and ECC C. For example, in a 2-hour pump run ECC C would deliver 480 potential high-intensity transient signals (HITS) compared with the 9600 from the ECC B during venous room air entrainment at 100 mL/min. There are substantial and significant air-handling differences between the ECCs from the four different manufacturers. The results from this work allow for objective characterization of ECCs air-separating ability. This additional information provides an opportunity for clinicians to potentially minimize the risks of arterial air embolization and its associated deleterious neurologic effects, while allowing clinicians to make better-informed consumer decisions.