Dynamic bubble trap can replace an arterial filter during cardiopulmonary bypass surgery

The scientific evidence of arterial line filtration in cardiopulmonary bypass

BACKGROUND

The indication for arterial line filtration (ALF) is to inhibit embolisation during cardiopulmonary bypass. Filtration methods have developed from depth filters to screen filters and from a stand-alone component to an integral part of the oxygenator. For many years, ALF has been a standard adopted by a majority of cardiac centres worldwide. The following review aims to summarize the available evidence in support for ALF and report on its current practice in Europe.

METHOD

The principles and application of ALF in Europe was investigated using a survey conducted in 2014. The scientific evidence for ALF was examined by performing a systematic literature search in six different databases, using the following search terms: "Cardiopulmonary bypass AND filters AND arterial". The primary endpoint was protection against cerebral injury verified by the degree of cerebral embolisation or cognitive tests. The secondary endpoint was improvement of the clinical outcome verified elsewise. Only randomised clinical trials were considered.

RESULTS

The response rate was 31% (n=112). The great majority (88.5%) of respondents were using ALF, following more than 10 years of experience. Integrated arterial filtration was used by 55%. Of respondents not using ALF, fifty-four percent considered starting using integrated arterial filtration. The systematic literature database search returned 180 unique publications where 82 were specifically addressing ALF in cardiopulmonary bypass. Only four out of the 82 identified publications fulfilled our inclusion criteria. Of these, three were more than 20 years old and based on the use of bubble oxygenation.

CONCLUSION

ALF is a standard implemented in a majority of cardiopulmonary bypass procedures in Europe. The level of scientific evidence available in support of current arterial line filtration methods in cardiopulmonary bypass is, however, poor. Large, well-designed, randomised trials are warranted.

In vitro air removal characteristics of two neonatal cardiopulmonary bypass systems: filtration may lead to fractionation of bubbles

Introduction of gaseous microemboli (GME) into the arterial line of a pediatric cardiopulmonary bypass (CPB) circuit may lead to cognitive decline and adverse outcomes of the pediatric patient.Arterial filters are incorporated into CPB circuits as a safeguard for gross air and to reduce GME. Recently, arterial filters were integrated in two neonatal oxygenators to reduce volume and foreign surface area. In this study a clinical CPB scenario was simulated. The oxygenators, the corresponding venous reservoirs and the complete CPB circuits were compared regarding air removal and bubble size distribution after the introduction of an air bolus or GME. During a GME challenge, the Capiox FX05 oxygenator removed a significantly higher volume of GME than the QUADROX-i Neonatal oxygenator (97% vs. 86%). Detailed air removal characteristics showed that more GME in the range of 20-50 µm were leaving the devices than were entering. This phenomenon seems to be more present in the Capiox FX05. The circuits were also challenged with an air bolus. Each individual component tested removed 99.9%, which resulted in an air volume reduction of 99.99% by either complete CBP circuit. Overall, we conclude that both CPB systems were very adequate in removing GME and gross air. The air removal properties of both systems are considered safe and reliable. Detailed GME distribution data show that the Capiox FX05 showed more small GME (<50 µm) due to fractionation of larger GME when compared to the QUADROX-i Neonatal. We may conclude that filtration may lead to fractionation.

Ultrasound destruction of air microemboli as a novel approach to brain protection in cardiac surgery

OBJECTIVE

Evaluation of a novel approach to eliminate air microemboli from extracorporeal circulation via ultrasonic destruction.

DESIGN

In vitro proof-of-concept study.

SETTING

Research laboratory.

PARTICIPANTS

None.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

An extracorporeal circulation device was filled with human blood circulating at 3 L/min. Air bubbles were injected into the system. For bubble destruction, the blood in the tubing system was repeatedly insonated for 3 minutes using a therapeutic 60-kHz device, with variation of intensity and duty cycle settings, ranging from 0.2 W/cm² to 1.0 W/cm² and from duty cycle 60% to continuous wave (CW). Number and diameter of air microemboli were counted upstream and downstream of the ultrasound device by a 2-channel microemboli Doppler detector. For safety assessment, circulating blood was insonated continuously for 2 hours at 0.8 W/cm² CW and compared with circulation without insonation; and standard blood parameters were analyzed. Without treatment, 1,313 to 1,580 emboli were detected upstream, diameter ranging between 10 and 130 μm. Ultrasound treatment eliminated up to 87% of all detected bubbles in cw application (p<0.01) and showed comparable effects at intensities from 0.4 W/cm² to 1.0 W/cm² cw. Bubbles sized>15 μm almost were eliminated completely (p<0.001). Pulsed wave application rendered inferior results (p>0.05). No relevant changes of blood parameters were observed compared with control circulation.

CONCLUSIONS

Ultrasound destruction of air emboli is a very efficient method to reduce number and size of emboli. Within the limits of safety assessment, the authors could not detect relevant side effects on standard blood parameters.

Initial results of an optimized perfusion system

BACKGROUND

In order to reduce the negative effects of extracorporeal circulation (ECC), the perfusion system and management were optimized at our institution. The goals of optimization were a reduction in the priming volume, in the foreign surface area and in microbubble activity, as well as optimization of suction blood management.

METHODS

Sixty patients were included in this retrospective study. Patients were assigned to two groups, with regard to the use of an optimized perfusion system (OPS-group, n=30) and a standard perfusion system (SPS-group, n=30). All patients underwent elective procedures.

RESULTS

There were no significant differences with respect to patient demographics and operation time. ECC time and cross-clamp time were significantly longer in the OPS group. Statistically significant differences in outcome between the two groups were seen with regard to the following variables: effective priming volume (OPS: 775±447ml; SPS: 1610±0ml; p<0.0001), hemoglobin drop after the start of ECC (OPS: 2.7±1.2g/dl; SPS: 4.2±0.8g/dl; p<0.0001), c-reactive protein on postoperative day 2 (OPS: 121.0±59.4 U/l; SPS: 164.0±50.2 U/l; p=0.003). With regard to the use of blood transfusions, a 33% reduction in the overall amount of transfused units was seen. The rate of patients without transfusions during the entire hospital stay increased from 37% (SPS) to 53% (OPS). The mean transfused red blood cell units per patient was lower in the OPS-group (1.6±2.4 units) than in the SPS-group (2.3±3.5 units).

CONCLUSION

With the described optimized perfusion system, a significantly lower priming volume, leading to less hemodilution after the onset of CPB, was achieved. The amount of blood transfusions and the inflammatory response were reduced.

Clinical Evaluation of the Air Removal Characteristics of an Oxygenator with Integrated Arterial Filter in a Minimized Extracorporeal Circuit

The use of minimized extracorporeal circuits (MECC) in cardiac surgery is an important measure to increase the biocompatibility of cardiopulmonary bypass during coronary artery bypass grafting (CABG). These circuits eliminate volume storage reservoirs and bubble traps to minimize the circuit. However, the reduction in volume may increase the risk of gaseous microemboli (GME). The MECC system as used by our group consists of a venous bubble trap, centrifugal pump, and an oxygenator. To further reduce the risk of introducing GME, an oxygenator with an integrated arterial filter was developed based on the concept of minimal volume and foreign surface. We studied the air removal characteristics of this oxygenator with and without integrated arterial filter. The quantity and volume of GME were measured with precision at both the inlet and outlet of the devices.

Our results showed that integration of an arterial filter into this oxygenator increased GME reducing capacity from 69.2% to 92%. Moreover, we were able to obtain data on the impact of an arterial filter on the exact size-distribution of GME entering the arterial line.

The present study demonstrates that an MECC system and oxygenator with integrated arterial filter significantly reduces the volume and size of GME. The use of an integrated arterial filter in an MECC system may protect the patient from the deleterious effects of CPB and may further improve patient safety.