In vivo analysis of the origin and characteristics of gaseous microemboli during catheter-mediated irreversible electroporation

Aims Irreversible electroporation (IRE) ablation is a non-thermal ablation method based on the application of direct current between a multi-electrode catheter and skin electrode. The delivery of current through blood leads to electrolysis. Some studies suggest that gaseous (micro)emboli might be associated with myocardial damage and/or (a)symptomatic cerebral ischaemic events. The aim of this study was to compare the amount of gas generated during IRE ablation and during radiofrequency (RF) ablation. Methods and results In six 60–75 kg pigs, an extracorporeal femoral shunt was outfitted with a bubble-counter to detect the size and total volume of gas bubbles. Anodal and cathodal 200 J IRE applications were delivered in the left atrium (LA) using a 14-electrode circular catheter. The 30 and 60 s 40 W RF point-by-point ablations were performed. Using transoesophageal echocardiography (TOE), gas formation was visualized. Average gas volumes were 0.6 ± 0.6 and 56.9 ± 19.1 μL (P < 0.01) for each anodal and cathodal IRE application, respectively. Also, qualitative TOE imaging showed significantly less LA bubble contrast with anodal than with cathodal applications. Radiofrequency ablations produced 1.7 ± 2.9 and 6.7 ± 7.4 μL of gas, for 30 and 60 s ablation time, respectively. Conclusion Anodal IRE applications result in significantly less gas formation than both cathodal IRE applications and RF applications. This finding is supported by TOE observations.

Air permeability, water penetration and water absorption to specify durability of eco-efficient concrete

The durability of eco-efficient, clinker reduced concrete is a key factor of its performance. In the presented study, different durability indicators of a newly developed eco-concrete composition (ECO) are tested versus standard normal concrete as reference (REF). The tested durability indicators are open porosity, water penetration depth, rate of water absorption by capillarity and two different methods of measuring air permeability (PermeaTORR AC device versus Testing bubble counter). The ECO mix and in particular its cementitious matrix is designed by a combined filler concept substituting Portland cement partially by properly selected limestone fillers of different grain sizes. The approach is based on a combination of particle packing optimization techniques and the reduction of water demand for certain flowability of the paste. Cement content is below the limits of traditional standards while w/c-ratio exceed such limits. While the performance of the eco-concrete in terms of workability and strength is at least equivalent to the standard mix, ecological impact indicators as global warming potential and embodied energy are substantially improved. Durability indicators overall show nearly equivalent performance of ECO and REF. In detail, the resulting air permeability coefficient tested with a bubble counter differs significantly from the coefficient tested by PermeaTORR.

Measurement of gaseous microemboli in the prime before the initiation of cardiopulmonary bypass

Introduction: The use of cardiopulmonary bypass is associated with a risk of neurocognitive deficit caused by gaseous microemboli. Flushing the empty bypass circuit with carbon dioxide, which is more soluble than air, may reduce the amount of gaseous microemboli in the priming solution before the initiating of cardiopulmonary bypass. Method: We measured the amount of gaseous microemboli in twenty primed bypass circuits. Ten circuits were flushed with carbon dioxide before being primed and ten circuits were non-flushed. All circuits in both groups were primed with crystalloid priming. An ultrasonic clinical bubble counter was used to count gaseous microemboli in the prime for 20 minutes. Results: The median numbers of gaseous microemboli counts were highest during the first minute in both groups, with a significantly lower median value in the group flushed with carbon dioxide (397.5) versus the non-flushed group (1900). In the 20th minute, the median values of gaseous microemboli were significantly lower (p<0.023) in the flushed (0.5) versus non-flushed (10.75) groups. The gaseous microembolic count in the flushed group remained lower than in the non-flushed group when tested minute by minute throughout the whole 20-minute period. Conclusion: Flushing the bypass circuits with carbon dioxide before priming significantly decreased the number of gaseous microemboli in the priming solution.

A clinical comparison of bubble elimination in Quadrox and Polystan oxygenators

Background: Microbubbles generated during heart surgery on extracorporeal circulation have been implicated as a possible cause of postoperative neurocognitive dysfunction and negative outcome. The main sources of microbubbles in the extracorporeal circuit are air leaking from the venous cannulation site, air delivered by drug and volume administration, during the taking of blood samples, during hemofiltration, and by using vacuum-assisted venous drainage (VAVD). Membrane oxygenators, although not designed for the elimination of gaseous microbubbles, can eliminate much of this air. Aim of the study / hypothesis: The aim of this study was to test the hypothesis that the amount of microbubbles passing through the oxygenator varies depending on the oxygenator design. Methods: one hundred patients undergoing aortic valve replacement with cardiopulmonary bypass (CPB) were included in a retrospective clinical trial assessing the bubble elimination of the two oxygenators routinely used in our clinic. The oxygenators (Quadrox-i Adult / Polystan Safe Maxi) are manufactured with the same hollow-fiber material, but display different designs. Bubbles were detected by a two-channel ultrasound bubble counter. The probes were placed directly at the inlet and the outlet of the oxygenators. The filtration index was calculated by the bubble counter as a measure of the percentage reduction of bubble volume and number. Results: The Quadrox has a significantly higher filtration index (92.3% [89.7; 95.1], median [25th,75th percentile]) than the Polystan (74.9% [64.2;80.9], p<0.001), indicating the superior ability of the Quadrox to eliminate microbubbles. Conclusion: Our study demonstrates major differences in the capacity of bubble elimination of the oxygenators being investigated, possibly depending on oxygenator design.