Bubble Counter for Measurement of Air Bubbles During Thoracic Stent-Graft Deployment in a Flow Model

Iatrogenic air embolism: influence of air bubble size on cerebral infarctions in an experimental in vivo and numerical simulation model

BACKGROUND

Cerebral infarctions resulting from iatrogenic air embolism (AE), mainly caused by small air bubbles, are a well-known and often overlooked event in endovascular interventions. Despite their significance, the underlying pathophysiology remains largely unclear.

METHODS

In 24 rats, AEs were induced using a microcatheter, positioned in the carotid artery via femoral access. Rats were divided into two study groups, based on the size of the bubbles (85 and 120 µm) and two sub-groups, differing in air volume (0.39 and 0.64 µl). Ultra-high-field magnetic resonance imaging (MRI) was performed 1.5 hours after intervention. MRI findings including the number, single volume and total volume of the infarctions were assessed. A software-based numerical simulation was performed to qualitatively assess the microvascular pathomechanisms.

RESULTS

In the study groups 22 of 24 rats (92%) revealed cerebral infarctions. The number of infarctions per rat was higher for the smaller bubbles, for the lower (medians: 5 vs 3; p=0.049) and higher air volume sub-groups (medians: 6 vs 4; p=0.012). Correspondingly, total infarction volume was higher for the smaller bubbles (1.67 vs 0.5 mm³; p=0.042). Simulations confirmed the results of the experiments and suggested that fusion of microbubbles to larger bubbles is the underlying pathomechanism of vascular occlusions.

CONCLUSION

In iatrogenic AE, the size of the bubbles can have a major impact on the number and total volume of cerebral infarctions. These findings can help to better understand the pathophysiology of this frequent, often underestimated adverse event in endovascular interventions.

Iatrogenic Air Embolisms During Endovascular Interventions: Impact of Origin and Number of Air Bubbles on Cerebral Infarctions

PURPOSE

Cerebral infarctions caused by air embolisms (AE) are a feared risk in endovascular procedures; however, the relevance and pathophysiology of these AEs is still largely unclear. The objective of this study was to investigate the impact of the origin (aorta, carotid artery or right atrium) and number of air bubbles on cerebral infarctions in an experimental in vivo model.

METHODS

In 20 rats 1200 or 2000 highly calibrated micro air bubbles (MAB) with a size of 85 µm were injected at the aortic valve (group Ao), into the common carotid artery (group CA) or into the right atrium (group RA) using a microcatheter via a transfemoral access, resembling endovascular interventions in humans. Magnetic resonance imaging (MRI) using a 9.4T system was performed 1 h after MAB injection followed by finalization.

RESULTS

The number (5.5 vs. 5.5 median) and embolic patterns of infarctions did not significantly differ between groups Ao and CA. The number of infarctions were significantly higher comparing 2000 and 1200 injected MABs (6 vs. 4.5; p < 0.001). The infarctions were significantly larger for group CA (median infarction volume: 0.41 mm3 vs. 0.19 mm3; p < 0.001). In group RA and in the control group no infarctions were detected. Histopathological analyses showed early signs of ischemic stroke.

CONCLUSION

Iatrogenic AEs originating at the ascending aorta cause a similar number and pattern of cerebral infarctions compared to those with origin at the carotid artery. These findings underline the relevance and potential risk of AE occurring during endovascular interventions at the aortic valve and ascending aorta.

Investigation of Experimental Endovascular Air Embolisms Using a New Model for the Generation and Detection of Highly Calibrated Micro Air Bubbles

BACKGROUND

Air embolism (AE), especially when affecting the brain, is an underrated and potentially life-threatening complication in various endovascular interventions. This study aims to investigate experimental AEs using a new model to generate micro air bubbles (MAB), to assess the impact of a catheter on these MAB, and to demonstrate the applicability of this model in vivo.

MATERIALS AND METHODS

Micro air bubbles were created using a system based on microfluidic channels. The MAB were detected and analyzed automatically. Micro air bubbles, with a target size of 85 µm, were generated and injected through a microcatheter. The MAB diameters proximal and distal to the catheter were assessed and compared. In a subsequent in vivo application, 2000 MAB were injected into the aorta (at the aortic valve) and into the common carotid artery (CCA) of a rat, respectively, using a microcatheter, resembling AE occurring during cardiovascular interventions.

RESULTS

Micro air bubbles with a highly calibrated size could be successfully generated (median: 85.5 µm, SD 1.9 µm). After passage of the microcatheter, the MAB were similar in diameter (median: 86.6 µm) but at a lower number (60.1% of the injected MAB) and a substantially higher scattering of diameters (SD 29.6 µm). In vivo injection of MAB into the aorta resulted in cerebral microinfarctions in both hemispheres, whereas injection into the CCA caused exclusively ipsilateral microinfarctions.

CONCLUSION

Using this new AE model, MAB can be generated precisely and reproducibly, resulting in cerebral microinfarctions. This model is feasible for further studies on the pathophysiology and prevention of AE in cardiovascular procedures.

Application of nondestructive mechanical characterization testing for creating in vitro vessel models with material properties similar to human neurovasculature

Vessel models are a first step in developing endovascular medical devices. However, these models, often made from glass or silicone, do not accurately represent the mechanical properties of human vascular tissue, limiting their use to basic training and proof-of-concept testing. This study outlines methods to quantify human vascular tissue mechanical properties and synthetic biomaterials for creating representative vessel models. Human vascular tissue was assessed and compared to silicone and new UV-cured polymers (VC-A30) using the following eight mechanical tests: compressive, shear, tensile dynamic elastic modulus, Poisson's ratio, hardness, radial force, compliance, and lubricity. Half of these testing methods were nondestructive, allowing for multiple mechanical and histological characterizations of the same human tissue sample. Histological evaluation of the cellular and extracellular matrix of the human vessels verified that the dynamic moduli and Poison's ratio tests were nondestructive. Fluid absorption by VC-A30 showed statistically significant softening of mechanical properties, stabilizing after 4 days in phosphate-buffered saline (PBS). Human vasculature exhibited notably similar results to VC-A30 in five of eight mechanical tests (≤30% difference) versus two of eight for standard silicone (≤38% difference). Results show that VC-A30 provides a new option for 3D-printing translucent in vitro vascular models with anatomically relevant mechanical properties. These new vessel analogs may simulate patient-specific vessel disease states, improve surgical training models, accelerate new endovascular device developments, and ultimately reduce the need for animal models.

Retrospective Comparative Study on Differences in Presence of Gas in the Aneurysm Sac after Endovascular Aortic Aneurysm Repair in Early Postoperative Period between Carbon Dioxide Flushing Technique and Saline Flushing of the Delivery System

BACKGROUND

Presence of gas is a frequent finding on early postoperative computed tomography angiography (CTA) after endovascular aortic aneurysm repair (EVAR) with unclear clinical relevance. The aim of this study is to examine and compare the presence of gas within the aneurysm sac following EVAR on early postoperative CTA after the use of carbon dioxide (CO₂) flushing technique with saline flushing alone.

METHODS

A retrospective analysis of patients undergoing standard, fenestrated EVAR (fEVAR) or branched EVAR (bEVAR) with flushing of the delivery system with CO₂ between January 2016 and August 2018 was undertaken. Data of a previous report using standard saline flushing were included. Patients were classified into 2 main groups: group 1 with saline flushing and group 2 with CO₂ flushing and 3 subgroups according to the type of endograft. The presence, position, and volume of gas in the postoperative CTA (within 10 days) was examined and analyzed in terms of anatomical and procedural risk factors.

RESULTS

Group 1 included 210 patients (mean age 73 ± 8, 84% males), while group 2 included 300 patients (mean age 70 ± 11, 68% males). Presence of gas was more common in group 1 (83, 39% vs. 64, 21%, P = 0.000). Volume of gas was larger in group 1 [0.41 mL (0.01-2.7) vs. 0.2 mL (0.02-1), P = 0.001). In standard EVAR with saline flushing (subgroup 1a), 59 patients (45%) had presence of gas with CO₂ flushing (subgroup 2a); 35 patients (25%) had presence of gas (P = 0.005). The mean gas volume was larger in subgroup 1a compared to 2a (0.40 ± 0.47 vs. 0.15 ± 0.17 mL, P = 0.000). The location of the gas was more frequent in contact with the anterior wall of the aorta in both groups, standard EVAR subgroups and fEVAR subgroups. The presence of gas in group 2 was associated with larger preoperative size of the aortic diameter (P = 0.03) and larger perfused lumen diameter (P = 0.05). The type of the graft was not associated with the presence of gas in the aneurysm sac on postoperative CTA. However, the presence of gas was more frequent in standard EVAR than fEVAR and bEVAR. Endoleak type II was not associated with the presence of gas.

CONCLUSIONS

CO₂ flushing of stent grafts during standard and complex EVAR prior to deployment reduces the frequency and volume of gas on postoperative CTA. This study indicates that the CO₂ flushing technique may effectively exchange trapped air for a less harmful gas in endografts.

Distribution of Air Embolization During TEVAR Depends on Landing Zone: Insights From a Pulsatile Flow Model

Purpose: To analyze the distribution of air bubbles in the supra-aortic vessels during thoracic stent-graft deployment in zones 2 and 3 in an aortic flow model. Materials and Methods: Ten identical, investigational, tubular, thoracic stent-grafts were deployed in a glass aortic flow model with a type I arch: 5 in zone 2 and 5 in zone 3. A pulsatile pump generated a flow of 5 L/min with systolic and diastolic pressures (±5%) of 105 and 70 mm Hg, respectively. The flow rates (±5%) were 300 mL/min in the subclavian arteries, 220 mL/min in the vertebral arteries, and 400 mL/min in the common carotid arteries (CCAs). The total amounts of air released in each supra-aortic branch and in the aorta were recorded. Results: The mean amounts of air measured were 0.82±0.23 mL in the zone-2 group and 0.94±0.28 mL in the zone-3 group (p=0.49). In the zone-2 group compared with zone 3, the amounts of released air were greater in the right subclavian artery (0.07±0.02 vs 0.02±0.02 mL, p<0.01) and right CCA (0.30±0.8 vs 0.18±07 mL, p=0.04). There were no differences between the groups concerning the mean amounts of air measured in the right vertebral and all left-side supra-aortic branches. The amount of air released in the descending aorta was significantly higher in the zone-3 group vs the zone-2 group (0.48±0.12 vs 0.13±0.08 mL, p<0.01). Small bubbles were observed continuously during deployment, whereas large bubbles appeared more commonly during deployment of the proximal stent-graft end and after proximal release of the stent-graft. Conclusion: Air is released into all supra-aortic branches and the descending aorta during deployment of tubular thoracic stent-grafts in zones 2 and 3 in an aortic flow model. Higher amounts of air were observed in right-side supra-aortic branches during deployment in zone 2, whereas significantly greater amounts of air were observed in the descending aorta during deployment in zone 3.