Cerebral arterial gas embolism in swine. Comparison of two sites for air injection

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.

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.

Multi-modality imaging assessment of microbubbles and cerebral emboli in left ventricular pulsed field ablation

BACKGROUND

Pulsed field ablation (PFA) may have a superior safety profile compared to other technologies, but it has the potential to cause gaseous microbubbles (MB), which may be associated with cerebral emboli. Limited relative safety data has been published regarding PFA in the left ventricle (LV).

METHODS

Healthy and chronic myocardial infarction (MI) swine underwent PFA (monopolar, biphasic, 25 Amps) in the LV using an irrigated focal catheter under intra-cardiac echocardiography (ICE) guidance for MB monitoring. Two control swine received air MBs through the lumen of the ablation catheter. Swine underwent brain MRI before and after PFA (or control air MB injection). Gross pathology and histology of brains with abnormal MRI findings were performed.

RESULTS

Four healthy and 5 chronic MI swine underwent 124 left ventricular PFA applications. No PFA-related MB formation was noted on ICE. Both control swine developed multiple acute emboli in the thalamus and caudate on DWI, ADC, and FLAIR brain MRI images in response to air MB injection. Of the 9 PFA swine, there were no abnormalities on ADC or FLAIR images. There was one hyperintense focus in the left putamen on the DWI trace image, but the absence of ADC or FLAIR affirmation suggested it was artifact. Gross pathology and histopathology of this region did not detect any abnormalities.

CONCLUSIONS

Focal monopolar biphasic PFA of both healthy and chronically infarcted left ventricular myocardium does not generate any MB or cerebral emboli observable on ICE and brain MRI.

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.

Iatrogenic cerebral arterial gas embolism from flushing of the arterial line in two calves

BACKGROUND

Measurement of invasive blood pressure as reflection of blood flow and tissue perfusion is often carried out in animals during general anesthesia. Intravascular cannulation offers the potential for gas to directly enter the circulation and lead to arterial gas embolism. Cerebral arterial gas embolism may cause a spectrum of adverse effects ranging from very mild symptoms to severe neurological injury and death. Although several experimental models of arterial gas embolism have been published, there are no known published reports of accidental iatrogenic cerebral arterial gas embolism from flushing of an arterial line in animals.

CASE PRESENTATION

A 7-day-old Red Holstein-Friesian calf (No. 1) and a 28-day-old Holstein-Friesian calf (No. 2) underwent hot iron disbudding and sham disbudding, respectively, under sedation and cornual nerve anesthesia. Invasive arterial blood pressure was measured throughout the procedure and at regular intervals during the day. Before disbudding, a sudden and severe increase of blood pressure was observed following flushing of the arterial line. Excitation, hyperextension of the limbs and rapid severe horizontal nystagmus appeared shortly thereafter. Over the following minutes, symptoms ameliorated and blood pressure normalized in both cases. Prompt diagnosis was missed in calf 1; supportive fluid therapy was provided. Severe deterioration of neurologic status occurred in the following 24 h and culminated with stupor. The calf was euthanized for ethical reasons and the histological examination revealed extensive cerebral injury. Treatment of calf 2 consisted of supportive fluid and oxygen therapy; furosemide (1 mg/kg IV) was injected twice. Calf 2 appeared clinically normal after 2 h and showed no neurologic sequelae on a 3-month-follow up period.

CONCLUSIONS

There are no known reports of cerebral arterial gas embolism following flushing of the auricular arterial line in calves. The injection of a small amount of air at high pressure in a peripheral artery may lead to a significant cerebral insult. The clinical presentation is non-specific and can favour misdiagnosis and delay of therapy.

Detection of cerebral arterial gas embolism using regional cerebral oxygen saturation, quantitative electroencephalography, and brain oxygen tension in the swine

BACKGROUND

Cerebral air emboli occur as a complication of invasive medical procedures. The sensitivity of cerebral monitoring methods for the detection of air emboli is not known. This study investigates the utility of electroencephalography and non-invasively measured cerebral oxygen saturation in the detection of intracerebrovascular air.

NEW METHOD

In 12 pigs oxygen saturation was continuously measured using transcranial near-infrared spectroscopy and oxygen tension was continuously measured using intraparenchymal probes. Additionally, quantitative electroencephalography and microdialysis were performed. Doses of 0.2, 0.4, 0.8, and 1.6 ml of air were injected into the cerebral arterial vasculature through a catheter.

RESULTS

Oxygen saturation and electroencephalography both reacted almost instantaneously on the air emboli, but were less sensitive than the intraparenchymal oxygen tension. There was reasonable correlation (ρ ranging from 0.417 to 0.898) between oxygen saturation, oxygen tension, electroencephalography and microdialysis values.

COMPARISON WITH EXISTING METHODS

Our study is the first to demonstrate the effects of cerebral air emboli using multimodal monitoring, specifically on oxygen saturation as measured using near-infrared spectroscopy.

CONCLUSIONS

Our results show that non-invasively measured oxygen saturation and quantitative electroencephalography can detect the local effects of air emboli on cerebral oxygenation, but with reduced sensitivity as compared to intraparenchymal oxygen tension. Prospective human studies using multimodal monitoring incorporating electroencephalography and oxygen saturation should be performed.

Hyperbaric oxygen does not improve cerebral function when started 2 or 4 hours after cerebral arterial gas embolism in swine

OBJECTIVE

Hyperbaric oxygenation is the accepted treatment for cerebral arterial gas embolism. Although earlier start of hyperbaric oxygenation is associated with better outcome, it is unknown how much delay can be tolerated before start of hyperbaric oxygenation. This study investigates the effect of hyperbaric oxygenation on cerebral function in swine when initiated 2 or 4 hours after cerebral arterial gas embolism.

DESIGN

Prospective interventional animal study.

SETTING

Surgical laboratory and hyperbaric chamber.

SUBJECTS

Twenty-two Landrace pigs.

INTERVENTIONS

Under general anesthesia, probes to measure intracranial pressure, brain oxygen tension (PbtO2), and brain microdialysis, and electrodes for electroencephalography were placed. The electroencephalogram (quantified using temporal brain symmetry index) was suppressed during 1 hour by repeated injection of air boluses through a catheter placed in the right ascending pharyngeal artery. Hyperbaric oxygenation was administered using U.S. Navy Treatment Table 6 after 2- or 4-hour delay. Control animals were maintained on an inspiratory oxygen fraction of 0.4.

MEASUREMENTS AND MAIN RESULTS

Intracranial pressure increased to a mean maximum of 19 mm Hg (SD, 4.5 mm Hg) due to the embolization procedure. Hyperbaric oxygenation significantly increased PbtO2 in both groups treated with hyperbaric oxygenation (mean maximum PbtO2, 390 torr; SD, 177 torr). There were no significant differences between groups with regard to temporal brain symmetry index (control vs 2-hr delay, p = 0.078; control vs 4-hr delay, p = 0.150), intracranial pressure, and microdialysis values.

CONCLUSIONS

We did not observe an effect of hyperbaric oxygenation on cerebral function after a delay of 2 or 4 hours. The injury caused in our model could be too severe for a single session of hyperbaric oxygenation to be effective. Our study should not change current hyperbaric oxygenation strategies for cerebral arterial gas embolism, but further research is necessary to elucidate our results. Whether less severe injury benefits from hyperbaric oxygenation should be investigated in models using smaller amounts of air and clinical outcome measures.

Animal models of cerebral arterial gas embolism

Cerebral arterial gas embolism is a dreaded complication of diving and invasive medical procedures. Many different animal models have been used in research on cerebral arterial gas embolism. This review provides an overview of the most important characteristics of these animal models. The properties discussed are species, cerebrovascular anatomy, method of air embolization, amount of air, bubble size, outcome parameters, anesthesia, blood glucose, body temperature and blood pressure.