An in vitro comparison of embolus differentiation techniques for clinically significant macroemboli: dual-frequency technique versus frequency modulation method

Real-Time Detection of Circulating Thrombi in an Extracorporeal Circuit Using Doppler Ultrasound: In-Vitro Proof of Concept Study

BACKGROUND

Thromboembolic stroke continues to be by far the most common severe adverse event in patients supported with mechanical circulatory assist devices. Feasibility of using Doppler ultrasound to detect circulating thrombi in an extracorporeal circuit was investigated.

METHODS

A mock extracorporeal circulatory loop of uncoated cardiopulmonary bypass tubing and a roller pump was setup. A Doppler bubble counter was used to monitor the mean ultrasound backscatter signal (MUBS). The study involved two sets of experiments. In Scenario 1, the circuit was sequentially primed with human blood components, and the MUBS was measured. In Scenario 2, the circuit was primed with heparinized fresh porcine blood, and the MUBS was measured. Fresh blood clots (diameter <1,000 microns, 1,000-5,000 microns, >5,000 microns) were injected into the circuit followed by protamine administration.

RESULTS

In Scenario 1 (n = 3), human platelets produced a baseline MUBS of 1.5 to 3.5 volts/s. Addition of packed human red blood cells increased the baseline backscatter to 17 to 21 volts/s. Addition of fresh frozen plasma did not change the baseline backscatter. In Scenario 2 (n = 5), the blood-primed circuit produced a steady baseline MUBS. Injection of the clots resulted in abrupt and transient increase (range: 3-30 volts/s) of the baseline MUBS. Protamine administration resulted in a sustained increase of MUBS followed by circuit thrombosis.

CONCLUSIONS

Doppler ultrasound may be used for real-time detection of circulating solid microemboli in the extracorporeal circuit. This technology could potentially be used to design safety systems that can reduce the risk of thromboembolic stroke associated with mechanical circulatory support therapy.

Femoral Nailing in a Porcine Model Causes Bone Marrow Emboli in the Lungs and Systemic Emboli in the Heart and Brain

Background

Shaft fractures of the femur are commonly treated with intramedullary nailing, which can release bone marrow emboli into the bloodstream. Emboli can travel to the lungs, impairing gas exchange and causing inflammation. Occasionally, emboli traverse from the pulmonary to the systemic circulation, hindering perfusion and resulting in injuries such as heart and brain infarctions, known as fat embolism syndrome. We studied the extent of systemic bone marrow embolization in a pig model.

Methods

Twelve anesthetized pigs underwent bilateral intramedullary nailing of the femur, while 3 animals served as sham controls. Monitoring included transesophageal echocardiography (TEE), pulse oximetry, electrocardiography, arterial blood pressure measurement, and blood gas and troponin-I analysis. After surgery, animals were monitored for 240 minutes before euthanasia. Post mortem, the heart, lungs, and brain were biopsied.

Results

Bone marrow emboli were found in the heart and lungs of all 12 of the pigs that underwent intramedullary nailing and in the brains of 11 of them. No emboli were found in the sham group. The pigs subjected to intramedullary nailing exhibited significant hypoxia (PaO2/FiO2 ratio, 410 mm Hg [95% confidence interval (CI), 310 to 510) compared with the sham group (594 mm Hg [95% CI, 528 to 660]). The nailing group exhibited ST-segment alterations consistent with myocardial ischemia and a significant increase in the troponin-I level compared with the sham group (1,580 ng/L [95% CI, 0 to 3,456] versus 241 ng/L [95% CI, 0 to 625] at the 240-minute time point; p = 0.005). TEE detected emboli in the right ventricular outflow tract, but not systemically, in the nailing group.

Conclusions

Bilateral intramedullary nailing caused bone marrow emboli in the lungs and systemic emboli in the heart and brain in this pig model. The observed clinical manifestations were consistent with coronary and pulmonary emboli. TEE detected pulmonary but not systemic embolization.

Clinical Relevance

Femoral intramedullary nailing in humans is likely to result in embolization as described in our pig model. Focused monitoring is necessary for detection of fat embolism syndrome. Absence of visual emboli in the left ventricle on TEE does not exclude the occurrence of systemic bone marrow emboli.

Diagnostic Accuracy of an Algorithm for Discriminating Presumed Solid and Gaseous Microembolic Signals During Transcranial Doppler Examinations

OBJECTIVE

The aim of the work described here was to assess the diagnostic accuracy of a new algorithm (SGA-a) for time-domain analysis of transcranial Doppler audio signals to discriminate presumed solid and gaseous microembolic signals and artifacts (SGAs).

METHODS

SGA-a was validated by human experts in an artifact cohort of 20 patients subjected to a 1-h transcranial Doppler exam before cardiac surgery (cohort 1). Emboli were validated in a cohort of 10 patients after aortic valve replacement in a 4-h monitoring period (cohort 2). The SGA misclassification rate was estimated by testing SGA-a on artifact-free test files of solid and gaseous emboli.

RESULTS

In cohort 1 (n = 24,429), artifacts were classified with an accuracy of 94.5%. In cohort 2 (n = 12,328), the accuracy in discriminating solid/gaseous emboli from artifacts was 85.6%. The 95% limits of agreement for, respectively, the numbers of presumed solids and gaseous emboli, artifacts and microembolic signals of undetermined origin were [-10, 10], [-14, 7] and [-9, 16], and the intra-class correction coefficients were 0.99, 0.99 and 0.99, respectively. The rate of misclassification of solid test files was 2%, and the rate of misclassification of gaseous test files was 12%.

CONCLUSION

SGA-a can detect presumed solid and gaseous microembolic signals and differentiate them from artifacts. SGA-a could be of value when both solid and gaseous emboli may jeopardize brain function such as seen during cardiac valve and/or aortic arch replacement procedures.

ASNM and ASN joint guidelines for transcranial Doppler ultrasonic monitoring: An update

Today, it seems prudent to reconsider how ultrasound technology can be used for providing intraoperative neurophysiologic monitoring that will result in better patient outcomes and decreased length and cost of hospitalization. An extensive and rapidly growing literature suggests that the essential hemodynamic information provided by transcranial Doppler (TCD) ultrasonography neuromonitoring (TCDNM) would provide effective monitoring modality for improving outcomes after different types of vascular, neurosurgical, orthopedic, cardiovascular, and cardiothoracic surgeries and some endovascular interventional or diagnostic procedures, like cardiac catheterization or cerebral angiography. Understanding, avoiding, and preventing peri- or postoperative complications, including neurological deficits following abovementioned surgeries, endovascular intervention, or diagnostic procedures, represents an area of great public and economic benefit for society, especially considering the aging population. The American Society of Neurophysiologic Monitoring and American Society of Neuroimaging Guidelines Committees formed a joint task force and developed updated guidelines to assist in the use of TCDNM in the surgical and intensive care settings. Specifically, these guidelines define (1) the objectives of TCD monitoring; (2) the responsibilities and behaviors of the neurosonographer during monitoring; (3) instrumentation and acquisition parameters; (4) safety considerations; (5) contemporary rationale for TCDNM; (6) TCDNM perspectives; and (7) major recommendations.

Cerebral Emboli Monitoring Using Transcranial Doppler Ultrasonography in Adults and Children: A Review of the Current Technology and Clinical Applications in the Perioperative and Intensive Care Setting

Transcranial Doppler (TCD) ultrasonography is the only noninvasive bedside technology for the detection and monitoring of cerebral embolism. TCD may identify patients at risk of acute and chronic neurologic injury from gaseous or solid emboli. Importantly, a window of opportunity for intervention-to eliminate the source of the emboli and thereby prevent subsequent development of a clinical or subclinical stroke-may be identified using TCD. In this review, we discuss the application of TCD sonography in the perioperative and intensive care setting in adults and children known to be at increased risk of cerebral embolism. The major challenge for evaluation of emboli, especially in children, is the need to establish the ground truth and define true emboli identified by TCD. This requires the development and validation of a predictive TCD emboli monitoring technique so that appropriately designed clinical studies intended to identify specific modifiable factors and develop potential strategies to reduce pathologic cerebral embolic burden can be performed.

Neurological impact of emboli during adult cardiac surgery

Objectives

This study draws on advances in Doppler ultrasound bubble sizing to investigate whether high volumes of macro-bubbles entering the brain during cardiac surgery increase the risk of new cerebral microbleeds (CMBs), ischemic MR lesions, or post-operative cognitive decline (POCD).

Methods

Transcranial Doppler (TCD) ultrasound recordings were analysed to estimate numbers of emboli and macrobubbles (>100 μm) entering the brain during cardiac surgery. Logistic regression was used to explore the hypothesis that emboli characteristics affect the incidence of new brain injuries identified through pre- and post-operative MRI and neuropsychological testing.

Results

TCD, MRI, and neuropsychological test data were compared between 28 valve and 18 CABG patients. Although valve patients received over twice as many emboli per procedure [median: 1995 vs. 859, p = .004], and seven times as many macro-bubbles [median: 218 vs. 28, p = .001], high volumes of macrobubbles were not found to be significantly associated with new CMBs, new ischaemic lesions, or POCD. The odds of acquiring new CMBs increased by approximately 5% [95% CI: 1 to 10%] for every embolus detected in the first minute after the release of the aortic cross-clamp (AxC). Logistic regression models also confirmed previous findings that cardiopulmonary bypass time and valve surgery were significant predictors for new CMBs (both p = .03). Logistic regression analysis estimated an increase in the odds of acquiring new CMBs of 6% [95% CI: 1 to 12%] for every minute of bypass time over 91 mins.

Conclusions

This small study provides new information about the properties and numbers of bubbles entering the brain during surgery, but found no evidence to substantiate a direct link between large numbers of macrobubbles and adverse cognitive or MR outcome.

Clinical Trial Registration URL - http://www.isrctn.com. Unique identifier: 66022965.

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Higher numbers of macrobubbles enter the brain during valve surgery compared to bypass graft surgery.

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Macrobubbles did not appear to be linked to new cerebral microbleeds, ischemic lesions, or cognitive decline.

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Emboli received following release of the aortic cross-clamp predicted new cerebral microbleeds.

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Other factors predicting new microbleeds included cardiopulmonary bypass duration and surgery type.

Operative strategies to reduce cerebral embolic events during on- and off-pump coronary artery bypass surgery: A stratified, prospective randomized trial

OBJECTIVE

To determine the impact of different aortic clamping strategies on the incidence of cerebral embolic events during coronary artery bypass grafting (CABG).

METHODS

Between 2012 and 2015, 142 patients with low-grade aortic disease (epiaortic ultrasound grade I/II) undergoing primary isolated CABG were studied. Those undergoing off-pump CABG were randomized to a partial clamp (n = 36) or clampless facilitating device (CFD; n = 36) strategy. Those undergoing on-pump CABG were randomized to a single-clamp (n = 34) or double-clamp (n = 36) strategy. Transcranial Doppler ultrasonography (TCD) was performed to identify high-intensity transient signals (HITS) in the middle cerebral arteries during periods of aortic manipulation. Neurocognitive testing was performed at baseline and 30-days postoperatively. The primary endpoint was total number of HITS detected by TCD. Groups were compared using the Mann-Whitney U test.

RESULTS

In the off-pump group, the median number of total HITS were higher in the CFD subgroup (30.0; interquartile range [IQR], 22-43) compared with the partial clamp subgroup (7.0; IQR, 0-16; P < .0001). In the CFD subgroup, the median number of total HITS was significantly lower for patients with 1 CFD compared with patients with >1 CFD (12.5 [IQR, 4-19] vs 36.0 [IQR, 25-47]; P = .001). In the on-pump group, the median number of total HITS was 10.0 (IQR, 3-17) in the single-clamp group, compared with 16.0 (IQR, 4-49) in the double-clamp group (P = .10). There were no differences in neurocognitive outcomes across the groups.

CONCLUSIONS

For patients with low-grade aortic disease, the use of CFDs was associated with an increased rate of cerebral embolic events compared with partial clamping during off-pump CABG. A single-clamp strategy during on-pump CABG did not significantly reduce embolic events compared with a double-clamp strategy.

Cerebral Microemboli Detection and Differentiation During Transcatheter Closure of Patent Ductus Arteriosus

The aim of this prospective study was to determine the frequency and composition of cerebral microemboli in a pediatric population, during transcatheter closure of patent ductus arteriosus (PDA). Multifrequency transcranial Doppler was used to monitor cerebral blood flow velocity (CBFV) and detect microembolic signals (MES) in the middle cerebral artery in 23 patients (median age 18 months). MES were automatically identified and differentiated according to composition; gaseous or solid. The procedure was divided into five periods: Arterial catheterization; venous catheterization; ductal catheterization; angiography; device placement and release. Timing of catheter manipulations and MES were registered and compared. MES were detected in all patients. The median number of signals was 7, (minimum 1, maximum 28). Over 95 % of all MES were gaseous. 11 % were detected during device placement while 64 % were detected during angiographic studies, significantly higher than during any other period (P < 0.001). There was a moderate correlation between the number of MES and volume of contrast used, (R = 0.622, P < 0.01). There was no correlation with fluoroscopic time or duration of procedure. This is the first study to investigate the timing and composition of cerebral microemboli during PDA occlusion. Microemboli were related to specific catheter manipulations and correlated with the amount of contrast used.