Paradoxical Symptomatic Air Embolism after Saline Contrast Transesophageal Echocardiography

Cardiovascular thrombotic complications in acute ischemic stroke assessed by chest spectral computed tomography during COVID-19

During the pandemic context, diagnostic algorithms had to be adapted considering the decimated medical personnel, local technical resources, and the likelihood of contamination. Given the higher probability of thrombotic complications related to COVID-19 and the availability of a dual-layer spectral computed tomography (CT) scanner, we have recently adopted the use of low-dose, non-gated, chest CT scans performed five minutes after contrast administration among patients admitted with acute ischemic stroke (AIS) undergoing cerebrovascular CT angiography. Dual-layer spectral CT comprises a single X-ray source and two-layer detector with different photon-absorption capabilities. In addition to conventional images, the two distinct energy datasets obtained enable multiparametric spectral analysis without need to change the original scanning protocol. The two spectral features that emerge as most useful for patients with AIS are virtual monoenergetic imaging and iodine-based results. Aside from the evaluation of lung parenchyma, this novel strategy enables ruling out cardioembolic sources and simultaneously providing evidence of pulmonary and myocardial injury in a single session and immediately after CT cerebrovascular angiography. Furthermore, it involves a non-invasive, seemingly accurate, unsophisticated, safer (very low radiation dose and no contrast administration), and cheaper tool for ruling out cardioembolic sources compared to transesophageal echocardiogram and cardiac CT. Accordingly, we sought to standardize the technical aspects and overview the usefulness of delayed-phase, low-dose chest spectral CT in patients admitted with AIS.

Practicability and Diagnostic Yield of One-Stop Stroke CT with Delayed-Phase Cardiac CT in Detecting Major Cardioembolic Sources of Acute Ischemic Stroke : A Proof of Concept Study

Purpose

Recurrent stroke is considered to increase the incidence of severe disability and death. For correct risk assessment and patient management it is essential to identify the origin of stroke at an early stage. Transthoracic echocardiography (TTE) is the initial standard of care for evaluating patients in whom a cardioembolic source of stroke (CES) is suspected but its diagnostic capability is limited. Transesophageal echocardiography (TEE) is considered as gold standard; however, this approach is time consuming, semi-invasive and not always feasible. We hypothesized that adding a delayed-phase cardiac computed tomography (cCT) to initial multimodal CT might represent a valid alternative to routine clinical echocardiographic work-up.

Material and Methods

Patients with suspected acute cardioembolic stroke verified by initial multimodal CT and subsequently examined with cCT were included. The cCT was evaluated for presence of major CES and compared to routine clinical echocardiographic work-up.

Results

In all, 102 patients with suspected acute CES underwent cCT. Among them 60 patients underwent routine work-up with echocardiography (50 TTE and only 10 TEE). By cCT 10/60 (16.7%) major CES were detected but only 4 (6.7%) were identified by echocardiography. All CES observed by echocardiography were also detected by cCT. In 8 of 36 patients in whom echocardiography was not performed cCT also revealed a major CES.

Conclusion

These preliminary results show the potential diagnostic yield of delayed-phase cCT to detect major CES and therefore could accelerate decision-making to prevent recurrence stroke. To confirm these results larger studies with TEE as the reference standard and also compared to TTE would be necessary.

Bubbles in the skin microcirculation underlying cutis marmorata in decompression sickness: Preliminary observations

INTRODUCTION

The cutaneous form of decompression sickness (DCS) known as cutis marmorata is a frequent clinical presentation. Beyond a general acceptance that bubbles formed from dissolved inert gas are the primary vector of injury, there has been debate about pathophysiology. Hypotheses include: 1) local formation of bubbles in the skin or its blood vessels; 2) arterialisation of venous bubbles across a right to left shunt (RLS) with local amplification in bubble size after reaching supersaturated skin via the arterial circulation; and 3) passage of arterialised venous bubbles to the cerebral circulation with stimulation of a sympathetically mediated vasomotor response.

METHODS

Four divers exhibiting cutis marmorata had the underlying tissue examined with ultrasound 4-5.5 hours after appearance of the rash. All subsequently underwent transthoracic echocardiography with bubble contrast to check for a RLS.

RESULTS

In all cases numerous small bubbles were seen moving within the skin microvasculature. No bubbles were seen in adjacent areas of normal skin. All four divers had a large RLS.

CONCLUSION

This is the first report of bubbles in skin affected by cutis marmorata after diving. The finding is most compatible with pathophysiological hypotheses one and two above. The use of ultrasound will facilitate further study of this form of DCS.

Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles

Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Evaluating the potential risks of bubble studies during echocardiography

Objective:

Cardiac shunts are often identified using bubble studies in echocardiography, with agitated saline. Previous studies have recommended various safe amounts of agitated saline. This poses a potential risk for air microembolism. The purpose of this study was to quantify the bubbles created by various quantities of agitated saline.

Methods:

A closed circuit was constructed with a HeartMate pneumatic ventricular assist pump and a cardiotomy reservoir to remove air during recirculation. One empty 10 mL syringe and one 10 mL syringe containing 1 mL of air and 9 mL of saline were attached to a three-way stopcock. The air/saline bolus was then agitated between the two syringes five times to create bubbles and injected into the tubing proximal to the HeartMate. An EDAC bubble detector sensor was attached prior to the saline injection site and distal to the HeartMate I to measure the size and volume of the bubbles. This technique was repeated using 0.5 mL of air and 9.5 mL of saline bolus and 2 mL of air and 8 mL of saline bolus. Each bolus was tested 20 times.

Results:

This study identifies the potential risks of air administration and proposes a safer air volume to agitate for the administration of a bubble study.

Conclusions:

Further studies should be conducted to create either a guideline or a standard for agitated saline administration by the Intersocietal Commission for the Accreditation of Echocardiography Laboratories (ICAEL) in order to minimize the risk of air microembolism

Reduced embolic load during clinical cardiopulmonary bypass using a 20 micron arterial filter

Objective:

To compare the efficiency of 20 and 40 µm arterial line filters during cardiopulmonary bypass for the removal of emboli from the extracorporeal circuit.

Methods:

Twenty-four adult patients undergoing surgery were perfused using a cardiopulmonary bypass circuit containing either a 20 µm or 40 µm arterial filter (n = 12 in both groups). The Emboli Detection and Classification system was used to count emboli upstream and downstream of the filter throughout cardiopulmonary bypass. The mean proportion of emboli removed by the filter was compared between the groups.

Results:

The 20 µm filter removed a significantly greater proportion of incoming emboli (0.621) than the 40 µm filter (0.334) (p=0.029). The superiority of the 20 µm filter persisted across all size groups of emboli larger than the pore size of the 40 µm filter.

Conclusion:

The 20 µm filter removed substantially more emboli than the 40 µm filter during cardiopulmonary bypass in this comparison.

A streamlined protocol for the use of the semi-sitting position in neurosurgery: a report on 48 consecutive procedures

The semi-sitting position has lost favor among neurosurgeons partly due to unproven assumptions of increased complications. Many complications have been associated with this position; the most feared: venous air embolism and paradoxical air embolism. We report on this retrospective study of the outcome over 4 years of 48 neurosurgical patients operated on consecutively using a standardized protocol: 41 (85%) in the semi-sitting position, and seven (15%) in the prone position. Procedures included: tumor resection (34), posterior fossa decompression (12), cyst resection (1) and resection of arteriovenous malformation (1). Pre-operative workup was standardized. Vigilant intra-operative observation was done by an experienced neuroanesthetist. Pertinent data was extracted from surgical records. Of the 48 patients, 10 (20.8%) were found to have a patent foramen ovale (PFO) on trans-esophageal echocardiography. Of these, four (40%) patients underwent procedures in the semi-sitting position while six (60%) did not. A clinically significant venous air embolism (VAE) was detected during 2 of the 41 semi-sitting procedures (4.9%). Neither patient suffered any obvious sequelae. No other morbidity was encountered associated with surgical position. Our study suggests that a model similar to ours is effective in preventing major complications associated with the semi-sitting position. The semi-sitting position is a safe, practical position that should be considered in appropriate cases. The fear of dreadful complications seems unwarranted.

Cardiac workup of ischemic stroke

Stroke is the leading cause of disability in developed countries and the third cause of mortality. Up to 15-30% of ischemic strokes are caused by cardiac sources of emboli being associated with poor prognosis and high index of fatal recurrence. In order to establish an adequate preventive strategy it is crucial to identify the cause of the embolism. After a complete diagnostic workup up to 30% of strokes remain with an undetermined cause, and most of them are attributed to an embolic mechanism suggesting a cardiac origin.There is no consensus in the extent and optimal approach of cardiac workup of ischemic stroke. Clinical features along with brain imaging and the study of the cerebral vessels with ultrasonography or MRI/CT based angiography can identify other causes or lead to think about a possible cardioembolic origin.Atrial fibrillation is the most common cause of cardioembolic stroke. Identification of occult atrial fibrillation is essential. Baseline ECG, serial ECG('s), cardiac monitoring during the first 48 hours, and Holter monitoring have detection rates varying from 4 to 8% each separately. Extended cardiac monitoring with event loop recorders has shown higher rates of detection of paroxysmal atrial fibrillation.Cardiac imaging with echocardiography is necessary to identify structural sources of emboli. There is insufficient data to determine which is the optimal approach. Transthoracic echocardiography has an acceptable diagnostic yield in patients with heart disease but transesophageal echocardiography has a higher diagnostic yield and is necessary if no cardiac sources have been identified in patients with cryptogenic stroke with embolic mechanism.

Cerebral ischemic events associated with 'bubble study' for identification of right to left shunts

BACKGROUND AND PURPOSE

Detection of an intracardiac shunt is frequently sought during the evaluation of patients with cryptogenic ischemic stroke and agitated saline intravenous injection, or "bubble study" (BS), is performed in most cases. We present the first attempt to identify the clinical features in patients who had cerebral ischemic events with BS.

METHODS

Using a list serve established by the American Academy of Neurology, a member posted a question regarding the safety of BS in patients with patent foramen ovale. A standardized questionnaire was used to gather data about patients with cerebral ischemic events, details of each case were reviewed, and the findings pooled.

RESULTS

Five patients with ischemic complications of BS (all female, aged 42 to 90 years) were identified from 4 institutions, 3 ischemic strokes and 2 transient ischemic attacks. Events occurred either during or within 5 minutes of BS. Early brain MRIs confirmed acute infarction in 3, including one who had transient symptoms. MRI infarct volumes were small, and deficits were mild in those who developed stroke. Diagnostic evaluation revealed a patent foramen ovale alone in one case, a pulmonary arteriovenous malformation in one case, and a patent foramen ovale and/or pulmonary shunt in 3 cases.

CONCLUSIONS

Ischemic cerebrovascular complications can occur in patients who undergo BS and are associated with the presence of cardiac or pulmonary shunts. The true incidence and degree of disability remains unknown, and further study is indicated to assess the impact of technical differences in BS methodology. Novel methods to promote physician communication such as the use of electronic list serves may reduce barriers to reporting of drug, technique, or device complications and should be explored to identify rare complications that otherwise will likely go unappreciated.

Cardiac workup of ischemic stroke: can we improve our diagnostic yield?

BACKGROUND AND PURPOSE

Discovering potential cardiac sources of stroke is an important part of the urgent evaluation of the ischemic stroke patient as it often impacts treatment decisions that are essential for determining secondary stroke prevention strategies, yet the optimal approach to the cardiac workup of an ischemic stroke patient is not known.

METHODS

A review of the literature concerning the utility of cardiac rhythm monitoring (ECG, telemetry, Holter monitors, and event recorders) and structural imaging (transthoracic and transesophageal echocardiography) was performed.

RESULTS

Data supporting a definitive, optimal, and cost-effective approach are lacking, though some data suggest that appropriate patient selection can improve the diagnostic and therapeutic yield of rhythm monitoring and echocardiography in the evaluation of stroke etiology.

CONCLUSIONS

Based on available data, an algorithmic approach for the evaluation of patients with acute ischemic cerebrovascular events that takes into account therapeutic and diagnostic yield as well as cost-efficiency is proposed.