Contrast-Enhanced Ultrasound Imaging in Detection of Changes in Cerebral Perfusion

Mechanical power of ventilation is associated with mortality in neurocritical patients: a cohort study

This study aimed to determine the predictive relevance of mechanical power in the clinical outcomes (such as ICU mortality, hospital mortality, 90-day mortality, length of ICU stay, and number of ventilator-free days at day 28) of neurocritical patients. This is a retrospective cohort analysis of an open-access clinical database known as MIMIC-III. The study included patients who had sustained an acute brain injury and required invasive ventilation for at least 24 h. Demographic parameters, disease severity scores (Glasgow coma scale), comorbidities, vital signs, laboratory parameters and ventilator parameters were collected within the first 24 h of ICU admission. The main outcome was the relationship between MP and ICU mortality. A total of 529 patients were selected for the study. The critical value of MP was 12.16 J/min, with the area under the curve (AUC) of the MP was 0.678 (95% CI 0.637-0.718), and compared to the GCS scores, the MP performed significantly better in discrimination (DeLong's test: p < 0.001). Among these patients elevated MP was associated to higher ICU mortality (OR 1.11; 95% CI 1.06-1.17; p < 0.001), enhanced the risk of hospital mortality, prolonged ICU stay, and decreased the number of ventilator-free days. In the subgroup analysis, high MP was associated with ICU mortality regardless of ARDS (OR 1.01, 95% CI 1.00-1.02, p = 0.009; OR 1.01, 95% CI 1.00-1.02, p = 0.018, respectively) or obesity (OR 1.01, 95% CI 1.00-1.02, p = 0.012; OR 1.01, 95% CI 1.01-1.02, p < 0.001, respectively). In neurocritical care patients undergoing invasive ventilation, elevated MP is linked to higher ICU mortality and a variety of other clinical outcomes.

Brain-lung interactions and mechanical ventilation in patients with isolated brain injury

During the last decade, experimental and clinical studies have demonstrated that isolated acute brain injury (ABI) may cause severe dysfunction of peripheral extracranial organs and systems. Of all potential target organs and systems, the lung appears to be the most vulnerable to damage after brain injury (BI). The pathophysiology of these brain–lung interactions are complex and involve neurogenic pulmonary oedema, inflammation, neurodegeneration, neurotransmitters, immune suppression and dysfunction of the autonomic system. The systemic effects of inflammatory mediators in patients with BI create a systemic inflammatory environment that makes extracranial organs vulnerable to secondary procedures that enhance inflammation, such as mechanical ventilation (MV), surgery and infections. Indeed, previous studies have shown that in the presence of a systemic inflammatory environment, specific neurointensive care interventions—such as MV—may significantly contribute to the development of lung injury, regardless of the underlying mechanisms. Although current knowledge supports protective ventilation in patients with BI, it must be born in mind that ABI-related lung injury has distinct mechanisms that involve complex interactions between the brain and lungs. In this context, the role of extracerebral pathophysiology, especially in the lungs, has often been overlooked, as most physicians focus on intracranial injury and cerebral dysfunction. The present review aims to fill this gap by describing the pathophysiology of complications due to lung injuries in patients with a single ABI, and discusses the possible impact of MV in neurocritical care patients with normal lungs.

Ultrasound for the Brain: A Review of Physical and Engineering Principles, and Clinical Applications

The emergence of new ultrasound technologies has improved our understanding of the brain functions and offered new opportunities for the treatment of brain diseases. Ultrasound has become a valuable tool in preclinical animal and clinical studies as it not only provides information about the structure and function of brain tissues but can also be used as a therapy alternative for brain diseases. High-resolution cerebral flow images with high sensitivity can be acquired using novel functional ultrasound and super-resolution ultrasound imaging techniques. The noninvasive treatment of essential tremors has been clinically approved and it has been demonstrated that the ultrasound technology can revolutionize the currently existing treatment methods. Microbubble-mediated ultrasound can remotely open the blood-brain barrier enabling targeted drug delivery in the brain. More recently, ultrasound neuromodulation received a great amount of attention due to its noninvasive and deep penetration features and potential therapeutic benefits. This review provides a thorough introduction to the current state-of-the-art research on brain ultrasound and also introduces basic knowledge of brain ultrasound including the acoustic properties of the brain/skull and engineering techniques for ultrasound. Ultrasound is expected to play an increasingly important role in the diagnosis and therapy of brain diseases.

Quantitative contrast-enhanced ultrasound of the brain on twin fetal lambs maintained by the extrauterine environment for neonatal development (EXTEND): initial experience

BACKGROUND

With the development of an artificial environment to support the extremely premature infant, advanced imaging techniques tested in this extrauterine system might be beneficial to evaluate the fetal brain.

OBJECTIVE

We evaluated the feasibility of (a) performing contrast-enhanced ultrasound (CEUS) and (b) quantifying normal and decreased brain perfusion in fetal lambs maintained on the extrauterine environment for neonatal development (EXTEND) system.

MATERIALS AND METHODS

Twin premature fetal lambs (102 days of gestational age) were transferred to the EXTEND system. Twin B was subjected to sub-physiological flows (152 mL/kg/min) and oxygen delivery (15.9 mL/kg/min), while Twin A was maintained at physiological levels. We administered Lumason contrast agent into the oxygenator circuit and performed serial CEUS examinations. We quantified perfusion parameters and generated parametric maps. We also recorded hemodynamic parameters, serum blood analysis, and measurements across the oxygenator. Postmortem MRIs were performed.

RESULTS

No significant changes in hemodynamic variables were attributable to CEUS examinations. On gray-scale images, Twin B demonstrated ventriculomegaly and progressive parenchymal volume loss culminating in hydranencephaly. By CEUS, Twin B demonstrated decreased peak enhancement and decreased overall parenchymal perfusion when compared to Twin A by perfusion parameters and parametric maps. Changes in perfusion parameters were detected immediately following blood transfusion. Postmortem MRI confirmed ultrasonographic findings in Twin B.

CONCLUSION

In this preliminary experience, we show that CEUS of the brain is feasible in fetal lambs maintained on the EXTEND system and that changes in perfusion can be quantified, which is promising for the application of CEUS in this extrauterine system supporting the premature infant.

Point-of-care ultrasound: its growing application in hospital medicine

Point-of-care ultrasound is emerging as an important adjunct to the clinical examination. Ultrasonography has long been seen as a modality for experts but this is changing and it is hoped that, with appropriate training, point-of-care ultrasound will become a modern-day diagnostic necessity.

Diagnosis of congenital and acquired focal lesions in the neck, abdomen, and pelvis with contrast-enhanced ultrasound: a pictorial essay

Contrast-enhanced ultrasound (CEUS) is a versatile imaging modality that improves the diagnostic potential of conventional ultrasound. It allows for portable imaging at the bedside. In this paper, we illustrate how CEUS can be used in evaluating several focal lesions in the pediatric population, including liver hemangioma, telangiectasias, splenic hamartomas, and bladder lesions. We describe the ultrasound findings and contrast enhancement patterns associated with these lesions. Findings are correlated with MRI, CT, and/or pathology when available. This paper demonstrates the value of CEUS in improving characterization of many focal lesions in the pediatric population.

CONCLUSION

CEUS is a valuable bedside technique for use in the pediatric population to evaluate focal lesions in various organs, and will allow for safe, more efficient diagnostic imaging. What is Known: • CEUS offers many advantages over CT and MRI and is underutilized in the United States. • It is only FDA approved for vesicoureteral reflux and liver in the pediatric population. However, off label uses are well described. What is New: • This pictorial essay describes ultrasound findings and contrast enhancement patterns associated with liver hemangioma, liver telangiectasia, splenic hamartoma, hemorrhagic ovarian cyst, urachal remnant, spinning top urethras, and kaposiform hemangioendothelioma. • We demonstrate the utility of CEUS in expanding the diagnostic potential of conventional ultrasound.

Repeatability of the "flash-replenishment" method in contrast-enhanced ultrasound for the quantitative assessment of hepatic microvascular perfusion

This study aimed to evaluate the feasibility and repeatability of the flash-replenishment method in contrast-enhanced ultrasound (CEUS) perfusion imaging and assess quantitatively microvascular perfusion in the liver. Twenty healthy New Zealand rabbits were submitted to CEUS perfusion imaging with continuous intravenous infusion. Using flash-replenishment kinetics, the dynamic process of depletion and refilling of microbubble contrast agent was recorded. The hepatic microvascular perfusion parameters were calculated, including region of interest, peak intensity (PI), area under the curve (AUC), and hepatic artery to vein transit time (HA-HVTT). A consistency test was performed for multiple measurements by the same operator and blind measurements by two different operators. The hepatic perfusion imaging of 3×10⁸ bubbles/min had minimal error and the best imaging effect and repeatability. The variability of the perfusion parameter measured at 3 cm depth under the liver capsule was at a minimum with coefficient of variation of 3.9%. The interclass correlation coefficient (ICC) of measurements taken by the same operator was 0.985, (95% confidence interval, CI=0.927-0.998). Measurements taken by two operators had good consistency and reliability, with the ICC of 0.948 (95%CI=0.853-0.982). The PI and AUC of liver parenchyma after reperfusion were lower than before blocking; and HA-HVTT was significantly longer than before blocking (P<0.05). The flash-replenishment method in CEUS perfusion imaging showed good stability and repeatability, which provide a valuable experimental basis for the quantitative assessment of hepatic microvascular perfusion in clinical practice.

Quantitative Evaluation of Hepatic Microvascular Perfusion after Ischemia-Reperfusion Injury in Rabbits by Contrast-Enhanced Ultrasound Perfusion Imaging

The aim of this study was to evaluate microvascular perfusion after liver ischemia-reperfusion injury (IRI) in rabbits using the "flash-replenishment" method of contrast-enhanced ultrasound (CEUS) perfusion imaging. Twenty-eight rabbits underwent either 30, 60 or 90 min of ischemia and 120 min of reperfusion. CEUS perfusion imaging was performed using the "flash-replenishment" model, and hepatic microvascular perfusion parameters, including peak intensity (PI), area under the curve (AUC), and hepatic artery-to-vein transit time (HA-HVTT), were calculated. Prolonged ischemia upregulated intracellular adhesion molecule-1 (ICAM-1), alanine transaminase (ALT) and aspartate transaminase (AST) levels. Longer ischemia decreased PI and AUC, but increased HA-HVTT. The perfusion parameters were significantly correlated with Suzuki's pathology scores and ALT and AST levels. The "flash-replenishment" method of CEUS perfusion imaging is an accurate and non-invasive method for evaluating hepatic microvascular perfusion and provides a valuable experimental basis for early prediction of liver IRI damage after liver transplantation or liver resection.

Acute respiratory distress syndrome in traumatic brain injury: how do we manage it?

Traumatic brain injury (TBI) is an important cause of morbidity and mortality worldwide. TBI patients frequently suffer from lung complications and acute respiratory distress syndrome (ARDS), which is associated with poor clinical outcomes. Moreover, the association between TBI and ARDS in trauma patients is well recognized. Mechanical ventilation of patients with a concomitance of acute brain injury and lung injury can present significant challenges. Frequently, guidelines recommending management strategies for patients with traumatic brain injuries come into conflict with what is now considered best ventilator practice. In this review, we will explore the strategies of the best practice in the ventilatory management of patients with ARDS and TBI, concentrating on those areas in which a conflict exists. We will discuss the use of ventilator strategies such as protective ventilation, high positive end expiratory pressure (PEEP), prone position, recruitment maneuvers (RMs), as well as techniques which at present are used for 'rescue' in ARDS (including extracorporeal membrane oxygenation) in patients with TBI. Furthermore, general principles of fluid, haemodynamic and hemoglobin management will be discussed. Currently, there are inadequate data addressing the safety or efficacy of ventilator strategies used in ARDS in adult patients with TBI. At present, choice of ventilator rescue strategies is best decided on a case-by-case basis in conjunction with local expertise.