Medical Definition of EmbolismEmbolus is a clot that forms in another place in the blood vessels of the brain, or some other part of the body, and travels up to embolism definition biology brain to block a smaller artery causing an embolic stroke. An embolus is an abnormal particle within definitkon bloodstream that can lodge embolism definition biology, and block, blood vessels. Emboli commonly arise from either the heart or the proximal trenbolone face bloat in the neck. The most common sources of emboli from the heart include thrombus from atrial fibrillation, mural thrombus following myocardial infarction and left ventricular dilatation. Rare embolic sources include bacterial vegetations in subacute bacterial endocarditis, embolism definition biology from heart valves or fragments from an atrial myxoma.
Embolus - an overview | ScienceDirect Topics
Embolus is a clot that forms in another place in the blood vessels of the brain, or some other part of the body, and travels up to the brain to block a smaller artery causing an embolic stroke. An embolus is an abnormal particle within the bloodstream that can lodge in, and block, blood vessels. Emboli commonly arise from either the heart or the proximal arteries in the neck. The most common sources of emboli from the heart include thrombus from atrial fibrillation, mural thrombus following myocardial infarction and left ventricular dilatation.
Rare embolic sources include bacterial vegetations in subacute bacterial endocarditis, calcium from heart valves or fragments from an atrial myxoma. Emboli can come from the proximal neck vessels artery to artery emboli and these usually relate to atheromatous disease. The emboli consist of plaque debris, cholesterol crystals or platelet emboli, which arise from ulcerated atheromatous plaque. Other types include fat from trauma and air from surgery.
An embolus is any abnormal mass of matter carried in the bloodstream and large enough to occlude a vessel. The various types of embolism are listed below: Thrombotic — thrombus formation in the leg and pelvic veins is the principal cause of pulmonary embolism and intraoperative and postoperative death.
In the retinal or choroidal vessels an embolus can originate from a thrombus on the mitral and aortic valves or from ulcerating atheromatous plaques in the aorta or carotid arteries. Another source may be a mural thrombus in the left ventricle.
Air embolism occurs when negative pressure in the neck veins follows thyroid surgery or when fluid or air is forced into the venous circulation during a blood transfusion. Frothing of the blood in the right ventricle interferes with ventricular pumping and is fatal.
Tumour emboli are usually small and not visible in the retinal circulation; larger metastases occur in the choroid. Fat and marrow embolization occurring after severe trauma to the limbs and trunk is accompanied by multiple fractures. Purpuric spots are seen on the upper thorax, and small haemorrhages are found in the retina. A severe form may rarely occur as Purtscher's retinopathy in which florid embolization of multiple small vessels occurs.
Septic emboli were described in the retina by Roth in , when subacute bacterial endocarditis was common. The typical Roth's spot has a white centre and red surround, and is thought to be the result of vascular damage from an impacted mass of white cells and bacteria in a retinal arteriole. The similarity between this appearance and the deposit of leukaemic cells or a simple infarct surrounded by red cells in a thrombocytopenic immunosuppressed patient has broadened the definition of Roth's spots in contemporary ophthalmology.
Amniotic fluid embolism is a complication of parturition, particularly when manipulation of the fetus is required. Release of amniotic fluid, vernix, hairs and fetal squames into the maternal circulation is commonly fatal. An embolus may arise from pneumothorax or pulmonary barotrauma but is most commonly iatrogenic. In neurosurgery, the usual cause of air embolism is the use of the sitting position for posterior fossa surgery.
A subatmospheric venous pressure at the operative site allows air to enter dural veins, which are held open by their structure. In open cardiac surgery, it is almost impossible to remove all traces of air from the cardiac chambers before closing the heart.
Some small degree of air embolism is almost inevitable in all types of intravenous therapy, but catastrophic air embolism can occur when compression bags are used to accelerate the flow rate of intravenous fluids or blood bags that accidentally already contain air. Early diagnosis of air embolism is essential in neurosurgery, and there are three principal methods in routine use. Bubbles in circulating blood give a very characteristic sound with a precordial Doppler probe.
The method is, if anything, too sensitive, because a shower of very small bubbles produces a particularly large signal. The simplest method is based on the end-expired carbon dioxide concentration, which is easily measured from capnography. Many factors influence the end-expiratory concentration page but a sudden decrease is likely to be either cardiac arrest or air embolism. Transoesophageal echocardiography is an efficient method of detecting air embolism and, furthermore, it is the only practicable method of detecting paradoxical air embolism see later.
Provided there is no major intracardiac right-to-left shunt, small quantities of air are filtered out by the lungs where they are gradually excreted and little harm results. Alveolar dead space is increased according to the proportion of the pulmonary circulation that is occluded. Pulmonary arterial pressure is increased by a large embolus due to the right ventricle working against an increased pulmonary vascular resistance.
Finally, in animal studies, airway resistance is increased following air embolism, an effect mediated by arachidonic acid metabolites, possibly in conjunction with platelet activation and stimulation of pulmonary nociceptors. Treatment then requires aspiration of air through a cardiac catheter, which is difficult. In lesser degrees of embolization during surgery, reduced cardiac output probably also contributes to the sudden reduction in end-expiratory P co 2.
Rarely, there may be passage of air emboli from the right to left heart without an overt right-to-left shunt. This is important because air then enters the systemic arterial circulation where there may be embolism and infarction, particularly of the brain. However, under many circumstances, such as following pulmonary embolism, right atrial pressure may be elevated to the point that a right-to-left shunt occurs.
Wong, in Stroke Sixth Edition , An embolus of merely a few millimeters may occlude the MCA stem. Some calcific plaques 59 may also embolize to the MCA but are too small to block the stem. Accumulating evidence indicates that inflammation is of key importance in atherosclerotic plaque destabilization, thrombo-embolism and stroke.
Inflammatory cells within plaque, particularly macrophages, are increasingly recognized as key mediators of lipid oxidation, plaque remodeling, and fibrous cap erosion and rupture, leading to acute thrombo-embolic events.
Imaging with fluorodeoxyglucose [FDG] positron-emission tomography PET has significant potential for non-invasive imaging of atherosclerotic inflammation, providing information about plaque biology associated with clinical events independently of the effect of the plaque on narrowing of the arterial lumen.
The same radiotracer might help to determine calcification in intracranial arterial stenosis. Furthermore, combining 18F-NaF with Gd-enhanced vessel wall imaging could further elucidate the link between local hemorrhage, microcalcification, progression to plaque rupture, and potential cerebrovascular event. Most of the embolic material is a small fragment of a vessel or cardiac wall thrombus or vegetation. Rarely, large-particle embolism may occur from fibrocartilaginous material.
Davies MD, Mark S. Allen MD, in Surgical Pitfalls , Peripheral tumor embolus during a pneumonectomy is a rare but potentially lethal complication. Whyte and colleagues 38 reported that the distribution of the emboli were most commonly major arterial sites: If a tumor embolus is suspected in the perioperative period, an angiogram should be performed. Once the diagnosis is confirmed, removal by an embolectomy is done if the patient is clinically stable enough to return to the operating room.
If a tumor is suspected pre- or intraoperatively within the pulmonary vein, a transesophageal echocardiogram is performed to assess intra-atrial involvement. Another technique described by Taber 36 is placement of a pursestring suture in the left atrium and transatrial digital palpation. If the tumor involves the left atrium or distal pulmonary vein, it may be removed with or without cardiopulmonary bypass.
Cardiac dysrhythmias, hypoperfusion cardiogenic shock, hypovolemia, sepsis , and vasoconstricting drugs digoxin, cocaine. Hypercoagulable states see Arterial entries, plus deficiencies of factor V Leiden, protein C or S, or antithrombin III , congestive heart failure, shock, portal hypertension, Budd-Chiari syndrome, malignancy, trauma, sclerotherapy, peritonitis, diverticulitis, pancreatitis, inflammatory bowel disease, intestinal obstruction, postoperative states.
Prashant Lotlikar, John R. Cooper, in Complications in Anesthesia Second Edition , After recognition, if the embolus is massive, CPB must be discontinued.
The patient is then placed in a steep Trendelenburg position, the aortic cannula is removed, and the CPB circuit is reprimed. Retrograde perfusion of the superior vena cava is initiated Fig. Consideration can then be given to pharmacologic interventions to reduce cerebral injury, including mannitol, steroids, and barbiturates. Postoperative interventions may include initiation of hyperbaric oxygen treatment, reverse Trendelenburg position, initiation of slight hyperventilation, and avoidance of hyperglycemia and hyponatremia.
Modak 1 , L. Arterial blockade by a thrombus or an embolus results in impaired cerebral perfusion. A complex biochemical cascade is triggered after an ischemic injury to the brain.
Oxidative stress plays a major role in the series of events. This usually takes place at the core of the ischemic stroke, and further expansion of the core depends on this biochemical cascade. Normal cell homeostasis depends on effective mitochondrial calcium buffering.
Increased calcium levels induce opening of the mitochondrial permeability transition pore, which results in diffusion of molecules including ROS from the mitochondria to the cytoplasm, further exacerbating mitochondrial dysfunction.
Along with leakage from the mitochondrial electron transport chain, free radicals are also generated via action of NADPH oxide synthases, xanthine oxidase, and cyclooxygenase Fig. The phase 1 results of the Mechanical Embolus Removal in Cerebral Ischemia MERCI 1 study were published in , 41 demonstrating safety and efficacy of a new mechanical thrombectomy device. In addition, benefit was seen up to 8 hours after symptom onset, compared to the 4. Unlike intravenous or intra-arterial rtPA, mechanical thrombectomy devices do not use potent thrombolytics and therefore represent a useful alternative treatment modality in those patients with thromboembolic stroke who have contraindications to systemic thrombolytic therapy.
Given its documented efficacy and relative safety, the FDA approved the use of the Merci Retriever in for revascularization in acute ischemic stroke.
The Merci Retrieval System, the prototype for mechanical thrombectomy devices, is composed of five essential subunits: First, the balloon guide catheter is navigated into the distal cervical arterial vessel. The distal access catheter is then advanced over the microcatheter to a position of stability, preferably at least as distal as the origin of the target vessel.
The microcatheter and guidewire are then advanced to the clot. The guidewire is then exchanged for the retriever device, and the retriever is deployed just beyond and within the clot. The retriever device has a natural coiled shape and, when deployed, acquires its coiled shape both distal and within the clot.
When the clot is engaged by the retriever catheter, the balloon is inflated and the interventionalist then performs a slow pull and holds while maintaining the position of the distal access catheter relative to the clot.
Next, the distal access catheter is secured relative to the microcatheter, and then all units are pulled proximally to the balloon catheter. While this maneuver is performed, aspiration through the balloon guide catheter is performed to minimize the likelihood of reembolization while the clot is withdrawn.
Once all units and the clot have entered the balloon catheter, the elements are then removed from the system and angiography is performed to examine for adequacy of recanalization and distal perfusion. Newer-generation MERCI thrombectomy devices utilize additional suture elements to improve clot retrieval.
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