Embolism

EMBOLISM (from Greek emballo - I throw in, I thrust in), the occlusion of blood or lymphatic vessels by particles and bodies brought along by the bloodstream or lymph flow. The occluding particles themselves are called e m b o l i. Emboli are not characteristic of normal blood and are usually observed under pathological conditions. However, even under physiological conditions, such as pregnancy or the postpartum period, embolism of the lung capillaries by chorionic villi particles is observed (in 75% of parturient women, Abrikosov). Embolism by megakaryocytes can also be observed in healthy people. These same types of embolism under pathological conditions, for example, in eclampsia, are expressed incomparably more significantly. Modern classification of embolism proceeds from the material substrate of the embolus-particles of thrombus, fat, air, etc.-and in addition takes into account localization and pathways of dissemination. A distinction is made between embolism of the lesser (pulmonary) circulation, embolism of the greater (systemic) circulation, and the rarer embolisms of the portal vein system. The pathways of dissemination of emboli usually correspond to the direction of the blood or lymph flow (Virchow). An exception is constituted by cases of retrograde embolism, observed in the inferior vena cava and much more rarely in the hepatic veins, when during marked venous stasis and even a reverse wave of blood in cases of tricuspid valve insufficiency, emboli can move in a direction opposite to the blood flow. Usually these are large, heavy emboli from the neck veins or from the right heart. Descending, such emboli can occlude the hepatic, renal, or iliac veins. Moving with the blood flow, emboli usually do not pass from the lesser circulation into the greater and vice versa, except in cases where there is a direct, sufficiently wide communication between the lesser and greater circulations in the form of a patent foramen ovale or ductus arteriosus (Botallo's duct). This type of embolism is termed paradoxical. Despite the fact that patency of the foramen ovale is observed in 20-25% (Chernihovsky), and according to some data even more frequently, paradoxical embolism is encountered rarely (1.2%, Lubarsch). Apart from cases of paradoxical embolism, the transfer of emboli from the lesser circulation to the greater is observed when the emboli themselves, by virtue of their small size and elasticity (fat droplets), pass through the capillary network of the lungs. In the occurrence of embolism of a particular organ, an essential role is played by the angioarchitectonics of the given region, in particular the angle of origin of the vessel: the smaller this angle, the easier an embolus penetrates into such a vessel. Therefore, embolism of the left hemisphere of the brain is observed more frequently than of the right; embolism of the left kidney more frequently than of the right. Submitting to the action of the law of gravity, emboli are observed somewhat more frequently in the lower half of the body; embolism of the branches of the abdominal aorta more frequently than of the brain. In the lungs, embolism of the lower sections is observed more frequently for the same reasons, and not because emboli in the majority of cases are brought from the inferior vena cava, since the doctrine of poor miscibility of blood from the inferior and superior venae cavae is currently abandoned. Embolism by detached parts of a thrombus is the most frequent type of embolism. Thrombi usually detach at the beginning of their formation or upon their septic and aseptic dissolution. This type of embolism is observed in both the lesser and greater circulations, with the detachment of venous thrombi, according to data by Lubarsch, Beneke, and others, being more frequent; venous thrombi give embolism in 60-70%, while cardiac and arterial ones in 42%. The size of emboli from detached parts of thrombi can be very diverse. Emboli of the arterial system are usually of small size (verrucae from valves, particles of mural thrombi of the left ventricle, etc.). As emboli from the venous system, one encounters casts of the vascular network of an entire region formed by thrombi, e.g., the small pelvis. Such emboli have the appearance of connected serpentine formations which, while closing the pulmonary artery, partly hang down into the right heart; from their shape one can sometimes determine from which region the given embolus detached. Emboli from thrombus particles found at autopsy do not always correspond in volume to their initial size, since subsequent thrombus formation can occur around the emboli, sometimes so significant that differential diagnostic difficulties may arise in recognizing a thrombus or an embolism. Small emboli lodging at the site of vessel division (as it were, sitting astride these places) may not occlude the vessel lumen entirely, especially in the pulmonary artery, and cause rapid blood clotting around them; such an embolus is easily confused with a postmortem clot. The practical significance of this type of embolism is very great. The majority of fatal pulmonary artery embolisms fall precisely on this type of embolism (see Pulmonales arteria, venae). The increased frequency of embolism noted in Western literature relates mainly to embolism by thrombus particles; therefore, the issues of treatment, diagnosis, and prevention of this type of embolism are closely related to the issues of thrombus formation (see Thrombus, Thrombosis). Embolism by thrombus particles in the arterial system is also dangerous by virtue of the possible occurrence of infarcts (see) in vital organs: brain embolism with paralysis or fatal outcome, coronary artery embolism with myocardial infarction, embolism of branches of the abdominal artery with intestinal necrosis and peritonitis, etc. (for details, see individual organs). Apart from mechanical vessel occlusion, thrombus particles are also dangerous in that they can be infected, and at the site of such emboli not only a circulatory disorder of a certain significance arises, but also an inflammatory focus. Upon septic dissolution of a thrombus, the danger arises of abscess development, e.g., at the site of the arisen infarction (see Metastasis). The fate of emboli from thrombus particles, if death has not ensued, is similar to the fate of a thrombus, namely, phenomena of organization, dissolution, etc. may occur (see Thrombus, Thrombosis). Fat embolism takes place in cases of the introduction of fat droplets into the bloodstream. The entry of fat into the blood is observed in trauma, especially fractures of tubular bones with fatty bone marrow, but sometimes a light bruise or even tapping is sufficient. Osteomyelitic operative trauma can also be accompanied by fat embolism. Trauma to adipose tissue, crushing of pelvic fat by the fetal head in difficult labor, operations on obese individuals, bruises of a fatty-degenerated liver—in all these cases fat embolism is possible. Fat droplets have been found in lung capillaries in diseases accompanied by convulsions (epilepsy, eclampsia, uremia). The practical significance of fat embolism depends on the amount of fat that has entered and on the localization of the emboli. If ³/₄ of the vascular network in the lungs is filled with fat, this leads to rapid death, but sometimes even smaller amounts of fat, having passed the lungs, reach the brain and result in a fatal outcome. At autopsy, petechial hemorrhages are usually found macroscopically. Petechial hemorrhages were also observed in fat embolism of the stomach, skin, etc. As for the fate of fat emboli, they are usually captured by the lining cells of the reticuloendothelium (Rössle), and in addition, the appearance of fat droplets in the urine is observed. Knowledge of the conditions for the occurrence of fat embolism is necessary to eliminate the possibilities of its occurrence. Parenchymal-cellular and tissue embolism are observed in cases of the introduction into vessels of cells or even entire pieces of tissue and organs. Cells enter vessels and cause embolism more frequently. To this type of embolism belongs embolism by bone marrow cells of the megakaryocyte type, both with normal bone marrow and especially with hyperplastic marrow; cases of embolism by osteoblasts and osteoclasts are also known. Here belong embolism by chorionic villi particles, embolism by liver cells in eclampsia, and embolism by neoplasm cells. In gross traumas, embolisms are known by entire sections of bone marrow with the hematopoietic and fatty parts (Tannenberg and W. Fischer-Wasels), liver tissue (Zenker, Schmorl), striated muscles (Werkgartner). Embolism of the newborn's coronary artery by cerebellar tissue upon damage to the tentorium cerebelli and the cerebellum itself has been described (Abrikosov). The danger of parenchymal-cellular embolism in the sense of circulatory disorders is not great, but in cases of embolism by malignant neoplasm cells, metastases may arise (see). Air and gas (nitrogen) embolism are possible either upon the entry of air from the outside or upon the release of blood gases in cases of a sharp drop in atmospheric pressure (caisson works). Air can enter from the outside into the venous system during trauma to large veins located close to the heart, by virtue of the negative pressure existing in them. Air embolisms are known via gaping vessels of the postpartum uterus upon its poor contraction and careless douching. Air embolism via veins in a gastric ulcer has been described (Aschoff). Air embolisms of the brain are observed during sharp coughing fits with rupture of alveolar septa, especially in small children with pertussis and measles. And finally, air or gas (nitrogen) embolism is known as an accident during operations on the lungs, in particular upon the induction of artificial pneumothorax (Fahr), during tubal insufflation. The practical significance of air embolism depends on the amount of air that has entered, on the rate of introduction of air, and on the distance of the site of introduction from the heart. Small portions of air that have entered the veins and then into the heart and lungs have no practical significance.

The danger of wounding the large veins of the neck during surgery has been exaggerated (Chernichovsky). In experimental gradual introduction of air (600 cm³ of air administered to a 9 kg dog over 1½ hours, Pashutin), death does not occur. The rapid introduction of even smaller amounts is fatal. If air is introduced far from the heart, it is resorbed, especially its oxygen component, or turns into a finely bubbled, less dangerous emulsion. The mechanism of vascular bed occlusion by air in cases where an air bubble stops in the right heart is peculiar. The air bubble compresses during heart contractions and then expands again without being pushed into the pulmonary artery, as a result of which even small portions of air can lead to death. Once in the lung capillaries, air bubbles cause ordinary mechanical occlusion, but if death does not ensue, they are quickly resorbed, and the danger of air embolism is eliminated. Other types of embolism are much rarer. These include embolism by animal parasites: Distoma haematobium, echinococcus cysts (Litten), liver fluke, trichinae, bladder worms of other helminths, Ankylostoma duodenale, etc. Embolism by foreign bodies is known in ragged wounds of large vessels during war. Bullets, shell fragments, and shreds of clothing have been observed as emboli. Bacterial emboli are possible only when a vessel is occluded by a whole colony of microorganisms. The circulation of individual bacteria in the blood does not constitute an embolism (Abrikosov). Bacterial or mycotic embolisms are observed in septic softening of thrombus and in septic endocarditis. The entry into the bloodstream of pigments—hemoglobinogenic, malarial, melanin in melanomas, coal—usually does not cause vascular occlusion and true embolism does not arise (Tannenberg, B. Fischer-Wasels); therefore, pigment embolisms can only be called such conditionally. Embolism of lymphatic vessels is observed mainly by tumor cells, bacteria, and pigment particles (microembolism). Significant disturbances of lymph circulation do not occur due to the presence of a rich network of lymphatic vessels. The practical significance of embolism of the lymphatic system is determined by the possible subsequent development of metastases. The significance of embolism for the organism is very great. Embolism can be a cause of death. Embolism can produce persistent changes in vital organs: brain softening with paralysis, myocardial infarction in coronary artery embolism, gangrene of the extremities, etc. Embolism can cause the development of metastasis. In each specific case of embolism, both the size of the embolus (which is of particular importance for the lesser circulation) and the localization of the embolism may prove decisive. Emboli of the greater circulation, as already mentioned above, usually do not reach significant size, and the question of their localization is decisive. Small emboli that enter the vascular network of an extremity may not even cause significant circulatory disturbances. In addition to local factors, which play a particularly essential role in the formation of metastasis from an embolus, the general state of the organism, especially the activity of the circulatory and respiratory organs, is of great importance. The outcome of pulmonary embolism depends on the ability of the lungs to compensate for the exclusion of entire areas of pulmonary parenchyma in lesser circulation embolism. With sufficient cardiac activity, embolisms lead less frequently to infarction due to possible collateral circulation (it must be remembered that not every infarction is the result of embolism—see Infarction), but on the other hand, the improvement of blood circulation, often in connection with medical intervention, can cause the formation of embolism in the presence of thrombi in both veins and arteries. Physical exertion or a nervous impulse with a rise in blood pressure can be the reason for the detachment of an embolus with subsequent occlusion of blood vessels in one area or another. Pulmonary artery embolism is relatively frequent in the postoperative period, mainly after operations on abdominal organs (see Postoperative period); timely performed Trendelenburg's operation (embolectomia a. pulmonalis) in such cases can save the patient's life. Of the 102 cases of pulmonary artery embolectomy described in the literature, recovery occurred in 8 cases. Embolisms of large arteries occur more frequently in the lower extremities than in the upper ones. The clinical picture in these cases consists of sharp, sudden, paroxysmal pains in the extremity and the disappearance of the pulse at the distal end of the artery. Pains are often localized peripheral to the embolus and are accompanied by pallor, depending more on vascular spasm than on complete obliteration of the main trunk; later, a decrease in sensitivity may appear. Skin pallor is subsequently replaced by a cyanotic color, the extremity becomes cold to the touch, and its function is sharply impaired. The further course and prognosis depend on: 1) the degree of vascular occlusion, 2) collateral circulation, and 3) infection joining in unfavorable cases. The matter relatively often ends in gangrene of the extremity and death. The most perfect and therapeutically best results are given by embolectomy, which consists in opening the vessel and extracting the thrombus with the subsequent application of a vascular suture. Portis and Roth found up to 1933 in the literature 131 cases of embolectomies of large arterial vessels; Zierold published 20 cases of large artery embolism, of which embolectomy was performed in 11, resulting in the restoration of circulation in the extremity in 8 patients. The restoration of circulation in the extremity after thrombus extraction depends mainly on the urgency of surgical intervention (the time limit is considered 10-12 hours from the onset of the embolism to the moment of operation) and on the severity of the general condition. Embolectomy has relative indications in embolism of the axillary, brachial, and popliteal arteries, since sufficient anastomoses usually exist in these areas. In some cases, the restoration of circulation in the extremity is possible also from conservative therapy (at the moment of embolism—morphine, oxygen inhalation, bloodletting; subsequently—elevated position of the extremity, local heat, infusion of saline solution, etc.) in the presence of sufficient vascular collaterals. A fatal outcome from fat embolism of the lungs occurs relatively rarely; for this, the introduction of a large amount of fat capable of turning off ¾ of the pulmonary circulation is necessary. Cases of air embolism are known after filling joint cavities, the abdominal cavity, and the perirenal cellular tissue with oxygen for diagnostic purposes. The appearance of air in veins is also observed apart from vascular wounds during sharp changes in external atmospheric pressure; an embolism of this kind is called gas embolism and is encountered (rarely) in divers and caisson workers. The entry of air into veins is accompanied by a whistling, gurgling sound, and the closer the vein is to the heart and the wider its diameter, the more distinctly the sound is heard. Phenomena of sharp asphyxia, patient restlessness, cold sweat, pallor of the skin with a cyanotic tint come to the foreground; then convulsive contractions of the facial muscles and extension of the trunk (resembling opisthotonus) with the patient unconscious, pupil dilation with the subsequent rapid cessation of respiration, frequent, small, rapidly disappearing pulse. The prognosis depends on the amount of air that entered the vein and the speed of therapeutic measures taken. According to Green, mortality is noted in 37.5% of cases. Treatment. Immediately as soon as the entry of air into the vein is noted, it is necessary to close the hole in the vessel with a finger or a tampon, apply a hemostatic forceps, and tie the peripheral and central ends of the vein. In the case when the formidable phenomena noted above have already set in, an attempt should be made to remove the air that got into the veins; for this, it is recommended to remove the ligature or clamp from the central end of the vein and, at the moment of exhalation, compress the chest from both sides, and at the moment of inhalation, close the hole in the vessel. It is also advised to produce suction of air from the wound with a rubber catheter and puncture the right ventricle of the heart with subsequent aspiration of foamy blood. It is also proposed in such cases to massage the heart after exposing it through the abdominal cavity and diaphragm. The prophylaxis of embolism is basically the same as that of thrombosis; it is necessary to strive to minimize operative trauma, combat dehydration of the organism, conduct preliminary preparation of the heart for surgery in cardiac patients, and apply early movements, leg massage, etc. in the postoperative period. To judge the true frequency of embolism is possible only on the basis of patho-anatomical autopsies. A number of embolisms proceed asymptomatically. It is extremely rare to directly see an embolism in a patient; Weber observed air bubbles in the arteries of the fundus oculi during air embolism. Sometimes one can feel a suddenly appeared dense painful plug in a subcutaneous vessel (Chernichovsky). Clinical diagnosis of embolism is made on the basis of the appearance of symptoms of circulatory disorder with or without the loss of function of one or another organ (see by organs). Common to all organs is the suddenness of appearance.

Furthermore, a thorough knowledge of the possible causes for the occurrence of embolism is absolutely necessary, and the diagnosis of embolism at autopsy requires great attention from the prosector and the observance of a number of special precautions. The detection of pulmonary artery embolism must be carried out in situ, before removing the organs of the thoracic cavity, because the embolus can easily fall out of the pulmonary artery. Then, as indicated above, the formation of a clot around the embolus can obscure the picture, and without careful incisions of such a clot, the embolism may be missed, since the embolus itself, in the form of a dry crumb, may be small and overlooked upon superficial examination. To detect air embolism, the chest must be opened before the skull, neck, and spine, because air can penetrate into the right heart through gaping veins. The sternum is lifted and separated by a transverse cut at the level of the second ribs. After opening the pericardial sac, water is poured into the cavity of the latter and the wall of the right ventricle of the heart is incised under water. The emergence of air bubbles from the incision of the right ventricle through the water under these conditions indicates air embolism. To distinguish air bubbles from cadaveric gases, it is recommended to pass the released bubbles through a solution of pyrogallol with caustic potash; this solution turns brown in the presence of air. Air embolism of the brain is diagnosed by a combination of data: hemorrhages, softening in the presence of appropriate prerequisites and in the absence of other causes (thrombosis, encephalitis, etc.), since the air bubbles themselves cannot be seen in the vessels of a corpse. Air embolism can also be determined by the presence of air bubbles in the coronary arteries of the heart, shining through the epicardium. Fat embolism is diagnosed by special staining of the organ for fat. With a significant amount of fat in the vessels of the lung, its presence can be macroscopically proven by squeezing droplets of fat from the lung under water, which then float to the surface. Embolism by small particles, especially microembolisms, can be proven by corresponding findings on histological preparations, but in a number of cases the diagnosis of embolism is made based on the totality of all data: the presence of thrombosis, endocarditis, trauma to adipose tissue, etc., due to the difficult detection of the embolus or its possible resorption (air). In cases of scarring of embolic infarctions, one speaks of embolic scars (cicatrix embolica) and then the diagnosis of a past embolism is made retrospectively. In conclusion, it must be emphasized once again that even with the most careful autopsy, finding the embolus is not easy and sometimes it is necessary to diagnose embolism solely on the basis of all autopsy data.