Acquired arteriovenous fistula
Introduction
Introduction to acquired arteriovenous fistula There is an abnormal channel between the artery and the vein called the arteriovenous fistula. Acquired arteriovenous fistula is caused by trauma, etc., and can also be caused by rupture of aneurysm. Due to the normal blood flow into the accompanying vein, arterial blood can cause local vasculopathy and local, peripheral circulation and systemic Hemodynamic changes. basic knowledge The proportion of the disease: the probability of the population is 0.086% Susceptible people: no specific population Mode of infection: non-infectious Complications: swelling
Cause
Acquired arteriovenous fistula
(1) Causes of the disease
Trauma is the main cause of acquired arteriovenous fistula, especially penetrating wounds, such as knife stab wounds, gunshot wounds, steel and glass fragments flying wounds, etc. The most common injuries and injuries in the same sheath are injured. The arteriovenous fistula is established by abnormal passages of the arteries and veins. Trauma is also a common cause during percutaneous transluminal angiography and surgery. Generally, the external penetrating wound is small, and adjacent muscles and soft tissues prevent blood outflow and form in local soft tissue. Hematoma, hematoma formation after the formation of arteriovenous wall, traumatic arteriovenous fistula caused by firearms such as shotguns, grenades, etc., there may be multiple fistulas between arteries and veins, crush injury can also cause arteriovenous fistula, such as spleen, When nephrectomy, spleen pedicle, large ligation of renal pedicle can occur arteriovenous fistula, shoulder, hip contusion can cause local arteriovenous fistula.
Other causes of arteriovenous fistula are rare, spontaneous aneurysm hardening gradually adheres, corrosion finally penetrates the accompanying vein; bacterial arteritis, bacteria staying at the bifurcation of the artery cause arterial perforation and access to the accompanying vein, Arteriovenous fistulas may occur.
(1) penetrating injury
The vast majority of acquired arteriovenous fistulas are caused by penetrating injuries, such as various puncture wounds, especially high-speed bullets, sodium iron and glass fragments. At the time of injury, the arteries and veins in the same sheath are damaged together. Fractures are the most common cause of percutaneous angiography and surgery because of sharp fractures or broken bones. The fourth and fifth lumbar intervertebral discs are close to the iliac vessels. Vascular injury causes aortic venous fistula. Generally, the external orifice of the penetrating wound is small. The adjacent muscles and soft tissues prevent a large amount of bleeding, and a hematoma is formed in the local soft tissue. After the hematoma is formed, the wall of the arteriovenous fistula is formed.
(2) crush injury
Parallel arterial and venous compressions can occur with arteriovenous fistula, iatrogenic injury such as splenectomy and nephrectomy, massive ligation of spleen and renal pedicle; femoral artery and vein ligation during amputation; upper extremity arteriovenous during thyroidectomy Large ligation, can occur arteriovenous fistula, external violence on soft tissue, soft tissue squeezed on the bone, such as the shoulder, buttocks can cause local arteriovenous fistula, skull fracture can cause arteriovenous fistula of meningeal blood vessels, etc. .
(3) Other reasons
Aneurysms gradually develop adhesions, corrosion, and finally break through the accompanying veins, and even arteriovenous fistulas can occur when tumor ulcers break into large blood vessel walls.
(two) pathogenesis
1. The site of occurrence
Traumatic arteriovenous fistula mainly occurs in the extremities, the lower extremities are more common than the upper extremities, and the lower extremity femoral arteries and veins are more common than the deep femoral arteries. Among the 27 cases reported by Zhang Peihua, the lower extremities accounted for 41% (8 cases of superficial arteriovenous fistula, 1 case of deep arteriovenous), upper limbs accounted for 33%, other parts accounted for 26% (such as common carotid artery - innominate vein, internal carotid artery - internal jugular vein, external carotid artery - facial vein, internal mammary artery - innominate vein, Shallow arteries and veins, forehead veins, etc.).
2. Pathology
In most patients, the distance between the artery and the vein can be quite small. The sacral branch only includes the adjacent vessel wall. In some patients, the fibrotic duct can separate the venous and venous, and the arteriovenous fistula often has a pseudoaneurysm, especially the trauma. To that, Elkin and Shumacker analyzed a group of 195 cases of traumatic arteriovenous fistula, 60% with pseudoaneurysm, most of which were placed between arteries and veins, and the rest could be separated from the iliac vein. Or on it.
Acquired arteriovenous fistula is almost a single branch, and most of the symptoms and signs are related to the "short circuit" between the high-pressure arterial system and the low-pressure venous system. The degree and location of the lesion determine its pathophysiological changes.
Typical lateral-lateral or "H"-type arteriovenous fistulas have proximal and distal arteries and veins that are connected by a lateral branch, forming a peripheral vascular bed, draining the arteriovenous via the distal end of the fistula, and nourishing the blood vessels. And the drainage branch constitutes a complete circulation path.
(1) Mouth resistance: The role of arteriovenous fistula (local, peripheral and central) is related to hemodynamic resistance. The larger the diameter of the fistula, the shorter the resistance, the smaller the resistance; the diameter of the fistula is small and the length is short. The resistance is relatively high. However, when the diameter reaches a certain level, compared with other factors such as the branching pathway, the resistance is not significant. At the same diameter, the resistance of the H-type arteriovenous fistula is higher than that of the lateral-lateral arteriovenous fistula. When multiple branches coexist, the combined force of the parallel branches is equal to the resultant force of the interaction of the resistances, which must be less than the resistance of the minimum resistance, and the combined force of the two parallel branches of the same diameter is equal to half of the resistance of the single branch. Although the blood flow through the two branches can be increased, it is rare to increase by a multiple.
(2) Local effects:
1 blood flow: the proximal arterial blood flow can be increased, the size of the fistula is the main determinant, in addition, the venous outflow tract resistance, the arterial collateral circulation and the peripheral vascular bed also play a role, the presence of the fistula can significantly reduce the proximal arterial resistance The blood flow during diastole is greatly increased, sometimes even reaching 80% to 90% of the maximum blood flow during systole. This blood flow phase is obviously different from the normal peripheral arteries. When resting, the normal arterial blood flow drops to the diastolic phase. 0, often maintained for a period of time, therefore, the presence of the fistula not only increases the velocity of the proximal arterial blood flow, but also reduces its pulsation.
The proximal venous blood flow is greatly increased and more pulsating, and the peak blood flow rate is consistent with arterial contraction. Due to the large venous compliance and low resistance of the proximal vein and its outflow tract, the pulsation is often rapidly weakened within the iliac crest, only at the proximal end. It is only obvious when the vein is narrow or occluded.
The proximal arterial blood flow direction is always toward the fistula, the proximal vein is always centripetal, the arterial collateral branch diverts to the periorbital blood, and the venous collateral blood flows to the heart. Due to anatomy and hemodynamic factors, the distal movement The venous blood can flow or flow away from the fistula or even stagnant. The direction of blood flow in the distal artery depends on the relative pressure of the mouth of the fistula and the inflow of the collateral. Three conditions may occur: A. The ratio of the mouth resistance to the proximal arterial resistance When the ratio of distal vascular bed resistance to collateral artery resistance is exceeded, the blood flow is in the normal direction, which is more common in small iliac crests, high resistance arteriovenous fistula and collateral arteries are less high, and high resistance, B. distal vascular bed resistance When the ratio of resistance to collateral arteries exceeds the ratio of mouthparts resistance to proximal arterial resistance, blood reflux is common in patients with large iliac crest, chronic, low-resistance arteriovenous fistula and collateral arteries, and C. ratios produce blood flow. Stasis, occasionally before the formation of large acute arteriovenous fistula collateral circulation, at this time, systolic blood flow in the normal direction, diastolic reflux, distal arterial blood reflux not only ingesting peripheral vascular bed nutrition, but also increase heart Dirty load, such as the fistula is quite small, the distal venous blood flow will be in the normal direction, which only occurs when the venous pressure of the nearest collateral joint exceeds the fistula; if the fistula is larger, the venous pressure at the fistula will Exceeding the distal venous pressure, but the valve with complete function between the fistula and the first branch of the vein will block the blood from flowing back. As the pressure increases, the distal vein gradually expands and the valve is closed, so in the large chronic arteriovenous fistula, blood The valve can be countercurrent to the distal vein via a dysfunctional valve.
2 blood pressure: the proximal arterial pressure is normal, large acute arteriovenous fistula, may have systolic and diastolic blood pressure; such as chronic arteriovenous fistula, proximal arterial dilatation, the pressure can exceed the normal anatomical level of the normal artery Pressure.
The distal arterial pressure is often reduced, the average blood pressure and pulse pressure will be lower than the proximal artery, the fistula is small, along the proximal artery, the fistula to the distal artery, the pressure is gradually reduced; when the fistula is large, the pressure at the fistula is obvious Lower, that is, the pressure decreases from the proximal artery to the fistula, but the pressure from the fistula to the distal artery will rise again. The reverse of the distal arterial pressure gradient will produce blood reflux, chronic arteriovenous fistula, with the diameter of the lateral branch artery The distal arterial pressure tends to increase, causing the distal arterial blood to flow back.
Although there is blood shunt through the fistula, due to the low resistance of the proximal venous outflow tract, the vein wall is well compliant, can adapt to the arterial blood flow without change, the proximal venous pressure is still maintained at a low level, 1 cm away from the fistula. The average venous pressure is 0 to 2.00 kPa (0 to 15 mmHg), and the pulse pressure is hardly more than 0.667 kPa (5 mmHg). If the proximal vein is compressed or blocked, the venous pressure will increase significantly and approach the pressure at the mouth of the fistula.
The distal venous pressure depends on the size of the fistula and the resistance to countercurrent flow. When the fistula is small, the peripheral to mouth pressure is gradually reduced. When the fistula is large, the venous pressure in the fistula area is greatly increased, and the function of the acute arteriovenous iliac vein valve is complete. Inhibition of blood reflux, the distal venous pressure may equal or exceed the distal arterial pressure; as the disease progresses into the chronic phase, the distal venous dilatation leads to venous valve dysfunction and the venous collaterals dilate, the distal venous pressure tends to decrease.
3 blood vortex: typical tremor and murmur of arteriovenous fistula, caused by abnormal blood flow phase caused by vibration of the relevant blood vessel wall, often associated with collateral formation, vascular tortuosity, aneurysm-like changes and sudden changes in vessel diameter, H-type Arteriovenous fistula is common.
4 Morphological changes: the movement of chronic arteriovenous fistula, the increase of venous blood flow, the morphological changes of angiogenesis, usually the mouth enlarges with the prolongation of the disease course, rarely spontaneously close or shrink, the most typical is the progressive arterial Growth and expansion, can be distorted and tumor-like changes, early thickening of the arterial wall, but eventually degenerative with smooth muscle atrophy, decreased elastic tissue and atheromatous plaque formation, the most obvious vasodilation near the fistula, such as The disease duration is more than 1 to 2 years, and the lesion is irreversible.
Proximal arterial growth, distortion is related to hemodynamic factors, the force of pulling the artery along the long axis of the artery is proportional to the longitudinal pressure gradient, the latter is a functional manifestation of blood flow velocity, the proximal vein has the same change, the vein wall Not only irregular thickening due to intimal hyperplasia and fibrosis, but also degenerative changes such as atherosclerosis and neoplastic changes, the inner elastic layer tends to break and disappear, and the endothelium damage of the lateral vein wall of the fistula may be Caused by blood spurt or vein wall vibration, the canine arteriovenous fistula experiment suggests that the thickening of the venous intima and medial membrane is related to the eddy current of the distal anastomosis and the kinetic energy transmitted into the adjacent tissue, and the collateral branch is established. The more the sacral blood passes through the varicose veins, the farther veins that grow into the distal side, unlike the proximal and proximal, distal veins, which can remain the same size or even smaller.
5 collateral circulation: arteriovenous fistula is an important reason to promote the formation of collaterals, and its abundance is far more than that of atherosclerotic lesions. The two theories about collateral formation are increased blood flow velocity and increased pressure through the collateral vessel. Studies have shown that the blood flow around the collaterals of the arteriovenous fistula often exceeds the blood flow around the occluded arteries. This is consistent with the first theory. When the fistula is present, blood can flow from the distal artery to the fistula, making the collaterals The outflow tract resistance is significantly reduced; when the artery is occluded, the collateral blood needs to flow to the vascular bed with relatively high peripheral resistance, so when the distal arterial blood flows countercurrently, the collateral blood flow of the arteriovenous fistula will be higher than the arterial occlusion disease. Holman et al. have long pointed out the importance of blood flow in the distal arteries. When the proximal arterial iliac crest is established or the distal artery is ligated in the proximal sac, the collateral formation is significantly reduced due to the suppression of blood reflux. When the artery is ligated at a single branch, a wide collateral circulation will form.
Arteriovenous iliac vein collateral formation may exceed the arterial collateral branch, leading to superficial varices, large acute arteriovenous fistula blood flows into the distal vein through the venous collateral, and valve closure prevents blood from flowing backwards, with the prolongation of the disease, the distal vein Valve insufficiency, by increasing the collateral venous branch to avoid blood reflux, the proximal vein occlusion, the largest formation of venous collaterals can be seen, allowing all the collateral blood to flow back in the distal vein.
(3) changes in peripheral circulation: arteriovenous fistula affects the blood supply of surrounding tissues, common peripheral tissues are pale, cyanosis, edema and pulse weakening, proximal to the fistula, arterial blood rapidly enters superficial veins and deep veins, skin, muscle and bone tissue The temperature is elevated; at the distal end of the fistula, the tissue temperature is often lower than normal, the peripheral oxygen and partial pressure of the muscle and bone tissue can be reduced, the venous oxygen saturation is lowered, and the lactic acid concentration is increased.
1 blood flow and blood pressure: when the fistula is small, the blood in the direction of normal blood flow of the distal artery and the blood of the collateral artery supply the peripheral arteries and their corresponding tissues, even if the fistula is large, the blood of the distal artery is countercurrent, far The blood flow of the collateral branch combined with a certain part must enter the peripheral supply vascular bed tissue again, that is, to some extent, the peripheral arterial blood can maintain its normal blood flow direction, such as large radial artery-cephalic arteriovenous fistula, peripheral The direction of blood flow is the same, the dividing point between the countercurrent and the downstream is in the shallow arch of the palm, the fistula is small, and the collateral artery is larger. Because of the compensatory dilatation of the small artery, the peripheral blood flow may not decrease; the fistula is larger, the collateral artery When less, the small arteries are not enough to maintain tissue nutrition, especially when the distal arteries have a large amount of blood reflux. Some patients do not affect the tissue nutrition, but the distal blood supply of the affected limbs is relatively reduced compared with the unaffected limbs.
Although the reduction of arteriolar resistance can make the blood flow relatively normal, the peripheral blood pressure can be increased or decreased due to the loss of the fistula energy. The literature reports that the lateral-lateral arteriovenous fistula of the radial artery-cephalic vein is 88% of the ipsilateral limb. The distal arterial pressure drops.
The effect of compression of the fistula on the relevant blood vessels: The study of the radial artery-cephalic arteriovenous fistula showed that when the proximal end of the radial artery was compressed, the peripheral blood flow and blood pressure were reduced. When the fistula was small, the compression of the proximal radial artery could eliminate the radial artery. The end of the blood flow, but the blood flow can flow from the distal end of the radial artery to the fistula, that is, the blood flow in the distal part of the radial artery; when the fistula is large, the compression of the proximal radial artery can increase the reverse blood flow at the distal end of the radial artery. The compression of the proximal artery can increase the "stolen blood" of the lateral branch around the fistula, further reducing the blood supply to the peripheral tissue, and oppressing the important collateral and ulnar artery also leads to a significant decrease in blood pressure and blood flow of the finger artery, although this method is When the mouth is large, the blood flow from the distal end of the radial artery can be reversed to the forward direction, or when the fistula is small, the blood flow can be increased. However, because the excessive blood flows through the low-resistance branch, the peripheral blood perfusion is reduced and the pressure is reduced. The collateral arteries can sometimes produce more severe vascular blood flow reduction than the compression proximal artery. Closing any outflow tract of the iliac crest, such as the proximal or distal vein, can increase the effective resistance of the iliac crest and the blood pressure and blood flow of the finger artery. Dagukou distal In the pulse, because the distal arterial blood flow is eliminated, all the collateral blood flows to the distal tissue, and the peripheral blood flow increases more obviously. If the fistula is small and the distal arterial blood flow is compliant, the distal artery can be compressed. Peripheral perfusion is reduced, depending on the blood volume of the collateral artery.
When the iliac crest and the proximal and distal arteries and veins are completely closed, the peripheral perfusion may increase or decrease according to the size of the fistula and the functional capacity of the collateral vessels. For example, the fistula and the lateral branches are larger, and the fistula and the four related vessels will be closed. Increase peripheral pressure and blood flow; if the fistula is small, the collateral circulation is less, it can lead to lower peripheral perfusion, the distal arterial blood is completely from the proximal artery, and the compression of the proximal artery will decrease the peripheral perfusion, the distal artery The antegrade blood flow is terminated and even replaced by reverse blood flow; if the distal arterial blood flow is reversed, compression of the proximal artery will result in an increase in reverse blood flow, further aggravating peripheral blood stealing.
(4) Systemic influence: The most basic pathophysiological change is the decrease of total peripheral resistance. It means that the left ventricular resistance is equal to the sum of the mouthparts resistance and the peripheral vascular bed resistance. The systemic blood flow is the blood flow output from the heart, perfusion of peripheral tissues; The branch blood flow is the blood flow through the collateral branch. The sum of the systemic blood flow and the sacral blood flow is equal to the cardiac output. When the total peripheral resistance of the arteriovenous fistula decreases, the body increases the heart discharge by increasing the heart rate and the stroke volume. The amount of increased cardiac output will maintain arterial pressure, reduce venous pressure and provide sufficient blood nutrition to the peripheral tissues. The increase in stroke volume is more conducive to venous return and increased blood volume. These compensatory mechanisms are in arteriovenous fistula. It plays an important role. When large arteriovenous decompensation, arterial pressure and systemic blood flow can be reduced, while systemic resistance and left and right atrial pressure are increased.
1 arterial pressure and left ventricular pressure: when the acute arteriovenous fistula is suddenly open, the peripheral resistance decreases significantly, and the arterial pressure drops linearly. After the increase of cardiac output and systemic resistance, the arterial pressure rapidly returns to the baseline level, according to the size of the fistula. The mean arterial pressure often decreases to a certain extent. Because the diastolic blood pressure drops more than the systolic blood pressure, the pulse pressure can be increased, but it can be inconsistent. Closing the acute arteriovenous fistula can cause a sudden increase in arterial pressure, while the spontaneous blood output and systemic resistance Decreased, arterial pressure quickly returned to the level before closure, most patients with chronic arteriovenous fistula, the average arterial pressure maintained in the normal range, but diastolic blood pressure can be reduced, pulse pressure widened (water pulse), compression or surgery to close the chronic arteriovenous The mouthwash response is similar to acute arteriovenous fistula.
Left ventricular systolic and end-diastolic pressure decreased in the opening of acute arteriovenous fistula, but end-diastolic pressure can quickly return to the level of near-opening. Closing the fistula can produce temporary systolic and end-diastolic pressure, large chronic Arteriovenous fistula, left ventricular end-diastolic pressure gradually increased, even severe heart failure can even kill.
2 venous pressure: when the arteriovenous fistula is open, the central venous pressure only rises a few millimeters of water column, which is difficult to detect. The pressure of the venous pool is reduced due to the increase of cardiac output, and the compliance of the vein itself can accommodate the increased venous volume. The venous pressure is often maintained at a normal level.
3 atrium, right ventricle and pulmonary artery pressure: the opening of the arteriovenous fistula increases the left and right atrium and the mean pulmonary artery pressure. The absolute range of the increase is small, which is related to the blood flow through the sacral branch. When the arteriovenous fistula is opened for the first time, right Ventricular systolic and end-diastolic pressures increase, but diastolic blood pressure can quickly return to pre-opening levels, and closing the fistula can reverse this process.
4 cardiac output, systemic blood flow and sacral blood flow: after the opening of acute arteriovenous fistula, cardiac output immediately increased, reaching a peak level within a few seconds, due to the rapid rise of blood flow from zero to close At the highest level, early blood flow through the vascular bed of the whole body is consistent with the decline of the mean arterial pressure in the early stage. Closing the fistula can reverse the course of the disease, the blood flow of the sacral branch drops to zero, and the blood flow of the system temporarily rises more than the level of the anterior The blood output decreased rapidly, and the increase of systemic blood flow was consistent with the temporary increase of systemic blood pressure, reflecting the body's regulation of excessive cardiac output through high-resistance peripheral vascular bed rather than low-resistance gargle, mouthwash, cardiac output The increase is equal to the blood flow of the sacral branch, the blood flow of the whole body is not reduced; the sputum is larger, and the blood flow of the sacral branch is more than 27% to 40% of the blood output of the anterior tibia. The increase of cardiac output may not be equal to the blood flow of the sacral branch. It can steal blood from the peripheral vascular bed, resulting in a decrease in systemic blood flow. Peripheral vascular compensatory contraction can prevent the reduction of mean arterial pressure. When the collateral blood flow exceeds 60% of the anterior cardiac output, the compensation is insufficient. Decreased blood flow to the whole body, according to the mouth Small, resting state of cardiac output increased in varying degrees, medium-sized sputum has no negative effect on increased cardiac output after exertion, 50% to 80% of patients with chronic arteriovenous fistula, closed mouth caused by cardiac output The amount is reduced.
5 heart rate and stroke output: When the cardiac output increases, there is an increase in heart rate and an increase in stroke output. The latter effect is more obvious. The opening of the acute arteriovenous fistula often causes the heart rate to temporarily increase, closing the fistula. Before the heart rate returns to normal levels, the short-term decline is lower than the pre-natal level. In patients with chronic arteriovenous fistula, the heart rate is often in the normal range. Nicoladoni (1875) and Branham (1890) reported that after pressing the fistula or the proximal artery of the fistula Heart rate slowed down. Most patients' heart rate slowed more than 4 times/min, which occurred after a transient increase in systemic arterial pressure, but high-dose atropine was blocked, suggesting that this heart rate changes from carotid sinus and Aortic arch baroreceptor induction, caused by vagus nerve mediated.
When the venous return of arteriovenous fistula is increased, the heart rate can be increased, and the cardiac output can be increased. The increased stroke volume is related to the increased cardiac output. It is easy to occur when the acetylcholine level is elevated and the sympathetic activity is enhanced. Increased myocardial contractility, under normal circumstances, subendocardial oxygen uptake, coronary blood flow and oxygen consumption are greater than subepicardar, and these differences can not be seen in moderate volume arteriovenous fistula, suggesting that when capacity increases, special At the tip of the left ventricle, the endocardial oxygen demand is relatively reduced.
6 heart: heart enlargement is common in patients with chronic arteriovenous fistula, which can be manifested as dilatation or hypertrophy. After a few months of persistent mouthwash, the heart gradually expands, and the mouth of the mouth can be enlarged by up to 80%. When compensating, the blood flow into the large venous system, the heart can be reduced at the beginning, the chronic arteriovenous fistula is closed, and the aorta and left ventricle are temporarily caused by incomplete emptying of the left heart and decreased blood flow to the vein. Increased sex, the right atrium and lung cone capacity decreased, closing the long-standing mouth can gradually reduce the heart, often return to normal within a few weeks.
7 blood volume: patients with chronic arteriovenous fistula often increase blood volume, more than 200 ~ 1000ml / m2 body surface area, excess blood exists in the dilated collateral circulation, including proximal arteriovenous, cardiac, central and collateral vessels, By increasing cardiac output to fill the sacral and systemic circulation to avoid blood sputum, the main factor limiting acute cardiac venous output in acute arteriovenous fistula is insufficient blood volume, rather than insufficient heart reserve.
The increase in plasma volume is mainly related to the increase of blood volume. It is activated by sodium and water storage mechanism. The decrease of arterial pressure reduces renal blood flow and glomerular filtration rate, and the renal tubular reabsorption increases, resulting in decreased urine output. Extracellular fluid. Accumulation and increased blood volume, renal blood flow decline can also activate the renin-angiotensin-aldosterone system, further increase renal sodium and liquid reabsorption, in addition to sodium retention, can also use protein storage to maintain plasma tension, once reached Normal blood volume, excess sodium and water in the body is excreted.
8 Heart failure: When blood is shunted from the artery to the vein, it can quickly cause heart failure, especially in the aorta-inferior vena cava arteriovenous fistula. If the fistula is small, heart failure may not occur or delay for several years. The direct relationship between increased blood volume and heart failure has been confirmed in animal experiments, but in the human body, heart failure occurs not only in terms of mouth size and cardiac output, but also depending on whether coronary or myocardial disease is present; Patients can not endure heart failure in the short term because their heart can tolerate increased circulating load for a long time.
Edema of acute arteriovenous fistula may be associated with increased local venous pressure. In heart failure, all clinical manifestations of fluid retention such as peripheral edema, pulmonary edema, ascites and weight gain may play an important role in the increase of aldosterone secretion. Mouthwash can cause a lot of diuretic.
9 mouthparts: arteriovenous fistula near the heart has greater influence on the whole body than peripheral arteriovenous fistula. When the fistula is located in the main central blood vessels (aorta and inferior vena cava), the proximal end is short due to its large diameter and short length. The resistance of the veins and veins is quite low; the fistula is located in the blood vessels of the limbs, and its diameter is small, and the centrifugal distance is large, so the circumflex resistance is higher. Some scholars believe that the pelvic and calf arteriovenous fistulas are more than the head, neck and The systemic influence of arteriovenous fistula of the upper extremity is large. This may be caused by hydrostatic pressure, which causes the affected blood vessels to dilate and the resistance to decrease. The arteriovenous fistula involving the branch of the portal vein system has less systemic influence than the other parts of the body. This may be related to The sinusoids are associated with high outflow resistance, but some mesenteric movements, intravenous arteriovenous fistulas, have a significantly increased cardiac output.
10 Summary: The opening of the arteriovenous fistula causes the total peripheral resistance to drop suddenly, resulting in a decrease in central arterial pressure, an increase in central venous pressure, a decrease in systemic blood flow, and blood from the artery into the vein, but can be corrected by a compensatory mechanism.
Increased central venous pressure enlarges the heart chamber and increases myocardial fiber end-diastolic stress. According to the Frank-Starling mechanism, the stroke volume is increased, the arterial pressure is decreased, and the baroreceptor produces a reflexive heart rate, which is enhanced by circulating acetylcholine and sympathetic catecholamine. Myocardial contraction, sympathetic adrenaline stimulates contraction of the small arteries to maintain central arterial pressure, but further reduces peripheral blood flow; central venous contraction promotes venous return to the heart, and these mechanisms synergistically increase cardiac output and aortic pressure, large Part of the heart function is well compensated, the increase in blood output increases the aortic pressure to normal level, the baroreceptor function is reduced, the heart rate returns to near normal state, and the peripheral vasoconstriction is relieved; although the systemic blood flow is reduced, When returning to near normal, such as extensive or myocardial damage, compensation will be incomplete, cardiac output increased but not enough to maintain peripheral blood flow, heart failure can occur, renin-angiotensin-aldosterone System activation causes sodium, water retention, while mobilizing protein storage, increasing plasma volume, blood volume Increase the heart enlargement and residual sacral circulation expansion, further promote venous blood reflux, improve cardiac output, good compensation, systemic blood flow can be increased to the pre-temporal level, electrolytes return to normal, with the progression of the disease, proximal movement, Venous dilation leads to the continuous expansion of the sacral branch, the sacral branch itself also expands, and the venous side supports continued formation. The final result is a further decrease in total peripheral resistance and an increase in cardiac output. Patients with coronary heart disease or myocardial disease, cardiac reserve Eventually it will be destroyed and heart failure will occur.
3. After classification, the arteriovenous fistula can be of different types. According to the surgical findings, it is divided into 4 types.
(1) Hole type: The injured arteriovenous vein is in close proximity, and there is a simple traffic passage in between.
(2) Catheter type: The arteries and veins are separated by a short distance, and there is a pipe in the middle (generally about 0.5 cm in length), and the channel is in the form of a cyst.
(3) Aneurysm type: There are both arteriovenous traffic channels and traumatic aneurysms, which are the result of injuries on both sides of the artery.
(4) cyst tumor type: after the arteriovenous injury, a common cystic tumor is formed, and the blood of the venous and venous blood is in this traffic.
Prevention
Acquired arteriovenous fistula prevention
This disease is caused by trauma, so there is no effective preventive measures, but for some iatrogenic injuries such as splenectomy and nephrectomy, large ligation of spleen and kidney pedicle; femoral artery ligation during amputation; thyroidectomy requires medical care The personnel were carefully examined after surgery to prevent the occurrence of arteriovenous fistula.
Complication
Acquired complications of arteriovenous fistula Complications swelling
For patients with acquired arteriovenous fistula, early surgery is recommended. If the preparation is insufficient, complications such as wound bleeding, infection, insufficient blood supply to the affected limb or swelling of the affected limb and superficial varices may occur after surgery. If the thrombus is caused by trauma, the thrombus is passed. Rinse mouth, enter the pulmonary artery will cause pulmonary embolism; if the aseptic technique is not strict in operation, it can also be complicated by sepsis; venous stasis can be followed by thrombosis, which can also lead to pulmonary embolism.
Symptom
Acquired arteriovenous fistula symptoms Common symptoms Partial skin of the limbs... Fatigue, dizziness, varicose veins, palpitations, chest muscles, muscle weakness, action, wall-like heart failure, shortness of breath
The diagnosis of arteriovenous fistula is generally not difficult. In the history of penetrating trauma, the patient may find a pulsatile mass on his own, and there is local snoring, swelling of one limb, varicose veins and venous valve insufficiency, and local skin temperature ratio of the limb. The contralateral side, the injured part has scars, murmurs and tremors should be considered in the diagnosis of arteriovenous fistula. Patients with acute arteriovenous fistula often have severe multiple trauma or penetrating injuries in the limbs. When examining patients, due to concentration The diagnosis and treatment of arteriovenous fistulas are often delayed in areas of severe damage to bones and soft tissues.
The arterial and venous traffic can be divided into direct and indirect. When the adjacent vein is injured at the same time, the wound edges directly meet each other, and direct traffic can be achieved within a few days, which is called direct arteriovenous fistula, such as wound of arterial vein. Can not directly align, but there is a hematoma between the two, after the hematoma, the formation of a capsule or tube between the artery and the vein, called indirect sputum.
The proximal arteries of the tendon are progressively dilated and elongated; the arterial wall is initially thickened, degenerative changes occur later, smooth muscle fibers are atrophied, elastic fibers are reduced, the wall is thinned, and atheromatous plaques are formed, such as large pupils, adjacent The main artery of the fistula can be inflated to form an aneurysm, and the distal artery is reduced due to a decrease in blood flow.
The vein gradually expands, the distal end can reach the last valve, and the proximal end can reach the vena cava. If the pupil is large, the pressure in the vein increases suddenly. After a few weeks of trauma, a local pulsatile mass can be seen due to venous expansion. It is a pseudoaneurysm, when the pupil is small, the vein is gradually dilated at the fistula, the intima is thickened, and the fibrous tissue is proliferated. Since the vein wall is gradually thickened, an "action-like wall" is formed, so the shape is about half a year after the trauma. It is difficult to distinguish between arteries or veins, degeneration of the vein wall, internal elastic layer secondary fissure and disappearance, distal vein dilatation and iliac crest length, followed by venous valve insufficiency and more severe venous insufficiency, arteriovenous fistula promotes a large number of collateral circulation Formation, the collateral circulation of the vein is even more than the collateral circulation of the artery, and the superficial vein is extensively varicose.
The fistula between the arteries and veins is relatively simple, most of the traumatic aneurysms can be located on the arterial side, the venous side, or between the arteries and veins.
(1) The arteries and veins are closely attached to a split pore, and some are accompanied by an aneurysm or a venous tumor.
Arteriovenous fistula: (1) arteriovenous veins close together, showing a fissure pore (2) arteriovenous close, accompanied by venous tumor.
(2) Simple traffic ducts, like the patent ductus arteriosus, some with aneurysms or venous tumors.
Arteriovenous fistula: (1) Traffic ducts with aneurysms. (2) Traffic catheters are accompanied by motion and venous tumors.
(3) saccular traffic, some with aneurysms or venous tumors.
Arteriovenous fistula: (1) saccular traffic with aneurysm (2) saccular traffic with movement, venous tumor traumatic arteriovenous fistula mainly occurs in the limbs, less head and neck, less chest and abdomen, in the limbs, lower limbs than the upper limbs More common; in the lower extremities, the superficial femoral artery is more common than the deep femoral artery.
Acute arteriovenous fistula
It can occur 1 hour after the injury. The amount of bleeding is large when wounded, but it is spray-like, but the wound is generally small. There is a hematoma in the lesion. Most of them have tremors and murmurs. Because the arteriovenous communication is often blocked by blood clots, it is mostly A few hours or a few days after the injury, the pulsatile mass or the affected area touched the tremor and the murmur. Most of the patients in the distal part of the arteriovenous fistula can still twitch and pulsate the arteries, but weaker than the healthy side.
2. chronic arteriovenous fistula
The clinical symptoms are gradually developed, mainly due to swollen limbs, pain, numbness, fatigue, neck, arteriovenous fistula, headache, dizziness, memory and vision loss, and other symptoms of insufficient blood supply to the brain. Venous fistula can be associated with chest tightness, palpitations, shortness of breath, and even heart failure. The main manifestations are as follows:
(1) Noise and tremor: Rough continuous rumbling "machine" murmurs can be heard near the mouth. The murmurs increase during systole and spread along the proximal and distal sides of the blood vessels. The diastolic phase diminishes but does not disappear. The bigger the mouth, the louder the noise, the corresponding body surface in the mouth can touch the tremor.
(2) venous insufficiency: due to high blood flow in the artery through the fistula into the vein, resulting in increased venous pressure, venous valve insufficiency, the arteriovenous fistula near or distal superficial veins significantly dilated and curved, venous return blocked There are edema, stasis dermatitis, pigmentation and ulceration at the distal end of the limb.
(3) Increased local skin temperature: The surface skin temperature of the arteriovenous fistula site is increased to different extents compared with the same site of the contralateral limb. The skin temperature of the distal part of the fistula is normal or lower than normal.
(4) Heart enlargement and heart failure: arterial blood flows through the fistula into the vein, and the amount of blood returning from the heart increases, which can cause the heart volume to be overloaded, causing the heart to expand, leading to heart failure, heart enlargement and heart failure. The size, location and length of the mouth are closely related. The closer to the heart, the more severe the heart failure, the arteriovenous fistula of the limb, the late heart failure, and the heart failure after the arteriovenous fistula operation can be improved. And cure.
The diagnosis of acquired arteriovenous fistula is generally not difficult. The patient has a history of trauma. The injured part often has a lump with continuous murmur and tremor. The course of the disease is slightly longer. The limb has swelling of the limb, varicose veins, venous insufficiency or chronic ulcer. The damaged local skin temperature is higher than the contralateral limbs, and the symptoms and signs of the heart may be enlarged. The diagnosis of arteriovenous fistula should be considered. The pressure of the fingers may cause the pulse rate to slow down, the blood pressure to rise, and the venous blood oxygen content in the lesion to increase. Arterial angiography shows that early imaging of the veins also contributes to the diagnosis of arteriovenous fistula. Patients with acute arteriovenous fistula are often accompanied by severe multiple trauma or multiple penetrating injuries of multiple limbs and neglect the diagnosis, which should be noted.
Examine
Acquired arteriovenous fistula examination
(a) arteriography
It can be clearly defined the location, size and circulation of nearby blood vessels and circulation of the collaterals. The mouth is small, the arteries are developed, and the veins near the fistula are also developed. However, the distal vein of the fistula is rarely displayed. When the mouth is large, it needs to be taken quickly. Arterial imaging can be seen in the film, but the dilated vein is developed near the iliac crest. The most clear part of the dilatation often indicates the site of the fistula. The distal vein of the fistula may show an increase in number and varicose veins.
(2) Determination of finger pressure mouth (Brankam sign)
Acupressure sputum to block blood shunt, measurement to block blood shunt, measure heart rate and blood pressure before and after blocking shunt, compare, after blocking blood shunt, heart rate is significantly slowed down, this is because the sputum is closed, forced blood In the normal capillary network circulation, the surrounding resistance is increased. At the same time, after the sputum is suddenly blocked, the blood volume that has been shunted through the sputum in the past is flowed into the peripheral arterial system, and the surrounding resistance increases and the extra blood volume suddenly increases in the arterial system. The blood pressure is increased, thereby correspondingly stimulating the nerve endings in the aortic decompression nerve and the carotid sinus, so that the vasomotor center suppresses and the pulse rate is slow.
(C) Determination of mean arterial pressure in arteries of the arteriovenous fistula
When the iliac crest and collateral circulation are small, the mean arterial pressure drop is particularly obvious; when the iliac crest is small, the mean arterial pressure at the distal end of the iliac crest is not changed much. The general arterial pressure measurement requires direct puncture of the artery, but by Doppler ultrasonography and Limb plethysmography can also measure arterial pressure at the distal end of the ankle.
(4) Determination of cardiac output
Echocardiography and indicator dilution mehods can measure cardiac output and understand cardiac function.
(5) Determination of venous blood oxygen
From the vein of the arteriovenous fistula or the blood from the proximal end of the fistula, compared with the venous blood test of the same part of the contralateral limb, the venous pressure on the affected side is higher than that of the normal limb, and the oxygen partial pressure is significantly increased.
(6) Determination of venous pressure
The venous pressure of the affected limb increased, and the increase in venous pressure near the fistula was more pronounced.
Diagnosis
Diagnosis and differentiation of acquired arteriovenous fistula
Acute arteriovenous fistula may appear immediately after the injury, or after the blood clots are dissolved in the arteriovenous communication. There is a hematoma in the lesion, most of which have tremors and murmurs. Most patients still have limbs at the distal end of the arteriovenous fistula. It can beat the arteries, but it is weaker than the healthy side. When the lower extremity femoral artery is accompanied by deep femoral artery injury, it can not beat the dorsal artery of the foot and has limb ischemia symptoms.
Patients with chronic arteriovenous fistula have swollen limbs, numbness, pain, fatigue, snoring in the pulsatile mass, heart failure can have chest tightness, palpitations, shortness of breath, common signs are:
There is noise and tremor in the 1 area. Regardless of the size of the arteriovenous fistula, a typical, rough and persistent rumble can be heard in the arteriovenous fistula. It is called machine-like noise, and the murmur is enhanced during the systole. The proximal and distal conduction of the main vessel, this murmur and pseudoaneurysm caused weak diastolic murmurs and systolic murmurs caused by arterial stenosis.
2 Pulse rate is accelerated: this is the result of a Braibridge reflex caused by an increase in venous return or an increase in cardiac workload due to a decrease in mean arterial pressure (Marey's law).
3 heart enlargement and heart failure: due to the rapid flow of blood into the vein through the pupil, the venous pressure increases, the amount of blood returning from the heart increases, causing the heart to expand, and the progressive enlargement of the heart can lead to heart failure, heart enlargement and heart failure. The size, location, and length of time of the fistula are closely related. The closer the heart is, such as the direct branching of the aortic arch (carotid artery, no arteries, subclavian artery) and the venous fistula formed by the accompanying vein, the heart failure occurs. Early and serious, Pate reported that arteriovenous fistula occurred in the direct branch of the aorta, heart failure occurred as early as 6 weeks after trauma, most of the arteriovenous fistula of the limb, and 9 cases of arteriovenous fistula occurred after cardiac resection. There are local pain, ascites and abdominal pain.
4 local warming increased: the skin temperature of the affected limb in the arteriovenous fistula area increased, the high arteriovenous fistula is far away, the skin temperature may be normal or lower than normal.
5 venous insufficiency: direct communication between arteries and veins, so that the venous increase, most patients, arteriovenous fistula near or distal superficial veins dilate and bend, skin pigmentation accompanied by calf cellulitis, toe or fingers often occur Ulcers, which behave like symptoms after deep phlebitis.
