Arteriovenous shunts

High-output" failure is a rare form of heart failure. In this condition, the demands of the body are so great that even increased cardiac output is insufficient. High-output failure can result from hyperthyroidism, beriberi, anemia, and arteriovenous shunts. This form of failure responds poorly to the drugs discussed in this chapter and should be treated by correcting the underlying cause. 

The blood of the patient, withdrawn from an artery near the wrist, is allowed to flow through the blood circuit, which includes the dialyzer, usually a blood pump plus monitoring instruments, and is returned to a nearby vein. The connections to the blood vessels are made via the so-called subcutaneous arteriovenous shunt this involves an artificial tube that connects the artery and vein underneath the wrist skin. 

Recombinant human erythropoietin (rHuEpo) may increase the risk of thrombosis (201). It has been reported that patients with carcinoma of the cervix who received chemotherapy and rHuEpo have an increased risk of symptomatic venous thrombosis (201). In clinical trials where the maintenance hematocrit was 3% on PROCRIT clotting of the arteriovenous shunts occurred at an annual rate of about 0.25 events per patient per year. However, other thrombotic conditions such as cerebrovascular events, transient ischemic attacks, myocardial infarction, or pulmonary embolism occurred at a rate of 0,04 events per patient per year (202). In a separate study of I, I I I untreated patients on hemodialysis, clotting of arteriovenous shunts occurred at a rate of 0.5 events per patient per year. In patients with chronic renal failure on hemodialysis who also had congestive heart failure, ischemic heart disease and venous thrombosis were increased in patients who were treated with PROCRIT targeted to a hematocrit level of 42 3% compared to those targeted to 30 3% (202). It has also been reported... 

CE-MRA also allows repetitive measurements to follow the passage of contrast bolus. Reduction in the number of slices and of in-plane resolution admits sequential measurements with a temporal resolution ofless than 1 s (Krings and Hans 2004). In combination with high resolution measurements, thus dynamic processes in arteriovenous shunts or for instance in steal phenomena can be studied (Fig. 5.7). 

Thrombosis of the cavernous sinus is characterized by proptosis, chemosis, impaired vision and ophthalmoplegia. If it is not septic, prognosis is good because of collateral drainage and spontaneous recanalization. The same symptoms, with the exception of a possible bruit, may result from arteriovenous shunting in carotid-cavernous fistulae. The treatment of choice in this case is endovascular occlusion (thrombosis ) of the cavernous sinus. 

A method for the direct observation of extracorporal thrombus formation has been introduced by Rowntree and Shionoya (1927). These first studies could provide evidence that anticoagulants like heparin and hirudin do inhibit thrombus development in arteriovenous shunts. Since today, the A-V-shunt thrombosis models have been often used to evaluate the antithrombotic potential of new compounds in different species including rabbits (Knabb et al. 1992), rats (Hara et al. 1995), pigs (Scott et al. 1994), dogs and cats (Best et al. 1938), and non-human primates (Yokoyama et al. 1995). 

Hepatic adverse effects secondary to antiemetic therapy are usually asymptomatic. Metoclopramide has been reported as causing cholestasis and the formation of arteriovenous shunts in the liver [12]. The 5HTj-receptor antagonists have all been documented as occasionally causing mild increases in liver fimction tests. Cholestatic jaundice has been reported with cyclizine, prochlorperazine and promethazine, and hepatitis has been reported with cyclizine. 

Feurle GE (1990) Arteriovenous shunting and cholestasis in hepatic hemangiomatosis associated with metoclopramide. Gastroenterology 99 258-262. Magueur E, Horgege H, Attali P, et al. (1991) Pharmacokinetics of metoclopramide in patients with liver cirrhosis. Br J Clin Pharmacol 31 185-187. Albani F, Tame MR, De Palma R, et al. (1991) Kinetics of intravenous metoclopramide in patients with hepatic cirrhosis. Eur ] Clin Pharmacol 40 423-425. 

He was hospitalized for revision of his arteriovenous shunt and postoperatively complained of symptoms of gastroesophageal reflux. This complaint prompted institution of cimetidine therapy. In view of the patient s impaired renal function, the usually prescribed dose was reduced by half. Three days later, the patient was noted to be confused. An initial diagnosis of dialysis dementia was made and the family was informed that dialysis would be discontinued. On teaching rounds, the suggestion was made that cimetidine be discontinued. Two days later the patient was alert and was discharged from the hospital to resume outpatient hemodialysis therapy. 

Activated charcoal, although unpalatable, appears to be relatively safe but constipation or mechanical bowel obstruction may be caused by repeated use. Aspiration of charcoal into the lungs can cause hypoxia through obstruction and arteriovenous shunting. Charcoal adsorbs and thus inactivates... 

Acute or chronic failure of the heart may result from disease of the myocardium itself, mainly ischaemic, or an excessive load imposed on it by arterial hypertension, valvular disease or an arteriovenous shunt. The management of cardiac failure requires both the relief of any treatable underlying or aggravating cause, and therapy directed at the failure itself. 

Thrombolysis may also be considered for ocular thrombosis (urokinase) and for thrombosed arteriovenous shunts (streptokinase). 

Adverse effects. A dose-dependent increase in arterial blood pressure follows the rise in red cell mass and encephalopathy may occur in some previously hypertensive patients. Arteriovenous shunts of dialysis patients, especially those that are compromised, may thrombose as a result of increased blood viscosity. 

Aetiopathogenesis As with spider naevi, the capillary dilatation causing palmar erythema is attributed to an increased oestrogen content of the blood, a rise in bile acids or endotoxins and an activation of vasodilating substances with more numerous arteriovenous shunts and a hypercirculatory syndrome. Portal hypertension is seen as an important codeterminant. The blossoming of spider naevi and palmar erythema is also observed in the phenomenon of haemodynamic-related resistance to diuretics. 

Arteriovenous shunts, arterioportal fistula Portal vein thrombosis... 

In theory, there are three causes for the occurrence of HPS (since hypoventilation is not deemed a possible cause) (1.) arteriovenous shunts, (2.) disturbed alveolo-capillary oxygen diffusion in terms of impaired diffusion-perfusion, and (3.) mismatches between ventilation and perfusion. Consequently, there are numerous liver diseases which are associated with HPS. Transient HPS in acute viral hepatitis A and B has recently been reported. (17, 38) (s. tab. 18.1)... 

Hypertrophic osteoarthropathy (hour-glass nails, clubbed fingers) (s. fig. 4.18), which has been known since 1884, is not caused by hypoxia, as has been assumed up to now. (18) The cause is to be found in the intrapulmonary arteriovenous shunts from the venous limb of the pulmonary vessels, megakaryocytes and thrombocyte aggregates pass directly through the shunts into the arterial limb and hence (unfiltered, uncatabolized or not... 

Jeffrey, G.R, Prince, R.L., van der Schaaf, A. Fatal intrapulmonary arteriovenous shunting in cirrhosis diagnosis by radionuclide lung perfusion scan. Med. J. Aust. 1990 152 549-553... 

Complex liver disorders very occasionally occur with metoclopramide, with cholestasis and opening of arteriovenous shunts in the liver (SEDA-16,419). In two cases a condition resembling Reye s syndrome has been seen (14). 

Contraindications Compensatory hypertension (arteriovenous shunt or coarctation of aorta), inadequate cerebral... 

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