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A well-functioning vascular access is essential for providing adequate life-sustaining treatment in patients with end stage renal disease on maintenance hemodialysis. The preferred long-term vascular access is the arteriovenous fistula (AVF), which is created using the vessels of the patient by surgically connecting an artery with a superficial vein to increase the blood flow (Qa) in the venous system, which will dilate allowing the insertion of two needles, one to carry the blood to the dialyzer, and the other to return the cleansed blood to the body with the aid of a dialysis machine. Unfortunately, the high prevalence of vascular disease of the hemodialysis patients make difficult to create an adequate AVF in as many as 20 to 60% of the patients.In these persons, a valid alternative is the arteriovenous graft: in graft method an artery is surgically connected to a vein with a short piece of synthetic soft tube which is implanted under the skin. Needles are inserted in the graft during the dialysis treatment. Compared to an AV, however, graft is at higher risk of complications. The most frequent complication is thrombosis (i.e. the formation of blood clot inside the graft). Usually, thrombosis is the consequence of an underlying significant stenosis (i.e. a greater than 50% narrowing of the vessel or graft lumen by comparison with the lumen of a normal adjacent vessel or graft) and its hemodynamic consequences of decreasing the access blood flow (Qa) and/or increasing pressure within the graft. Therefore, all vascular access guidelines recommend regular noninvasive screening programs of grafts for timely identification of a stenosis associated with some type of functional or hemodynamic impairment, because its repair may prevent thrombosis and lengthen the useful life of the access. Screening methods include clinical monitoring and surveillance, which uses special equipment either to assess the hemodynamic consequences of stenosis by measuring Qa and static venous intra-access pressure ratio (VAPR) or to visualize the stenosis by means of duplex ultrasound (DU). Guidelines also state that there is insufficient evidence to prefer one method to another due to the lack of adequate comparative studies. The purpose of our study is to identify an optimal screening program for stenosis detection and elective repair by comparing the diagnostic performance for stenosis and incipient thrombosis of all the available screening tools in the same graft population
Full description
A well-functioning vascular access (a system that allows the blood of the patient to leave the body, be brought to the artificial kidney or dialyzer to be cleaned and return the cleansed blood to the body) is essential for providing adequate life-sustaining treatment in patients with end stage renal disease on maintenance haemodialysis.
The preferred long-term vascular access is the arteriovenous fistula (AVF), which is created using the vessels of the patient by surgically connecting an artery with a superficial vein to increase the blood flow (Qa) in the venous system, which after few weeks will dilate (maturation) allowing the insertion of two needles, one to carry the blood to the dialyzer (arterial needle), and the other to return the cleansed blood to the body (venous needle) with the aid of a dialysis machine, equipped with a blood pump and pressure sensors at the level of the "arterial" and "venous" needle to monitor for needles dislodgment.
Unfortunately, the high prevalence of vascular disease of the haemodialysis patients makes difficult to create an adequate AVF in as many as 20 to 60% of the patients.
In these persons, a valid alternative is the arteriovenous graft: in graft method an artery is surgically connected to a vein with a short piece of synthetic soft tube which is implanted under the skin. Needles are inserted in the graft during the dialysis treatment.
Compared to an AV, however, graft is at higher risk of complications. The most frequent and feared complication is thrombosis (i.e. the formation of blood clot inside the graft).
Usually, thrombosis is the consequence of an underlying stenosis (i.e. a greater than 50% narrowing of the vessel or graft lumen by comparison with the lumen of a normal adjacent vessel or graft due to the thickening of the vessels and/or the graft wall) and its hemodynamic consequences of decreasing the access blood flow (Qa) and/or increasing pressure within the graft. Less frequently thrombosis occurs in the absence of significant stenosis and may be triggered by a drop in the patient's arterial blood pressure (hypotension).
All vascular access guidelines recommend regular non-invasive screening programs of grafts for timely identification of a stenosis associated with some type of functional or hemodynamic impairment, because its repair may prevent thrombosis and lengthen the useful life of the access.
Non-invasive screening methods include clinical monitoring (i.e. noting signs of access dysfunction during the haemodialysis session) and surveillance, which uses special equipment either to assess the hemodynamic consequences of stenosis by measuring Qa and static venous intra-access pressure ratio (VAPR) or to visualize the stenosis by means of duplex ultrasound (DU).
In graft, all guidelines have opted for surveillance. However, they also state that there is insufficient evidence to prefer one technique to another because of the lack of adequate comparative studies.
Indeed, the great majority of the studies have evaluated the ability of detecting stenosis and predicting incipient thrombosis (within 1 to 3 months) by one surveillance method, and very few have compared two-to-three techniques at the best (1).
The purpose of the investigators was to compare in the same graft population the diagnostic performance of all the currently available screening tools in detecting stenosis and predicting incipient thrombosis (to identify the best criteria for elective stenosis repair).
The primary aim of the study was to identify an optimal screening program to reduce the risk of thrombosis in graft by assessing the diagnostic accuracy (i.e. sensitivity, false positive rate, positive and negative predictive value, and area under the receiver operator curve) of all the available screening tools and the occurrence of acute hypotension and identify the best threshold/s for continuous variables in a) detecting stenosis, b) predicting incipient thrombosis (within a 4-month period following graft assessment for stenosis).
The following screening methods will be tested:
Subsequently all grafts underwent the biplanar Digital Subtraction Angiography (DSA), our gold standard for stenosis detection. The access was visualized in its entirety from the feeding artery to the right atrium seeking for the presence of stenosis. Each stenosis was graded with regard to location and degree as outlined for DU and was considered significant (StA) when the lumen reduction was > 50%. To ensure blinding the investigator performing DSA was unaware of the results of the other screening strategies.
Secondary aims of the study were to assess:
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Data sourced from clinicaltrials.gov
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