Role of Surveillance for Hemodialysis Access Catherine K. Chang and Thomas S. Huber The role of surveillance for permanent hemodialysis arteriovenous access, both autogenous (arteriovenous fistula [AVF]) and prosthetic (arteriovenous graft [AVG]), remains unresolved. Simplistically, clinical monitoring refers to the “examination and evaluation of vascular access by means of physical examination to detect physical signs that suggest the presence of dysfunction,” and surveillance refers to the “periodic evaluation of the vascular access by using tests that may involve special instrumentation and for which an abnormal test result suggests the presence of dysfunction” as defined by Work. Several of the national practice guidelines, most notably the National Kidney Foundation–Kidney Disease Outcome Quality Initiative (KDOQI), recommend surveillance as a supplement to clinical monitoring. Indeed, one of the two overarching goals of the KDOQI Guidelines is to detect access dysfunction before thrombosis. However, the level 1 evidence from randomized trials does not support routine surveillance and remediation for AVG, and there is a paucity of evidence for AVF. Notably, surveillance does not appear to improve access outcome in terms of functional patency, but it is significantly more expensive. The goal of identifying significant lesions destined to cause access thrombosis and correcting these lesions before any untoward event while avoiding unnecessary procedures is admirable, but it remains elusive. Justification Routine surveillance of AVG and AVF seems justified given their natural history and the costs and morbidity associated with failure. Notably, all types of permanent access have a limited life expectancy and ultimately fail or thrombose. The most common mode of failure for AVG is the development of a hemodynamically significant stenosis at the venous outflow (usually the anastomosis) secondary to intimal hyperplasia. Access thrombosis mandates attempts to remove the thrombus and restore the access and/or establish an alternative access, commonly a tunneled dialysis catheter. This care process and untoward series of events often mandates hospital admission and is associated with significant cost and inconvenience to the patient. Theoretically, identifying these significant outflow lesions and preemptive correction with either open or endovascular treatment could prolong access patency and avoid the sequence of adverse events associated with thrombosis. Surveillance is predicated on the assumptions that the various screening tools can identify a significant stenosis, that these “failing” accesses are destined to fail in the near future, that remedial intervention can prolong patency, and that the outcomes after remediation for the “failing” access are superior to those after a thrombosed access. Unfortunately, not all of these assumptions are necessarily true. The various surveillance techniques (detailed below) are quite good for identifying access stenoses, although the positive predictive value of these lesions in terms of near-term access thrombosis is somewhat limited. Additionally, preemptive angioplasty can stimulate or exacerbate the intimal hyperplastic process and thereby potentially accelerate the failure mode while incurring additional health care costs. Clinical Monitoring and Surveillance Techniques Clinical monitoring refers to the use of the patient’s history, physical examination, and access history to detect dysfunction; surveillance refers to the serial use of special tests or instrumentation. Access dysfunction on physical examination is suggested by the absence of a thrill (possible access thrombosis), the presence of a pulse (possible venous outflow stenosis), the presence of significant arm edema or venous collaterals (possible venous outflow stenosis) and diminished pulses within the AVG upon compression (possible arterial inflow problem). Prolonged bleeding at the cannulation sites after dialysis sessions suggests a venous outflow problem, whereas a decrease in the urea clearance with dialysis with a stable dialysis prescription also suggests dysfunction. Urea clearance is calculated by Kt/V, where K is clearance of urea calculated before and after dialysis, t is duration of dialysis, and V is urea distribution volume. The most common surveillance techniques include blood flow monitoring (a), static venous dialysis pressures (VP), and duplex ultrasound. These techniques are widely used throughout dialysis centers and are familiar to most dialysis care providers. Access blood flow is most commonly determined based upon the Fick principle and calculated by injecting ice-cold saline through the arterial side of the access and measuring the change in temperature at the venous side with the change in temperature corresponding to a specific flow rate. VP is measured by connecting a manometer to the arterial dialysis needle before starting the pump, and this value can be normalized to the systemic blood pressure to determine a static venous pressure ratio. Notably, both of these techniques (a and VP) are surrogates for stenoses within the access. Duplex ultrasound can be used to directly measure stenoses within the access or the anastomoses based upon the peak systolic velocities (PSV). Duplex ultrasound can also be used to calculate access flow by measuring the blood flow velocity and the cross-sectional area of the access. Although duplex ultrasound is familiar to vascular surgeons, the requisite equipment is not usually available in most dialysis centers, unlike the equipment needs for the a and VP measurements. Recommendations From National Guidelines The KDOQI guidelines recommend “an organized monitoring/surveillance approach with regular assessment of clinical parameters of the AV access and HD (hemodialysis) adequacy” based upon their position that “prospective surveillance of fistulas and grafts for hemodynamically significant stenosis, when combined with correction of the anatomic stenosis, may improve patency rates and may decrease the incidence of thrombosis.” The guidelines state that intra-access flow (a), static venous pressure measurements (VP), and duplex ultrasound are the “preferred” surveillance techniques for AVGs, and flow measurements, physical examination, and duplex ultrasound are “preferred” for AVFs. The guidelines recommend referral for further access imaging for persistent abnormalities in any of the monitoring or surveillance parameters, but they emphasize the importance of following trends rather than reacting to a single measurement. They define a static VP threshold for referral of 0.5 for both AVG and AVFs and a flow rate threshold of less than 600 mL/min for AVGs and less than 500 mL/min for AVFs. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Technical Aspects of Percutaneous Carotid Angioplasty and Stenting for Arteriosclerotic Disease In-Situ Treatment of Aortic Graft Infection with Prosthetic Grafts and Allografts Treatment of Acute Upper Extremity Venous Occlusion Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join Tags: Current Therapy in Vascular and Endovascular Surgery Aug 25, 2016 | Posted by admin in CARDIOLOGY | Comments Off on Role of Surveillance for Hemodialysis Access Full access? Get Clinical Tree
Role of Surveillance for Hemodialysis Access Catherine K. Chang and Thomas S. Huber The role of surveillance for permanent hemodialysis arteriovenous access, both autogenous (arteriovenous fistula [AVF]) and prosthetic (arteriovenous graft [AVG]), remains unresolved. Simplistically, clinical monitoring refers to the “examination and evaluation of vascular access by means of physical examination to detect physical signs that suggest the presence of dysfunction,” and surveillance refers to the “periodic evaluation of the vascular access by using tests that may involve special instrumentation and for which an abnormal test result suggests the presence of dysfunction” as defined by Work. Several of the national practice guidelines, most notably the National Kidney Foundation–Kidney Disease Outcome Quality Initiative (KDOQI), recommend surveillance as a supplement to clinical monitoring. Indeed, one of the two overarching goals of the KDOQI Guidelines is to detect access dysfunction before thrombosis. However, the level 1 evidence from randomized trials does not support routine surveillance and remediation for AVG, and there is a paucity of evidence for AVF. Notably, surveillance does not appear to improve access outcome in terms of functional patency, but it is significantly more expensive. The goal of identifying significant lesions destined to cause access thrombosis and correcting these lesions before any untoward event while avoiding unnecessary procedures is admirable, but it remains elusive. Justification Routine surveillance of AVG and AVF seems justified given their natural history and the costs and morbidity associated with failure. Notably, all types of permanent access have a limited life expectancy and ultimately fail or thrombose. The most common mode of failure for AVG is the development of a hemodynamically significant stenosis at the venous outflow (usually the anastomosis) secondary to intimal hyperplasia. Access thrombosis mandates attempts to remove the thrombus and restore the access and/or establish an alternative access, commonly a tunneled dialysis catheter. This care process and untoward series of events often mandates hospital admission and is associated with significant cost and inconvenience to the patient. Theoretically, identifying these significant outflow lesions and preemptive correction with either open or endovascular treatment could prolong access patency and avoid the sequence of adverse events associated with thrombosis. Surveillance is predicated on the assumptions that the various screening tools can identify a significant stenosis, that these “failing” accesses are destined to fail in the near future, that remedial intervention can prolong patency, and that the outcomes after remediation for the “failing” access are superior to those after a thrombosed access. Unfortunately, not all of these assumptions are necessarily true. The various surveillance techniques (detailed below) are quite good for identifying access stenoses, although the positive predictive value of these lesions in terms of near-term access thrombosis is somewhat limited. Additionally, preemptive angioplasty can stimulate or exacerbate the intimal hyperplastic process and thereby potentially accelerate the failure mode while incurring additional health care costs. Clinical Monitoring and Surveillance Techniques Clinical monitoring refers to the use of the patient’s history, physical examination, and access history to detect dysfunction; surveillance refers to the serial use of special tests or instrumentation. Access dysfunction on physical examination is suggested by the absence of a thrill (possible access thrombosis), the presence of a pulse (possible venous outflow stenosis), the presence of significant arm edema or venous collaterals (possible venous outflow stenosis) and diminished pulses within the AVG upon compression (possible arterial inflow problem). Prolonged bleeding at the cannulation sites after dialysis sessions suggests a venous outflow problem, whereas a decrease in the urea clearance with dialysis with a stable dialysis prescription also suggests dysfunction. Urea clearance is calculated by Kt/V, where K is clearance of urea calculated before and after dialysis, t is duration of dialysis, and V is urea distribution volume. The most common surveillance techniques include blood flow monitoring (a), static venous dialysis pressures (VP), and duplex ultrasound. These techniques are widely used throughout dialysis centers and are familiar to most dialysis care providers. Access blood flow is most commonly determined based upon the Fick principle and calculated by injecting ice-cold saline through the arterial side of the access and measuring the change in temperature at the venous side with the change in temperature corresponding to a specific flow rate. VP is measured by connecting a manometer to the arterial dialysis needle before starting the pump, and this value can be normalized to the systemic blood pressure to determine a static venous pressure ratio. Notably, both of these techniques (a and VP) are surrogates for stenoses within the access. Duplex ultrasound can be used to directly measure stenoses within the access or the anastomoses based upon the peak systolic velocities (PSV). Duplex ultrasound can also be used to calculate access flow by measuring the blood flow velocity and the cross-sectional area of the access. Although duplex ultrasound is familiar to vascular surgeons, the requisite equipment is not usually available in most dialysis centers, unlike the equipment needs for the a and VP measurements. Recommendations From National Guidelines The KDOQI guidelines recommend “an organized monitoring/surveillance approach with regular assessment of clinical parameters of the AV access and HD (hemodialysis) adequacy” based upon their position that “prospective surveillance of fistulas and grafts for hemodynamically significant stenosis, when combined with correction of the anatomic stenosis, may improve patency rates and may decrease the incidence of thrombosis.” The guidelines state that intra-access flow (a), static venous pressure measurements (VP), and duplex ultrasound are the “preferred” surveillance techniques for AVGs, and flow measurements, physical examination, and duplex ultrasound are “preferred” for AVFs. The guidelines recommend referral for further access imaging for persistent abnormalities in any of the monitoring or surveillance parameters, but they emphasize the importance of following trends rather than reacting to a single measurement. They define a static VP threshold for referral of 0.5 for both AVG and AVFs and a flow rate threshold of less than 600 mL/min for AVGs and less than 500 mL/min for AVFs. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Technical Aspects of Percutaneous Carotid Angioplasty and Stenting for Arteriosclerotic Disease In-Situ Treatment of Aortic Graft Infection with Prosthetic Grafts and Allografts Treatment of Acute Upper Extremity Venous Occlusion Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join
a), static venous dialysis pressures (VP), and duplex ultrasound. These techniques are widely used throughout dialysis centers and are familiar to most dialysis care providers. Access blood flow is most commonly determined based upon the Fick principle and calculated by injecting ice-cold saline through the arterial side of the access and measuring the change in temperature at the venous side with the change in temperature corresponding to a specific flow rate. VP is measured by connecting a manometer to the arterial dialysis needle before starting the pump, and this value can be normalized to the systemic blood pressure to determine a static venous pressure ratio. Notably, both of these techniques (
a and VP) are surrogates for stenoses within the access. Duplex ultrasound can be used to directly measure stenoses within the access or the anastomoses based upon the peak systolic velocities (PSV). Duplex ultrasound can also be used to calculate access flow by measuring the blood flow velocity and the cross-sectional area of the access. Although duplex ultrasound is familiar to vascular surgeons, the requisite equipment is not usually available in most dialysis centers, unlike the equipment needs for the 
a and VP measurements.
a), static venous pressure measurements (VP), and duplex ultrasound are the “preferred” surveillance techniques for AVGs, and flow measurements, physical examination, and duplex ultrasound are “preferred” for AVFs. The guidelines recommend referral for further access imaging for persistent abnormalities in any of the monitoring or surveillance parameters, but they emphasize the importance of following trends rather than reacting to a single measurement. They define a static VP threshold for referral of 0.5 for both AVG and AVFs and a flow rate threshold of less than 600 mL/min for AVGs and less than 500 mL/min for AVFs.
