Dialysis needle hemodynamics in arterio-venous fistulae: a technical report.

BACKGROUND: Vascular access is the lifeline for end-stage renal disease patients needing hemodialysis treatment. For dialysis treatment two needles are placed into the vascular access. Few studies on needle hemodynamics have been published. METHODS: We investigated needle hemodynamics by means of Doppler ultrasonography, both in B-mode and in pulsed Doppler mode. RESULTS: Direct visualization of the needles, turbulence around the arterial needle and blood flow jet from the venous needle are presented. CONCLUSIONS: Ultrasound investigation of the hemodynamics of the dialysis needles is feasible. The extreme blood flow jet through the arterial needle was directed in all patients to the anterior vessel wall.

Comparison between two on-line reversed line position hemodialysis vascular access flow measurement techniques: saline dilution and thermodilution.

Periodical access flow measurements can predict the development and presence of vascular access flow-limiting stenosis and subsequent thrombosis. Access flow measurement has become a standard in vascular access care. Different techniques to measure access flow are available. The aim of this study was to compare an integrated access flow measurement device, based on thermodilution (Blood Temperature Monitor, BTM, Fresenius Medical Care, Bad Homburg, Germany), with the gold standard, the HD01 (Transonic Systems Inc., Ithaca, NY), whose technique is based on saline dilution. In 40 patients with end-stage renal disease, 40 vascular accesses were studied to determine the correlation between access flow measurements by both techniques. Reproducibility of access flow measurements by both techniques was assessed in 20 patients on a weekly interval.A total of 40 measurement series were performed. Average access flow measured with the saline technique and the thermodilution technique was 1053 (+/-495) ml/min and 1034 (+/-527) ml/min, respectively (p = ns) (n = 40). Correlation between access flow measurements by both techniques expressed in R was 0.79 (r = 0.89). Reproducibility of saline and thermodilution subsequent measurements with a weekly interval, expressed in relative difference (Delta xrel) was 13 (+/-11)% and 24 (+/-14)%, respectively (p < 0.01) (n = 20).BTM access flow measurements correlated well with the HD01 access flow measurements. However, the better reproducibility of HD01 and shorter measurement time compared with BTM access flow measurements should be considered when implementing access flow measurement to prevent vascular access failure.

Long-term arterial adaptation to high blood flow in the feeding artery of vascular access for hemodialysis.

PURPOSE: Arteries continuously respond to changing tissue demands and to hemodynamic conditions by altering their diameter and wall structure. The relatively slow dilatation of the feeding artery of vascular accesses continues at least two years after access creation with a continuous decrease in wall shear rate (WSR), which however, remains highly supra-physiological. The aim of this study was to test the hypothesis that after a longer time period the WSR returns to its baseline value. METHODS: In a cross-sectional study patients with arteriovenous fistulae were classified into four groups according to the access vintage (from new access to accesses older than six years). The WSR, cross-sectional area, and mean circumferential wall stress were measured and compared between groups. RESULTS: WSR decreased from group 1 (fistula < ninety days old) to group 4 (fistulae > six years old) with a concomitant increase in internal diameter. Patients with the oldest access had normal WSR values (compared to the contralateral brachial artery) and the largest internal diameter of the feeding artery. In diabetic patients the absolute values of WSR were higher and internal diameter was lower compared to nondiabetic patients. CONCLUSIONS: Brachial artery WSR is normal in accesses older than six years with an increased internal diameter and wall cross-sectional area as compared to "younger" accesses. This suggests a process of vascular remodeling with an increase in vascular wall mass and normalization of WSR to physiologic values at the price of increased mean cross-sectional wall stress.

Effect of online haemodialysis vascular access flow evaluation and pre-emptive intervention on the frequency of access thrombosis.

Introduction. Guidelines advocate surveillance of vascular access to reduce incidences of thrombosis. However, the value of online vascular access flow monitoring is still under debate. Methods. Through a systematic literature search, the effect of online access flow surveillance combined with pre-emptive intervention on thrombosis frequency is reviewed. Results. Due to methodological differences, adequate comparison of the individual study results is not possible. Moreover, the methodological quality of most of the included studies is not suitable for an adequate statistical analysis of the results. Conclusion. Until now, there is no conclusive evidence that online access flow evaluation has a significant effect on the rate of thrombosis. Future large-scale studies with adequate study design, adequate surveillance and intervention protocols and, possibly, better pre-emptive intervention alternative(s) are necessary.

Impact of a quality improvement programme based on vascular access flow monitoring on costs, access occlusion and access failure.

BACKGROUND: Vascular access thrombosis is a substantial source of morbidity in chronic haemodialysis patients. Periodical access flow measurements can predict the presence of vascular access stenosis and provide an opportunity for early intervention to prevent subsequent vascular access thrombosis. By this system of quality improvement, vascular access-related costs might be reduced. The aim of this study was to analyse the cost impact of a quality improvement programme based on periodic access flow measurements. METHODS: The number and costs of vascular access interventions (summary of angiography, percutaneous transluminal angioplasty, catheter placement, hospitalization days and costs for surgery) in the period 2001-2003 (quality improvement period; QIP, 218.6 patient-years observed) were retrospectively compared with a reference period (RP, 1996-1998, 214.4 patient-years observed) during which no access flow was measured. All access flow measurements were done on a regular base and interventions were performed according to the Kidney Disease Outcome Quality Initiative. RESULTS: Surgical thrombectomy procedures were significantly less during the QIP (0.25 +/- 0.57 events/patient-year) compared with RP (0.63 +/- 1.06 events/patient-year; P = 0.000), whereas access loss was not significantly different. During the QIP, 205 radiological interventions were performed (0.88 +/- 1.16 events/patient-year), and in the RP around 48 (0.33 +/- 0.65 events/patient-year; P = 0.000). Access-related costs tended to be lower during the QIP compared with the RP. The cost reduction appeared to be limited to patients with arteriovenous graft (AVG), in which access-related costs were significantly lower during the QIP (2360.95 euro +/- 2838.17 euro patient-year) compared with the RP (4003.96 euro +/- 3810.92 euro patient-year; P = 0.012), but not in patients with arteriovenous fistula (AVF). CONCLUSION: A quality improvement programme based on periodical access flow measurement reduced the number of acute vascular access failures due to thrombotic events and also significantly reduced health care costs in patients with AVG, but not in patients with AVF. The quality improvement programme had no effect on access survival.

The relation between vascular access flow and different types of vascular access with systemic hemodynamics in hemodialysis patients.

Access flow (Qa) has an important effect on systemic hemodynamics in dialysis patients. A Qa : cardiac output (CO) ratio higher than 0.3 is considered a risk factor for high-output cardiac failure. However, the effect of different types of vascular access in hemodialysis patients has not yet been studied. The aim of the present study was to assess the relationship between Qa and systemic hemodynamics and to compare systemic hemodynamics between patients with elbow/upperarm access with forearm access types. Qa, CO, cardiac index (CI), central blood volume (CBV), and peripheral vascular resistance (PVR) were studied by the saline dilution technique in 58 hemodialysis patients (18 with elbow/upperarm access; 40 with forearm access types). This article found that Qa was significantly and positively related to CO and CI, and inversely related to PVR. CBV, Qa, and presence of cardiac failure were independent determinants of CI. Qa and the Qa : CO ratio were significantly higher, and PVR significantly lower, in patients with elbow/upperarm access compared to patients with forearm access types. When patients with cardiac failure were excluded, CO and CI were also significantly higher in patients with elbow/upperarm access types. Eleven percent of patients with elbow/upperarm fistula had a Qa : CO ratio above 0.3. In conclusion, Qa is strongly related to systemic hemodynamics in dialysis patients. In patients without cardiac failure, CO and CI are significantly higher in patients with elbow/upperarm access compared to patients with forearm access types. However, only a small percentage of patients with elbow/upperarm fistulae appeared to be in the risk zone for development of high-output cardiac failure.