Study of arteriovenous fistula function by the temperature gradient method using the Twister™ device.

INTRODUCTION: Periodic blood flow (QA) measurement is the preferred way for arteriovenous fistula (AVF) surveillance in chronic hemodialysis (HD) patients. Objectives. 1) Assess the efficacy of the temperature gradient method (TGM) on the QA determinations using the Twister™ device and to compare the functional results with the Delta-H method. 2) Evaluate the effect of blood pressure on the AVF function. Patients and method. We measured the QA non invasively in 30 AVF (24 radial and 6 brachial; mean duration 53.4 +/- 78.5 months) during HD in 30 stable patients (mean age 59.9 +/- 14.1 years, males 60 %, females 40 %; mean time on HD 37.4 +/- 40.6 months, diabetic nephropathy 20 %) by the TGM, described and validated by Wijnen et al (Kidney Int 2007;72:736). The QA was calculated from the temperature values obtained by means of the blood temperature monitor (BTM), integrated into the Fresenius Medical Care 4008-S machine, at normal and reverse configurations of the HD blood lines, with no need for a thermal bolus. The Twister™ device was used for reversing the blood lines without the need to disconnect them from the AVF lines nor to stop the blood pump. The QA was measured within the first hour of two consecutive HD sessions (the values were averaged). The mean arterial pressure MAP (diastolic pressure + 1/3 pulse pressure) was calculated simultaneous with the QA. In addition, the AVF blood flow was also determined during the same week in all patients by the Delta-H method using the Crit-Line III Monitor (ABF-mode, HemaMetrics, USA) during HD (manually switching lines).

RESULTS: The mean QA was 1132.5 +/- 515.4 ml/min (range, 446-2233 ml/min). The mean coefficient of variation for duplicate QA measurements was 6.8 +/- 4.7 %; the MAP was not different when the reproducibility tests were performed (96.1 +/- 13.7 versus 96.6 +/- 12.8 mmHg, p = .72). No significant difference was found when comparing the mean QA between diabetic (n = 6, 966.4 +/- 340.7 ml/min) and nondiabetic (n = 24, 1174.4 +/- 548.3 ml/min) patients (p = .39). The mean QA was similar for patients with mean MAP < 100 mmHg (n = 18, 1101.0 +/- 552.7 ml/min) and for patients with mean MAP >_ 100 mmHg (n = 12, 1180.4 +/- 473.3 ml/min) (p = .69). No correlation was found between the mean QA and: age (r = 0.09, p = .62), time on HD (r = 0.06, p = .76), MAP (r = -0.21, p = .27), Kt/V index (r = 0.12, p = .51), distance between needles (r = - 0.17, p = .37) and AVF duration (r = -0.01, p = .96). The mean time required to measure QA with the TGM using the Twister™ device (5.9+/- 1.9 min) was significantly shorter compared with the Delta-H technique (26.8 +/- 1.9 min) or with the TGM (n = 35, 8.9 +/- 3.5 min, manually reversing lines) reported by Wijnen et al (Kidney Int 2007;72:736).) (for both comparisons, p < .001). The mean QA obtained by the TGM was not different when compared to mean ABF determined by the Delta-H method (1138.4 +/- 502.3 ml/min) (p=.83).The calculated values of AVF blood flow obtained by TGM were highly correlated with those determined by the Delta-H technique (r = 0.963, p < .001).

CONCLUSIONS: 1) The TGM is a valuable and reproducible indicator of QA during HD. 2) The Twister™ device is useful to reduce the time for QA measurement by the TGM. 3) The AVF blood flow values obtained by the TGM and the Delta-H technique correlated highly with each other. 4) It has been shown the lack of relationship between the AVF function and the patient's blood pressure.