Extracellular volume (ECV) of arms, trunk, and legs determined from segmental bioimpedance data in 11 healthy men (31.6 +/- 7 yr) obtained at the end of a 30-min equilibration phase in the supine body position was compared with ECV determined from whole body measurements (ECVWB). ECV was calculated from extracellular resistance (RECV) identified from the bioimpedance spectrum for a range of 10 frequencies. Whole body RECV (527.6 +/- 55.6 Omega) was equal to the sum of RECV in the arms, trunk, and legs (241.6 +/- 36. 3, 49.2 +/- 5.1, and 236.3 +/- 25.5 Omega, respectively). The sum of equilibrated ECV in arms (1.31 +/- 0.25 liters), trunk (10.08 +/- 1.65 liters), and legs (2.80 +/- 0.82 liters) was smaller than ECVWB (20.90 +/- 2.59 liters). In six subjects who changed from a standing to a supine body position, ECV decreased in arms (-2.59 +/- 2.51%, P = NS) and legs (-10.96 +/- 3.02%, P < 0.05) but increased in the trunk (+4.2 +/- 3.2%, P < 0.05). ECVWB also decreased (-4.98 +/- 1. 41%, P < 0.05). However, the sum of segmental extracellular volumes remained unchanged (-0.06 +/- 0.07%, P = NS). The sum of segmental ECVs is not sensitive to changes in body position, which otherwise interferes with the estimation of ECV in bioimpedance analysis when ECVWB is used.

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Background/Aim: Recirculation measured by thermodilution includes effects caused by access and cardiopulmonary recirculation. The aims of this study were to illustrate the accuracy of thermodilution in measurement of hemodialysis recirculation and also to identify a sensitive and specific threshold to detect access recirculation. Methods: 110 studies were performed in 19 patients. Recirculation obtained directly by the blood temperature monitor (BTM) was compared to that calculated from access blood flow, pump blood flow, and cardiac output determined by ultrasound dilution using the hemodialysis monitor (HDM). Results: A highly significant linear correlation was obtained between repeated BTM recirculation measurements (R_{BTM, 2} = 0.99·R_{BTM, 1} – 0.22%, r² = 0.99). There were no significant differences between repeated BTM recirculation measurements with correct placement (11.4 ± 7.1 vs. 10.9 ± 7.4%, p = NS) or reversed placement (30.0 ± 15.6 vs. 30.2 ± 15.9%, p = NS) of blood lines. A strong linear relationship was obtained between the recirculation determined by thermodilution and the recirculation calculated from HDM measurements (R_calc = 0.98·R_BTM – 1.49%, r² = 0.95). The mean recirculation obtained by BTM was not significantly different from the recirculation calculated by HDM with correct placement (9.5 ± 2.2 vs. 8.6 ± 2.5%, p = NS) or with reversed placement (25.4 ± 7.8 vs. 23.8 ± 7.7%, p = NS) of blood lines. When a recirculation greater than 15% measured by the BTM was considered as the threshold at which true access recirculation occurred, sensitivity and specificity of the thermodilution method to detect access recirculation were 93 and 98%, respectively. Conclusions: Recirculation measurements made by the BTM are accurate and precise. Even though BTM thermodilution includes effects of cardiopulmonary recirculation, so that low levels of access recirculation might not be detected, a BTM recirculation >15% represents a highly significant access recirculation.

Native fistulae are assumed to remain patent even with low access flows and are likely to cause access recirculation in high efficiency treatments done with high extracorporeal blood flows. We tested whether frequent recirculation measurements could be used to identify fistulae at risk to fail because of low access flow. High efficiency hemodialysis was delivered by 2008H machines equipped with blood temperature monitors (BTM) to measure recirculation within the first hour of every hemodialysis treatment. Access flow was measured when two consecutive BTM recirculation measurements exceeded a threshold of 15%. If access flow was < 500 ml/min, patients were referred for fistula revision. Eighty patients with native AV fistulae were studied for a period of 6 months. Nine of 11 interventions performed during the whole observation period were triggered by a BTM recirculation above the threshold. Two fistulae thrombosed in spite of a BTM recirculation below the threshold. One fistula with a BTM recirculation above the threshold had an access flow of 1,550 ml/min and was not referred for revision. BTM recirculation to detect fistulae for revision is sensitive (81.8%) and specific (98.6%) in the presence of cardiopulmonary recirculation and can be done with minimum intervention and without loss of efficient treatment time.

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