Leypoldt JK, Cheung AK, Kamerath CD, Steuer RR, Germain M,
Collins S, Braden G, et al
Vascular access blood flow rates measured from increases in
hematocrit when applying ultrafiltration
Am Soc Nephrol
J Am Soc Nephrol (abstract)
(Sep) 7:1412 1996
Indicator dilution methods have recently been successfully used to measure
access blood flow. This technique requires reversing the blood lines and
injecting an indicator, usually a small bolus of normal saline, into the
venous return line followed by detecting the resulting dilution of the
blood in the arterial line. Dilution of the dialyzer arterial blood by the
saline bolus has been measured both by changes in ultrasound velocity and
by light absorption. In this study, instead of a bolus injection, the
concentration effect caused by ultrafiltration was used as a continuous
indicator of flow. The concentration effect was detected by light
absorbance and scattering using the Crit-Line (trademark) instrument. The
small change in hematocrit caused by ultrafiltration allowed more accurate
measurements at low access flow rates but at higher flow rates large errors
were encountered.
Comment: Perhaps if higher ultrafiltration rates could be achieved
and tolerated for brief intervals, this method might have clinical value
and eliminate the necessity for saline injection. However, the method
depends heavily on an accurate measurement of the ultrafiltration rate as
well as achieving a significant hemoconcentration of the blood as it passes
through the dialyzer. The saline injection method allows more accurate
measurement at all access flow rates and is not limited by ultrafiltration
or a high preexisting hematocrit.
(Thomas A. Depner, M.D., University of California at Davis)
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Am Soc Nephrol
Basic hemodialysis :
Vascular Access: graft/fistula