Initial Systolic Time Interval as a predictor of intradialytic hypotension

In the treatment of kidney failure by haemodialysis the normal function of the
kidneys is replaced by intermittent dialysis sessions. Although this artificial
process mimics the physiological process by the kidneys, the intermittent
character of the treatment creates unphysiological differences in
concentrations and in fluid shifts across the compartments. As a consequence,
sudden drops in blood pressure may occur during the dialysis sessions. A
diagnostic method that predicts the occurrence of these drops in blood pressure
will facilitate measures for the prevention of this occurrence and will
therefore serve the well-being of the patients and the adequacy and efficiency
of the treatment.

The objective of the study is to develop a non-invasive method to detect the
early signs of oncoming hypotension during haemodialysis in order to prevent
these from occurring

The study concerns the evaluation of a method of measurement by comparison with
other methods and with the occurrence of hypotensive periods. Fourty-five
patients who are treated at the haemodialysis unit of the VU University
medical center will be measured twice during standard dialysis treatments in
order to establish the reproducibility of the observations. The course of the
initial systolic time interval (ISTI) and the respiratory change (delta-ISTI)
will be recorded throughout the dialysis session These measures will be
compared with standard clinical parameters: the simultaneous non-invasively
recorded haematocrit value and manual blood pressure readings every 15 minutes,
and with calf-impedance and hydration status before haemodialysis.

An additional number of four electrodes, similar to ECG-electrodes, will be
attached to the patient in order to measure the ISTI parameters. (In another
measurement unit an additional number of two electrodes are applied to measure
the ECG separately from the other electrodes). A small electrical current of
0.3 mA rms will be transmitted through the thorax applied by the two outer
electrodes, having a frequency of 64 kHz. The frequency of this current is well
above the range of biological excitation and the amplitude is well below the
range of biological excitation or sensing. The method is safe to be used on the
haemodialysis unit. The method is non-invasive. Participating in the study
contains no burden and no risk for the subjects. The nature or duration of the
dialysis treatment will not change.
For comparison with the ISTI parameters, extracellular water and total body
water are measured before haemodialysis via four electrodes placed on the wrist
and ankle, using the commercially available Body Composition Monitor (BCM,
Fresenius Medical Care). Also for comparison with the ISTI parameters, calf
extracellular resistance is continuously measured throughout the haemodialysis
session using four electrodes, placed on the lateral aspect of the calf. Also
this equipment is commercially available (Hydra 4200, Xitron Technologies, San
Diego, CA, USA). Also these measurements contain no burden and no risk for the
subjects. The nature or duration of the dialysis treatment will not change. The
BCM-measurement before haemodialysis will take only a couple of minutes.