Reconstruction of venous pressure in haemodialysis patients

Blood pressure instability is the most frequent complication of haemodialysis treatments, Individualised control of fluid removal that takes into account impaired physiological responses, is the key to improved stability. The cardiopulmonary reflex, the first line of defence to prevent hypotension caused by hypovolaemia, is mainly dependant on the central venous pressure (CVP). Until now only invasive methods are available for the measurement of CVP. A system for observing the venous pressure based on cardiac output, blood pressure and heart rate measurements combined with additional information about the patients heart condition (hypertrophy and contractility) was developed, The core of this system is an inverted non-pulsatile model of the heart which enables the reconstruction of the venous pressure. A cross cheek of the calculated venous pressure values by using relative blood volume measurements was applied to 12 different patients. The reconstructed venous pressure is linearly volume dependent and stays inside the known physiological range. It decreases during the dialysis treatment from very high values (12 mmHg) in the heavily fluid overloaded stage, towards near normal values (3 mmHg) when reaching dry weight. The results are reproducible and patient specific. The venous pressure can be used as a much better indicator for oncoming hypotension episodes then the mean arterial pressure