A new method of continuous haemoglobinometric measurement of blood volume during haemodialysis.

Since the total amount of haemoglobin in blood is constant during haemodialysis, haemoglobin concentration reflects changes of blood volume caused by ultrafiltration and solute transport. Haemoglobin concentration therefore could serve as a control parameter for ultrafiltration. Blood is taken continuously from the arterial blood line at the very small rate of 0.1 ml/h and diluted at a constant ratio of 1/200 by a sterile solution 0.05 per cent NH3. By the diluting medium the erythrocytes are haemolysed and the haemoglobin is transformed into oxyhaemoglobin. The haemoglobin concentration is determined measuring the absorbance at 415 nm. The error in the measurement of the haemoglobin concentration is less than 3 per cent. The method was tested in vivo during 10 haemodialysis treatments of five patients. Haemoglobin concentration appeared to reflect the well-known effects of ultrafiltration, of food intake and changes of position (sitting, lying). If the body weight approached the suspected dry weight, haemoglobin concentration increased more rapidly. During high ultrafiltration rates (1.0 litre/h) and sudden changes of ultrafiltration rate haemoglobin concentration seemed to be unevenly distributed in the vascular space. If haemoglobin concentration indeed reflects changes in blood volume the method can be used to study the relationship between blood volume and blood pressure in haemodialysis therapy and to control ultrafiltration.