VALIDATION IN THE SHEEP OF AN ULTRASOUND VELOCITY DILUTION TECHNIQUE FOR HEMODIALYSIS GRAFT FLOW

Background. A simple, rapid, inexpensive method for measuring the flow in a patient's vascular access would permit routine monitoring during haemodialysis, and hence provide information of access graft deterior ation sufficiently early to increase the success of minimally invasive remedial procedures. This paper reports the validation of such a meth od in animals. Methods. A PTFE graft was implanted in sheep between th e carotid artery and the jugular vein. While the sheep was under gener al anaesthesia and on an haemodialysis circuit, ultrasound velocity in its blood was perturbed by the injection of a 5-10 ml bolus of isoton ic NaCl. The pump tubing flow was measured by a transit-time blood how meter. This how was combined with the areas of perturbation generated by the injection before and after mixing in the access flow to estima te graft flow. The calculated graft flow was compared to flow measured directly by a transit-time probe on the same carotid artery. Results. Over a 10 fold range, 120-1260 ml/min, graft flow measured by ultraso und velocity dilution agreed well with graft flow measured directly wi th a scatter of 76 ml/min about the regression line. Conclusion. Ultra sound velocity dilution provides a method for measuring how in the gra ft accurate enough for clinical evaluation of patients on dialysis.