Validation in the sheep of an ultrasound velocity dilution technique for haemodialysis graft flow

BACKGROUND: A simple, rapid, inexpensive method for measuring the flow in apatient's vascular access would permit routine monitoring duringhaemodialysis, and hence provide information of access graft deteriorationsufficiently early to increase the success of minimally invasive remedialprocedures. This paper reports the validation of such a method in animals.METHODS: A PTFE graft was implanted in sheep between the carotid artery andthe jugular vein. While the sheep was under general anaesthesia and on anhaemodialysis circuit, ultrasound velocity in its blood was perturbed bythe injection of a 5-10 ml bolus of isotonic NaCl. The pump tubing flow wasmeasured by a transit-time blood flow meter. This flow was combined withthe areas of perturbation generated by the injection before and aftermixing in the access flow to estimate graft flow. The calculated graft flowwas compared to flow measured directly by a transit-time probe on the samecarotid artery. RESULTS: Over a 10-fold range, 120-1260 ml/min, graft flowmeasured by ultrasound velocity dilution agreed well with graft flowmeasured directly with a scatter of 76 ml/min about the regression line.CONCLUSION: Ultrasound velocity dilution provides a method for measuringflow in the graft accurate enough for clinical evaluation of patients ondialysis.