The assessment of a rteriovenous fistulae created for haemodialysis from pressure and thermal dilution measurements

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Abstract
A technique for the assessment of arteriovenous fistulae created for hemodialysis was described. This involves the measurement of intrafistula pressures and useful fistula flow (UFF). The latter was defined as the maximum blood flow available for twin needle hemodialysis without recirculation and without unacceptable pressures in the arterial (A) and venous (V) lines. The test circuit resembles that used for conventional hemodialysis except there is A and V line pressure and temperature monitoring and no dialyzer. Intrafistula pressures are measured at the time of insertion of the fistula needles. A and V line pressures are then recorded as the extracorporeal blood flow rate is increased in increments from 0 to 500 ml/min. A check for recirculation is made at each flow rate. A bolus of cold saline causes a momentary decrease in A line temperature when recirculation is present; when there is no recirculation, A line temperature remains constant. The blood flow rate at which recirculation is first detected will be above the useful fistula flow by definition. This technique allows identification of those patients who obtain high blood flows at the expense of recirculation and thus dialyze inefficiently. Combined pressure and thermal dilution measurements yield valuable information in the investigation of failing or problem fistulae.

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