A Model Of Quantifying Phosphate Removal In Conventional Hemodialysis Therapy

ObjectivesHyperphosphataemia is one of the most common complications of maintenance hemodialysis patients.Elevated serum phosphate has been implicated particularly in the development of cardiovascular structural and functional abnormalities. Hyperphosphatemia has long been recognized as motivation to metastatic calcification and disorders of parathyroid function.Furthermore,elevated serum phosphorous is associated with reduced survival in MHD patients.The phosphate balance is usually obtained by dietary phosphate control,conventional dialysis removal and phosphate binders.The quantification of these three factors will be very helpful in reducing the morbidity of MHD patients induced by hyperphosphatemia. The calculation of the amount of phosphate removed by once hemodialysis treatment are reported differently.The aim of this study was to develop a simple formula to estimate phosphate removal by once hemodialysis therapy and to provide the guidance for treatments of hyperphosphatemia in clinic.MethodsFifty four Patients enrolled in this study were selected from the hemodialysis center of Huashan hospital and divided into two groups.One group was designed to generate a phosphate removal model,then this model was further validated in another group of patients obtained in a new date-set.All patients underwent MHD stably,absent of residual renal function and easily to be communicated with.Blood samples were obtained on Wednesday or Thursday before the dialysis for phosphate concentration measurements.Meanwhile,the dialysate samples were also collected for phosphate detection at 5min,30min,1h,2h,3h,4h after the start of dialysis procedure.The ultrafiltrate volumes,dialysis time as well as blood flows were also recorded at the same time.A curve which described how the dialysate phosphate concentration changed during the dialysis process should be introduced here since the total amount of phosphate removal was estimated from the area under the curve and dialysate volume(AUC/v).The model was developed using the single factor analytic approach and correlation coefficient analytic approach considering phosphate removal as dependent variable and plasma phosphate concentrations,dialysis time,ultrafiltrate volumes,blood flows as predictor variables.The data of another group of patients were used to test the precision of the model by Pearson correlation coefficient method.Results The average phosphate concentrations of dialysate in the dialysis process were 0.35mmol/L at the 5min point,0.28 mmol/L at the 30min point,0.23 mmol/L at the 1h point,0.19 mmol/L at the 2h point,0.17 mmol/L at the 3h point and 0.14 mmol/L at the 4h point.Conventional dialysis removed 760mg phosphate during per four-hour treatment,50%of phosphate removal mass were between 600-900mg.The first hour of treatment removed 35%of the total mass,the second hour of treatment removed 25%of the total mass,the third hour of treatment removed 22%of the total mass and the fourth hour removed 19%of the total mass.After the single factor analytic approach and correlation coefficient analytic approach,the best model to describe the removal of phosphate as a function of treatment variables was found to be:total mass=0.65×Vol+0.03×Vel+0.097×T+5.16×C -16.4 where total mass is the predicted amount of phosphate removed per dialysis given in mmol/dialysis, ultrafiltrate volume(Vol)is given in L,blood flows(Vel) is given in ml/min,time(T) is given in min,C represents phosphate concentrations in plasma measured before dialysis in mmol/L.According to the parameter of each variable,we found that time was more effective than plasma phosphate concentrations,blood flows and ultrafiltrate volumes.To evaluate the equation showed above,the data of another part of population were used.Comparison of predicted to the calculated phosphate mass removal yielded a Pearson correlation coefficient of 0.94,which demonstrated that the model was highly validated.ConclusionsWe present another approach to quantify phosphate removal during conventional hemodialysis by a simple formula,which will provide us the further knowledge of phosphate balance in the body and facilitate the clinic choice of diet prescriptions and medications.