Application Of Bioelectrical Impedance Analysis To Estimate Nutritional Status Of Dialysis Patients

The First Part Background:The incidence of chronic kidney disease(CKD)in the world is gradually increasing,the disease is usually hidden initially,and many patients have entered a severe stage when they found it,and eventually developed into end-stage renal disease(ESRD).These patients have to use kidney replacement therapy like hemodialysis(HD),peritoneal dialysis(PD)or kidney transplantation.Currently,because of the shortage of kidney source,high transplantation costs and some patients’ intolerance to postoperative immunosuppressive drugs,dialysis is still the main therapy for ESRD patients.In recent years,with the improvement of dialysis technology,the prognosis of patients has been greatly improved,but compared with the general population,ESRD patients still have a high all-cause mortality and cardiovascular mortality.Many factors affect the prognosis of patients with HD and PD,such as dialysis adequacy,hydration status,and nutritional status.Recently,the impact of malnutrition on the prognosis of dialysis patients has been valued by clinicians increasingly.Many researches believe that dual-energy X-ray absorption(DEXA)is the gold standard for assessing nutritional status,but its cost is high,and it requires professional operation,so it is rarely used in clinical applications.According to the differences in the composition of various tissues of the human body,it exhibits different electrical conductivity.In recent years,the bioelectrical impedance analysis(BIA)has been applied to the evaluation of human body components.The bioelectrical impedance analysis takes the human body as a uniformly distributed cylindrical conductor,we can obtain the corresponding BIA variables,with applying a safe constant current to the human body.Then calculate the the content of each component of the human body,such as fat mass(FM),fat-free mass(FFM),total body water(TBW),combining with height and weight,and FFM reflects the nutritional status of the human body.Bioelectrical impedance analysis has the advantages of non-invasive,convenient,economic,and good repeatability.It is generally used abroad for nutritional assessment of healthy people and disease states,but there are few relevant studies in China,and the calculation formula of human body composition is generally based on foreign healthy people,so it may have poor accuracy for Chinese dialysis patients.Purpose:1.Compare the differences between the BIA method and the DEXA method on the nutritional assessment of hemodialysis patients and peritoneal dialysis patients in China,and explore the reasons for the differences.2.Compare the differences between the BIA method and the DEXA method for nutritional assessment of healthy volunteers in China,and explore the reasons for the differences.Methods:1.Recruited dialysis patients who were hospitalized in the Blood Purification Center of the First Affiliated Hospital of Zhengzhou University or the Nephrology Department of the First Affiliated Hospital of Zhengzhou University from September 2018 to August 2019.Inclusion criteria:patients with maintenance hemodialysis or peritoneal dialysis,dialysis age≥3 months;age≥18 years,<80 years;signed informed consent.Exclusion criteria:patients with cirrhosis or tumors;patients with heart implants or pacemakers;patients with amputation or paralysis;without informed consent.And recruited healthy volunteers from September 2019 to October 2019,inclusion criteria:age≥18 years old,<80 years old;sign informed consent.Exclusion criteria:history of major diseases such as kidney,liver,respiratory system,cardio-cerebrovascular system;history of hypertension;history of diabetes;amputation or paralysis;no informed consent.2.The subjects took a light diet the day before the test,and kept fasted,watered for at least 8 hours.Firstly,measured the height(cm)and weight(kg)with an ultrasonic height and weight scale,then measured the impedance data such as resistance and reactance using the Xitron 4200 bioelectrical impedance spectrum measuring instrument,and extracted the data of frequency at 50 kHz.Subsequently,the subjects were measured by a whole body dual-energy X-ray absorptiometer,and the content of each component of muscle,fat and bone minerals is analyzed by a professional dual-energy X-ray analyst.3.Screened the representative formulas of FFM for bioelectrical impedance evaluation,apply these formulas to the nutritional evaluation of dialysis patients and healthy volunteers in China.Independent sample t test,chi-square test,or non-parametric test were used to compare the differences between dialysis patients and healthy volunteers in population measurement,BIA-related variables,and laboratory test results.The measurement results were compared between groups,Pearson correlation analysis and Bland-Altman consistency test.P<0.05 thought the difference was statistically significant.Results:1.Baseline data characteristics:A total of 132 participants were recruited in this study,including 102 dialysis patients and 30 healthy volunteers.General information shows that there is no significant difference in male ratio,age,height,weight,and BMI between dialysis patients and healthy volunteers.However,the resistance,reactance,serum albumin,and hemoglobin of healthy volunteers are higher than those of dialysis patients.The impedance coefficient(H2/R50)and creatinine are lower than those of dialysis patients.2.From the published literature,selected the calculation formulas of bioelectrical impedance method to evaluate FFM:Kyle et al.formula,FFM-Kyle=-4.104＋(0.518×H2/R50)+(0.231×W)+(0.130×Xc50)+(4.229×sex)male=1,female＝0;Sun SS et al.formula,Male:FFM-ss=-10.68+(0.65×H2/R50)+(0.26×W)+(0.02×R50);Female:FFM-SS=-9.53+(0.69×H2/R50)+(0.17×W)+(0.02×R50)3.Evaluation results of FFM calculated by BIA formulas applied to Chinese population:The Kyle et al.formula and Sun SS et al.formula were applied to the dialysis patients and healthy volunteers in this study respectively.The results showed there were a few of differences in the assessment of FFM-Kyle method,FFM-ss method,and DEXA method,which applied to healthy volunteers.However,there were significant differences in the three methods,which applied to dialysis patients.The assessment of dialysis patients and healthy volunteers is consistent with the correlation coefficient between FFM-Kyle method and the DEXA method,but Bland-Altman analysis showed that the FFM-Kyle method has a greater bias in evaluating FFM for dialysis patients than healthy volunteers,and the consistency is worse than healthy volunteers;The correlation coefficient of FFM-ss method and the DEXA method for evaluating FFM of dialysis patients is lower than that of healthy volunteers.Bland-Altman analysis showed that the bias of FFM-ss method for evaluating dialysis patients is also greater than that of healthy volunteers.Moreover,the bias was increased compared with FFM-Kyle method.Conclusions:Compared with the measurement results of DEXA method,the evaluation results of foreign BIA formulas are different in the Chinese healthy population,and this difference was more obvious in dialysis patients.Maybe these BIA formulas can not eatimate the nutritional status of dialysis patients accurately.The Second PartBackground:From the first part of this study,it can be seen that the foreign BIA calculation formulas for FFM are not suitable for Chinese dialysis patients,but the accurate nutrition assessment for dialysis patients is very important.The incidence of malnutrition in dialysis patients is very high,and malnutrition is an independent risk factor for the prognosis of all-cause death and cardiovascular death,currently,there is no recognized FFM prediction formula for dialysis patients.Purpose:Taking the measurement results of dual-energy X-ray absorption method as the reference standard,and the FFM evaluation formula for Chinese dialysis patients was developed based on the anthropometrics and BIA-related variables of dialysis patients in this study.Methods:1.Objects:The hemodialysis patients and peritoneal dialysis patients in the first part of this study.2.Using a multiple linear regression analysis model,enter the gender,age,weight,resistance,reactance,impedance coefficient(H2/R50)and other variables that may be significative for predicting FFM.The variables that are significative for FFM prediction will be input into the prediction formula by highest correlation coefficient and the smallest standard error of estimated.Moreover,the dialysis patients were randomly divided into two groups,and a FFM prediction formula was developed according to the relevant variables respectively,then the formula was verified using double cross-validation technology.If the results of double cross-validation were similar,all dialysis patients were combined to develop a new BIA formula for calculating FFM of dialysis patients.P<0.05 thought the difference was statistically significant.Results:1.Baseline data characteristics:A total of 102 dialysis patients were recruited in this study.After being randomly divided into two groups,there were 51 people in both group,and there was no significant difference in male ratio,age,height,weight,BMI,electrical,resistance,H2/R50 between the two groups.2.Preliminary prediction formula:The prediction formula of dialysis population in group 1:FFM1=11.437+(0.246×H2/R50)+(0.342×W)+(3.865×sex)male=1,female=0;and the prediction formula of dialysis population in group 2:FFM2=-8.386+(0.462×H2/R50)+(0.251×W).The prediction results of Using FFM1 formula were:(50.05±11.25)kg,SEE=2.26 kg for group 1 population,(50.45±8.36)kg,SEE=2.65 kg for group 2 verification;The prediction results of Using FFM2 formula were:(50.64±7.68)kg,SEE=2.23 kg for group 2 population,(50.74±11.04)kg,SEE=2.97 kg for group 1 verification.The prediction results and cross-validation results of the two groups were similar.3.Final prediction formula:According to all dialysis patients in this study,the final prediction formula was developed:FFM-new=5.783+(0.313×H2/R50)+(0.311×W)+(3.047×sex)male=1,female=0,the decision coefficient is 0.939,SEE=2.42 kg.4.Compared with the Kyle et al.and Sun SS et al.formulas in the first part of this study,the FFM-new formula has the smallest SEE for FFM prediction in dialysis patients.Conclusions:We developed a new BIA formula for predicting FFM from Chinese dialysis patients,which may provide certain application value for clinical nutrition monitoring in Chinese dialysis patients.