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Saudi Journal of Kidney Diseases and Transplantation
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ORIGINAL ARTICLE  
Year : 2011  |  Volume : 22  |  Issue : 6  |  Page : 1149-1154
The deleterious effect of metabolic acidosis on nutritional status of hemodialysis patients


1 Division of Nephrology, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran
2 Division of Nephrology, Hashemi Nejad Hospital, Tehran University of Medical Sciences, Tehran, Iran

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Date of Web Publication8-Nov-2011
 

   Abstract 

One of the main causes of protein-energy malnutrition in patients on maintenance hemodialysis (MHD) is metabolic acidosis. The aim of this study was to evaluate the effect of metabolic acidosis on nutritional status in a group of MHD patients with adequately delivered dialysis treatment. Of 165 eligible anuric MHD outpatients with Kt/V ≥ 1 and no underlying inflammatory diseases, 47 subjects were enrolled. In order to evaluate the effect of different parameters on serum albumin, we measured the pre-dialysis serum albumin, blood pH, serum bicarbonate (HCO 3‾ ), Kt/V, normalized protein catabolic rate (nPCR) and body mass index (BMI) in these patients. The mean age of the study patients was 55 ± 13.8 years; there were 22 females and six diabetics. The average Kt/V was 1.22 ± 0.16, pH was 7.40 ± 0.15, serum HCO 3‾ was 23.18 ± 2.38 mEq/L, serum albumin was 4.03 ± 0.56 g/dL, nPCR was 1.00 ± 0.16 g/kg/day, post-dialysis body weight was 58.50 ± 11.50 kg and BMI was 23.47 ± 2.70 kg/m 2 . There was a statistically significant direct correlation between serum albumin and BMI (r = 0.415, P = 0.004), and between serum albumin and serum HCO 3 (r = 0.341, P = 0.019). On multiple regression analysis, the predictors of serum albumin were serum HCO3‾ and BMI (direct effect) and nPCR (inverse effect). In 17 patients on MHD with serum HCO3‾ <22 mEq/L, there was a significant inverse correlation between HCO 3 and nPCR (r = 0.492, P = 0.045), and these patients had significantly lower serum albumin compared with patients with serum HCO3‾ >22 mEq/L (P = 0.046). These data demonstrate that patients on MHD with metabolic acidosis had a lower serum albumin concentration despite adequate dialysis treatment. The inverse effect of nPCR on serum albumin concentration in acidotic MHD patients may be due to hypercatabolism in the setting of metabolic acidosis, leading to deleterious effects on the nutritional status of patients on MHD.

How to cite this article:
Soleymanian T, Ghods A. The deleterious effect of metabolic acidosis on nutritional status of hemodialysis patients. Saudi J Kidney Dis Transpl 2011;22:1149-54

How to cite this URL:
Soleymanian T, Ghods A. The deleterious effect of metabolic acidosis on nutritional status of hemodialysis patients. Saudi J Kidney Dis Transpl [serial online] 2011 [cited 2019 Dec 5];22:1149-54. Available from: http://www.sjkdt.org/text.asp?2011/22/6/1149/87219

   Introduction Top


Malnutrition occurs in a large number of patients on maintenance hemodialysis (MHD) and is associated with increased morbidity and mortality. [1],[2] Low serum albumin is a strong predictor of death in dialysis patients. [3] Many renal failure patients have progressive wasting and malnutrition despite apparently adequate dialysis, [4] and there is progressive decline of lean body mass in patients with end-stage renal disease (ESRD), [5] indicating on-going catabolism of muscle proteins. Studies have indicated that one of the major causes of malnutrition in these patients is systemic acidosis. [6],[7],[8],[9],[10],[11] Metabolic acidosis, by causing both malnutrition [12],[13],[14] and inflammation, [15],[16] may play a major role in increased mortality of chronic kidney disease (CKD) patients. The aim of this study was to evaluate the role of low serum bicarbonate on serum albumin concentration and normalized protein catabolic rate (nPCR) in a group of well-dialyzed MHD patients.


   Subjects and Methods Top


One-hundred and sixty-five of the in-center HD patients on regular MHD at the Division of Nephrology, Hashemi Nejad Hospital, Tehran, Iran, were studied. Forty-seven of these anuric patients, including 25 males and 22 females, were included in the study. All study patients had two consecutive mean Kt/V ≥1, no cachexia [body mass index (BMI) <19], neoplasia, systemic disease or recent acute illnesses. All the patients were dialyzed by acetate HD thrice weekly, each session lasting at least 240 minutes, and with appropriate polysulfone membrane, blood flow rate and dialysate flow rate. The underlying renal disease was diabetes in six patients, autosomal-dominant polycystic kidney disease in five patients and chronic hypertension and unknown nephropathy in 32 patients.

Samples for blood urea nitrogen (BUN) were drawn from the arterial side of the arteriovenous fistula at the beginning and end of a dialysis session and at the start of the next dialysis session. The duration of each dialysis session, duration of time between dialysis sessions and inter-dialysis weight gain were recorded. Blood for laboratory data were drawn from the arterial side of the AV fistula at the start of the dialysis session.

In order to evaluate the role of different parameters on patients' serum albumin concentration, as expression of nutritional status, arterial pH, serum bicarbonate (HCO3 - ), serum albumin (Alb), KT/V, nPCR and BMI were measured. All data are expressed as mean ± SD. Pearson correlation, linear regression analysis and student's t test were used for statistical evaluation.


   Results Top


The mean age of the study patients was 55 ± 13.8 years. Other data are mentioned in [Table 1]. There was significant direct correlation between serum albumin and BMI (P = 0.004, r = 0.415) [Figure 1] and significant direct correlation between serum albumin and serum bicarbonate (P = 0.019, r: 0 = 341) [Figure 2]. There was no significant correlation between serum albumin and KT/V, age or sex.
Figure 1: Correlation between serum albumin concentration and body mass index.

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Figure 2: Correlation between serum albumin concentration and serum bicarbonate levels.

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Table 1: Descriptive statistics of 47 patients on maintenance hemodialysis.

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Multiple regression analysis of the data [Table 2] indicated that the predictors of serum albumin concentration are serum bicarbonate concentration and BMI (direct effect) and nPCR (inverse effect).
Table 2: Multivariate analysis of the data obtained.

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In patients (17 cases) with serum HCO3 - ≤22 mEq/L, there was a significant inverse correlation between serum HCO3 - and nPCR (P = 0.045, r = 0.492) [Figure 3]. Patients with serum HCO3 - concentration ≤22 mEq/L showed significantly lower serum albumin concentration compared with patients with serum HCO3 - >22 mEq/L (P = 0 0.046).
Figure 3: Correlation between serum bicarbonate levels and normalized protein catabolic rate.

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   Discussion Top


There is on-going catabolism of muscle proteins in dialysis patients. [5] Continuing catabolism in the presence of adequate dialysis [4] implies that some other factors contribute to the malnutrition of patients on HD. Low serum albumin concentration is one of the most sensitive indices of malnutrition in HD patients, [17],[18] and evidence indicates that metabolic acidosis contributes to the low level of serum albumin in dialysis patients. [8],[10],[11],[19],[20] Also, there is an association between low serum albumin, as expression of malnutrition, and mortality in HD patients. [21],[22],[23]

Several mechanisms contribute to this. They include increased protein catabolism [24],[25] through augmentation of the transcription of genes encoding proteins of the ATP-dependent ubiquitin-proteasome pathway, [26] and also directly stimulating oxidative catabolism through activation of branched-chain α-keto acid dehydrogenase;[27] decreased protein synthesis; insulin resistance; decrease in serum leptin level; and inflammation. [28],[29],[30],[31],[32],[33] Moreover, several studies have shown that correction of metabolic acidosis causes an improvement in nutritional status in HD patients. [34],[35],[36]

The effect of metabolic acidosis on nutritional status and survival of HD patients is a controversial issue. While some studies have shown that mild to moderate metabolic acidosis in HD patients indicates a higher protein intake and better nutritional status and survival, [15],[37],[38],[39],[40],[41],[42],[43] others believe that metabolic acidosis in CKD and dialysis patients, through catabolism of endogenous protein and inflammation, induce protein-energy malnutrition and poor outcome.7, 8, 20, 32, 34, 44

In a recent study of 56,385 maintenance HD patients across the United States by Wu et al, [45] the authors reported that after adjusting for case-mix and nine markers of malnutrition inflammation complex syndrome (MICS), patients with HCO3 - values >22 mEq/L had a lower death risk.

In this study, we analyzed the effects of different parameters on serum albumin concentration. Patients with adequate dialysis prescription were enrolled; therefore, dose of dialysis had no effect on serum albumin concentration. Significant direct correlation between serum albumin concentration and BMI indicated that serum albumin is a perfect marker of nutritional status of MHD patients. According to multiple regression analysis of data, serum HCO3 - concentration and BMI showed positive effect on serum albumin concentration, and nPCR had a negative effect. As the variations in nPCR and serum albumin concentration are in the opposite direction, it seems extremely unlikely that a change in the dietary intake could be an explanation for the observed changes. The direct effect of serum HCO3 - and inverse effect of nPCR on serum albumin is consistent with the concept that acidosis in HD patients with adequate dialysis prescription probably is a result of catabolism and breakdown of the endogenous proteins, leading to high nPCR in these patients.

In conclusion, we found that patients on MHD with metabolic acidosis had lower serum albumin concentration despite adequate dialysis treatment. There was an inverse effect of nPCR on serum albumin concentration in acidotic MHD patients, indicating that metabolic acidosis, probably by augmenting catabolism of endogenous protein, exerts a deleterious effect on nutritional status of MHD patients.

 
   References Top

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Correspondence Address:
Tayebeh Soleymanian
Division of Nephrology, Shariati Hospital, Tehran University of Medical Sciences, Tehran
Iran
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PMID: 22089772

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