Assessing the Nutritional Status of Patients with End-Stage Renal Disease

Physiological monitoring and control in hemodialysis: state of the art and outlook

Medical devices for monitoring and feedback control of physiological parameters of the dialysis patient were introduced in the early 1990s. They have a wide range of applications, aiming at increasing the safety and ensuring the efficiency of the treatment, and at an improved restoration of physiological conditions, leading to an overall reduction in morbidity and mortality. Such devices include sensors for the measurement of temperature, optical parameters and sound speed in blood, and electrical characteristics of the human body, and other parameters. Essential for the development of these devices is a detailed understanding of the pathophysiological background of a therapeutical problem. There is still a large potential to introduce new devices for further therapy improvement and automation. Also, the size of the hemodialysis market appears attractive; however, a new product has to meet several specific requirements in order to also become commercially successful. This review describes the therapeutic and technical principles of several available devices, reports on concepts for possible future devices, and presents a short overview on the market environment.

Prealbumin, mortality, and cause-specific hospitalization in hemodialysis patients

BACKGROUND

Prealbumin (transthyretin) is a hepatic secretory protein thought to be important in the evaluation of nutritional deficiency and nutrition support. Prior studies have suggested that the serum prealbumin concentration is independently associated with mortality in hemodialysis patients, even with adjustment for serum albumin and other nutritional parameters.

METHODS

To determine whether prealbumin was independently associated with mortality and morbidity (cause-specific hospitalization) in hemodialysis patients, we analyzed data on 7815 hemodialysis patients with at least one determination of serum prealbumin during the last three months of 1997. Unadjusted, case mix-adjusted, and multivariable-adjusted relative risks of death were calculated for categories of serum prealbumin using proportional hazards regression. We also determined whether the prealbumin concentration was associated with all-cause, cardiovascular, infection-related, and vascular access-related hospitalization.

RESULTS

The relative risk (RR) of death was inversely related to the serum prealbumin concentration. Relative to prealbumin > or =40 mg/dL, the adjusted RRs of death were 2.41, 1.85, 1.49, and 1.23 for prealbumin <15, 15-20, 20-25, and 25-30 mg/dL, respectively. The adjusted RRs of hospitalization due to infection were 2.97, 1.95, 1.81, and 1.61 for prealbumin <15, 15-20, 20-25, and 25-30 mg/dL, respectively. The adjusted RRs of vascular access-related hospitalization were 0.48, 0.52, 0.58, and 0.71 for prealbumin <15, 15-20, 20-25, and 25-30 mg/dL, respectively. While serum albumin was strongly associated with mortality and all-cause hospitalization, it was not associated with hospitalization due to infection, and lower levels were associated with higher rather than lower rates of vascular access-related hospitalization.

CONCLUSION

In hemodialysis patients, lower prealbumin concentrations were associated with mortality and hospitalization due to infection, independent of serum albumin and other clinical characteristics. Higher prealbumin concentrations were associated with vascular access-related hospitalization. In light of these findings, more intensive study into the determinants and biological actions of prealbumin (transthyretin) in end-stage renal disease is warranted.

Prealbumin is as important as albumin in the nutritional assessment of hemodialysis patients

BACKGROUND

Although serum prealbumin is considered a valid indicator of nutritional status in hemodialysis patients, there is relatively little evidence that its determination is of major prognostic significance. In this study, we aimed to determine the independent association of serum prealbumin with survival in hemodialysis patients, after adjusting for serum albumin and other indicators of protein energy nutritional status.

METHODS

Serum prealbumin was measured in more than 1600 maintenance hemodialysis patients. We determined the correlations among prealbumin and other indicators of nutritional status, including serum albumin, and bioimpedance-derived indicators of body composition. The relationship between serum prealbumin and survival was determined using proportional hazards regression.

RESULTS

The serum albumin was directly correlated with the serum prealbumin (r = 0.47, P < 0.0001), but still explained <25% of the variability in prealbumin. Prealbumin was inversely related to mortality, with a relative risk reduction of 6% per 1 mg/dL increase in prealbumin, even after adjusting for case mix, serum albumin, and other nutritional indicators. The increase in risk with lower serum prealbumin concentrations was observed whether the serum albumin was high or low.

CONCLUSION

In hemodialysis patients, the serum prealbumin provides prognostic value independent of the serum albumin and other established predictors of mortality in this population.

Amino acid losses during hemodialysis with polyacrylonitrile membranes: effect of intradialytic amino acid supplementation on plasma amino acid concentrations and nutritional variables in nondiabetic patients

BACKGROUND

Malnutrition is highly prevalent in hemodialysis patients. Amino acid (AA) losses during the dialysis procedure may be a contributing factor.

OBJECTIVES

The objectives of this study were 1) to prospectively evaluate AA losses and their effect on plasma AA concentrations during dialysis with polyacrylonitrile at baseline and after administration of AAs by intradialysis and 2) to investigate the effects of intradialytic AA supplementation on nutritional status.

DESIGN

Seventeen stable patients without diabetes who were receiving hemodialysis were studied. In the first phase, AA losses were evaluated over 2 wk in 10 patients randomly assigned to receive AA supplementation. AA losses were analyzed during the first week without supplementation and during the second week with AA administration. In the second phase, the patients' nutritional status was investigated after 3 mo of AA supplementation and was compared with those in 7 patients not receiving AAs.

RESULTS

Mean +/- SD) AA losses during a 4-h dialysis session were 12 +/- 2 g; there was a significant decrease in plasma AA concentrations (386 +/- 298 micromol/L for essential and 902 +/- 735 micromol/L for nonessential AAs). After administration of AAs, the losses increased to 28 +/- 4 g. However, this procedure produced a positive net balance of AAs (10.6 +/- 5.6 g for total AAs), preventing a reduction in plasma concentrations. After 3 mo of AA administration, there was a significant increase in protein catabolic rate and serum albumin and transferrin. This improvement occurred without any change in the dialysis dose, ruling out the possibility that an increase in dialysis efficiency played a role.

CONCLUSIONS

Intradialysis adequately provides AA supplements, prevents reductions in plasma AA concentrations, and favorably affects the nutritional status of patients receiving hemodialysis.

Relating protein intake to nutritional status in haemodialysis patients: how to normalize the protein equivalent of total nitrogen appearance (PNA)?

BACKGROUND

The protein equivalent of total nitrogen appearance (PNA) is assumed to be a reliable estimate of dietary protein intake in haemodialysis patients. Protein requirements are related to body size. In order to standardize PNA to individual differences in body size, PNA is normalized to various terms related to the patient's body weight. It is not clear which is the most appropriate method to normalize PNA.

METHODS

We calculated five commonly used variants of normalized PNA and related them to indices of nutritional status in 57 stable chronic haemodialysis patients, 57 +/- 15 (mean +/- SD) years of age. PNA, determined by direct dialysate quantification, was normalized to actual post-dialysis dry body weight (DBW), normal body weight (DBWnormal), lean body mass (LBM), normal lean body mass (LBMnormal), and 'normalized' body weight (N). Nutritional status was assessed using an index of nutrition composed of anthropometry derived parameters and plasma albumin concentration.

RESULTS

PNA(DBW) (0.85 +/- 0.14 g/kg/d) tended to be higher than PNA(DBWnormal) (0.81 +/- 0.14 g/kg/d). PNA(LBM) (1.17 +/- 0.19 g/kg/d) did not differ from PNA(LBMnormal) (1.19 +/- 0.21 g/kg/d). PNA(N) (1.06 +/- 0.14 g/kg/d) was significantly higher than PNA(DBW) and PNA(DBWnormal), but lower than PNA(LBM) and PNA(LBMnormal). Actual PNA (61 +/- 13 g/d) correlated significantly with DBW (r=0.52) and LBM (r=0.63) indicating that large patients eat more protein. Interestingly, actual PNA correlated with plasma albumin (r=0.33) and with the overall index of nutrition (r=0.27) as well. PNA(DBW) correlated negatively with relative DBW (r=-0.32), expressed as a percentage of normal values, indicating that PNA(DBW) is relatively high in underweight patients. In contrast, PNA(DBWnormal) correlated positively with all nutritional parameters as well as with the overall index of nutrition (r=0.33). PNAN and PNA(LBM) did not correlate with the nutritional status, but PNA(LBMnormal) correlated positively with relative DBW (r=0.50) and with overall nutritional status (r=0.34). PNA(DBWnormal) and PNA(LBMnormal) in well-nourished patients showed overlap with the values in patients with evident malnutrition, despite the positive correlation of the normalized PNA values with nutritional status.

CONCLUSIONS

Normalizing PNA by DBWnormal and LBMnormal appeared to be the most appropriate method to standardize protein intake in haemodialysis patients. Since actual PNA is the purest estimate of protein intake that correlated with nutritional status, we recommend to evaluate actual PNA as well in studies that relate protein intake to patient outcome.