Quantitative Estimation of Dietary Therapy in Hemodialysis Patients

Analysis Based on a Biological Model

Abstract

A quantitative understanding of dietary contents is undoubtedly important in hemodialysis patients. Until now no simple method to evaluate dietary contents has been available. We have developed a simple method to calculate the amounts of protein, sodium and potassium intake in hemodialysis patients, and compared Gotch's formula based on a urea kinetics model with our simple method.
[Method]
In 15 chronic dialysis patients in nutritionally steady state, urea clearance and the pre-, post-, dialytic body weight, BUN, serum [Na⁺] and [K⁺], and the same parameters bofore the next hemodialysis, were measured. From these values, the total body fluid volume (V) and urea generation rate (Gu) can be obtained based on urea kinetics (Gotch's formula).
On the other hand, V and Gu were also obtained by the simple method by assuming that dry weight is equal to normal V. From Gu (mg/mm), obtained either by means of Gotch' s formula ( I ) or the simple method ( I ), protein catabolic rate (PCR) can be estimated { (PCR (g/day) = (Gu +1.2) X 9.35}; and it was assumed that PCR is equal to the amount of protein intake. The amount of sodium intake was calculated as the change in the product of V and serum CNa⁺), by assuming that the absolute amount of intracellular effective osmotic cations was constant. The amount of potassium intake was calculated in the same manner.
[Results]
1. The postdialytic V and the amount of protein intake determined respectively by means of ( I ) and (II) were30.9 ± 1.6l (57 ± 2% body weight) and 32.2 ± 1.5/ (59 ± 2% body weight), and 66 ± 2g/day (1.3g/kg/day). and 69 ± 3g/day (1.3g/kg/day). Highly significant correlations were found between the two methods (p<0.001, p<0.001).
2. Highly significant correlations for the amounts of sodium and potassium intake were also found between the two methods (p<0.001, P<0.001). Sodium intake determined by methods ( I ) and (II) respectively was 334 ± 38mEq/interdialysis (187 ± 21mEq/day) and 328 ± 38mEq/interdialysis (183 ± 21mEq/day). Potassium intake was 73 ±4mEq/interdialysis (41 ± 2mEq/day), and 76 ± 4rnEq/interdialysis (42 ± 2mEq/day), respectively.
[Conclusion]
We have developed a simple method to calculate the amounts of protein, sodium, potassium intake in hemodialysis patients without carrying out a dietary investigation or measuring extracellular fluid volume and confirmed that it is useful. We believe that this method will prove to be a useful tool for assessing a nutritional state and examining the relation between protein intake and anemia or between sodium intake and blood pressure.