Nutritional evaluation of hemodialysis patients using an impedance index

Malnutrition is frequent in chronic hemodialysis patients. Standard nutritional evaluation is based on anthropometric, laboratory and clinical parameters from which a malnutrition index can be derived. Bioelectrical impedance, more rapid and practical, can be used to evaluate body composition. The goals of our study were to: 1) evaluate the incidence of and some of the factors associated with malnutrition in hemodialysis patients; 2) assess the accuracy of a scoring system based on impedance results to identify malnourished patients as defined by the malnutrition index (based on anthropometric, laboratory and clinical parameters). Standard nutritional evaluation and impedance measurements were performed on 33 chronic hemodialysis patients. Using malnutrition index, 18 patients (54%) were severely or moderately malnourished. Dietary assessment revealed a high proportion of patients with insufficient protein or calorie intake. By multiple regression analysis, the only factor significantly correlated with the malnutrition index was calorie intake (r = 0.44); age, sex, years on hemodialysis, protein intake were not. Results obtained with impedance were strongly correlated to those obtained with anthropometry for the proportion of fat mass (r = 0.72) and lean body mass (r = 0.71) and for the malnutrition index (r = 0.78). The sensitivity of the scoring system based on impedance to identify moderately or severely malnourished patients as determined by standard nutritional evaluation was 100% and its specificity was 80%. The positive and negative predictive values were respectively 85% and 100%. In summary, malnutrition is frequent and associated with low caloric intake. Bioelectrical impedance, with the use of the scoring system we describe, can be used to correctly evaluate the nutritional status of hemodialysis patients.

Persistent hyperkalemia in a patient with diabetes mellitus: a reversible defect in kaliuresis during bicarbonaturia

The purpose of this report is to apply recent advances in the understanding of the physiology of the excretion of potassium to a patient who had hyperkalemia due to a low rate of excretion of potassium. The defect was first suspected during therapy for diabetic ketoacidosis, when the concentration of potassium in plasma was unusually high (7.3 mmol/l) on admission and the deficit of potassium, as judged from the quantity of potassium infused to maintain normokalemia (40 mmol/24 h), was much less than expected. After recovery from diabetic ketoacidosis, hyperkalemia persisted despite near-normal values for creatinine and glucose in plasma. Excretion of potassium was low, considering the stimulus of hyperkalemia, and did not rise appreciably after the acute or chronic administration of a mineralocorticoid. The transtubular potassium concentration gradient (TTKG) did not exceed 6 after a large dose of fludrocortisone (200 micrograms) was administered. Notwithstanding, the TTKG rose to 14.4 following the intake of acetazolamide. We speculate that the basis for the hyperkalemia was type II hypoaldosteronism.

Studies to determine the basis for hyperkalemia in recipients of a renal transplant who are treated with cyclosporine

Hyperkalemia is commonly encountered in patients who receive a renal transplant and the immunosuppressive drug, cyclosporine. There is also a high incidence of hypertension (which is thought to be due to expansion of the extracellular fluid volume) and hyperchloremic metabolic acidosis in this group of patients. This constellation of findings led to the suspicion of the possibility that their basis might be type II hypoaldosteronism. To test this hypothesis, 12 patients with hyperkalemia (plasma K+, 5.1 +/- 0.2 mmol/L at the time of study) while receiving cyclosporine were studied. Patients who had diabetes mellitus, those receiving drugs known to cause hyperkalemia (e.g., beta blockers, angiotensin-converting enzyme inhibitors, K(+)-sparing diuretics), or those with a serum creatinine greater than 200 mumol/L were excluded. The renal response to hyperkalemia was inappropriate because the transtubular K+ concentration gradient (TTKG) was only 4.3 +/- 0.4 compared with a TTKG of 13 +/- 1, 2 h after 50 mmol of KCl was given to normal subjects. The TTKG, after administration of 200 micrograms of fludrocortisone, was still very low (5.6 +/- 0.6) in the patients compared with that of controls (12 +/- 1). After administration of 250 to 500 mg of acetazolamide to increase the delivery of bicarbonate to the distal nephron, the TTKG rose significantly to 11 +/- 1 in patients on cyclosporine, compared with 17 +/- 1 in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Interpretation of the urine osmolality: the role of ethanol and the rate of excretion of osmoles

One purpose of this report is to illustrate that calculating the rate of excretion of osmoles in the urine can be of value in the differential diagnosis of hypernatremia and polyuria. A second purpose is to illustrate a clinical example where the osmolality of the urine did not reflect the lack of action of ADH. A patient with ethanol intoxication seemed to have central diabetes insipidus on clinical grounds. However, the osmolality of the urine was 287 mosm/kg H2O, a value which made this diagnosis unlikely. Since the concentration of ethanol in plasma was 119 mmol/L, we suspected that the urine contained an appreciable quantity of alcohol; this might obscure the lack of action of ADH. A study was performed to document the quantitative relationship between the concentrations of ethanol in plasma and urine. The concentration of ethanol in the urine was approximately 1.4-fold greater than in plasma. Using this correction factor, the osmolality of the urine adjusted for ethanol in the patient was only 120 mosm/kg H2O, a value more consistent with the diagnosis of central diabetes insipidus.

Modulation of the secretion of potassium by accompanying anions in humans

In animals, secretion of potassium (K) in the cortical collecting duct (CCD) is modulated by the properties of the accompanying anion. In humans, results are inconclusive as previous studies have not differentiated between a kaliuresis due to a rise in the concentration of K from one due to an increase in the volume of urine. Our purpose was to study the effects of chloride (Cl) and bicarbonate on the secretion of K in the CCD in humans using the transtubular K concentration gradient (TTKG), a semi-quantitative index of secretion of K in the terminal CCD. After control blood and urine samples were obtained, all subjects ingested 0.2 mg fludrocortisone to ensure that mineralocorticoids were not limiting the secretion of K. The anionic composition of the urine was varied using three protocols: Normal subjects (N = 11) ingested cystine and methionine to induce sulfaturia; nine subjects with a contracted ECF volume (to lower the concentration of Cl in the urine) were also studied during sulfaturia following the ingestion of cystine and methionine; 13 normovolemic subjects were studied during bicarbonaturia following the ingestion of acetazolamide. When the concentration of Cl in the urine was greater than 15 mmol/liter, sulfate had no effect on the TTKG. With lower concentrations of Cl in the urine, the TTKG rose 1.5-fold. The TTKG rose 1.8-fold in the presence of bicarbonaturia despite concentrations of Cl in the urine that were greater than 15 mmol/liter, suggesting that bicarbonate has additional effects on this K secretory process. At comparable concentrations of sulfate and bicarbonate in the urine, the TTKG was increased only with bicarbonaturia.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephron site responsible for the reduced kaliuretic response to mineralocorticoids during hypokalemia in rats

Rats with hypokalemia induced by eating a low-K diet have a diminished kaliuretic response to mineralocorticoids. The purpose of this study was to determine if this was the due to a lower rate of net secretion of K in the cortical collecting duct (CCD) and/or an enhanced rate of reabsorption of K in the medullary collecting duct (MCD). Secondary active secretion of K in the CCD raises the [K] in the lumen as compared to the plasma [TF/P)K). If the (TF/P)K is greater than 1, there was secondary active secretion of K in this nephron segment. The (TF/P)K in the CCD was measured by microcatheterization of the collecting duct. Three groups of rats were studied: rats on a low-K diet with and without the acute administration of DOCA, and rats on a normal-K diet treated with DOCA on a chronic basis. Rats on the low-K diet had a (TF/P)K of 0.8 +/- 0.11; this value did not rise to values significantly greater than 1 after the acute administration of DOCA (1.4 +/- 0.35). In contrast, chronic administration of DOCA to rats fed a normal-K diet did result in a (TF/P)K which was significantly greater than unity (3.1 +/- 0.39). The degree of hypokalemia was not significantly different in these rats. The absolute and fractional reabsorption of K in the MCD was not different in the rats on the low-K diet with or without DOCA. We conclude that the nephron segment which is responsible for the reduced kaliuretic response to mineralocorticoids is the CCD.

Removal of an inorganic acid load in subjects with ketoacidosis of chronic fasting

When a large inorganic acid load is ingested by normals, the proton load is eliminated because the rate of excretion of ammonium can rise to 200 to 300 mmol/day. In subjects with ketoacidosis of chronic fasting, such a large increase in the rate of excretion of ammonium might not be possible because of ATP balance considerations in proximal cells. Subjects with ketoacidosis of chronic fasting excreted less net acid as defined in the conventional way when they consumed a large inorganic acid load (136 +/- 6 vs. 176 +/- 26 mmol/day in control fasted subjects). Nevertheless, the vast majority of this inorganic acid load was eliminated because they were in steady state and had only a slightly lower concentration of bicarbonate (13 +/- 0.6 vs. 15 +/- 0.5 mmol/liter) and ketoacid anions (3.3 +/- 0.2 vs. 5.5 +/- 0.2 mmol/liter) in their blood. Using a definition of net acid excretion where the component of bicarbonate loss was expanded to include "potential bicarbonate" (ketoacid anions) in the urine, the rate of excretion of net acid was higher in subjects who ingested the inorganic acid load, owing to a much lower rate of excretion of ketoacid anions (9 +/- 2 vs. 120 +/- 7 mmol/day). This lower rate of excretion was not only due to a lower filtered load, but also to a higher fractional reabsorption of ketoacid anions during acidosis (97 +/- 0.1 vs. 77 +/- 0.2%). This higher fractional reabsorption could not be explained by a lower filtered load of ketoacid anions or to a restricted intake of sodium.(ABSTRACT TRUNCATED AT 250 WORDS)

The excretion of ammonium ions and acid base balance

The role of the kidney in acid base balance is to generate "new" bicarbonate ions, largely as a result of the excretion of ammonium ions. Three points will be covered in this review. First, we challenge the traditional view that the proximal nephron reclaims filtered bicarbonate ions, whereas, the distal nephron generates "new" bicarbonate ions. Virtually all "new" bicarbonate ions are generated in the proximal convoluted tubule during glutamine metabolism; very little is formed at distal sites. Second, the excretion of ammonium ions plays an important role in acid base balance only during chronic ketoacidosis, in response to diarrhea, in chronic renal insufficiency, and in distal renal tubular acidosis. Third, although the excretion of ammonium ions is said to signal the addition of bicarbonate ions to the extracellular fluid, the anion excreted with the ammonium cation is also important for acid base balance.

The transtubular potassium concentration in patients with hypokalemia and hyperkalemia

It is advantageous to make an independent assessment of the potassium (K) secretory process and the luminal flow rate in the renal cortex to evaluate K handling by the kidney during hypokalemia or hyperkalemia. The transtubular potassium concentration gradient (TTKG) is a semiquantitative index of the activity of the K secretory process. The purpose of this study was to define expected values for the TTKG in normal subjects with hypokalemia or following an acute K load. During hypokalemia of non-renal origin, the TTKG was 0.9 +/- 0.2; in contrast, the TTKG was significantly higher during the hypokalemia of hyperaldosteronism, 6.7 +/- 1.3. The TTKG was 11.8 +/- 3.6, 2 hours after normokalemic subjects received 0.2 mg 9 alpha-fludrocortisone (9 alpha-F). To obtain expected values during hyperkalemia, normal subjects ingested 50 mmol potassium chloride; 2 hours later, the TTKG was 13.1 +/- 3.8. Therefore, the expected value for the TTKG must be interpreted relative to the concentration of K in the plasma. Circumstances were also defined where the TTKG is low despite hyperaldosteronism, namely, during a water diuresis and pre-existing hypokalemia.

Urine electrolytes and osmolality: when and how to use them

The purpose of this review is to provide an update on the use of the urine electrolyte and osmolality measurements in patients with disorders of fluid, electrolytes, and/or acid-base metabolism. It is critical to appreciate that there are no 'normal values' for these parameters, only 'expected values' relative to clinical situations. Pitfalls in the interpretation of each electrolyte in the urine are also provided. To detect a mild to moderate degree of reduction of the 'effective' intravascular volume, both urine sodium (Na) and chloride (Cl) concentrations should be measured. Pitfalls in this assessment are abnormal renal and adrenal function and the use of diuretics. Insights into the etiology of the low 'effective' intravascular volume can be deduced by comparing the urine Na, potassium (K), and Cl concentrations. The urine net charge (Cl vs. Na + K) is the most reliable way to estimate the urine ammonium concentration short of its direct measurement, an assay that is not provided by most laboratories. This measurement is important in the differential diagnosis of hyperchloremic metabolic acidosis. To examine the renal response to hypokalemia or hyperkalemia, the two components of K excretion (K secretion and urine flow rate) should be examined separately. The former is evaluated using the transtubular K, concentration gradient. The urine osmolality is used to assess antidiuretic hormone action and the osmolality of the renal medulla and to determine the etiology of polyuria and/or hypernatremia. The urine osmolality can also be used to assess the ammonium concentration, using the urine osmolal gap, and to detect unusual urine osmoles.

Ammonium excretion in chronic metabolic acidosis: benefits and risks

The expected renal response to a chronic acid load is an enhanced rate of ammonium production and excretion. Notwithstanding, high rates of ammonium production and/or excretion on a chronic basis may have detrimental consequences to patients. Examples discussed include the loss of extra lean body mass during chronic fasting, an accelerated rate of progression of renal insufficiency and possibly destruction of the medullary area of the kidney owing to local alkalinization.

Urine electrolytes in the assessment of extracellular fluid volume contraction

The purpose of this study was to determine which urine electrolytes should be measured to confirm that the extracellular fluid (ECF) volume is depleted. ECF volume contraction was induced by furosemide administration to rats consuming an electrolyte-free diet. An external potassium balance was achieved by replacing potassium losses with KHCO3 and KCl so that the sodium and chloride deficits were comparable (equivalent to a 30% reduction in ECF volume). As expected, the urine sodium and chloride concentrations fell to 2 +/- 0.3 mmol/l and 3 +/- 0.3 mmol/l, respectively. Rats were then randomized to receive 50-75% of their sodium or chloride deficit as either: NaCl (control group), NH4Cl or NaHCO3 to mimic clinical situations associated with ECF volume contraction. In the NaCl group, the urine sodium and chloride concentrations remained low (6 +/- 2 mmol/l and 7 +/- 2 mmol/l), consistent with persistent ECF volume contraction. Although the NH4Cl group continued to have a low urine sodium concentration (2 +/- 0.2 mmol/l), there was now a marked increase in the urine chloride concentration (51 +/- 7 mmol/l; p less than 0.01 vs. NaCl group). In contrast, although the NaHCO3 group continued to have a low urine chloride concentration (2 +/- 1 mmol/l), there was a significant increase in the urine sodium concentration (19 +/- 3 mmol/l; p less than 0.01 vs. NaCl group). We conclude that the clinical assessment of ECF volume by urine electrolytes requires an evaluation of both the urine sodium and chloride concentrations.

What is the underlying defect in patients with isolated, proximal renal tubular acidosis?

Our aim in this article is to propose a new hypothesis concerning the etiology of renal tubular acidosis (RTA) in that subgroup of patients who have the isolated, primary type of proximal RTA. We suggest that their underlying disorder is a more alkaline intracellular pH of the proximal convoluted tubule. Increased alkalinity of proximal tubular cells would explain the low rate of bicarbonate reabsorption per liter glomerular filtration and the decreased rate of ammonium excretion despite a low urine pH and the presence of chronic metabolic acidosis. Additional diagnostic tests to evaluate this hypothesis in this specific subgroup of patients with proximal RTA are also outlined.