Frequent Hemodialysis Network (FHN) randomized trials: study design.

Observational studies suggest improvements with frequent hemodialysis (HD), but its true efficacy and safety remain uncertain. The Frequent Hemodialysis Network Trials Group is conducting two multicenter randomized trials of 250 subjects each, comparing conventional three times weekly HD with (1) in-center daily HD and (2) home nocturnal HD. Daily HD will be delivered for 1.5-2.75 h, 6 days/week, with target eK(t)/V(n) > or = 0.9/session, whereas nocturnal HD will be delivered for > or = 6 h, 6 nights/week, with target stdK(t)/V of > or = 4.0/week. Subjects will be followed for 1 year. The composite of mortality with the 12-month change in (i) left ventricular mass index (LVMI) by magnetic resonance imaging, and (ii) SF-36 RAND Physical Health Composite (PHC) are specified as co-primary outcomes. The seven main secondary outcomes are between group comparisons of: change in LVMI, change in PHC, change in Beck Depression Inventory score, change in Trail Making Test B score, change in pre-HD serum albumin, change in pre-HD serum phosphorus, and rates of non-access hospitalization or death. Changes in blood pressure and erythropoiesis will also be assessed. Safety outcomes will focus on vascular access complications and burden of treatment. Data will be obtained on the cost of delivering frequent HD compared to conventional HD. Efforts will be made to reduce bias, including blinding assessment of subjective outcomes. Because no large-scale randomized trials of frequent HD have been previously conducted, the first year has been designated a Vanguard Phase, during which feasibility of randomization, ability to deliver the interventions, and adherence will be evaluated.

Comorbidity assessment using the Index of Coexistent Diseases in a multicenter clinical trial.

BACKGROUND: The Hemodialysis (HEMO) Study is a multicenter trial designed to determine whether hemodialysis dose and membrane flux affect survival. Comorbid conditions are also important determinants of survival, and thus, an accurate and reliable method to assess comorbidity was required. Comorbidity was being assessed at baseline and annually in the HEMO Study using the Index of Coexistent Disease (ICED). We describe the instrument, its implementation in the HEMO Study, and the results of comorbidity assessment in the first 1000 randomized patients in the trial. METHODS: The ICED aggregated the presence and severity of 19 medical conditions and 11 physical impairments within two scales: the Index of Disease Severity (IDS) and the Index of Physical Impairment (IPI). The final ICED score was determined by an algorithm combining the peak scores for the IDS and IPI. The range of the ICED was from 0 to 3, reflecting increasing severity. RESULTS: Study personnel at 15 clinical centers were trained to update and abstract data from the dialysis medical records. Availability of data, measures of construct validity, and measures of reliability were adequate; 99.8% and 60.6% of patients had comorbid conditions in at least one IDS or IPI category, respectively. The distribution of patients by ICED level was 0 (0.2%), 1 (34.9%), 2 (31.2%), and 3 (33.7%). In multivariable analysis, the following factors were significantly associated with more severe comorbidity: older age, diabetes and other causes of renal disease, a lower level of education, employment status (unemployed and retired), longer duration of dialysis, and lower serum creatinine. There was a significant variation in the severity of comorbidity among clinical centers after adjustment for other factors. The R2 of the model was 25.3%, indicating that a substantial proportion of the variation in the ICED was not explained by these factors. CONCLUSIONS: We conclude that comorbidity assessment using the ICED is feasible in multicenter clinical trials of dialysis patients. There is a large burden of comorbidity in dialysis patients, which is not well explained by the cause of renal disease, demographic, and socioeconomic factors and common clinical and laboratory measurements. These variables should not be considered substitutes for comorbid conditions in case-mix adjustment. Comorbidity assessment is useful to describe the sample population, to improve the precision of the treatment effect, and to use possibly as an outcome measurement.

Factors associated with the prevalence of arteriovenous fistulas in hemodialysis patients in the HEMO study. Hemodialysis (HEMO) Study Group.

BACKGROUND: Arteriovenous (AV) fistulas are the vascular access of choice for hemodialysis patients, but only about 20% of hemodialysis patients in the United States dialyze with fistulas. There is little information known about the factors associated with this low prevalence of fistulas. METHODS: Multiple logistic regression analysis was used to evaluate the independent contribution of factors associated with AV fistula use among patients enrolled in the HEMO Study. The analysis was conducted in 1824 patients with fistulas or grafts at 45 dialysis units (15 clinical centers). RESULTS: Thirty-four percent of the patients had fistulas. The prevalence of fistulas varied markedly from 4 to 77% among the individual dialysis units (P < 0.001). Multiple regression analysis revealed five demographic and clinical factors that were each independently associated with a lower likelihood of having a fistula, even after adjustment for dialysis unit. Specifically, the prevalence of fistulas was lower in females than males [adjusted odds ratio (AOR) 0.37, 95% CI, 0.28 to 0.48], lower in patients with peripheral vascular disease than in those without (AOR 0.55, 95% CI, 0.38 to 0.79), lower in blacks than in non-blacks (AOR 0.64, 95% CI, 0.46 to 0.89), lower in obese patients (AOR per 5 kg/m(2) body mass index, 0.76, 95% CI, 0.65 to 0.87), and lower in older patients (AOR per 10 years, 0.85, 95% CI, 0.78 to 0.94). The differences in the prevalence of fistulas among the dialysis units remained statistically significant (P < 0.001) after adjustment for these demographic and clinical factors. Finally, there were substantial variations in the prevalence of fistulas even among dialysis units in a single metropolitan area. CONCLUSIONS: Future efforts to increase the prevalence of fistulas in hemodialysis patients should be directed at both hemodialysis units and patient subpopulations with a low fistula prevalence.

Plasma glutathione peroxidase and its relationship to renal proximal tubule function.

Selenium-dependent extracellular glutathione peroxidase (E-GPx) is found in plasma and other extracellular fluids. Previous studies have indicated that patients with chronic renal failure on dialysis have low plasma GPx activity. In this study, dialysis patients had approximately 40% of control plasma GPx activity, while anephric individuals had lowest plasma GPx activities ranging from 2 to 22% of control. The residual plasma GPx activity in anephric individuals could be completely precipitated by anti-E-GPx antibodies, indicating that all plasma GPx activity can be attributed to E-GPx in both normal and anephric individuals. Plasma GPx activity rises rapidly following kidney transplantation, often reaching normal values within 10 days. The plasma GPx activity in some transplanted patients rises to levels higher than the normal range, followed by a return to the normal range. Since E-GPx in the kidney is primarily synthesized in the proximal tubules, we investigated whether nephrotoxic agents known to disrupt proximal tubule function also affected plasma GPx activity. The beta-lactam antibiotic cephaloglycin rapidly caused a decrease in plasma GPx activity in rabbits. In addition, the chemotherapeutic agent ifosfamide caused a decrease in plasma GPx activity in pediatric osteosarcoma patients. Fanconi syndrome associated with either ifosfamide therapy or valproic acid therapy also caused a decrease in plasma GPx activity. Thus plasma GPx activity is related to kidney function and is decreased in certain situations where nephrotoxic drugs are administered. Monitoring plasma GPx activity may have predictive value in evaluating the function of transplanted kidneys or in predicting those patients particularly at risk of nephrotoxic injury associated with certain medications.

Effect of aldosterone on renal potassium conservation in the rat.

The importance of reduced plasma aldosterone concentration (PAC) in renal potassium (K) conservation is unclear. Thus we examined the effect of aldosterone on incipient, developing, and established renal K conservation. Adrenalectomized (ADX) dexamethasone-replaced rats were continuously treated with high, normal, or low dosages of aldosterone during 4 days of dietary K restriction and were compared with rats without aldosterone replacement. High and normal aldosterone replacement reduced the fall in urinary K excretion and led to significantly lower plasma [K], skeletal muscle tissue K content, renal tissue K content, and greater negative cumulative balance of K compared with low aldosterone replacement. Likewise, plasma [K] and skeletal muscle tissue K content were significantly less in intact rats after 3 days of K deprivation and chronic treatment with aldosterone. Acute aldosterone treatment significantly increased urinary K excretion by isolated perfused kidneys. We conclude that incipient, developing, and established renal K conservation is not independent of mineralocorticoid activity and that the rapid fall in PAC during K depletion is necessary for maximal renal K conservation.

Cryptococcal peritonitis in peritoneal dialysis patients: a case report.

Peritonitis in patients on chronic peritoneal dialysis remains a major problem. Most commonly this is due to bacterial infection, but fungal peritonitis is also a treatment dilemma. Peritonitis due to Cryptococcus neoformans is an unusual event, with fewer than ten cases reported. This case report documents a case of cryptococcal peritonitis in a diabetic man on prednisone and azathioprine for suspected chronic inflammatory demyelinating polyneuropathy. The organism was also cultured in the cerebrospinal fluid and urine and high cryptococcal antigen titers were found in the blood indicating systemic infection. The peritoneal catheter was removed, immunosuppression was withdrawn and he was treated with systemic antifungal therapy. He died suddenly nine weeks following the diagnosis and at post mortem was found to have evidence of cryptococcosis in lung, spleen and brain. The case demonstrates that cryptococcal peritonitis in patients on peritoneal dialysis should prompt a search for systemic infection and may require prolonged therapy.

Human kidney proximal tubules are the main source of plasma glutathione peroxidase.

The sites of synthesis of extracellular (E) glutathione peroxidase (GPX), a unique selenoglycoprotein present in plasma, are not known. To investigate the possibility that the kidney is the main source for the plasma GPX, we examined GPX activities and selenium concentrations in the plasma of patients with renal failure on dialysis and nephrectomized patients before and after kidney transplantation. Plasma GPX activities in these patients were 42, 22, and 180% of normal EGPX activity, respectively, whereas plasma Se levels were within the normal range. Twenty-four hours after nephrectomy of anesthetized rats, plasma GPX activity was 30.0 +/- 6.4% of the activity at zero time. Northern hybridization analysis of eight human tissues probed with EGPX and cellular glutathione peroxidase (CGPX) cDNA revealed that the ratio of EGPX to CGPX was highest in the kidney. cRNA in situ hybridization studies on kidney slices showed that only proximal tubular epithelial cells and parietal epithelial cells of Bowman's capsule contained EGPX transcripts. Caki-2, a proximal tubular renal carcinoma cell line, makes and actively secretes EGPX. Taken together, these results strongly suggest that kidney proximal tubular cells are the main source for GPX activity in the plasma.

Hemolytic uremic syndrome due to Escherichia coli O157: H7 in a child with multiple infections.

Hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia, and uremia; it is a common cause of acute renal failure in children. Although many microbial agents have been associated with HUS, only Escherichia coli O157: H7 has been clearly demonstrated to be a major cause of this illness. A case is presented of a healthy 4-year-old boy who had a recent varicella infection; when evaluated for HUS his blood and stool cultures both grew Salmonella montevideo and blood cultures grew group A beta-hemolytic streptococci. A stool cultured on MacConkey-sorbitol agar also grew E. coli O157: H7. An eightfold rise in serum antibodies to E. coli O157: H7 lipopolysaccharide was also demonstrated. The child recovered completely and was healthy 3 years later. Although this child had several infectious agents anecdotally associated with HUS, appropriate culture of stool showed that he also had E. coli O157: H7 infection. Previous cases thought to be due to other pathogens may similarly have been caused by co-infection with E. coli O157: H7.

Potassium homeostasis during angiotensin-converting enzyme inhibition with enalapril.

The effect of angiotensin-converting enzyme (ACE) inhibition on renal and extrarenal potassium (K) regulation was examined. Six healthy men were studied in double-blinded crossover fashion on placebo or enalapril, 80 mg/day. On day 4, the subjects were given an intravenous infusion of KCl and on day 5 an oral dose of 10% NH4Cl. Treatment with enalapril decreased plasma aldosterone and increased plasma renin activity (PRA), epinephrine and norepinephrine, but did not affect serum glucose, plasma insulin or basal plasma K. Maximal increases in plasma K during K infusion or NH4Cl ingestion were similar during enalapril and placebo treatment. With enalapril treatment urinary K excretion was unchanged following K loading but moderately reduced following NH4Cl loading. We conclude that ACE inhibition does not acutely impair K homeostasis in men with normal renal function.

Mechanism of potassium depletion during chronic metabolic acidosis in the rat.

Pair-fed rats on a normal K diet were given either 1.5% NH4Cl or water for 4 days. The acid-fed animals developed metabolic acidosis, negative K balance, and K depletion. Urinary Na excretion and urinary flow were not different between the groups beyond the first day. After the 4 days, isolated kidneys from animals in each of these groups were perfused at normal pH and bicarbonate concentrations. Urinary K excretion was similar between the groups despite the potassium depletion in the acid-fed animals. In contrast, isolated kidneys from animals with comparable K depletion induced by dietary K restriction readily conserved K (fractional excretion 0.35 +/- 0.04 vs. 0.83 +/- 0.09 by the kidneys from acid-fed animals, P less than 0.01). Sodium excretion and urinary flow were similar among the three groups of isolated kidneys. Plasma aldosterone concentrations were greater in the acid-fed rats after the 4 days of NH4Cl ingestion than in the control animals (43 +/- 10 vs. 10 +/- 2 ng/dl, P less than 0.01). Adrenalectomized rats were treated with either normal (4 micrograms/day) or high (22 micrograms/day) aldosterone replacement while ingesting NH4Cl for 4 days. Only in the presence of high aldosterone replacement did the acid-fed adrenalectomized animals develop K depletion. We conclude that chronic metabolic acidosis stimulates aldosterone secretion, and that aldosterone maintains the inappropriately high urinary potassium excretion and K depletion seen in this acid-base disorder.

Effect of potassium concentration and ouabain on the renal adaptation to potassium depletion in isolated perfused rat kidney.

Renal adaptation for potassium (K) conservation has been demonstrated in isolated perfused kidneys from rats within 3 days of K depletion and appears to be independent of aldosterone and sodium excretion. This study was designed to investigate whether the renal adaptation for K conservation is independent of ambient [K] and renal tissue levels of K and whether ouabain may have effects on K excretion, which are in contrast to the effects on K excretion in normal animals. In the first study, rats K depleted for 3 days received 2500 mu equiv. KCI intraperitoneally, while other K-depleted rats and a group of control diet animals received intraperitoneal H2O alone to determine whether simple restoration of K deficits would reverse the renal adaptation for K conservation. Intraperitoneal KCI increased plasma [K] and kidney tissue K significantly within 3 h in the K-repleted group compared with the K-depleted rats. Isolated Kidneys were perfused from the three groups of rats 3 h after intraperitoneal injection. Despite K repletion in vivo, perfused kidneys from the K-repleted group still had significantly decreased K excretion (1.28 +/- 0.085 mu equiv./min) compared with controls (2.05 +/- 0.291 mu equiv./min), and K excretion was still not different from the K-depleted group (0.57 +/- 0.134 mu equiv./min). However, fractional K excretion by the kidneys from K-repleted rats was increased above K-depleted kidneys (0.48 +/- 0.051 vs. 0.18 +/- 0.034, p less than 0.01). Despite the increased renal tissue K in K-repleted kidneys at the start of perfusion (285 +/- 5.1 vs. 257 +/- 5.4 mu equiv./g), by the end of the perfusion tissue K in perfused kidneys was identical in all three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of an intrinsic renal adaptation for K+ conservation in short-term K+ depletion.

Renal potassium conservation occurs within 3 days of potassium deprivation by a mechanism that appears to be independent of mineralocorticoids and sodium and anion excretion. To examine whether the mechanism involves an intrinsic renal adaptation, urinary potassium excretion was measured in isolated perfused kidneys from rats maintained on a normal or K+-free diet for 3 days. Perfusions were carried out with a K+ concentration that averaged 3.5 mM and with glucose (5 mM) as the only substrate. Both absolute (UKV) and fractional K+ excretion (FEK) were substantially less in kidneys from animals on K+-free diets compared with controls. These differences in K+ excretion were not explained by changes in GFR, urine flow rate, urine pH, or sodium, chloride, or ammonium excretion. The K+ content of renal tissue was not different in the perfused and nonperfused kidneys from rats receiving K+-free diets compared with controls. Suppression of K+ excretion by amiloride (10(-4) M) suggested that, as in vivo, tubular secretion of K+ in the perfused normal kidney accounts for 90% of the urinary K+ excretion and that tubular K+ secretion is reduced in isolated kidneys from animals on a K+-free diet. Further studies of isolated kidneys from adrenalectomized (ADX) rats receiving aldosterone and dexamethasone replacement and fed a normal or K-free diet also revealed significantly lower UKV and FEK in kidneys from animals on K+-free diets. K+ content of renal tissue was not different in the ADX animals on a K+-free diet compared with ADX rats on normal K+ intake. These studies indicate that within 72 h of dietary K+ deprivation an intrinsic renal adaptive process to conserve potassium is activated that is independent of renal potassium content, aldosterone, and urinary factors that can alter K+ excretion such as flow, pH, ammonium, sodium, and anions. This regulatory mechanism, which has a substantial influence on potassium excretion, remains to be elucidated.