Glucose modulation of the disposal of an acute potassium load in patients with end-stage renal disease

Plant-based diets and postprandial hyperkalemia

This Letter to the Editor is a response to St-Jules and Fouque and their interpretation of postprandial hyperkalemia, especially regarding plant-based diets. Based on the reviewed literature review, potassium kinetic studies cited by the authors include only 1 study with a food-based intervention that actually showed reduced postprandial hyperkalemia with plant-based diets. The remainder of the studies used potassium salts or supplements that behave differently compared with whole plant foods. As such, we recommend avoiding restriction of whole plant foods in patients with chronic kidney disease when solely based on the theoretical risk of postprandial hyperkalemia.

Response to "Plant-based diets and postprandial hyperkalemia"

Diet therapy for hyperkalemia in people with chronic kidney disease (CKD) has shifted considerably in recent years with the observations that reported potassium intake is weakly, or not at all, associated with plasma potassium levels in this population. One of the lingering debates is whether dietary potassium presents a risk of hyperkalemia in the postprandial state. Although there is general agreement about the need for additional research, the commentary by Varshney et al contends that the available research sufficiently demonstrates that high-potassium plant foods do not pose a risk of postprandial hyperkalemia. Others argue that this remains unsettled science. Although the traditional approach of providing people with CKD lists of high-potassium foods to limit or avoid may be unnecessary, those at high risk of hyperkalemia should be encouraged to consume balanced meals and control portions, at least until some of the key research gaps in this area are resolved. This editorial critiques the analyses offered by Varshney et al and explains the rationale for a more cautious approach to care.

Hyperkalemia and Plant-Based Diets in Chronic Kidney Disease

Traditional dietary guidelines for patients with kidney disease recommend restriction of plant foods due to concerns about hyperkalemia and associated adverse events. Studies conducted over several decades have shown that the basis for these guidelines does not match the evidence. Serum potassium levels can be elevated in patients with reduced kidney function after consumption of foods with potassium-based additives or with highly concentrated potassium content such as juices, dried fruit, or purees. However, plant foods may have certain qualities that may blunt potassium retention including their alkalinizing effects, the lack of bioavailable potassium, and the impact of dietary fiber in organic plant foods on colonic potassium excretion. Furthermore, there are many benefits of plant foods that patients with kidney disease may be missing by excluding them from their diets by recommending the historical low-potassium "renal diet." Revised dietary recommendations for kidney health may encourage patient-centered kidney recipes that revolve around plant foods and do not restrict them.

Still no direct evidence of postprandial hyperkalemia with plant foods

Although St-Jules et al have presented the case for postprandial hyperkalemia with food, including plant foods, there (still) is little to no direct evidence supporting the occurrence of postprandial hyperkalemia, mostly due to a lack of studies performed exclusively using food. Food is different than salts or supplements, and it is likely that a banana behaves differently than potassium salts. A growing body of evidence supports the use of plant foods without causing hyperkalemia in patients with kidney disease. Currently, only 1 study has reported on the postprandial effects of hyperkalemia. In this study, there was a substantial reduction in the instances of postprandial hyperkalemia in participants consuming a diet that included more plant foods and more fiber. At the time of this writing, there is no evidence to support risk or safety of certain foods with regard to postprandial hyperkalemia, and additional research is warranted.

Potassium and fiber: a controversial couple in the nutritional management of children with chronic kidney disease

BACKGROUND

Fruit and vegetable intake is commonly discouraged in children with chronic kidney disease (CKD) to avoid hyperkalemia. However, direct evidence in support of this widespread practice is lacking. Furthermore, the resultant restricted fiber exposure may deprive CKD patients from potential health benefits associated with the latter. Therefore, we investigated associations between dietary potassium intake, fiber intake, and serum potassium levels in pediatric CKD.

METHODS

This study is a longitudinal analysis of a 2-year, prospective, multi-institutional study, following children with CKD at 3-month intervals. At each visit, dietary potassium and fiber intake were assessed, using 24-h recalls and 3-day food records. On the same occasion, serum potassium concentrations were determined. Associations between dietary potassium intake, dietary fiber intake, and serum potassium concentrations were determined using linear mixed models.

RESULTS

Fifty-two CKD patients (7 transplant recipients, none on dialysis) aged 9 [4;14] years with an estimated glomerular filtration rate (eGFR) of 49 [25;68] mL/min/1.73 m² were included. For every g/day decrease in dietary potassium intake, the estimated mean daily fiber intake was 5.1 g lower (95% confidence interval (CI), 4.3-5.9 g/day; p < 0.001). Neither dietary potassium intake (p = 0.40) nor dietary fiber intake (p = 0.43) was associated with circulating potassium in a model adjusted for time point, eGFR, treatment with a renin-angiotensin-aldosterone system blocker, serum bicarbonate concentration, and body surface area.

CONCLUSIONS

Dietary potassium and fiber intake are closely related but were not associated with circulating potassium levels in pediatric CKD. A higher-resolution version of the graphical abstract is available as Supplementary information.

Can Novel Potassium Binders Liberate People with Chronic Kidney Disease from the Low-Potassium Diet? A Cautionary Tale

The advent of new potassium binders provides an important breakthrough in the chronic management of hyperkalemia for people with CKD. In addition to the direct benefits of managing hyperkalemia, many researchers and clinicians view these new medications as a possible means to safely transition patients away from the low-potassium diet to a more healthful eating pattern. In this review, we examine the mechanisms of potassium binders in the context of hyperkalemia risk related to dietary potassium intake in people with CKD. We note that whereas these medications target hyperkalemia caused by potassium bioaccumulation, the primary evidence for restricting dietary potassium is risk of postprandial hyperkalemia. The majority of ingested potassium is absorbed alongside endogenously secreted potassium in the small intestines, but the action of these novel medications is predominantly constrained to the large intestine. As a result and despite their effectiveness in lowering basal potassium levels, it remains unclear whether potassium binders would provide protection against hyperkalemia caused by excessive dietary potassium intake in people with CKD. Until this knowledge gap is bridged, clinicians should consider postprandial hyperkalemia risk when removing restrictions on dietary potassium intake in people with CKD on potassium binders.

Fiber intake and health in people with chronic kidney disease

Emerging evidence suggests that diet, particularly one that is rich in dietary fiber, may prevent the progression of chronic kidney disease (CKD) and its associated complications in people with established CKD. This narrative review summarizes the current evidence and discusses the opportunities for increasing fiber intake in people with CKD to improve health and reduce disease complications. A higher consumption of fiber exerts multiple health benefits, such as increasing stool output, promoting the growth of beneficial microbiota, improving the gut barrier and decreasing inflammation, as well decreasing uremic toxin production. Despite this, the majority of people with CKD consume less than the recommended dietary fiber intake, which may be due in part to the competing dietary potassium concern. Based on existing evidence, we see benefits from adopting a higher intake of fiber-rich food, and recommend cooperation with the dietitian to ensure an adequate diet plan. We also identify knowledge gaps for future research and suggest means to improve patient adherence to a high-fiber diet.

Dietary Potassium Intake and All-Cause Mortality in Adults Treated with Hemodialysis

BACKGROUND AND OBJECTIVES

Dietary potassium restriction in people receiving maintenance hemodialysis is standard practice and is recommended in guidelines, despite a lack of evidence. We aimed to assess the association between dietary potassium intake and mortality and whether hyperkalemia mediates this association.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A total of 8043 adults undergoing maintenance hemodialysis in Europe and South America were included in the DIETary intake, death and hospitalization in adults with end-stage kidney disease treated with HemoDialysis (DIET-HD) study. We measured baseline potassium intake from the Global Allergy and Asthma European Network food frequency questionnaire and performed time-to-event and mediation analyses.

RESULTS

The median potassium intake at baseline was 3.5 (interquartile range, 2.5-5.0) g/d. During a median follow-up of 4.0 years (25,890 person-years), we observed 2921 (36%) deaths. After adjusting for baseline characteristics, including cardiac disease and food groups, dietary potassium intake was not associated with all-cause mortality (per 1 g/d higher dietary potassium intake: hazard ratio, 1.00; 95% confidence interval [95% CI], 0.95 to 1.05). A mediation analysis showed no association of potassium intake with mortality, either through or independent of serum potassium (hazard ratio, 1.00; 95% CI, 1.00 to 1.00 and hazard ratio, 1.01; 95% CI, 0.96 to 1.06, respectively). Potassium intake was not significantly associated with serum levels (0.03; 95% CI, -0.01 to 0.07 mEq/L per 1 g/d higher dietary potassium intake) or the prevalence of hyperkalemia (≥6.0 mEq/L) at baseline (odds ratio, 1.11; 95% CI, 0.89 to 1.37 per 1 g/d higher dietary potassium intake). Hyperkalemia was associated with cardiovascular death (hazard ratio, 1.23; 95% CI, 1.03 to 1.48).

CONCLUSIONS

Higher dietary intake of potassium is not associated with hyperkalemia or death in patients treated with hemodialysis.

Hyperkalemia in patients undergoing hemodialysis: its pathophysiology and management

Potassium is a major intracellular cation in the body, regulating membrane potential of excitable cells, such as cardiomyocytes and skeletal muscle cells. Because the kidney plays a critical role in controlling potassium balance, the elevation in serum potassium levels is one of the most common complications in patients with maintenance hemodialysis (MHD). In addition to reduced renal potassium excretion, the alteration in body potassium distribution owing to comorbid conditions may also contribute to dyskalemia. Besides potassium elimination through hemodialysis in MHD patients, accumulating data indicate the potential importance of extra‐renal elimination involving the gastrointestinal system, which can be affected by the inhibitors of the renin‐angiotensin‐aldosterone system. In this article, the literature on potassium physiology in MHD patients is reviewed with an emphasis on the changes from individuals with normal kidney function. This article also summarizes the findings of recent studies on dietary control, dialysate prescription, and pharmacological therapy.

Consensus-Based Recommendations for the Management of Hyperkalemia in the Hemodialysis Setting

Hyperkalemia (serum K⁺ >5.0 mmol/L) is commonly observed among patients receiving maintenance hemodialysis and associated with increased risk of cardiac arrhythmias. Current international guidelines may not reflect the latest evidence on managing hyperkalemia in patients undergoing hemodialysis, and there is a lack of high-quality published studies in this area. This consensus guideline aims to provide recommendations in relation to clinical practice. Available published evidence was evaluated through a systematic literature review, and the nominal group technique was used to develop consensus recommendations from a panel of experienced nephrologists, covering monitoring, dietary restrictions, prescription of K⁺ binders, and concomitant prescription of renin-angiotensin-aldosterone system inhibitors. Recent studies have shown that K⁺ binders reduce the incidence of hyperkalemia, but further evidence is needed in areas including whether reduced-K⁺ diets or treatment with K⁺ binders improve patient-centered outcomes. Treatment of hyperkalemia in the hemodialysis setting is complex, and decisions need to be tailored for individual patients.

Effect of intestinal dialysis using polyethylene glycol on fluid balance and thirst in maintenance hemodialysis patients: A comparative study

High inter-dialytic weight gains (IDWG) and Hyperkalemia have been associated with adverse outcomes like poor quality of life and high mortality. Thirst remains an unsolved problem in hemodialysis (HD) patients. The aim of this study was to evaluate the effect of polyethylene glycol (PEG) based intestinal dialysis on IDWG, thirst and biochemical parameters. A prospective interventional evidenced based paired comparative single center study was conducted. Thirty-five anuric patients on weekly thrice HD were studied for four consecutive dialysis weeks. Before the mid-week dialysis day of week 3, Patients received 2 L PEG solution. The primary end points were change in mean relative IDWG and change in mean subjective thirst feeling as measured on visual analog scale (VAS) with secondary endpoints being change in small molecule clearance. There was significant reduction in IDWG after the therapy from 3 ± 0.81 L to 2.35 ± 0.72 (P = 0.002). The therapy also reduced the % IDWG BW from 5.1 ± 1.7% to 4.15 ± 1.6% (P = 0.017). No change in thirst was seen, that is, 6.16 ± 0.66, 6.14 ± 0.64, and 6.16 ± 0.65 (P = 0.986). A multivariate linear regression did not reveal any effect of age, gender, and co-morbidities on the reduction of IDWG and thirst. The therapy achieved a significant urea, creatinine, and potassium reduction of 8.23%, 8.13%, and 8.33% respectively with an increase in sodium levels by 0.86%. This modality reduced the IDWG, was found to be a potent treatment modality for hyperkalemia but did not affect thirst sensation even after consumption of 2 L solution.

Regulation of muscle potassium: exercise performance, fatigue and health implications

This review integrates from the single muscle fibre to exercising human the current understanding of the role of skeletal muscle for whole-body potassium (K⁺) regulation, and specifically the regulation of skeletal muscle [K⁺]. We describe the K⁺ transport proteins in skeletal muscle and how they contribute to, or modulate, K⁺ disturbances during exercise. Muscle and plasma K⁺ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance. Moderate elevations of plasma and interstitial [K⁺] during exercise have beneficial effects on multiple physiological systems. Severe reductions of the trans-sarcolemmal K⁺ gradient likely contributes to muscle and whole-body fatigue, i.e. impaired exercise performance. Chronic or acute changes of arterial plasma [K⁺] (hyperkalaemia or hypokalaemia) have dangerous health implications for cardiac function. The current mechanisms to explain how raised extracellular [K⁺] impairs cardiac and skeletal muscle function are discussed, along with the latest cell physiology research explaining how calcium, β-adrenergic agonists, insulin or glucose act as clinical treatments for hyperkalaemia to protect the heart and skeletal muscle in vivo. Finally, whether these agents can also modulate K⁺-induced muscle fatigue are evaluated.

Does dietary potassium intake associate with hyperkalemia in patients with chronic kidney disease?

Background

Dietary potassium restriction is a strategy to control hyperkalemia in chronic kidney disease (CKD). However, hyperkalemia may result from a combination of clinical conditions. This study aimed to investigate whether dietary potassium or the intake of certain food groups associate with serum potassium in the face of other risk factors.

Methods

We performed a cross-sectional analysis including a nondialysis-dependent CKD (NDD-CKD) cohort and a hemodialysis (HD) cohort. Dietary potassium intake was assessed by 3-day food records. Underreporters with energy intake lower than resting energy expenditure were excluded. Hyperkalemia was defined as serum potassium &gt;5.0 mEq/L.

Results

The NDD-CKD cohort included 95 patients {median age 67 [interquartile range (IQR) 55–73] years, 32% with diabetes mellitus (DM), median estimated glomerular filtration rate 23 [IQR 18–29] mL/min/1.73 m2} and the HD cohort included 117 patients [median age 39 (IQR 18–67) years, 50% with DM]. In NDD-CKD, patients with hyperkalemia (36.8%) exhibited lower serum bicarbonate and a tendency for higher serum creatinine, a higher proportion of DM and the use of renin–angiotensin–aldosterone system blockers, but lower use of sodium bicarbonate supplements. No association was found between serum and dietary potassium (r = 0.01; P = 0.98) or selected food groups. Conditions associated with hyperkalemia in multivariable analysis were DM {odds ratio [OR] 3.55 [95% confidence interval (CI) 1.07–11.72]} and metabolic acidosis [OR 4.35 (95% CI 1.37–13.78)]. In HD, patients with hyperkalemia (50.5%) exhibited higher serum creatinine and blood urea nitrogen and lower malnutrition inflammation score and a tendency for higher dialysis vintage and body mass index. No association was found between serum and potassium intake (r = −0.06, P = 0.46) or food groups. DM [OR 4.22 (95% CI 1.31–13.6)] and serum creatinine [OR 1.50 (95% CI 1.24–1.81)] were predictors of hyperkalemia in multivariable analyses.

Conclusions

Dietary potassium was not associated with serum potassium or hyperkalemia in either NDD-CKD or HD patients. Before restricting dietary potassium, the patient’s intake of potassium should be carefully evaluated and other potential clinical factors related to serum potassium balance should be considered in the management of hyperkalemia in CKD.

Plant-based diets to manage the risks and complications of chronic kidney disease

Traditional dietary recommendations for patients with chronic kidney disease (CKD) focus on the quantity of nutrients consumed. Without appropriate dietary counselling, these restrictions can result in a low intake of fruits and vegetables and a lack of diversity in the diet. Plant nutrients and plant-based diets could have beneficial effects in patients with CKD: increased fibre intake shifts the gut microbiota towards reduced production of uraemic toxins; plant fats, particularly olive oil, have anti-atherogenic effects; plant anions might mitigate metabolic acidosis and slow CKD progression; and as plant phosphorus has a lower bioavailability than animal phosphorus, plant-based diets might enable better control of hyperphosphataemia. Current evidence suggests that promoting the adoption of plant-based diets has few risks but potential benefits for the primary prevention of CKD, as well as for delaying progression in patients with CKD G3-5. These diets might also help to manage and prevent some of the symptoms and metabolic complications of CKD. We suggest that restriction of plant foods as a strategy to prevent hyperkalaemia or undernutrition should be individualized to avoid depriving patients with CKD of these potential beneficial effects of plant-based diets. However, research is needed to address knowledge gaps, particularly regarding the relevance and extent of diet-induced hyperkalaemia in patients undergoing dialysis.

Evidence in support of hyperkalaemia management strategies: A systematic literature review

BACKGROUND

Hyperkalaemia is a potentially life-threatening condition that can be managed with pharmacological and non-pharmacological approaches. With the recent development of new hyperkalaemia treatments, new information on safe and effective management of hyperkalaemia has emerged.

OBJECTIVES

This systematic literature review (SLR) aimed to identify all relevant comparative and non-comparative clinical data on management of hyperkalaemia in adults. Our secondary aim was to assess the feasibility of quantitatively comparing randomised controlled trial (RCT) data on the novel treatment sodium zirconium cyclosilicate (ZS) and established pharmacological treatments for the non-emergency management of hyperkalaemia, such as the cation-exchangers sodium/calcium polystyrene sulphonate (SPS/CPS).

METHODS

MEDLINE, Embase and the Cochrane Library were searched on 3^rd April 2017, with additional hand-searches of key congresses and previous SLRs. Articles were screened by two independent reviewers. Eligible records reported interventional or observational studies of pharmacological or non-pharmacological management of hyperkalaemia in adults.

RESULTS

Database searches identified 2,073 unique records. Two hundred and one publications were included, reporting 30 RCTs, 29 interventional non-RCTs and 43 observational studies. Interventions investigated in RCTs included ZS (3), SPS/CPS (3), patiromer (4) and combinations of temporising agents (6 RCTs). A robust and meaningful indirect treatment comparison between ZS and long-established cation-binding agents (SPS/CPS) was infeasible because of heterogeneity between studies (including time points and dosing) and small sample size in SPS/CPS studies.

CONCLUSIONS

Despite hyperkalaemia being associated with several chronic diseases, there is a paucity of high-quality randomised evidence on long-established treatment options (SPS and CPS) and a limited evidence base for hyperkalaemia management with these agents.

Sodium-Reduced Meat and Poultry Products Contain a Significant Amount of Potassium from Food Additives

BACKGROUND

Sodium-reduced packaged food products are increasingly available to consumers; however, it is not clear whether they are suitable for inclusion in a potassium-reduced diet. For individuals with impaired renal potassium excretion caused by chronic kidney disease and for those taking certain medications that interfere with the rennin-angiotensin aldosterone axis, the need to limit dietary potassium is important in view of the risk for development of hyperkalemia and fatal cardiac arrhythmias.

OBJECTIVE

The primary objective of this study was to determine the impact of the reduction of sodium in packaged meat and poultry products (MPPs) on the content of potassium and phosphorus from food additives.

DESIGN

This was a cross-sectional study comparing chemically analyzed MPPs (n=38, n=19 original, n=19 sodium-reduced), selected from the top three grocery chains in Canada, based on market share sales. All MPPs with a package label containing a reduced sodium content claim together with their non-sodium-reduced packaged MPP counterparts were selected for analysis. The protein, sodium, phosphorus, and potassium contents of sodium-reduced MPPs and the non-sodium-reduced (original) MPP counterparts were chemically analyzed according to the Association of Analytical Communities official methods 992.15 and 984.27 and compared by using a paired t test. The frequency of phosphorus and potassium additives appearing on the product labels' ingredient lists were compared between groups by using McNemar's test.

RESULTS

Sodium-reduced MPPs (n=19) contained 44% more potassium (mg/100 g) than their non-sodium-reduced counterparts (n=19) (mean difference [95% CI): 184 [90-279]; P=0.001). The potassium content of sodium-reduced MPPs varied widely and ranged from 210 to 1,500 mg/100 g. Potassium-containing additives were found on the ingredient list in 63% of the sodium-reduced products and 26% of the non-sodium-reduced products (P=0.02). Sodium-reduced MPPs contained 38% less sodium (mg/100 g) than their non-sodium-reduced counterparts (mean difference [95% CI]: 486 [334-638]; P<0.001). The amounts of phosphorus and protein, as well as the frequency of phosphorus additives appearing on the product label ingredient list, did not significantly differ between the two groups.

CONCLUSIONS

Potassium additives are frequently added to sodium-reduced MPPs in amounts that significantly contribute to the potassium load for patients with impaired renal handling of potassium caused by chronic kidney disease and certain medications. Patients requiring potassium restriction should be counseled to be cautious regarding the potassium content of sodium-reduced MPPs and encouraged to make food choices accordingly.

Nutrient Non-equivalence: Does Restricting High-Potassium Plant Foods Help to Prevent Hyperkalemia in Hemodialysis Patients?

Hemodialysis patients are often advised to limit their intake of high-potassium foods to help manage hyperkalemia. However, the benefits of this practice are entirely theoretical and not supported by rigorous randomized controlled trials. The hypothesis that potassium restriction is useful is based on the assumption that different sources of dietary potassium are therapeutically equivalent. In fact, animal and plant sources of potassium may differ in their potential to contribute to hyperkalemia. In this commentary, we summarize the historical research basis for limiting high-potassium foods. Ultimately, we conclude that this approach is not evidence-based and may actually present harm to patients. However, given the uncertainty arising from the paucity of conclusive data, we agree that until the appropriate intervention studies are conducted, practitioners should continue to advise restriction of high-potassium foods.

Gut sensing of potassium intake and its role in potassium homeostasis

Extracellular K(+) homeostasis has been explained by feedback mechanisms in which changes in extracellular K(+) concentration drive renal K(+) excretion directly or indirectly via stimulating aldosterone secretion. However, this cannot explain meal-induced kaliuresis, which often occurs without increases in plasma K(+) or aldosterone concentrations. Recent studies have produced evidence supporting a feedforward control in which gut sensing of dietary K(+) increases renal K(+) excretion (and extrarenal K(+) uptake) independent of plasma K(+) concentrations, namely, a gut factor. This review focuses on these new findings and discusses the role of gut factor in acute and chronic regulation of extracellular K(+) as well as in the beneficial effects of high K(+) intake on the cardiovascular system.

Potassium balances in maintenance hemodialysis

Potassium is abundant in the ICF compartment in the body and its excretion primarily depends on renal (about 90%), and to a lesser extent (about 10%) on colonic excretion. Total body potassium approximated to 50mmol/kg body weight and 2% of total body potassium is in the ECF compartment and 98% of it in the intracellular compartment.Dyskalemia is a frequent electrolyte imbalance observed among the maintenance hemodialysis patients. In case of hyperkalemia, it is frequently "a silent and a potential life threatening electrolyte imbalance" among patients with ESRD under maintenance hemodialysis. The prevalence of hyperkalemia in maintenance HD patients was reported to be about 8.7-10%. Mortality related to the hyperkalemia has been shown to be about 3.1/1,000 patient-years and about 24% of patients with HD required emergency hemodialysis due to severe hyperkalemia. In contrast to the hyperkalemia, much less attention has been paid to the hypokalemia in hemodialysis patients because of the low prevalence under maintenance hemodialysis patients. Severe hypokalemia in the hemodialysis patients usually was resulted from low potassium intake (malnutrition), chronic diarrhea, mineralocorticoid use, and imprudent use of K-exchange resins. Recently, the numbers of the new patients with advanced chronic kidney disease undergoing maintenance hemodialysis are tremendously increasing worldwide. However, the life expectancy of these patients is still much lower than that of the general population. The causes of excess mortality in these patients seem to various, but dyskalemia is a common cause among the patients with ESRD undergoing hemodialysis.

Hyperkalaemia in the age of aldosterone antagonism

Hyperkalaemia is well recognized as a medical emergency. However, with the publication of trials showing benefit with renin-aldosterone axis suppression in heart failure, the epidemiology of patients presenting with hyperkalaemia has changed. The reported incidence of rate of serious hyperkalaemia (>6.0 mEq/l of potassium) ranges from 6 to 12% in patients on spironolactone with congestive cardiac failure (CCF). A rational choice of therapy based on present evidence is different from the traditionally used algorithm, given our understanding of the physiology relevant to this patient group. This article discusses the changing face of hyperkalaemia and the present evidence and discusses options in treatment of hyperkalaemia.

Serum potassium and outcomes in CKD: insights from the RRI-CKD cohort study

BACKGROUND AND OBJECTIVES

The relationship between serum potassium (S(K)) and mortality in chronic kidney disease (CKD) has not been systematically investigated.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We examined the predictors and mortality association of S(K) in the Renal Research Institute CKD Study cohort, wherein 820 patients with CKD were prospectively followed at four US centers for an average of 2.6 years. Predictors of S(K) were investigated using linear and repeated measures regression models. Associations between S(K) and mortality, the outcomes of ESRD, and cardiovascular events in time-dependent Cox models were examined.

RESULTS

The mean age was 60.5 years, 80% were white, 90% had hypertension, 36% had diabetes, the average estimated GFR was 25.4 ml/min per 1.73 m(2), and mean baseline S(K) was 4.6 mmol/L. Higher S(K) was associated with male gender, lower estimated GFR and serum bicarbonate, absence of diuretic and calcium channel blocker use, diabetes, and use of angiotensin-converting enzyme inhibitors and/or statins. A U-shaped relationship between S(K) and mortality was observed, with mortality risk significantly greater at S(K) < or = 4.0 mmol/L compared with 4.0 to 5.5 mmol/L. Risk for ESRD was elevated at S(K) < or = 4 mmol/L in S(K) categorical models. Only the composite of cardiovascular events or death as an outcome was associated with higher S(K) (> or = 5.5).

CONCLUSIONS

Although clinical practice usually emphasizes greater attention to elevated S(K) in the setting of CKD, our results suggest that patients who have CKD and low or even low-normal S(K) are at higher risk for dying than those with mild to moderate hyperkalemia.

Recent advances in understanding integrative control of potassium homeostasis

The potassium homeostatic system is very tightly regulated. Recent studies have shed light on the sensing and molecular mechanisms responsible for this tight control. In addition to classic feedback regulation mediated by a rise in extracellular fluid (ECF) [K(+)], there is evidence for a feedforward mechanism: Dietary K(+) intake is sensed in the gut, and an unidentified gut factor is activated to stimulate renal K(+) excretion. This pathway may explain renal and extrarenal responses to altered K(+) intake that occur independently of changes in ECF [K(+)]. Mechanisms for conserving ECF K(+) during fasting or K(+) deprivation have been described: Kidney NADPH oxidase activation initiates a cascade that provokes the retraction of K(+) channels from the cell membrane, and muscle becomes resistant to insulin stimulation of cellular K(+) uptake. How these mechanisms are triggered by K(+) deprivation remains unclear. Cellular AMP kinase-dependent protein kinase activity provokes the acute transfer of K(+) from the ECF to the ICF, which may be important in exercise or ischemia. These recent advances may shed light on the beneficial effects of a high-K(+) diet for the cardiovascular system.

Hyperkalemia: a review

Potassium is the principal intracellular cation, and maintenance of the distribution of potassium between the intracellular and the extracellular compartments relies on several homeostatic mechanisms. When these mechanisms are perturbed, hypokalemia or hyperkalemia may occur. This review covers hyperkalemia, that is, a serum potassium concentration exceeding 5 mmol/L. The review includes a discussion of potassium homeostasis and the etiologies of hyperkalemia and focuses on the prompt recognition and treatment of hyperkalemia. This disorder should be of major concern to clinicians because of its propensity to cause fatal arrhythmias. Hyperkalemia is easily diagnosed, and rapid and effective treatments are readily available. Unfortunately, treatment of this life-threatening condition is often delayed or insufficiently attentive or aggressive.

Effect of Oral Glucose Administration on Serum Potassium Concentration in Hemodialysis Patients

BACKGROUND

Extrarenal potassium disposal is particularly critical in patients with end-stage renal disease. Exogenous insulin stimulates this disposal by enhancing potassium uptake into cells in hemodialysis (HD) patients and healthy subjects. However, the effect of physiological levels of endogenous insulin on this disposal in these patients or healthy subjects is unknown.

METHODS

Effects of an oral glucose tolerance test (37.5, 75, and 150 g) on serum potassium levels were determined in 13 HD patients and 7 healthy controls. Serum potassium and insulin levels and plasma aldosterone and epinephrine levels were measured before and after glucose loads.

RESULTS

In HD patients and controls, serum insulin levels increased to a similar magnitude in parallel with increased serum glucose levels, but serum potassium levels decreased significantly only in HD patients. In HD patients, plasma aldosterone or epinephrine levels were not changed significantly after a glucose load. In HD patients, the decrease in serum potassium levels was dependent on the increase in serum insulin levels and was more prominent when 150 g of glucose was administered. In HD patients, the decrease in serum potassium levels correlated negatively (r = -0.45; P < 0.001) with the increase in serum insulin levels, and maximal decrease in serum potassium levels correlated negatively (r = -0.54; P < 0.001) with maximal increase in serum insulin levels.

CONCLUSION

Endogenous production of physiological concentrations of insulin in response to exogenous glucose administration decreases serum potassium levels only in HD patients, independently of plasma aldosterone and epinephrine levels.

Insulin and mineralocorticoids influence on extrarenal potassium metabolism in chronic hemodialysis patients

Insulin-mineral corticoids effects on extrarenal K+ metabolism in dialysis patients. During the inter-dialytic interval in dialyzed patients, hydrogen and potassium ions are regulated by extrarenal mechanisms. We studied the hormonal and acidotic effects on the extrarenal potassium metabolism, in selected, anuric and stable, hemodialysis patients. Fifteen patients, were grouped according to the mean mid-week pre-dialysis K+ over the past 12 months: > 6.0 mEq/L (G1, n=5), = 5.1-6.0 mEq/L (G2, n=5), < or = 5.0 mEq/L (G3, n=5). After a mid-week hemodialysis session and 12 h fasting, they received 1 g/Kg glucose p.os (A). Insulin, aldosterone, renin, pH, HCO3-, glucose, body weight, blood pressure and heart rate were measured before and 60' after the meal. We recorded the same parameters, except insulin, in 15 patients, similarly grouped, before hemodialysis (T0) and on 3 consecutive off dialysis days (T1-T3); G1 received fluorohydrocortisone (FHC) 0.1 mg-0.3 mg/day, according to body weight and G3 spironolactone (SLT) 200 mg per day. G2 were controls (B). (A) A significant rise in glycemia (81 +/- 23 to 157 +/- 52 mg/dL, P<0.001) and insulin (11.8 +/- 6.2 to 46.8 +/- 19.5 microU/mL, P<0.001), with a drop in K+ (5.1 +/- 0.6 to 4.8 +/- 0.7 mEq/L, P=0.001) and aldosterone (453 +/- 373 to 383 +/- 364 pg/mL, P<0.01), were noted at T60 vs. T0, in all groups. Insulin levels correlated negatively (r=-0.54, P<0.04) to serum K+ at T60, in all patients. (B) No major pH, HCO3 and aldosterone changes were observed in the 3 groups. Despite that, K+ dropped in G1 by FHC (6.7 +/- 0.9 to 5.9 +/- 0.6 mEq/L, P<0.05), rose in G3 by SLT (4.4 +/- 0.4 to 5.4 +/- 0.3 mEq/L, P<0.05) and remained unchanged in controls (5.8 +/- 0.2 to 5.8 +/- 0.6 mEq/L), (T0 vs T3 pre-dialysis values). Glucose significantly lowered K+ by promoting adequate insulin secretion. Drugs affecting aldosterone action significantly influenced potassium metabolism. Acid-base balance was not important in K+ handling in steady state anuric dialysis patients.

Hyperkalemia in dialysis patients

Serious hyperkalemia is common in patients with end-stage renal disease (ESRD) and accounts for considerable morbidity and death. Mechanisms of extrarenal disposal of potassium (gastrointestinal excretion and cellular uptake) play a crucial role in the defense against hyperkalemia in this population. In this article we review extrarenal potassium homeostasis and its alteration in patients with ESRD. We pay particular attention to the factors that influence the movement of potassium across cell membranes. With that background we discuss the emergency treatment of hyperkalemia in patients with ESRD. We conclude with a review of strategies to reduce the risk of hyperkalemia in this population of patients.

Effects of recombinant human growth hormone on muscle protein turnover in malnourished hemodialysis patients

To assess the effect of recombinant human growth hormone (rhGH) on muscle protein metabolism in uremic patients with malnutrition, forearm [3H]phenylalanine kinetics were evaluated in six chronically wasted (body weight 79% of ideal weight) hemodialysis (HD) patients in a self-controlled, crossover study. Forearm protein dynamics were evaluated before, after a 6-wk course of rhGH (5 mg thrice weekly) and after a 6-wk washout period. After rhGH: (a) forearm phenylalanine net balance--the difference between phenylalanine incorporation into and phenylalanine release from muscle proteins--decreased by 46% (-8+/-2 vs. -15+/-2 nmol/min x 100 ml at the baseline and -11+/-2 after washout, P < 0.02); (b) phenylalanine rate of disposal, an index of protein synthesis, increased by 25% (25+/-5 vs. 20+/-5 at the baseline and 20+/-4 after washout, P < 0.03); (c) phenylalanine rate of appearance, an index of protein degradation, was unchanged (33+/-5 vs. 35+/-5 at the baseline and 31+/-4 after washout); (d) forearm potassium release declined (0.24+/-0.13 vs. 0.60+/-0.15 microeq/min at the baseline, and 0.42+/-0.20 microeq/min after washout P < 0.03); (e) changes in the insulin-like growth factor binding protein (IGFBP)-1 levels and insulin-like growth factor-I (IGF-I)/IGFBP-3 ratios accounted for 15.1% and 47.1% of the percent variations in forearm net phenylalanine balance, respectively. Together, these two factors accounted for 62.2% of variations in forearm net phenylalanine balance during and after rhGH administration. These data indicate: (a) that rhGH administration in malnourished hemodialysis patients is followed by an increase in muscle protein synthesis and by a decrease in the negative muscle protein balance observed in the postabsorptive state; and (b) that the reduction in net protein catabolism obtained with rhGH can be accounted for by the associated changes in circulating free, but not total, IGF-I levels.

Potassium homeostasis and its disturbances in children

Although only 2% of the body potassium is present in the extracellular space, its concentration is finely regulated by the internal balance, or distribution of potassium between the intracellular and extracellular compartments, and by the external balance, or difference between intake and output of potassium. Internal balance is modulated by a host of factors, including insulin, epinephrine, extracellular pH and plasma tonicity. Potassium output from the body is mainly determined by renal excretion. Renal secretion of potassium takes place predominantly in the principal cells of late distal and cortical collecting tubules, by a process involving the accumulation of potassium in the cell by the activity of the basolateral Na+,K(+)-ATPase and its exit through luminal conductive channels. The factors regulating renal potassium secretion are potassium intake, rate of tubular fluid flow, distal sodium delivery, acid-base status and aldosterone. Hypokalaemia may result from a low potassium intake, excessive gastrointestinal, cutaneous or renal losses and altered body distribution. Aetiological diagnosis and therapy are best accomplished when the acid-base status is assessed at the same time. Before establishing the diagnosis of hyperkalaemia, spurious hyperkalaemia due to haemolysis or release of potassium from cells during clot retraction (pseudohyperkalaemia) should be ruled out. Hyperkalaemia may result from exogenous or endogenous loading, decreased renal output and altered body distribution. Acute hyperkalaemia represents an emergency situation which requires immediate therapy.