Hyperkalemia and hyporeninemic hypoaldosteronism

Predictors of hyperkalemia and death in patients with cardiac and renal disease

Predictors of hyperkalemia in patients with cardiovascular disease (CVD; defined as patients with hypertension and heart failure) and associated chronic kidney disease (CKD) are not well established. The aim of this study was to ascertain risk factors of hyperkalemia (defined as serum potassium concentration >5.0 mEq/L) and associated all-cause mortality in patients with CVD treated with antihypertensive drugs that impair potassium homeostasis. In a retrospective analysis using a logistic regression model, risk factors for hyperkalemia and all-cause mortality were analyzed in 15,803 patients with CVD treated with antihypertensive drugs. The mean estimated glomerular filtration rate and mean serum potassium concentration were 55.55 ml/min/1.73 m(2) and 4.06 mEq/L, respectively. Hyperkalemia was observed in 24.5% of study patients and 1.7% of total hospital admissions. Compared to patients with normokalemia, those with hyperkalemia had a higher percentage of death (6.25% vs 2.92%, p = 0.0001) and admissions (7.80% vs 5.04%, p = 0.0001). Predictors of hyperkalemia were CKD stage (odds ratio [OR] 2.14, 95% confidence interval [CI] 2.02 to 2.28), diabetes mellitus (OR 1.59, 95% CI 1.47 to 1.72), coronary artery disease (OR 1.32, 95% CI 1.21 to 1.43), and peripheral vascular disease (OR 1.55, 95% CI 1.36 to 1.77). Predictors of all-cause mortality were CKD stage (OR 1.26, 95% CI 1.12 to 1.43), hyperkalemic event (OR 1.56, 95% CI 1.30 to 1.88), age (OR 1.04, 95% CI 1.03 to 1.05), and hospitalization (OR 1.04, 95% CI 1.04 to 1.05). In conclusion, hyperkalemia is encountered frequently in patients with established CVD who are taking antihypertensive drugs and is associated with increases in all-cause mortality and hospitalizations. Advanced CKD, diabetes mellitus, coronary artery disease, and peripheral vascular disease are independent predictors of hyperkalemia.

Electrolyte disturbances associated with commonly prescribed medications in the intensive care unit

Electrolyte imbalances are common in critically ill patients. Although multiple disease states typically encountered in the intensive care unit may be responsible for the development of electrolyte disorders, medications may contribute to these disturbances as well. Medications can interfere with the absorption of electrolytes, alter hormonal responses affecting homeostasis, as well as directly impact organ function responsible for maintaining electrolyte balance. The focus on this review is to identify commonly prescribed medications in the intensive care unit and potential electrolyte disturbances that may occur as a result of their use. This review will also discuss the postulated mechanisms associated with these drug-induced disorders. The specific drug-induced electrolyte disorders discussed in this review involve abnormalities in sodium, potassium, calcium, phosphate, and magnesium. Clinicians encountering electrolyte disturbances should be vigilant in monitoring the patient's medications as a potential etiology. Insight into these drug-induced disorders should allow the clinician to provide optimal medical management for the critically ill patient, thus improving overall healthcare outcomes.

Diabetes and drug-associated hyperkalemia: effect of potassium monitoring

BACKGROUND

Renin-angiotensin-aldosterone system (RAAS) inhibitors are associated with hyperkalemia, but there is little evidence demonstrating patients who receive potassium monitoring have a lower rate of hyperkalemia.

OBJECTIVE

To evaluate the association between potassium monitoring and serious hyperkalemia-associated adverse outcomes among patients with diabetes newly initiating RAAS inhibitor therapy.

DESIGN

Retrospective observational study.

PARTICIPANTS

Patients with diabetes without end-stage renal disease initiating RAAS inhibitor therapy between 2001 and 2006 at three integrated health care systems.

MEASUREMENTS

Potassium monitoring and first hyperkalemia-associated adverse event during the initial year of therapy. Hyperkalemia-associated adverse events included hospitalizations, emergency department visits or deaths within 24 h of hyperkalemia diagnosis and/or diagnostic potassium >or=6 mmol/l. Incidence rates were calculated in person-years (p-y). We used inverse probability propensity score weighting to adjust for differences between patients with and without monitoring; Poisson regression was used to obtain adjusted relative risks.

RESULTS

A total of 19,391 of 27,355 patients (71%) received potassium monitoring. Serious hyperkalemia-associated events occurred at an incidence rate of 10.2 per 1,000 p-y. Compared to patients without monitoring, adjusted relative risk of hyperkalemia-associated adverse events among all patients with monitoring was 0.50 (0.37, 0.66); in the subset of patients who also had chronic kidney disease (n = 2,176), adjusted relative risk was 0.29 (0.18, 0.46).

CONCLUSIONS

Patients prescribed RAAS inhibitors who have both diabetes and chronic kidney disease and receive potassium monitoring are less likely to experience a serious hyperkalemia-associated adverse event compared to similar patients who did not receive potassium monitoring. This evidence supports existing consensus-based guidelines.

Blood pressure drug therapy and electrolyte disturbances

Antihypertensive pharmacologic treatment may be associated with diverse disturbances of electrolyte homeostasis. These drug-induced disorders are relatively common, typically including hyponatraemia, hypokalaemia, hyperkalaemia, hypomagnesaemia, hypophosphataemia and hypercalcaemia. Diuretics, beta-blockers, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are particularly likely to cause these complications. Recognised risk factors include high-dosage regimens (especially diuretics), old age, diabetes and impairment of renal function. Strategies to prevent these adverse drug reactions involve careful consideration of risk factors and clinical and laboratory evaluation in the course of treatment.

[Water and electrolyte disturbances in critical care]

Management of critically ill patients regularly involves the treatment of water and electrolyte disturbances. Moreover, critical care itself may contribute to volume overload and electrolyte abnormalities. Initial therapy should be followed by consequent diagnostic evaluation. The shift of volume and potassium in severe pancreatitis, for example, may lead to a life-threatening situation. In brain-dead patients, successful organ donation is facilitated by careful maintenance of water and electrolyte homeostasis.

Laboratory evaluation of potassium and creatinine among ambulatory patients prescribed spironolactone: are we monitoring for hyperkalemia?

BACKGROUND

Serum potassium and creatinine evaluation is recommended in patients prescribed spironolactone, yet the proportion of ambulatory patients chronically dispensed spironolactone receiving evaluation is not well understood.

OBJECTIVE

To estimate the rate of potassium and creatinine evaluation and identify factors associated with conducting these tests among ambulatory patients dispensed spironolactone.

METHODS

A retrospective cohort study was designed to evaluate patients at 10 health maintenance organizations with ongoing spironolactone dispensing for one year (N = 2257). Potassium and creatinine evaluation were determined from administrative data. Associations between patient characteristics and laboratory testing were assessed, using logistic regression modeling.

RESULTS

Serum creatinine and potassium were evaluated in 72.3% of patients during a 13 month period. The likelihood of potassium and creatinine monitoring was greater among patients who were older (OR 1.28; 95% CI 1.17 to 1.41 per decade of life); male (OR 1.25; 95% CI 1.01 to 1.54); had diabetes (OR 1.63; 95% CI 1.31 to 2.03); received concomitant therapy with angiotensin-converting enzyme inhibitors/angiotensin receptor blockers (OR 2.23; 95% CI 1.74 to 2.87), potassium supplements (OR 1.96; 95% CI 1.51 to 2.54), or digoxin (OR 2.10 95% CI 1.48 to 2.98); or had more outpatient visits (OR 1.31; 95% CI 1.19 to 1.44). Among patients with heart failure (n = 790), factors associated with the incidence of laboratory testing were diabetes (OR 1.64, 95% CI 1.14 to 2.34), outpatient visits (OR 1.20; 95% CI 1.02 to 1.41), and digoxin therapy (OR 2.26; 95% CI 1.38 to 3.69).

CONCLUSIONS

Three-fourths of ambulatory patients dispensed spironolactone receive recommended laboratory evaluation, with monitoring more likely to be completed in patients prescribed concomitant therapy with drugs that increase hyperkalemia risk, older patients, and those with diabetes.

Racial Differences in Potassium Response to Spironolactone in Heart Failure

Evidence of racial differences in aldosterone concentrations and K+ disposition suggests that response to aldosterone antagonism might vary by race. The authors sought to determine whether K+ response to spironolactone differs between African Americans and Caucasians with heart failure. Heart failure patients of African-American (n = 34) or Caucasian (n = 17) race were started on spironolactone 12.5 mg/d, with up-titration as tolerated. Laboratory values and drug therapy were similar between racial groups at baseline. Spironolactone was titrated to a median dose of 25 mg/d in both groups. Neither concomitant medications nor serum creatinine changed significantly in either group during spironolactone dose titration. Median serum K+ concentrations increased by 0.5 mEq/L (range, -0.7 to 1.6 mEq/L) in Caucasians, but only 0.1 mEq/L (range, -0.8 to 0.9 mEq/L) in African Americans; p < 0.01. These data suggest that African Americans with heart failure may be less responsive to the renal effects of spironolactone.

Hyperkalemic distal renal tubular acidosis associated with Rett syndrome

Renal function was studied in a 7-year-old girl with Rett syndrome (RS) complicated by persistent hyperchloremic hyperkalemic metabolic acidosis. The acidosis was associated with a urine pH above 5.5, positive urinary anion gap and decreased potassium excretion. Plasma renin activity, aldosterone and cortisol levels were normal. Therapy with sodium bicarbonate failed to lower urine pH below 5.5 or increase potassium excretion. Hydrochlorothiazide administration resulted in a fall in urine pH below 5.5 and an increase in potassium excretion as a result of increased distal sodium delivery and increased sodium reabsorption in the distal nephron. We conclude that a voltage-dependent type of derangement in the distal nephron, rather than aldosterone deficiency, is responsible for the impairment in urinary acidification observed in this patient. Early detection of impaired renal acidification in RS may prevent or slow the progression of growth failure.

Aldosterone antagonists in the treatment of heart failure

PURPOSE

The clinical benefits, adverse effects, pharmacokinetics, and recommendations for the appropriate use of the aldosterone antagonists spironolactone and eplerenone in patients with heart failure are reviewed.

SUMMARY

Heart failure is a clinical syndrome characterized by the functional inability of the ventricle to meet the metabolic demands of the body. Renal hypoperfusion occurs as a result of reduced cardiac output, resulting in the activation of the renin-angiotensin-aldosterone system, which compensates for the hypoperfusion. However, this contributes to the pathology of the disease by, among other actions, increasing the release of aldosterone. Aldosterone has been shown to cause coronary inflammation, cardiac hypertrophy, myocardial fibrosis, ventricular arrhythmias, and ischemic and necrotic lesions. There are currently two aldosterone antagonists commercially available in the United States, spironolactone and eplerenone. Spironolactone is a nonselective aldosterone antagonist, and eplerenone is selective to the aldosterone receptor. Although numerous clinical trials have evaluated the efficacy of each drug, no studies have directly compared spironolactone and eplerenone. Both have been shown to improve morbidity and mortality in patients with advanced heart failure. Adverse effects of both spironolactone and eplerenone include potentially life-threatening hyperkalemia, which can be induced by renal insufficiency, diabetes mellitus, advanced heart failure, advanced age, and concurrent drug therapy.

CONCLUSION

Spironolactone and eplerenone are life-saving agents in patients with advanced heart failure and may benefit patients with mild heart failure. Potassium and renal function must be routinely assessed to minimize the risk of life-threatening hyperkalemia.

New strategies for treatment of heart failure with aldosterone antagonists and the risk of hyperkalaemia

Since the publication of The Randomized Aldactone Study (RALES) in 1999, the association of angiotensin-converting enzyme (ACE) inhibitors and spironolactone has been largely used for the treatment of congestive heart failure (CHF). Although this study had shown a diminished morbimortality in patients with CHF that are treated with spironolactone and ACE inhibitors and a low risk (2%) of development of severe hyperkalaemia, other clinical studies have shown higher rates of hyperkalaemia and serious adverse clinical events culminating in death. Therefore, the identification of risk factors for the development of hyperkalaemia in CHF patients, close monitoring of serum potassium and determination of renal function before and after the initiation of combined therapy or after a dose increment, should be routinely performed. It is strongly recommended that these drugs be initiated in low doses and that the increment in dose should only occur after considering all safety issues.

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.

Relationship between impaired aldosterone response to adrenocorticotropic hormone and prevalence of hemodialysis in type 2 diabetic patients without azotemia

The present prospective observational study was designed to assess the prevalence of hemodialysis in type 2 diabetic patients with an impairment of plasma aldosterone responsiveness to adrenocorticotropic hormone (ACTH). Sixty seven patients (43 men and 24 women) were selected. The inclusion criteria were age < 65 years; presence of normoalbuminemia (serum albumin > 3.6 g/dl); and absence of azotemia (serum creatinine < or = 1.2 mg/dl in males, and < or = 1.0 mg/dl in females). Soluble alpha(1-24)-ACTH was injected intramuscularly in a single dose of 0.25 mg after overnight recumbency. The area under the aldosterone curve (aldosterone AUC) was calculated. The diabetic patients were divided into two groups according to the levels of aldosterone AUC. Patients with an aldosterone AUC in the range of 0-381 were considered poor responders (n = 31) and those with an AUC of 397-1,007 were considered good responders (n = 36). The follow-up was performed during a 144-month period. The end point of the study was the introduction of hemodialysis. A total of 14 patients (12 poor responders and 2 good responders; p < 0.001) were introduced to hemodialysis. The prevalence of hemodialysis in the poor responders (5.74 per 100 patient-years) was significantly higher (p < 0.001, log-rank test) than that in the good responders (0.68 per 100 patient-years). One possible explanation is that an inappropriate level of salt intake relative to the impaired plasma aldosterone control may have contributed to the high prevalence of risks and hemodialysis in the poor responders.

Pharmacotherapy in congestive heart failure: aldosterone receptor antagonism: interface with hyperkalemia in heart failure

Aldosterone receptor antagonism (ARA) is an increasingly well-accepted element of heart failure therapy. The experimental underpinnings for the use of ARA in heart failure are strong being linked to a variety of tissue-based cardiac effects characteristic of drugs in this class. However, the benefits of ARA therapy do not come without some risk since drugs in this class are potent inhibitors of renal potassium (K+) elimination. Thus, some increment in serum K+, up to and including the development of overt hyperkalemia (typically defined as a serum K+ value in excess of 6.0 mEq/L), is to be expected whenever they are used. Hyperkalemia attributable to ARA relates to several factors including ARA dose, patient predisposition to hyperkalemia, as in the case of renal failure, and dietary intake of K+. The risk of some change in serum K+ with ARA should not be a deterrent to use of drugs in this class but, rather should prompt careful surveillance for the onset of this potentially life-threatening electrolyte disturbance. The frequency of such scrutiny should be patient-specific and based on the constellation of risk factors for hyperkalemia.

Acid-base and electrolyte abnormalities observed in patients receiving cardiovascular drugs

Cardiovascular drugs can cause a variety of acid-base and electrolyte abnormalities that need to be considered when clinicians manage the large number of patients who receive these agents. Diuretic-induced metabolic alkalosis is the most common acid-base disorder observed and is associated with hypokalemia. Drug-induced hyperkalemia is the most important cause of increased potassium levels in everyday clinical practice. Multifactorial-origin diuretic-induced hyponatremia is mostly due to thiazides and should be carefully managed. This review focuses on the pathogenetic mechanisms as well as on the treatment of these metabolic derangements that are commonly encountered in patients who receive cardiovascular drugs.

Perioperative management of patients with chronic kidney disease or ESRD

The perioperative management of patients with chronic kidney disease (CKD) or dialysis-dependent end-stage renal disease (ESRD) is complicated by both the underlying renal dysfunction, with associated disturbances of fluid and electrolyte homeostasis and altered drug clearance, and the presence of associated co-morbid conditions, including diabetes mellitus, chronic hypertension and cardiovascular and cerebrovascular disease. The impact of CKD on fluid and electrolyte management, haematological and cardiovascular complications and drug management in the perioperative period are reviewed. Special issues related to the management of haemodialysis and peritoneal dialysis patients in the perioperative period are also reviewed.

Hyperkalemia, congestive heart failure, and aldosterone receptor antagonism

Hyperkalemia is a common occurrence in patients with congestive heart failure, particularly when renal failure coexists. The level of renal function in congestive heart failure is often difficult to ascertain because good measurement tools for estimation of renal function are not available. Serum creatinine values have often been offered as a good gauge of renal function, although in most cases true renal function is appreciably lower than the estimate derived from a specific serum creatinine value. Thus, patients with congestive heart failure very commonly, particularly in the advanced stages of the disease, have moderate renal insufficiency, either due to specific heart failure-related renal perfusion changes or as the result of renal involvement from the same processes having caused the heart failure, as is the case with diabetes. It is in this setting of mild-to-moderate levels of renal failure that therapies, such as angiotensin-converting inhibitors, angiotensin-receptor blockers, and aldosterone-receptor antagonists, are administered either individually or collectively. Each of these drug classes reduces the homeostatic ability to eliminate ingested potassium loads by the renal route and increase the tendency to evolve into a hyperkalemic state. This is noteworthy because aldosterone-receptor antagonists are increasingly considered as important therapies in the long-term management of heart failure. Spironolactone has been employed in this capacity and a new aldosterone-receptor antagonist, eplerenone, will become available in the near future, which further increases the importance of evaluating and treating the hyperkalemia risk in a timely manner.

Hyperkalemia: An adaptive response in chronic renal insufficiency

BACKGROUND

Hyperkalemia is a common feature of chronic renal insufficiency, usually ascribed to impaired K+ homeostasis. However, various experimental observations suggest that the increase in extracellular [K+] actually functions in a homeostatic fashion, directly stimulating renal K+ excretion through an effect that is independent of, and additive to, aldosterone.

METHODS

We have reviewed relevant studies in experimental animals and in human subjects that have examined the regulation of K+ excretion and its relation to plasma [K+].

RESULTS

Studies indicate that (1) extracellular [K+] in patients with renal insufficiency correlates directly with intracellular K+ content, and (2) hyperkalemia directly promotes K+ secretion in the principal cells of the collecting duct by increasing apical and basolateral membrane conductances. The effect of hyperkalemia differs from that of aldosterone in that K+ conductances are increased as the primary event. The changes in principal cell function and structure induced by hyperkalemia are indistinguishable from the effects seen in adaptation to a high K+ diet.

CONCLUSIONS

We propose that hyperkalemia plays a pivotal role in K+ homeostasis in renal insufficiency by stimulating K+ excretion. In patients with chronic renal insufficiency, a new steady state develops in which extracellular [K+] rises to the level needed to stimulate K+ excretion so that it again matches intake. When this new steady state is achieved, plasma [K+] remains stable unless dietary intake increases, glomerular filtration rate falls, or drugs are given that disrupt the new balance.

Disorders of potassium homeostasis. Hypokalemia and hyperkalemia

This article reviews the diagnosis and management of clinical disorders of potassium balance, with particular attention to the critically ill patient. The normal regulation of potassium balance is reviewed as a background for understanding these disorders, followed by a discussion of the causes and management of hypo- and hyperkalemia. Practical guidelines are presented for acute and chronic management.

Sustained-release potassium chloride overdose

BACKGROUND

Although ingestion of sustained-release potassium supplements can cause life-threatening hyperkalemia in patients with abnormal renal function, only a few previous reports suggest that this may occur in patients with normal renal function. We report 2 cases of hyperkalemia in patients with normal renal function who developed hyperkalemia after ingesting sustained-release potassium preparations and describe the use of radiography and whole-bowel irrigation in their care.

CASE REPORTS

The first patient is a 50-year-old woman who ingested 100 K-Dur tablets (each tablet containing 750 mg KCl or 10 mEq potassium) in a suicide attempt 1 hour prior to presenting to the emergency department. She developed a peak serum potassium level of 9.7 mEq/L and had transient, potentially life-threatening electrocardiographic changes. The second patient was a 17-year-old man who ingested 20 to 30 Klor-Con tablets (each tablet containing 750 mg KCl or 10 mEq potassium) in a suicide attempt 10 hours prior to presentation. Although he developed a peak serum potassium level of 6.1 mEq/L, he had a persistently normal electrocardiogram. In both patients, the tablets were visualized on abdominal radiographs and the gastrointestinal tracts of both were successfully decontaminated using whole-bowel irrigation.

DISCUSSION

Although the sensitivity and specificity are unknown, the abdominal radiograph appears to be useful in detecting sustained-release potassium tablets. Whole-bowel irrigation as a primary method of gastrointestinal decontamination also appears to be effective although its use is not previously reported for sustained-release potassium overdoses.

Serious adverse events experienced by patients with chronic heart failure taking spironolactone

In patients with chronic heart failure, spironolactone added to conventional treatment may lead to serious and, occasionally, fatal hyperkalaemia. In some cases this seems to happen because spironolactone causes diarrhoea. Four cases involving men with New York Heart Association functional class III heart failure are presented. As these cases revealed, close monitoring of blood chemistry is mandatory after starting spironolactone, and patients should be advised to stop spironolactone immediately if diarrhoea develops.

Pharmacotherapy in congestive heart failure: Hyperkalemia in congestive heart failure

Hyperkalemia is not an uncommon occurrence in the congestive heart failure patient, particularly when renal failure coexists. Hyperkalemia in CHF is typically medication-related. Its occurrence is inevitably linked to the simultaneous ingestion of angiotensin-converting enzyme inhibitors and beta-blockers, and more recently, aldosterone receptor antagonists, such as spironolactone. The most devastating consequence of hyperkalemia is its cardiotoxicity that can be fairly insidious in its rate of development. The therapy of hyperkalemia in congestive heart failure can involve both acute and semiacute management phases. Acute hyperkalemia management includes measures that block the adverse membrane effects of hyperkalemia, such as intravenous calcium administration, and efforts to shift potassium intracellularly, such as occurs with intravenous bicarbonate and/or inhaled beta-agonists. Semiacute management of hyperkalemia includes measures to increase urinary potassium excretion and administration of binding resins, such as Kayexalate®. Prevention is the cornerstone of hyperkalemia management in the heart failure patient and requires that careful attention be directed to both identifying exogenous sources of potassium and pinpointing the maximum tolerable dose of either an angiotensin-converting enzyme inhibitor or an angiotensin-receptor blocker. (c)2001 by CHF, Inc.

Drug-induced hyperkalemia: old culprits and new offenders

Prescribed medications, over-the-counter drugs, and nutritional supplements are used by many patients. Although most of these products are well tolerated, drug-induced hyperkalemia may develop in patients with underlying renal impairment or other abnormalities in potassium handling. Drug-induced hyperkalemia most often occurs from impaired renal potassium excretion. However, disturbed cellular uptake of a potassium load as well as excessive ingestion or infusion of potassium-containing substances may also occur. Physicians must be aware of medications that can precipitate hyperkalemia, how these drugs induce alterations in potassium homeostasis, and the patient characteristics that increase the risk of hyperkalemia.

Effects of spironolactone on systolic blood pressure in experimental diabetic rats

BACKGROUND

Mineralocorticoid hormones, which maintain electrolyte balance and blood pressure, are thought to be associated not only with the expression of renal 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), but also with that of intracellular mineralocorticoid receptors (MRs). The present study was designed to test whether the mineralocorticoid action of glucocorticoid corticosterone on renal MR is involved in the development of diabetes-associated hypertension by measuring the alterations of renal 11beta-HSD2.

METHOD

We measured the mean systolic blood pressure, renal 11beta-HSD1, and mRNA levels in streptozotocin (STZ)-induced diabetic rats that received spironolactone, insulin, or no treatment, and in nondiabetic controls that received spironolactone.

RESULTS

Four weeks after an injection of STZ, the renal 11beta-HSD2 and mRNA levels were significantly lower in diabetic rats than in control rats, and the mean systolic blood pressure was 14.8% higher in diabetic rats than in controls. Subcutaneous injections of spironolactone into diabetic rats for three weeks partially reversed the decrease in renal 11beta-HSD2 activity and gene expression, and prevented the mean systolic blood pressure elevation. Spironolactone treatment for one week also resulted in a significant reduction in mean systolic blood pressure during the development of diabetic hypertension. However, treatment with STZ did not significantly decrease the renal 11beta-HSD1 activity and mRNA expression, and spironolactone treatment did not exert a significant effect on this enzyme in STZ-induced diabetic rats.

CONCLUSION

In the development of diabetes-induced hypertension, the effect of spironolactone on mean systolic blood pressure may be associated with the mineralocorticoid effects of corticosterone on renal MR, as well as an alteration of renal 11beta-HSD2 activity and its mRNA expression in insulin-dependent diabetic rats.

Distal tubule bicarbonate reabsorption in intact and remnant diabetic kidneys

BACKGROUND

In the diabetic patient, hyperkalemia and hyperchloremic metabolic acidosis has been attributed to one or more of the following factors associated with diabetic nephropathy: hypoaldosteronism, altered potassium homeostasis, or a distal tubular (DT) defect in hydrogen ion secretion. To evaluate maximal in vivo DT acidification in streptozotocin (STZ) diabetes, unidirectional bicarbonate reabsorption (JHCO3) was measured in DTs after acid loading and in surviving DT after 2/3 nephrectomy (Nx).

METHODS

Acid gavage induced hyperchloremic metabolic acidosis in four groups of rats: diabetic rats with hyperglycemia two (a) and (b) eight weeks after STZ injection, (c) diabetic rats with tight glucose control two weeks after STZ injection and insulin pump implantation; and (d) control nondiabetic rats. Another group of diabetic rats underwent (e) Nx one week after STZ injection; these rats were neither acid loaded nor pump implanted.

RESULTS

In the acidotic rats, the plasma potassium concentration, the plasma and urine acid-base parameters in the three STZ diabetic groups was not different from control rats, whereas JHCO3 fluxes were brisk without important differences between groups. In Nx rats, although the plasma potassium concentration and acid-base status were normal, surviving JHCO3 fluxes were still brisk and not different from the acid-loaded rats.

CONCLUSIONS

These in vivo measurements indicate there is no impairment in DT unidirectional bicarbonate reabsorption in the intact or remnant STZ diabetic kidney.

Biology of renal aging in humans

Advancing age is usually accompanied by a decline in glomerular filtration rate and an increased incidence of certain renal and electrolyte disorders. These include an increased susceptibility to acute renal failure, hypo- and hypernatremia, hyperkalemia, and hypertension. This report discusses anatomic and physiological observations related to the aged human kidney and explores the various theories and postulated mechanisms underlying these changes.

Hyper- and hypoaldosteronism

Aldosterone participates in blood volume and serum potassium homeostasis, which in turn regulate aldosterone secretion by the zona glomerulosa of the adrenal cortex. Autonomous aldosterone hypersecretion leads to hypertension and hypokalemia. Improved screening techniques have led to a re-evaluation of the frequency of primary aldosteronism among adults with hypertension, recognizing that normokalemic cases are more frequent than was previously appreciated. The genetic basis of glucocorticoid remediable aldosteronism has been elucidated and adequately explains most of the pathophysiologic features of this disorder. A new form of familial aldosteronism has been described, familial hyperaldosteronism type II; linkage analysis and direct mutation screening has shown that this disorder is unrelated to mutations in the genes for aldosterone synthase or the angiotensin II receptor. The features of aldosterone hypersecretion may be due to non-aldosterone-mediated mineralocorticoid excess. These include two causes of congenital adrenal hyperplasia (11 beta-hydroxylase deficiency and 17 alpha-hydroxylase deficiency), the syndrome of apparent mineralocorticoid excess (AME) due to 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) deficiency, primary glucocorticoid resistance, Liddle's syndrome due to activating mutations of the renal epithelial sodium channel, and exogenous sources of mineralocorticoid, such as licorice, or drugs, such as carbenoxolone. The features of mineralocorticoid excess are also often seen in Cushing's syndrome. Hypoaldosteronism may lead to hypotension and hyperkalemia. Hypoaldosteronism may be due to inadequate stimulation of aldosterone secretion (hyporeninemic hypoaldosteronism), defects in adrenal synthesis of aldosterone, or resistance to the ion transport effects of aldosterone, such as are seen in pseudohypoaldosteronism type I (PHA I). PHA I is frequently due to mutations involving the amiloride sensitive epithelial sodium channel. Gordon's syndrome (PHA type II) is due to resistance to the kaliuretic but not sodium reabsorptive effects of aldosterone for which the genetic basis is still unknown. This review aims to provide a survey of the clinical disorders of aldosterone excess and deficiency and their clinical management, with a focus on primary aldosteronism and isolated aldosterone deficiency.

Renin-aldosterone system can respond to furosemide in patients with hyperkalemic hyporeninism

Thirty-four patients (65.3+/-3.3 years of age, mean+/-SEM) with hyperkalemia (serum potassium >5.0 mEq/L) had measurement of their renin-aldosterone system. Nineteen patients (56%) had plasma renin activity (PRA) >1.5 ng/mL/h, which was not low, while 15 (44%) had PRA <1.5. Twelve of the 15 hyporeninemic hyperkalemic patients were studied to determine whether their renin-aldosterone system responded to 2 weeks of furosemide, 20 mg daily. Four were nonresponders: PRA averaged 0.3+/-0.1 ng/mL/h, and it did not increase with furosemide or respond to captopril before or after furosemide. Eight patients were responders: PRA averaged 0.6+/-0.2 ng/mL/h and increased with furosemide to 5.5+/-3.4 ng/mL/h. Captopril failed to increase PRA before furosemide, but PRA increased to 15.3+/-8.4 ng/mL/h after furosemide. Plasma aldosterone was low in both nonresponders and responders (3.5+/-1.2 ng/dL vs 5.8+/-2.5 ng/dL) and did not increase significantly with furosemide (4.3+/-1.7 ng/dL vs 8.7+/-2.5 ng/dL). Serum potassium did not fall and therefore did not limit the rise in aldosterone. Renin responders had greater body weight, were predominantly female (6/8 vs 2/4) and were more likely to have diabetes mellitus (7/8 vs 0/4). Plasma atrial natriuretic peptide (ANP) fell with furosemide in 8 of 8 responders and in 1 of the 2 nonresponders in whom it was measured. Neither group had suppressed plasma prorenin levels, indicating no suppression of renin gene expression. These results indicate that many hyperkalemic patients do not have suppressed PRA. Further, a majority of patients with suppressed PRA have high levels of ANP and can respond to diuretic therapy with a rise in PRA and a fall in ANP, suggesting physiologic suppression of the renin system by volume expansion. A minority of hyperkalemic patients with suppressed PRA had PRA that did not increase under these study conditions.

Hyponatraemia: biochemical and clinical perspectives

Hyponatraemia is a common bio-chemical abnormality, occurring in about 15% of hospital inpatients. It is often associated with severe illness and relatively poor outcome. Pathophysiologically, hyponatraemia may be spurious, dilutional, depletional or redistributional. Particularly difficult causes and concepts of hyponatraemia are the syndrome of inappropriate antidiuresis and the sick cell syndrome, which are discussed here in detail. Therapy should always be targeted at the underlying disease process. 'Hyponatraemic symptoms' are of doubtful importance, and may be more related to water overload and/or the causative disease, than to hyponatraemia per se. Artificial elevation of plasma sodium by saline infusion carries the risk of induction of osmotic demyelination (central pontine myelinolysis).

Hyperkalemia in the elderly: drugs exacerbate impaired potassium homeostasis

OBJECTIVE

To review the pathophysiology underlying the predisposition to hyperkalemia in the elderly; the medications that disrupt potassium balance and promote the development of hyperkalemia in the elderly; the prevention of hyperkalemia in elderly patients treated with potassium-altering medications; and the appropriate management of hyperkalemia when it develops.

METHODS AND MAIN RESULTS

A MEDLINE search of the literature (1966-1996) using the terms hyperkalemia, drugs, elderly, and treatment was conducted and pertinent review articles, textbooks, and personal files were consulted. Elderly subjects appear to be predisposed to the development of hyperkalemia on the basis of both innate disturbances in potassium homeostasis and comorbid disease processes that impair potassium handling. Hyperkalemia in the elderly is most often precipitated by medications that impair cellular uptake or renal disposal of potassium. This electrolyte disorder is best prevented by recognition of at-risk physiology in the aged, avoidance of therapy with certain high-risk medications, and monitoring of plasma potassium concentration and renal function at intervals appropriate for the medication prescribed. Management of hyperkalemia entails identification of the clinical manifestations of severe hyperkalemia, stabilization of cardiac tissue, promotion of cellular potassium uptake, and ultimately removal of potassium from the body.

CONCLUSIONS

Geriatric patients should be considered at risk of developing hyperkalemia, especially when they are prescribed certain medications. Potassium levels should be monitored at appropriate intervals when these patients are treated with potassium-altering medications. Appropriate management of hyperkalemia in the elderly can avoid life-threatening neuromuscular and cardiac complications.

Impact of the initial levels of laboratory variables on survival in chronic dialysis patients

Besides the age at start of dialysis and the presence of diabetes mellitus, serum albumin has been shown to be a significant predictor of survival in prevalent dialysis patients. However, this was not evaluated in incipient dialysis patients. The initial biochemical variables were retrieved for a large dialysis population (N = 1,982) who were started on chronic dialysis in Okinawa, Japan from 1971 to 1990. Biochemical data that included blood urea nitrogen, serum creatinine, serum electrolytes (sodium, potassium, calcium, and phosphate), total cholesterol, triglyceride, total protein, serum albumin, and hematocrit obtained just before the first dialysis session were available for 1,491 (75.2%) patients. Six hundred sixty-four (43.2%) patients died by the end of 1993. Cox proportional analysis adjusted for sex, age, year of start of dialysis, presence of diabetes mellitus, and the laboratory variables was performed to examine the significance of the initial biochemical data on survival. The risk ratio was 0.577 (P = 0.0025) in serum albumin, 1.291 (P = 0.0138) in serum potassium, and 0.966 (P = 0.0202) in serum sodium. The study results support the notion that nutritional status is important for survival in chronic dialysis patients. Causes of hypoalbuminemia, hyperkalemia, and hyponatremia should be evaluated carefully at initiation of dialysis.

Acid-base disorders in medicine

The practice of internal medicine involves daily exposure to abnormalities of acid-base balance. A wide variety of disease states either predispose patients to develop these conditions or lead to the use of medications that alter renal, gastrointestinal, or pulmonary function and secondarily alter acid-base balance. In addition, primary acid-base disease follows specific forms of renal tubular dysfunction (renal tubular acidosis). We review the acid-base physiologic functions of the kidney and gastrointestinal tract and the current understanding of acid-base pathophysiologic conditions. This includes a review of whole animal and renal tubular physiologic characteristics and a discussion of the current knowledge of the molecular biology of acid-base transport. We stress an approach to diagnosis that relies on knowledge of acid-base physiologic function, and we include discussion of the appropriate treatment of each disorder considered. Finally, we include a discussion of the effects of acidosis and alkalosis on human physiologic functions.

Hyperkalaemia in diabetes: prevalence and associations

Hyperkalaemia is associated with diabetes, but there are no recent reports of its prevalence and associations. Serum potassium concentrations were measured in all 1764 patients attending a diabetic clinic over a 12-month period and found to be > 5.0 mmol/l in 270 (15%), and > 5.4 mmol/l in 67 (4%). There was no other evident cause of hyperkalaemia in 41 of these 67 patients. These data serve to highlight the risk of dangerous hyperkalaemia in diabetic patients, particularly with concurrent administration of angiotensin-converting-enzyme inhibitors and potassium-sparing diuretics.