Hyperkalemic hyperchloremic metabolic acidosis: pathophysiologic insights

Fludrocortisone Is an Effective Treatment for Hyperkalaemic Metabolic Acidosis in Kidney Transplant Recipients on Tacrolimus: A Case Series

BACKGROUND

Hyperkalaemia with metabolic acidosis is common but under-reported following kidney transplantation. Calcineurin inhibitors, such as tacrolimus, are widely used in the management of transplant patients and are associated with the development of hyperkalaemia. We report on 10 renal transplant patients, treated with fludrocortisone, following identification of hyperkalaemic metabolic acidosis.

RESULTS

All 10 patients were male aged (mean ± SD) 53.0 ± 13.2 years; 7 were Caucasian and 3 South Asian. Before and after fludrocortisone administration, respective (mean ± SD) serum potassium was 6.1 ± 0.4 mmol/L and 5.3 ± 0.3 mmol/L (p = 0.0002); serum bicarbonate 18.5 ± 1.6 mmol/L and 20.5 ± 2.3 mmol/L (p = 0.002); serum sodium 135 ± 4.6 mmol/L and 137 ± 2.2 mmol/L (p = 0.0728); serum creatinine 181 ± 61 μmol/L and 168 ± 64 μmol/L (p = 0.1318); eGFR 42 ± 18 mL/min and 46 ± 18 mL/min (p = 0.0303); blood tacrolimus 10.1 ± 2.9 ng/mL and 10.4 ± 1.4 ng/mL (p = 0.7975); and blood pressure 129 ± 15/79 ± 25 mm Hg and 126 ± 24/75 ± 7 mm Hg. Pre-fludrocortisone, there were 7 episodes of serum potassium ≥6.5 mEq/L, with 4 patients requiring admission for the treatment of hyperkalaemia. Following fludrocortisone, no patients had hyperkalaemia requiring inpatient management.

CONCLUSIONS

Treatment of hyperkalaemic metabolic acidosis in transplant patients on tacrolimus with low-dose fludrocortisone resulted in rapid correction of hyperkalaemia and acidosis without significant effects on blood pressure or serum sodium. Fludrocortisone can be an effective short-term option for the treatment of hyperkalaemic metabolic acidosis in kidney transplant recipients on tacrolimus; however, patient selection remains important in order to reduce to risk of potential adverse effects.

Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders

We discuss the use of urine electrolytes and urine osmolality in the clinical diagnosis of patients with fluid, electrolytes, and acid-base disorders, emphasizing their physiological basis, their utility, and the caveats and limitations in their use. While our focus is on information obtained from measurements in the urine, clinical diagnosis in these patients must integrate information obtained from the history, the physical examination, and other laboratory data.

Hyperkalemia: pathophysiology, risk factors and consequences

There have been significant recent advances in our understanding of the mechanisms that maintain potassium homoeostasis and the clinical consequences of hyperkalemia. In this article we discuss these advances within a concise review of the pathophysiology, risk factors and consequences of hyperkalemia. We highlight aspects that are of particular relevance for clinical practice. Hyperkalemia occurs when renal potassium excretion is limited by reductions in glomerular filtration rate, tubular flow, distal sodium delivery or the expression of aldosterone-sensitive ion transporters in the distal nephron. Accordingly, the major risk factors for hyperkalemia are renal failure, diabetes mellitus, adrenal disease and the use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers or potassium-sparing diuretics. Hyperkalemia is associated with an increased risk of death, and this is only in part explicable by hyperkalemia-induced cardiac arrhythmia. In addition to its well-established effects on cardiac excitability, hyperkalemia could also contribute to peripheral neuropathy and cause renal tubular acidosis. Hyperkalemia-or the fear of hyperkalemia-contributes to the underprescription of potentially beneficial medications, particularly in heart failure. The newer potassium binders could play a role in attempts to minimize reduced prescribing of renin-angiotensin inhibitors and mineraolocorticoid antagonists in this context.

Hyperchloremic normal gap metabolic acidosis

Metabolic acidosis is defined as a pathologic process that, when unopposed, increases the concentration of hydrogen ions (H+) in the body and reduces the bicarbonate (HCO3-) concentration. Metabolic acidosis can be of a kidney origin or an extrarenal cause. Assessment of urinary ammonium excretion by calculating the urine anion gap or osmolal gap is a useful method to distinguish between these two causes. Extrarenal processes include increased endogenous acid production and accelerated loss of bicarbonate from the body. Metabolic acidosis of renal origin is due to a primary defect in renal acidification with no increase in extrarenal hydrogen ion production. This situation can occur because either the renal input of new bicarbonate is insufficient to regenerate the bicarbonate lost in buffering endogenous acid as with distal renal tubular acidosis (RTA) or the RTA of renal insufficiency, or the filtered bicarbonate is lost by kidney wasting as in proximal RTA. In either condition, because of loss of either NaHCO3 (proximal RTA) or NaA (distal RTA), effective extracellular volume is reduced and as a result the avidity for chloride reabsorption derived from the diet is increased and results in a hyperchloremic normal gap metabolic acidosis. The RTA of renal insufficiency is also characterized by a normal gap acidosis, however, with severe reductions in the glomerular filtration rate an anion gap metabolic acidosis eventually develops.

A physiology-based approach to a patient with hyperkalemic renal tubular acidosis

Hyperkalemic renal tubular acidosis is a non-anion gap metabolic acidosis that invariably indicates an abnormality in potassium, ammonium, and hydrogen ion secretion. In clinical practice, it is usually attributed to real or apparent hypoaldosteronism caused by diseases or drug toxicity. We describe a 54-year-old liver transplant patient that was admitted with flaccid muscle weakness associated with plasma potassium level of 9.25 mEq/L. Additional investigation revealed type 4 renal tubular acidosis and marked hypomagnesemia with high fractional excretion of magnesium. Relevant past medical history included a recent diagnosis of Paracoccidioidomycosis, a systemic fungal infection that is endemic in some parts of South America, and his outpatient medications contained trimethoprim-sulfamethoxazole, tacrolimus, and propranolol. In the present acid-base and electrolyte case study, we discuss a clinical approach for the diagnosis of hyperkalemic renal tubular acidosis and review the pathophysiology of this disorder.

A mouse model of pseudohypoaldosteronism type II reveals a novel mechanism of renal tubular acidosis

Pseudohypoaldosteronism type II (PHAII) is a genetic disease characterized by association of hyperkalemia, hyperchloremic metabolic acidosis, hypertension, low renin, and high sensitivity to thiazide diuretics. It is caused by mutations in the WNK1, WNK4, KLHL3 or CUL3 gene. There is strong evidence that excessive sodium chloride reabsorption by the sodium chloride cotransporter NCC in the distal convoluted tubule is involved. WNK4 is expressed not only in distal convoluted tubule cells but also in β-intercalated cells of the cortical collecting duct. These latter cells exchange intracellular bicarbonate for external chloride through pendrin, and therefore, account for renal base excretion. However, these cells can also mediate thiazide-sensitive sodium chloride absorption when the pendrin-dependent apical chloride influx is coupled to apical sodium influx by the sodium-driven chloride/bicarbonate exchanger. Here we determine whether this system is involved in the pathogenesis of PHAII. Renal pendrin activity was markedly increased in a mouse model carrying a WNK4 missense mutation (Q562E) previously identified in patients with PHAII. The upregulation of pendrin led to an increase in thiazide-sensitive sodium chloride absorption by the cortical collecting duct, and it caused metabolic acidosis. The function of apical potassium channels was altered in this model, and hyperkalemia was fully corrected by pendrin genetic ablation. Thus, we demonstrate an important contribution of pendrin in renal regulation of sodium chloride, potassium and acid-base homeostasis and in the pathophysiology of PHAII. Furthermore, we identify renal distal bicarbonate secretion as a novel mechanism of renal tubular acidosis.

Hyperkalemic Forms of Renal Tubular Acidosis: Clinical and Pathophysiological Aspects

In contrast to distal type I or classic renal tubular acidosis (RTA) that is associated with hypokalemia, hyperkalemic forms of RTA also occur usually in the setting of mild-to-moderate CKD. Two pathogenic types of hyperkalemic metabolic acidosis are frequently encountered in adults with underlying CKD. One type, which corresponds to some extent to the animal model of selective aldosterone deficiency (SAD) created experimentally by adrenalectomy and glucocorticoid replacement, is manifested in humans by low plasma and urinary aldosterone levels, reduced ammonium excretion, and preserved ability to lower urine pH below 5.5. This type of hyperkalemic RTA is also referred to as type IV RTA. It should be noted that the mere deficiency of aldosterone when glomerular filtration rate is completely normal only causes a modest decline in plasma bicarbonate which emphasizes the importance of reduced glomerular filtration rate in the development of the hyperchloremic metabolic acidosis associated with SAD. Another type of hyperkalemic RTA distinctive from SAD in which plasma aldosterone is not reduced is referred to as hyperkalemic distal renal tubular acidosis because urine pH cannot be reduced despite acidemia or after provocative tests aimed at increasing sodium-dependent distal acidification such as the administration of sodium sulfate or loop diuretics with or without concurrent mineralocorticoid administration. This type of hyperkalemic RTA (also referred to as voltage-dependent distal renal tubular acidosis) has been best described in patients with obstructive uropathy and resembles the impairment in both hydrogen ion and potassium secretion that are induced experimentally by urinary tract obstruction and when sodium transport in the cortical collecting tubule is blocked by amiloride.

Mechanism of Hyperkalemia-Induced Metabolic Acidosis

Background Hyperkalemia in association with metabolic acidosis that are out of proportion to changes in glomerular filtration rate defines type 4 renal tubular acidosis (RTA), the most common RTA observed, but the molecular mechanisms underlying the associated metabolic acidosis are incompletely understood. We sought to determine whether hyperkalemia directly causes metabolic acidosis and, if so, the mechanisms through which this occurs.Methods We studied a genetic model of hyperkalemia that results from early distal convoluted tubule (DCT)-specific overexpression of constitutively active Ste20/SPS1-related proline-alanine-rich kinase (DCT-CA-SPAK).Results DCT-CA-SPAK mice developed hyperkalemia in association with metabolic acidosis and suppressed ammonia excretion; however, titratable acid excretion and urine pH were unchanged compared with those in wild-type mice. Abnormal ammonia excretion in DCT-CA-SPAK mice associated with decreased proximal tubule expression of the ammonia-generating enzymes phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase and overexpression of the ammonia-recycling enzyme glutamine synthetase. These mice also had decreased expression of the ammonia transporter family member Rhcg and decreased apical polarization of H⁺-ATPase in the inner stripe of the outer medullary collecting duct. Correcting the hyperkalemia by treatment with hydrochlorothiazide corrected the metabolic acidosis, increased ammonia excretion, and normalized ammoniagenic enzyme and Rhcg expression in DCT-CA-SPAK mice. In wild-type mice, induction of hyperkalemia by administration of the epithelial sodium channel blocker benzamil caused hyperkalemia and suppressed ammonia excretion.Conclusions Hyperkalemia decreases proximal tubule ammonia generation and collecting duct ammonia transport, leading to impaired ammonia excretion that causes metabolic acidosis.

New options for the management of chronic hyperkalemia

Hyperkalemia is a frequently detected electrolyte abnormality that can cause life-threatening complications. Hyperkalemia is most often the result of intrinsic (decreased glomerular filtration rate; selective reduction in distal tubule secretory function; impaired mineralocorticoid activity; and metabolic disturbances, such as acidemia and hyperglycemia) and extrinsic factors (e.g., drugs, such as renin-angiotensin-aldosterone system inhibitors, and potassium intake). The frequent use of renin-angiotensin-aldosterone system inhibitors in patients who are already susceptible to hyperkalemia (e.g., patients with chronic kidney disease, diabetes mellitus, or congestive heart failure) contributes to the high incidence of hyperkalemia. There is a need to understand the causes of hyperkalemia and to be aware of strategies addressing the disorder in a way that provides the most optimal outcome for affected patients. The recent development of 2 new oral potassium-binding agents has led to the emergence of a new paradigm in the treatment of hyperkalemia.

Non-Anion Gap Metabolic Acidosis: A Clinical Approach to Evaluation

Acid-base disturbances can result from kidney or nonkidney disorders. We present a case of high-volume ileostomy output causing large bicarbonate losses and resulting in a non-anion gap metabolic acidosis. Non-anion gap metabolic acidosis can present as a form of either acute or chronic metabolic acidosis. A complete clinical history and physical examination are critical initial steps to begin the evaluation process, followed by measuring serum electrolytes with a focus on potassium level, blood gas, urine pH, and either direct or indirect urine ammonium concentration. The present case was selected to highlight the differential diagnosis of a non-anion gap metabolic acidosis and illustrate a systematic approach to this problem.

Drug-induced acid-base disorders

The incidence of acid-base disorders (ABDs) is high, especially in hospitalized patients. ABDs are often indicators for severe systemic disorders. In everyday clinical practice, analysis of ABDs must be performed in a standardized manner. Highly sensitive diagnostic tools to distinguish the various ABDs include the anion gap and the serum osmolar gap. Drug-induced ABDs can be classified into five different categories in terms of their pathophysiology: (1) metabolic acidosis caused by acid overload, which may occur through accumulation of acids by endogenous (e.g., lactic acidosis by biguanides, propofol-related syndrome) or exogenous (e.g., glycol-dependant drugs, such as diazepam or salicylates) mechanisms or by decreased renal acid excretion (e.g., distal renal tubular acidosis by amphotericin B, nonsteroidal anti-inflammatory drugs, vitamin D); (2) base loss: proximal renal tubular acidosis by drugs (e.g., ifosfamide, aminoglycosides, carbonic anhydrase inhibitors, antiretrovirals, oxaliplatin or cisplatin) in the context of Fanconi syndrome; (3) alkalosis resulting from acid and/or chloride loss by renal (e.g., diuretics, penicillins, aminoglycosides) or extrarenal (e.g., laxative drugs) mechanisms; (4) exogenous bicarbonate loads: milk-alkali syndrome, overshoot alkalosis after bicarbonate therapy or citrate administration; and (5) respiratory acidosis or alkalosis resulting from drug-induced depression of the respiratory center or neuromuscular impairment (e.g., anesthetics, sedatives) or hyperventilation (e.g., salicylates, epinephrine, nicotine).

Integration of the response to a dietary potassium load: a paleolithic perspective

Our purpose is to integrate new insights in potassium (K(+)) physiology to understand K(+) homeostasis and illustrate some of their clinical implications. Since control mechanisms that are essential for survival were likely developed in Paleolithic times, we think the physiology of K(+) homeostasis can be better revealed when viewed from what was required to avoid threats and achieve balance in Paleolithic times. Three issues will be highlighted. First, we shall consider the integrative physiology of the gastrointestinal tract and the role of lactic acid released from enterocytes following absorption of sugars (fruit and berries) to cause a shift of this K(+) load into the liver. Second, we shall discuss the integrative physiology of WNK kinases and modulation of delivery of bicarbonate to the distal nephron to switch the aldosterone response from sodium chloride retention to K(+) secretion when faced with a K(+) load. Third, we shall emphasize the role of intra-renal recycling of urea in achieving K(+) homeostasis when the diet contains protein and K(+).

Severe hyperkalemia requiring hospitalization: predictors of mortality

Introduction

Severe hyperkalemia, with potassium (K⁺) levels ≥ 6.5 mEq/L, is a potentially life-threatening electrolyte imbalance. For prompt and effective treatment, it is important to know its risk factors, clinical manifestations, and predictors of mortality.

Methods

An observational cohort study was performed at 2 medical centers. A total of 923 consecutive Korean patients were analyzed. All were 19 years of age or older and were hospitalized with severe hyperkalemia between August 2007 and July 2010; the diagnosis of severe hyperkalemia was made either at the time of admission to the hospital or during the period of hospitalization. Demographic and baseline clinical characteristics at the time of hyperkalemia diagnosis were assessed, and clinical outcomes such as in-hospital mortality were reviewed, using the institutions' electronic medical record systems.

Results

Chronic kidney disease (CKD) was the most common underlying medical condition, and the most common precipitating factor of hyperkalemia was metabolic acidosis. Emergent admission was indicated in 68.6% of patients, 36.7% had electrocardiogram findings typical of hyperkalemia, 24.5% had multi-organ failure (MOF) at the time of hyperkalemia diagnosis, and 20.3% were diagnosed with severe hyperkalemia at the time of cardiac arrest. The in-hospital mortality rate was 30.7%; the rate was strongly correlated with the difference between serum K⁺ levels at admission and at their highest point, and with severe medical conditions such as malignancy, infection, and bleeding. Furthermore, a higher in-hospital mortality rate was significantly associated with the presence of cardiac arrest and/or MOF at the time of diagnosis, emergent admission, and intensive care unit treatment during hospitalization. More importantly, acute kidney injury (AKI) in patients with normal baseline renal function was a strong predictor of mortality, compared with AKI superimposed on CKD.

Conclusions

Severe hyperkalemia occurs in various medical conditions; the precipitating factors are similarly diverse. The mortality rate is especially high in patients with severe underlying disease, coexisting medical conditions, and those with normal baseline renal function.

Differential diagnosis of nongap metabolic acidosis: value of a systematic approach

Nongap metabolic acidosis is a common form of both acute and chronic metabolic acidosis. Because derangements in renal acid-base regulation are a common cause of nongap metabolic acidosis, studies to evaluate renal acidification often serve as the mainstay of differential diagnosis. However, in many cases, information obtained from the history and physical examination, evaluation of the electrolyte pattern (to determine if a nongap acidosis alone or a combined nongap and high anion gap metabolic acidosis is present), and examination of the serum potassium concentration (to characterize the disorder as hyperkalemic or hypokalemic in nature) is sufficient to make a presumptive diagnosis without more sophisticated studies. If this information proves insufficient, indirect estimates or direct measurement of urinary NH(4)(+) concentration, measurement of urine pH, and assessment of urinary HCO(3)(-) excretion can help in establishing the diagnosis. This review summarizes current information concerning the pathophysiology of this electrolyte pattern and the value and limitations of all of the diagnostic studies available. It also provides a systematic and cost-effective approach to the differential diagnosis of nongap metabolic acidosis.

Evaluation of renal tubular acidosis

Renal tubular acidoses (RTA) comprises of a group of disorders characterized by a low capacity for net acid excretion and persistent hyperchloremic, metabolic acidosis. The RTAs are classified into chiefly three types (types 1,2 and 4) based on clinical and laboratory characteristics. Correct diagnosis involves careful evaluation, including exclusion of other entities causing acidosis. A variety of tests are required to be administered in a stepwise fashion for the diagnosis and characterization of RTA.

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.

Human and murine phenotypes associated with defects in cation-chloride cotransport

The diuretic-sensitive cotransport of cations with chloride is mediated by the cation-chloride cotransporters, a large gene family encompassing a total of seven Na-Cl, Na-K-2Cl, and K-Cl cotransporters, in addition to two related transporters of unknown function. The cation-chloride cotransporters perform a wide variety of physiological roles and differ dramatically in patterns of tissue expression and cellular localization. The renal-specific Na-Cl cotransporter (NCC) and Na-K-2Cl cotransporter (NKCC2) are involved in Gitelman and Bartter syndrome, respectively, autosomal recessive forms of metabolic alkalosis. The associated phenotypes due to loss-of-function mutations in NCC and NKCC2 are consistent, in part, with their functional roles in the distal convoluted tubule and thick ascending limb, respectively. Other cation-chloride cotransporters are positional candidates for Mendelian human disorders, and the K-Cl cotransporter KCC3, in particular, may be involved in degenerative peripheral neuropathies linked to chromosome 15q14. The characterization of mice with both spontaneous and targeted mutations of several cation-chloride cotransporters has also yielded significant insight into the physiological and pathophysiological roles of several members of the gene family. These studies implicate the Na-K-2Cl cotransporter NKCC1 in hearing, salivation, pain perception, spermatogenesis, and the control of extracellular fluid volume. Targeted deletion of the neuronal-specific K-Cl cotransporter KCC2 generates mice with a profound seizure disorder and confirms the central role of this transporter in modulating neuronal excitability. Finally, the comparison of human and murine phenotypes associated with loss-of-function mutations in cation-chloride cotransporters indicates important differences in physiology of the two species and provides an important opportunity for detailed physiological and morphological analysis of the tissues involved.

Hypokalaemia and hyperkalaemia

Disturbances in potassium homoeostasis presenting as low or high serum potassium are common, especially among hospitalised patients. Given the fact that untreated hypokalaemia or hyperkalaemia is associated with high morbidity and mortality, it is critical to recognise and treat these disorders promptly. In this article, normal potassium homoeostasis is reviewed initially and then a pathophysiological approach to work-up and management of hypokalaemia and hyperkalaemia is presented. Recent advances with respect to the role of kidney in handling of the potassium, the regulation of renal ion transporters in hypokalaemia, and treatment of hypokalaemia and hyperkalaemia will be discussed.

Hyperkalemia in hospitalized patients

OBJECTIVE

Evaluate the prevalence of hyperkalemia (potassium > 5.5 mmol/l) in hospitalized patients not on dialysis, as well as the association of medications, impaired renal function and comorbid conditions with hyperkalemia.

DESIGN

A retrospective case-control method.

SETTING

A tertiary care teaching hospital.

PATIENTS

Hyperkalemic adults not on dialysis with age and sex matched controls.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The use of medications associated with hyperkalemia and renal function using a calculated creatinine clearance were compared in the hyperkalemic and control groups.

RESULTS

35 adult patients with hyperkalemia who were not receiving dialysis were identified, with a prevalence in the hospitalized population of 3.3%. The hyperkalemic patients were older than the general hospital population (p < 0.05). Compared with controls, hyperkalemic patients: had a lower creatinine clearance (p < 0.05), were more likely to be taking angiotensin-converting enzyme inhibitors (p < 0.05), and had an increased frequency of diabetes mellitus (p < 0.001). All of the control patients survived their hospitalization, but the mortality rate in the hyperkalemic group was 17% (p < 0.0001). None of the deaths were directly attributable to hyperkalemia.

CONCLUSIONS

Hyperkalemia is more frequent in older patients and is usually mild. Hyperkalemia is associated with diabetes mellitus, diminished renal function and the use of angiotensin-converting enzyme inhibitors. An elevated serum potassium level in a hospitalized patient may be a marker for a significantly increased risk of death, which is due to underlying medical problems and is not a consequence of the hyperkalemia.