Intractable hyponatremia complicated by a reset osmostat: a case report

BACKGROUND

Hyponatremia associated with a low serum osmolality is a common and confounding electrolyte disorder. Correcting hyponatremia is also complicated, especially in the setting of chronic hyponatremia. Here, we provide a rational approach to accurately detecting and safely treating acute on chronic euvolemic hyponatremia in the setting of acute polydipsia with a chronic reset osmostat.

CASE PRESENTATION

A 71-year-old hispanic gentleman with chronic hyponatremia presented with hiccups, polydipsia, and a serum sodium concentration of 120 mEq/L associated with diffuse weakness, inattentiveness, and suicidal ideation. Symptomatic euvolemic hyponatremia warranted hypertonic saline treatment in the acute phase and water restriction in the chronic phase. Both interventions resulted in improvement in symptoms and/or the serum sodium concentration, but to a serum sodium level that persistently remained below the normal range. Remarkably, the urine osmolality appropriately fell when the serum sodium concentration fell below 126 mEq/L. Also remarkable was the appropriate increase in urine osmolality when the serum sodium concentration exceeded 126 mEq/L. The preservation of both concentration and dilution, albeit at a lower-than-normal serum osmolality, shows that the osmostat regulating antidiuretic hormone release had been "reset." Both physiologic and pharmacologic resetting of the osmostat are discussed.

CONCLUSIONS

Preservation of urinary concentrating and diluting ability at a lower-than-normal serum sodium concentration, especially in the setting of chronic hyponatremia, is diagnostic of a reset osmostat. The presence of a reset osmostat often confounds the treatment of concomitant acute hyponatremia. Early recognition of a reset osmostat avoids the need to normalize serum sodium concentration, expedites hospital discharge, and limits potential harm from overcorrecting acute hyponatremia.

Syndrome of inappropriate antidiuretic hormone secretion

Hyponatremia is the most frequent electrolytic disorder in hospitalized patients, and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), the most frequent cause of hiponatremia with clinically normal extracellular volume. It consists of a disorder of the regulation of body water that obeys to different causes, mainly cancer, pulmonary illnesses, disorders of the central nervous system and diverse drugs. As in any hiponatremia it a physiological knowledge of the regulation of body water and sodium is essential as well as the application of precise diagnostic criteria in order to manage the problem with an effective treatment. The available data until the moment show that the clinical diagnosis of SIADH made by professionals is mainly not supported on the established criteria drawn by experts and this lack of accuracy probably hits in the therapeutic result. The basis of the treatment of the SIADH is to correct its cause, water restriction, solutes (sodium chloride) and the use of vaptans in case of failure of the previous measures.

Low Creatininuria due to Hyponatremia Is Reversible in Many Patients

BACKGROUND

Chronic hyponatremia has been reported to be associated with low solute intake and low creatinine excretion (reflecting likely sarcopenia). We wanted to study the effect, on the long term, of correction of hyponatremia on solute and creatinine excretion in chronic SIADH.

METHODS

We made a retrospective review of clinical and biochemical data of patients with euvolemic hyponatremia. We analyzed 24-h urine solute and creatinine excretion in volunteers with hyponatremia induced by dDAVP over 4 days, in 12 patients with chronic SIADH (>1 month) before and after a few days of SNa correction and in 12 patients (6 women and 6 men) before and after 3 months of SNa correction by a vaptan or urea.

RESULTS

We confirm a low urine creatinine and solute excretion only in patients with chronic hyponatremia (>1 month). Correction of SNa (from 127 ± 2.3 mEq/L to 139 ± 2.8 mEq/L) for >3 months, in the 12 patients (mean age 58 ± 18), was associated with an increase in 24-h creatinine excretion (from 986 ± 239 to 1,238 ± 220 mg; p < 0.02) and in patients treated with a vaptan (n = 5) solute excretion increased from 656 ± 207 mmol/24 h to 960 ± 193 mmol/24 h (p < 0.02). Sodium excretion increased also in the 12 patients (from 100 ± 53 mEq/24 h to 169 ± 38 mEq/24 h; p < 0.01).

CONCLUSION

Chronic hyponatremia (>1 month) is associated with a decrease in solute output (or intake) and in creatinine excretion. In many patients, these abnormalities are reversible in the long term.

The vasopressin-aquaporin-2 pathway syndromes

Vasopressin is the key hormone involved in water conservation and regulation of water balance, essential for life. In the renal collecting duct, vasopressin binds to the V2 receptor, increasing water permeability through activation of aquaporin-2 redistribution to the luminal membrane. This mechanism promotes rapid water reabsorption, important for immediate survival; however, only recently it has become clear that long-term adverse effects are associated with alterations of the vasopressin-aquaporin-2 pathway, leading to several syndromes associated with water balance disorders. The kidney resistance to the vasopressin action may cause severe dehydration for patients and, conversely, nonosmotic release of vasopressin is associated with water retention and increasing the circulatory blood volume. This chapter discusses the relevance of the altered vasopressin-aquaporin-2 pathway in some diseases associated with water balance disorders, including congenital nephrogenic diabetes insipidus, syndrome of inappropriate secretion of antidiuretic hormone, nephrogenic syndrome of inappropriate antidiuresis, and autosomal dominant polycystic kidney disease. The emerging picture suggests that targeting the vasopressin-AQP2 axis can provide therapeutic benefits in those patients.

Hyponatremia presenting with hourly fluctuating urine osmolality

SUMMARY

The etiology of hyponatremia is assessed based on urine osmolality and sodium. We herein describe a 35-year-old Asian man with pulmonary tuberculosis and perforated duodenal ulcer who presented with hyponatremia with hourly fluctuating urine osmolality ranging from 100 to 600 mosmol/kg, which resembled urine osmolality observed in typical polydipsia and SIADH simultaneously. Further review revealed correlation of body temperature and urine osmolality. Since fever is a known non-osmotic stimulus of ADH secretion, we theorized that hyponatremia in this patient was due to transient ADH secretion due to fever. In our case, empiric exogenous glucocorticoid suppressed transient non-osmotic ADH secretion and urine osmolality showed highly variable concentrations. Transient ADH secretion-related hyponatremia may be underrecognized due to occasional empiric glucocorticoid administration in patients with critical illnesses. Repeatedly monitoring of urine chemistries and interpretation of urine chemistries with careful review of non-osmotic stimuli of ADH including fever is crucial in recognition of this etiology.

LEARNING POINTS

Hourly fluctuations in urine osmolality can be observed in patients with fever, which is a non-osmotic stimulant of ADH secretion. Repeated monitoring of urine chemistries aids in the diagnosis of the etiology underlying hyponatremia, including fever, in patients with transient ADH secretion. Glucocorticoid administration suppresses ADH secretion and improves hyponatremia even in the absence of adrenal insufficiency; the etiology of hyponatremia should be determined carefully in these patients.

Focus on neonatal and infantile onset of nephrogenic syndrome of inappropriate antidiuresis: 12 years later

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD), first described in 2005, is a rare genetic X-linked disease, presenting with hyponatremia, hyposmolarity, euvolemia, inappropriately concentrated urine, increased natriuresis, and undetectable or very low arginine-vasopressine (AVP) circulating levels. It can occur in neonates, infants, or later in life. NSIAD must be early recognized and treated to prevent severe hyponatremia, which can show a dangerous impact on neonatal outcome. In fact, it potentially leads to death or, in case of survival, neurologic sequelae. This review is an update of NSIAD 12 years after the first description, focusing on reported cases of neonatal and infantile onset. The different molecular patterns affecting the AVP receptor 2 (V2R) and determining its gain of function are reported in detail; moreover, we also provide a comparison between the different triggers involved in the development of hyponatremia, the evolution of the symptoms, and modality and efficacy of the different treatments available.

Diabetes Insipidus and Syndrome of Inappropriate Antidiuretic Hormone in Critically Ill Patients

Diabetes insipidus and the syndrome of inappropriate antidiuretic hormone secretion lie at opposite ends of the spectrum of disordered renal handling of water. Whereas renal retention of water insidiously causes hypotonic hyponatremia in syndrome of inappropriate antidiuretic hormone secretion, diabetes insipidus may lead to free water loss, hypernatremia, and volume depletion. Hypernatremia and hyponatremia are associated with worse outcomes and longer intensive care stays. Moreover, pathologies causing polyuria and hyponatremia in patients in intensive care may be multiple, making diagnosis challenging. We provide an approach to the diagnosis and management of these conditions in intensive care patients.

Practical document on the management of hyponatremia in critically ill patients

Hyponatremia is the most prevalent electrolyte disorder in Intensive Care Units. It is associated with an increase in morbidity, mortality and hospital stay. The majority of the published studies are observational, retrospective and do not include critical patients; hence it is difficult to draw definitive conclusions. Moreover, the lack of clinical evidence has led to important dissimilarities in the recommendations coming from different scientific societies. Finally, etiopathogenic mechanisms leading to hyponatremia in the critical care patient are complex and often combined, and an intensive analysis is clearly needed. A study was therefore made to review all clinical aspects about hyponatremia management in the critical care setting. The aim was to develop a Spanish nationwide algorithm to standardize hyponatremia diagnosis and treatment in the critical care patient.

Pharmacological Chaperones as Potential Therapeutic Strategies for Misfolded Mutant Vasopressin Receptors

Pharmacological chaperones recently opened new possibilities in G protein-coupled receptor drug discovery. Even more interestingly, some unique ligands combine pharmacological chaperoning and biased agonism properties, boosting their therapeutic interest in many human diseases resulting from G protein-coupled receptor mutation and misfolding. These compounds displaying dual characteristics would constitute a perfect treatment for congenital Nephrogenic Diabetes Insipidus, a typical conformational disease. This X-linked genetic pathology is mostly associated with inactivating mutations of the renal arginine-vasopressin V2 receptor leading to misfolding and intracellular retention of the receptor, causing the inability of patients to concentrate their urine in response to the antidiuretic hormone. Cell-permeable pharmacological chaperones have been successfully challenged to restore plasma membrane localization of many V2 receptor mutants. In addition, different classes of specific ligands such as antagonists, agonists as well as biased agonists of the V2 receptor have proven their usefulness in rescuing mutant receptor function. This is particularly relevant for small-molecule biased agonists which only trigger Gs protein activation and cyclic adenosine monophosphate production, the V2-induced signaling pathway responsible for water reabsorption. In parallel, high-throughput screening assays based on receptor trafficking rescue approaches have been developed to discover novel V2 pharmacological chaperone molecules from different chemical libraries. These new hit compounds, which still need to be pharmacologically characterized and functionally tested in vivo, represent promising candidates for the treatment of congenital Nephrogenic Diabetes Insipidus.

Cardiorenal Syndrome: Role of Arginine Vasopressin and Vaptans in Heart Failure

Heart and kidney failure continued to be of increasing prevalence in today's society, and their comorbidity has synergistic effect on the morbidity and mortality of patients. Cardiorenal syndrome (CRS) is a complex disease with multifactorial pathophysiology. Better understanding of this pathophysiological network is crucial for the successful intervention to prevent advancement of the disease process. One of the major factors in this process is neurohormonal activation, predominantly involving renin-angiotensin-aldosterone system (RAAS) and arginine vasopressin (AVP). Heart failure causes reduced cardiac output/cardiac index (CO/CI) and fall in renal perfusion pressures resulting in activation of baroreceptors and RAAS, respectively. Activated baroreceptors and RAAS stimulate the release of AVP (non-osmotic pathway), which acts on V₂ receptors located in the renal collecting ducts, causing fluid retention and deterioration of heart failure. Effective blockade of AVP action on V₂ receptors has emerged as a potential treatment option in volume overload conditions especially in the setting of hyponatremia. Vasopressin receptor antagonists (VRAs), such as vaptans, are potent aquaretics causing electrolyte-free water diuresis without significant electrolyte abnormalities. Vaptans are useful in hypervolemic hyponatremic conditions like heart failure and liver cirrhosis, and euvolemic hyponatremic conditions like syndrome of inappropriate anti-diuretic hormone secretion. Tolvaptan and conivaptan are pharmaceutical agents that are available for the treatment of these conditions.

Physiopathology, clinical diagnosis, and treatment of hyponatremia

Hyponatremia is the commonest electrolyte disorder encountered in clinical practice. It develops when the mechanisms regulating water and electrolyte handling are impaired, which in many instances occur in the setting of concurrent diseases such as heart failure, liver failure, renal failure etc… Hyponatremia as an electrolyte disorder has several specificities: when profound it can be quickly fatal and when moderate it carries a high risk of mortality and morbidity, but at the same time incorrect treatment of profound hyponatremia can lead to debilitating neurological disease and it remains unclear if treatment of moderate hyponatremia is associated with a decrease in mortality and morbidity. A proper diagnosis is the keystone for an adequate treatment for hyponatremia and in the last few years many diagnosis algorithms have been developed to aid in the evaluation of the hyponatremic patient. Also because of the availability of vasopressin receptor antagonists and the advances made in the research regarding complications associated with hyponatremia treatment, new treatment recommendations have been published recently by several panels. This review will discuss the physiopathology, epidemiology, and clinical manifestations of hyponatremia and also the diagnosis and the treatment of this disorder with special emphasis on the complication from overly rapid correction of hyponatremia.

SIAD: practical recommendations for diagnosis and management

Hyponatremia is the commonest electrolyte disturbance encountered in hospitalized patients, and the syndrome of inappropriate antidiuresis (SIAD) is the most frequent underlying disorder. There is a well-recognized relationship between hyponatremia and increased morbidity and mortality. Therefore, to provide appropriate treatment is critical to improve the clinical outcome related to SIAD-hyponatremia. There have been important advances in the treatment of SIAD over the last decade, leading to the publication of several clinical guidelines. In particular, the introduction of the vasopressin-2 receptor antagonists provides a potent pharmacological tool to target the underlying pathophysiology of SIAD. The evidence base recommendations of the available therapies for SIAD are discussed in this study. Fluid restriction is considered the first-line therapy by the recent published guidelines, but it is certainly ineffective or unfeasible in many patients with SIAD. We discuss a number of relevant points to the use of fluid restriction in this study, including the lack of good evidence-based recommendations to support its use. Conversely, the clinical efficacy of oral tolvaptan in SIAD supported by good quality randomized, placebo controlled, clinical trials. However, the cost of the therapy and the need for long-term safety data may limit its widespread use. Finally, new recommendations for the management of acute hyponatremia with a focus on the use of bolus therapy with 3 % hypertonic sodium chloride are described in this study.

Hyponatremia in Cirrhosis--Pathogenesis, Treatment, and Prognostic Significance

Cirrhosis is characterized by systemic and splanchnic vasodilation that leads to excessive nonosmotic secretion of vasopressin (antidiuretic hormone). Hyponatremia is a common electrolyte abnormality in advanced liver disease that results from the impaired ability of the kidney to excrete solute-free water that leads to "dilutional" hyponatremia-water retention disproportionate to the retention of sodium. Hyponatremia in liver diseases carries the prognostic burden, correlates with the severity of cirrhosis, and, in recent studies, has also been implicated in the pathogenesis of hepatic encephalopathy. The current treatment options are limited to conventional therapies like fluid restriction, and the outcomes are unsatisfactory. Although currently available vasopressin (V2 receptors) antagonists have been shown to increase serum sodium concentrations and improve ascites control, their role in the treatment of hyponatremia in liver disease patients remains questionable because of adverse effect profiles, high cost, and poor data on long-term mortality benefits. More information is needed to argue the benefits vs risks of short-term use of vaptans for correction of hyponatremia especially just hours-to-days before liver transplant.

Hyponatremia in cirrhosis: Pathophysiology and management

Hyponatremia is frequently seen in patients with ascites secondary to advanced cirrhosis and portal hypertension. The development of ascites in patients with cirrhosis is multi-factorial. Portal hypertension and the associated systemic vasodilation lead to activation of the sodium-retaining neurohumoral mechanisms which include the renin-angiotensin-aldosterone system, sympathetic nervous system and antidiuretic hormone (ADH). The net effect is the avid retention of sodium and water to compensate for the low effective circulatory volume resulting in the development of ascites. Although not apparent in the early stages of cirrhosis, the progression of cirrhosis and ascites leads to impairment of the kidneys to eliminate solute- free water. This leads to additional compensatory mechanisms including non-osmotic secretion of ADH, also known as arginine vasopressin, further worsening excess water retention and thereby hyponatremia. Hyponatremia is associated with increased morbidity and mortality in patients with cirrhosis, and is an important prognostic marker both before and after liver transplant. The management of hyponatremia in this setting is a challenge as conventional therapy for hyponatremia including fluid restriction and loop diuretics are frequently inefficacious. In this review, we discuss the pathophysiology and various treatment modalities, including selective vasopressin receptor antagonists, for the management of hyponatremia in patients with cirrhosis.

Hyponatremia in Patients with Cirrhosis of the Liver

Hyponatremia is common in cirrhosis. It mostly occurs in an advanced stage of the disease and is associated with complications and increased mortality. Either hypovolemic or, more commonly, hypervolemic hyponatremia can be seen in cirrhosis. Impaired renal sodium handling due to renal hypoperfusion and increased arginine-vasopressin secretion secondary to reduced effective volemia due to peripheral arterial vasodilation represent the main mechanisms leading to dilutional hyponatremia in this setting. Patients with cirrhosis usually develop slowly progressing hyponatremia. In different clinical contexts, it is associated with neurological manifestations due to increased brain water content, where the intensity is often magnified by concomitant hyperammonemia leading to hepatic encephalopathy. Severe hyponatremia requiring hypertonic saline infusion is rare in cirrhosis. The management of asymptomatic or mildly symptomatic hyponatremia mainly rely on the identification and treatment of precipitating factors. However, sustained resolution of hyponatremia is often difficult to achieve. V2 receptor blockade by Vaptans is certainly effective, but their long-term safety, especially when associated to diuretics given to control ascites, has not been established as yet. As in other conditions, a rapid correction of long-standing hyponatremia can lead to irreversible brain damage. The liver transplant setting represents a condition at high risk for the occurrence of such complications.

Role of vaptans in the management of hydroelectrolytic imbalance in liver cirrhosis

Ascites and hyponatremia are the most common complications in patients with liver cirrhosis and develop as a consequence of a severe impairment of liver function and portal hypertension. Increasing evidences support the central role of renal function alterations in the pathogenesis of hydroelectrolytic imbalances in cirrhotic patients, thus implying a dense cross-talk between liver and kidney in the systemic and splanchnic vascular homeostasis in such subjects. Since Arginin Vasopressin (AVP) hyperincretion occurs at late stage of cirrhosis and plays an important role in the development of refractory ascites, dilutional hyponatremia and finally hepato-renal syndrome, selective antagonists of AVP receptors V₂ (vaptans) have been recently introduced in the therapeutic algorithm of advanced cirrhotic patients. Despite the promising results of earlier phase-two studies, randomized controlled trials failed to find significant results in terms of efficacy of such drugs both in refractory ascites and hyponatremia. Moreover, concerns on their safety profile arise, due to the number of potentially severe side effects of vaptans in the clinical setting, such as hypernatremia, dehydration, renal impairment, and osmotic demyelination syndrome. More robust data from randomized controlled trials are needed in order to confirm the potential role of vaptans in the management of advanced cirrhotic patients.

Hyponatremia: A practical approach

Hyponatremia is an important and common clinical problem. The etiology is multifactorial. Hyponatremia may be euvolemic, hypovolemic or hypervolemic. Proper interpretation of the various laboratory tests helps to differentiate the various types of hyponatremia. Treatment varies with the nature of onset -acute or chronic, severity and symptoms. Normal saline forms the mainstay of treatment for hypovolemic hyponatremia while 3% NaCl and fluid restriction are important for euvolemic hyponatremia. Hypervolemic hyponatremia responds well to fluid restriction and diuretics. There have been several recent advances in the last year with revision in the guidelines for treatment and availability of vaptans. Judicious use of vaptans may help in treatment of hyponatremia.

Vasopressin receptors and pharmacological chaperones: from functional rescue to promising therapeutic strategies

Conformational diseases result from protein misfolding and/or aggregation and constitute a major public health problem. Congenital Nephrogenic Diabetes Insipidus is a typical conformational disease. In most of the cases, it is associated to inactivating mutations of the renal arginine-vasopressin V2 receptor gene leading to misfolding and intracellular retention of the receptor, causing the inability of patients to concentrate their urine in response to the antidiuretic hormone. Cell-permeable pharmacological chaperones have been successfully challenged to restore plasma membrane localization of the receptor mutants and to rescue their function. Interestingly, different classes of specific ligands such as antagonists (vaptans), agonists as well as biased agonists of the V2 receptor have proven their usefulness as efficient pharmacochaperones. These compounds represent a potential therapeutic treatment of this X-linked genetic pathology.

Hyponatremia in cirrhosis and vaptans

Hyponatremia is a common problem in patients with advanced cirrhosis. Hyponatremia in cirrhosis includes two distinct types: hypovolemic hyponatremia, and hypervolemic or dilutional hyponatremia. The former is characterized by low blood sodium, low blood volume, dehydration and prerenal renal dysfunction, not accompanied by edema and ascites, while the latter is characterized by insufficient circulatory volume and dilutional hyponatremia, accompanied by edema and ascites. Hyponatremia is closely related to various complications of cirrhosis and to early mortality after liver transplantation. Vaptans, a class of selective non-peptide arginine vasopressin (AVP) receptor antagonists, act by antagonizing specifically the effects of AVP V₂ receptor located in the renal collecting tubules to inhibit water reabsorption without affecting electrolytes excretion. Vaptans has been evaluated by several clinical trials for their role in the management of hyponatremia. The short-term treatment with vaptans is associated with a marked increase in renal solute-free water excretion and improvement of hyponatremia with no apparent adverse reactions. The discovery of vaptans is considered a new milestone in the management of hyponatremia in cirrhosis.