Hyponatremia: diagnosis, complications, and management including V2 receptor antagonists

Hyponatremia and cyst growth in neonatal polycystic kidney disease: a case for aquaretics?

Hyponatremia is a common complication in neonatal polycystic kidney disease and is thought to be due to water retention. Aquaretics are drugs that promote free water excretion by blocking the arginine vasopressin receptor type 2 (AVPR2) in the collecting duct and thus impair urinary concentration. AVPR2 is also a key stimulant for cyclic AMP production in the collecting duct and in this way promotes cyst proliferation and pathologic kidney growth in autosomal dominant polycystic kidney disease (ADPKD). Consequently, the aquaretic tolvaptan is now used to slow down progression of ADPKD in adult patients. Whether this beneficial effect on retarding cystic disease progression also extends to recessive forms of polycystic kidney disease (PKD) is currently not known. A recent case report in Pediatric Nephrology touches on the intersecting indications for tolvaptan for both hyponatremia and cyst retardation in neonatal PKD and suggests that use for one indication may have beneficial effects on the other.

Effect of tolvaptan on renal water and sodium excretion and blood pressure during nitric oxide inhibition: a dose-response study in healthy subjects

BACKGROUND

Tolvaptan is a selective vasopressin receptor antagonist. Nitric Oxide (NO) promotes renal water and sodium excretion, but the effect is unknown in the nephron's principal cells. In a dose-response study, we measured the effect of tolvaptan on renal handling of water and sodium and systemic hemodynamics, during baseline and NO-inhibition with L-NMMA (L-NG-monomethyl-arginine).

METHODS

In a randomized, placebo-controlled, double blind, cross over study, 15 healthy subjects received tolvaptan 15, 30 and 45 mg or placebo. L-NMMA was given as a bolus followed by continuous infusion during 60 min. We measured urine output (UO), free water clearance (CH2O), fractional excretion of sodium (FENa), urinary aquaporin-2 channels (u-AQP2) and epithelial sodium channels (u-ENaCγ), plasma vasopressin (p-AVP) and central blood pressure (cBP).

RESULTS

During baseline, FENa was unchanged. Tolvaptan decreased u-ENaCγ dose-dependently and increased p-AVP threefold, whereas u-AQP2 was unchanged. During tolvaptan with NO-inhibition, UO and CH2O decreased dose-dependently. FENa decreased dose-independently and u-ENaCγ remained unchanged. Central BP increased equally after all treatments.

CONCLUSIONS

During baseline, fractional excretion of sodium was unchanged. During tolvaptan with NO-inhibition, renal water excretion was reduced dose dependently, and renal sodium excretion was reduced unrelated to the dose, partly via an AVP dependent mechanism. Thus, tolvaptan antagonized the reduction in renal water and sodium excretion during NO-inhibition. Most likely, the lack of decrease in AQP2 excretion by tolvaptan could be attributed to a counteracting effect of the high level of p-AVP.

TRIAL REGISTRATION

Clinical Trial no: NCT02078973 . Registered 1 March 2014.

Management Challenges in a Child with Chronic Hyponatremia: Use of V2 Receptor Antagonist

Chronic hyponatremia is very rare in children and is often seen in the setting of congestive heart failure or liver failure in adults. Here, we report an 8-year-old child with hypothalamic glioma who presented with severe hyponatremia. Initial management consisted of fluid restriction. This was very difficult for the child to follow and the child developed bizarre drinking habits requiring intervention from child psychiatry. So therapy was initiated with low dose V2 receptor antagonist under close inpatient monitoring. While initial response was reassuring, her sodium levels tended to drift down with longer duration of treatment requiring us to increase the dose frequently. Her response to therapy and her stable clinical situation off therapy suggest that she may have reset osmostat.

Osmotic Pressure in Clinical Medicine with an Emphasis on Dialysis

Since the beginning of life of the first multicellular organisms, the preservation of a physiologic milieu for every cell in the organism has been a critical requirement. A particular range of osmolality of the body fluids is essential for the maintenance of cell volume. In humans the stability of electrolyte concentrations and their resulting osmolality in the body fluids is the consequence of complex interactions between cell membrane functions, hormonal control, thirst, and controlled kidney excretion of fluid and solutes. Knowledge of these mechanisms, of the biochemical principles of osmolality, and of the relevant situations occurring in disease is of importance to every physician. This comprehensive review summarizes the major facts on osmolality, its relation to electrolytes and other solutes, and its relevance in physiology and in disease states with a focus on dialysis-related considerations.

Anoxic Brain Injury Secondary to Metabolic Encephalopathy

PURPOSE

To discuss the clinical case of a patient suffering visual dysfunction secondary to a metabolic brain injury, the patient's visual rehabilitative treatment, and outcomes.

CASE REPORT

A 24-year-old Caucasian male presented to the Southern Arizona Veteran's Affairs Healthcare System's Traumatic Brain Injury (TBI) eye clinic for evaluation and treatment of visual dysfunction secondary to an anoxic brain injury suffered 4 months before. Symptoms included persistent right homonymous hemianopia, oculomotor dysfunction, and a visual information processing deficit. After 5 weeks of vision rehabilitation, the patient was reassessed and displayed significant improvement in both signs and symptoms.

CONCLUSIONS

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a metabolic syndrome that causes hyponatremia and, in severe cases, encephalopathy and anoxic brain injury. Damage to the visual pathways can produce visual field, ocular motility, and binocular vision deficits. Comprehensive treatment including rehabilitative vision therapy bolstering the natural neuroplasticity process can provide improvements in patients' quality of life.

Current and Potential Therapeutic Strategies for Hemodynamic Cardiorenal Syndrome

BACKGROUND

Cardiorenal syndrome (CRS) encompasses conditions in which cardiac and renal disorders co-exist and are pathophysiologically related. The newest classification of CRS into seven etiologically and clinically distinct types for direct patient management purposes includes hemodynamic, uremic, vascular, neurohumoral, anemia- and/or iron metabolism-related, mineral metabolism-related and protein-energy wasting-related CRS. This classification also emphasizes the pathophysiologic pathways. The leading CRS category remains hemodynamic CRS, which is the most commonly encountered type in patient care settings and in which acute or chronic heart failure leads to renal impairment.

SUMMARY

This review focuses on selected therapeutic strategies for the clinical management of hemodynamic CRS. This is often characterized by an exceptionally high ratio of serum urea to creatinine concentrations. Loop diuretics, positive inotropic agents including dopamine and dobutamine, vasopressin antagonists including vasopressin receptor antagonists such as tolvaptan, nesiritide and angiotensin-neprilysin inhibitors are among the pharmacologic agents used. Additional therapies include ultrafiltration (UF) via hemofiltration or dialysis. The beneficial versus unfavorable effects of these therapies on cardiac decongestion versus renal blood flow may act in opposite directions. Some of the most interesting options for the outpatient setting that deserve revisiting include portable continuous dobutamine infusion, peritoneal dialysis and outpatient UF via hemodialysis or hemofiltration.

KEY MESSAGES

The new clinically oriented CRS classification system is helpful in identifying therapeutic targets and offers a systematic approach to an optimal management algorithm with better understanding of etiologies. Most interventions including UF have not shown a favorable impact on outcomes. Outpatient portable dobutamine infusion is underutilized and not well studied. Revisiting traditional and novel strategies for outpatient management of CRS warrants clinical trials.

Diagnosis and Management of Hyponatremia in Patients with Aneurysmal Subarachnoid Hemorrhage

Hyponatremia is the most common, clinically-significant electrolyte abnormality seen in patients with aneurysmal subarachnoid hemorrhage. Controversy continues to exist regarding both the cause and treatment of hyponatremia in this patient population. Lack of timely diagnosis and/or providing inadequate or inappropriate treatment can increase the risk of morbidity and mortality. We review recent literature on hyponatremia in subarachnoid hemorrhage and present currently recommended protocols for diagnosis and management.

Effect of vasopressin antagonism on renal handling of sodium and water and central and brachial blood pressure during inhibition of the nitric oxide system in healthy subjects

BACKGROUND

Tolvaptan is a selective vasopressin receptor antagonist (V2R) that increases free water excretion. We wanted to test the hypotheses that tolvaptan changes both renal handling of water and sodium and systemic hemodynamics during basal conditions and during nitric oxide (NO)-inhibition with L-NG-monomethyl-arginine (L-NMMA).

METHODS

Nineteen healthy subjects were enrolled in a randomized, placebo-controlled, double-blind, crossover study of two examination days. Tolvaptan 15 mg or placebo was given in the morning. L-NMMA was given as a bolus followed by continuous infusion during 60 minutes. We measured urine output(UO), free water clearance (CH2O), fractional excretion of sodium (FENa), urinary aquaporin-2 channels (u-AQP2) and epithelial sodium channels (u-ENaCγ), plasma vasopressin (p-AVP), central and brachial blood pressure(cBP, bBP).

RESULTS

During baseline conditions, tolvaptan caused a significant increase in UO, CH2O and p-AVP, and FENa was unchanged. During L-NMMA infusion, UO and CH2O decreased more pronounced after tolvaptan than after placebo (-54 vs.-42% and -34 vs.-9% respectively). U-AQP2 decreased during both treatments, whereas u-ENaCγ decreased after placebo and increased after tolvaptan. CBP and bBP were unchanged.

CONCLUSION

During baseline conditions, tolvaptan increased renal water excretion. During NO-inhibition, the more pronounced reduction in renal water excretion after tolvaptan indicates that NO promotes water excretion in the principal cells, at least partly, via an AVP-dependent mechanism. The lack of decrease in u-AQP2 by tolvaptan could be explained by a counteracting effect of increased plasma vasopressin. The antagonizing effect of NO-inhibition on u-ENaC suggests that NO interferes with the transport via ENaC by an AVP-dependent mechanism.

Individuality of the plasma sodium concentration

Older literature has suggested that the plasma sodium concentration is not individual, that it is neither intrinsic to an individual nor reproducible, longitudinally. We recently observed that the plasma sodium concentration is heritable. Because demonstrable heritability requires individuality of the relevant phenotype, we hypothesized that the plasma sodium concentration was substantially individual. In two large health plan-based cohorts, we demonstrated individuality of the plasma sodium concentration over a 10-yr interval; the intraclass correlation coefficient (ICC) averaged 0.4-0.5. The individuality of plasma sodium increased significantly with age. Plasma sodium individuality was equal to or only slightly less than that for plasma glucose but was less than the individuality for creatinine. The individuality of plasma sodium was further confirmed by comparing the Pearson correlation coefficient for within-individual versus between-individual pairs of sodium determinations and via application of the agreement index. Furthermore, the distribution of all sodium determinations for all participants within a population was similar to the distribution for the mean sodium concentration for individuals within that population. Therefore, the near-normal distribution of plasma sodium measurements within a population is likely not attributable to assay-specific factors but rather to genuine and durable biological variability in the osmotic set point. In aggregate, these data strongly support the individuality of the plasma sodium concentration. They further indicate that serial plasma sodium values for any given individual tend to cluster around a patient-specific set point and that these set points vary among individuals.

Renal aquaporins and water balance disorders

BACKGROUND

Aquaporins (AQPs) are a family of proteins that can act as water channels. Regulation of AQPs is critical to osmoregulation and the maintenance of body water homeostasis. Eight AQPs are expressed in the kidney of which five have been shown to play a role in body water balance; AQP1, AQP2, AQP3, AQP4 and AQP7. AQP2 in particular is regulated by vasopressin.

SCOPE OF REVIEW

This review summarizes our current knowledge of the underlying mechanisms of various water balance disorders and their treatment strategies.

MAJOR CONCLUSIONS

Dysfunctions of AQPs are involved in disorders associated with disturbed water homeostasis. Hyponatremia with increased AQP levels can be caused by diseases with low effective circulating blood volume, such as congestive heart failure, or osmoregulation disorders such as the syndrome of inappropriate secretion of antidiuretic hormone. Treatment consists of fluid restriction, demeclocycline and vasopressin type-2 receptor antagonists. Decreased AQP levels can lead to diabetes insipidus (DI), characterized by polyuria and polydipsia. In central DI, vasopressin production is impaired, while in gestational DI, levels of the vasopressin-degrading enzyme vasopressinase are abnormally increased. Treatment consists of the vasopressin analogue dDAVP. Nephrogenic DI is caused by the inability of the kidney to respond to vasopressin and can be congenital, but is most commonly acquired, usually due to lithium therapy. Treatment consists of sufficient fluid supply, low-solute diet and diuretics.

GENERAL SIGNIFICANCE

In recent years, our understanding of the underlying mechanisms of water balance disorders has increased enormously, which has opened up several possible new treatment strategies. This article is part of a Special Issue entitled Aquaporins.

A few clinical aspects of sodium homeostasis disorders

In this review three major issues of sodium homeostasis are addressed. Specifically, volume-dependent (salt-sensitive) hypertension, sodium chloride content of maintenance fluid and clinical evaluation of hyponatremia are discussed. Regarding volume-dependent hypertension the endocrine/paracrine systems mediating renal sodium retention, the relationship between salt intake, plasma sodium levels and blood pressure, as well as data on the dissociation of sodium and volume regulation are presented. The concept of perinatal programming of salt-preference is also mentioned. Some theoretical and practical aspects of fluid therapy are summarized with particular reference to using hypotonic sodium chloride solution for maintenance fluid as opposed to the currently proposed isotonic sodium chloride solution. Furthermore, the incidence, the aetiological classification and central nervous system complications of hyponatremia are presented, too. In addition, clinical and pathophysical features of hyponatremic encephalophathy and osmotic demyelinisation are given. The adaptive reactions of the brain to hypotonic stress are also described with particular emphasis on the role of brain-specific water channel proteins (aquaporin-4) and the benzamil-inhibitable sodium channels. In view of the outmost clinical significance of hyponatremia, the principles of efficient and safe therapeutic approaches are outlined. Orv. Hetil., 2013, 154, 1488–1497.

Vaptans: A new option in the management of hyponatremia

Arginine vasopressin (AVP) plays an important role in water and sodium homeostasis. It acts via three receptor subtypes-V1a, V1b, and V2-distributed widely throughout the body. Vaptans are nonpeptide vasopressin receptor antagonists (VRA). By property of aquaresis, VRAs offer a novel therapy of water retention. Conivaptan is a V1a/V2 nonselective VRA approved for euvolemic and hypervolemic hyponatremia. Tolvaptan is the first oral VRA. Other potential uses of this new class of drugs include congestive heart failure (CHF), cirrhosis of liver, syndrome of inappropriate secretion of antidiuretic hormone, polycystic kidney disease, and so on. These novel drugs score over diuretics as they are not associated with electrolyte abnormalities. Though much remains to be elucidated before the VRAs are applied clinically, the future holds much promise.

Neurologic Implications of Critical Illness and Organ Dysfunction

Critical illness has consequences for the nervous system. Patients experiencing critical illness are at risk for common global neurologic disturbances, such as delirium, long-term cognitive dysfunction, ICU-acquired weakness, sleep disturbances, recurrent seizures, and coma. In addition, complications related to specific organ dysfunction may be anticipated. Cardiovascular disease presents the possibility for CNS injury after cardiac arrest, sequelae of endocarditis, aberrancies of blood flow autoregulation, and malperfusion. Respiratory disease is known to cause short-term effects of hypoxia and long-term effects after ARDS. Sepsis encephalopathy and sickness behavior syndrome are early signs of infection in patients. In addition, commonly encountered organ dysfunction including uremia, hepatic failure, endocrine, and metabolic disturbances present with neurologic findings which may manifest in the critically ill patient as well.

Preoperative serum sodium is associated with cancer-specific survival in patients with upper urinary tract urothelial carcinoma treated by nephroureterectomy

OBJECTIVES

To assess the impact of preoperative serum sodium concentration on the prognosis of patients with upper urinary tract urothelial carcinoma treated by nephroureterectomy.

METHODS

The clinical records of 139 patients treated for upper urinary tract urothelial carcinoma by nephroureterectomy were retrospectively reviewed. Recurrence-free and cancer-specific survival curves were calculated using the Kaplan-Meier method, with the difference between curves evaluated using the log-rank test. A multivariate analysis was carried out by Cox's proportional hazard model to identify prognostic factors.

RESULTS

The median (range) follow-up time was 27 (1-139) months. The median (range) preoperative serum sodium was 141 (134-147) mEq/L. Five-year cancer-specific survival estimates for patients above and below the median preoperative serum sodium were 81.7% (95% confidence interval: 68.7-89.7) and 50.6% (95% confidence interval: 30.3-67.8), respectively. In the multivariate analysis, preoperative sodium concentration, pathological T stage, and lymphovascular invasion were independent and significant prognostic factors for cancer-specific survival. A prognostic model of risk classification for cancer-specific survival involving these parameters was developed, and 5-year cancer-specific survival estimates were 29.9% (95% confidence interval: 14.5-47.0) for the poor risk group (hazard ratio 19.95 [95% confidence interval: 8.5-46.6]; P < 0.001), 81.6% (95% confidence interval: 55.2-93.3) for the intermediate risk group (hazard ratio 5.70 [95% confidence interval: 1.27-25.5]; P = 0.022) and 97.9% (95% confidence interval 85.9-99.7) for the favorable risk group.

CONCLUSION

These findings suggest for the first time that a low preoperative sodium level predicts a poor survival in upper urinary tract urothelial carcinoma patients treated by nephroureterectomy.

Urea for treatment of acute SIADH in patients with subarachnoid hemorrhage: a single-center experience

Background

Hyponatremia occurring as a result of the syndrome of inappropriate antidiuretic hormone secretion (SIADH) or cerebral salt wasting syndrome is a common complication in patients with subarachnoid hemorrhage (SAH). The efficacy and safety of urea as treatment for SIADH-induced hyponatremia has not been reported in this population.

Methods

This is a retrospective analysis of all patients admitted to our department for nontraumatic SAH between January 2003 and December 2008 (n = 368). All patients with SIADH-induced hyponatremia (plasma sodium < 135 mEq/L, urine sodium > 20 mEq/L, and osmolality > 200 mOsm/kg; absence of overt dehydration or hypovolemia; no peripheral edema or renal failure; no history of adrenal or thyroid disease) routinely received urea per os when hyponatremia was associated with clinical deterioration or remained less than 130 mEq/L despite saline solution administration.

Results

Forty-two patients developed SIADH and were treated with urea. Urea was started after a median of 7 (IQR, 5–10) days and given orally at doses of 15–30 g tid or qid for a median of 5 (IQR, 3–7) days. The median plasma sodium increase over the first day of treatment was 3 (IQR, 1–6) mEq/L. Hyponatremia was corrected in all patients, with median times to Na⁺ >130 and >135 mEq/L of 1 (IQR, 1–2) and 3 (IQR, 2–4) days, respectively. Urea was well tolerated, and no adverse effects were reported.

Conclusions

Oral urea is an effective and well-tolerated treatment for SIADH-induced hyponatremia in SAH patients.

Effect of grapefruit juice on the pharmacokinetics of tolvaptan, a non-peptide arginine vasopressin antagonist, in healthy subjects

PURPOSE

Tolvaptan is a selective vasopressin V2 receptor antagonist that can be given orally once daily for treatment of clinically significant hypervolemic and euvolemic hyponatremia (US and Europe) or extracellular volume expansion despite taking other diuretics (Japan). In vitro studies indicated that tolvaptan was a CYP3A4 substrate.

METHODS

A single-center, randomized, crossover trial of 60-mg tolvaptan with 240 mL of water or with 240 mL of reconstituted grapefruit juice (washout period of 72 h between doses) was conducted in 20 healthy subjects. Blood samples for tolvaptan plasma concentrations were obtained for 48 h postdose.

RESULTS

All subjects completed the trial. Following co-administration with grapefruit juice, tolvaptan concentrations were elevated compared with tolvaptan alone for only 16 h postdose; consequently, the mean elimination half-life of tolvaptan was unchanged, 5.7 vs 5.1 h respectively. The mean maximal plasma concentration (C(max)) and the area under the curve (AUC(∞)) of tolvaptan were increased 1.86- and 1.56-fold respectively when co-administered with grapefruit juice.

CONCLUSIONS

It appears that grapefruit juice increases the bioavailability of tolvaptan, but does not affect its systemic elimination. The adverse event profile was consistent with the aquaretic effect of tolvaptan as urinary frequency, thirst, and dry mouth were the most frequently reported events.