Physiology and Pathophysiology of Water Homeostasis

Edelman Gamblegrams: a tool to teach and learn disorders of water/plasma tonicity homeostasis

This article introduces an innovative teaching and learning tool called "Edelman Gamblegrams" that aims to help medical learners better understand disorders related to water/plasma tonicity homeostasis, i.e., hyponatremia and hypernatremia. Gamblegrams, named after physician James L. Gamble, are bar diagrams displaying the relative abundance of extracellular anions and cations and are commonly used in the analysis of acid-base disorders. The Edelman equation represents the physiological variables that determine plasma sodium concentration, namely, total body sodium mass, total body potassium mass, and total body water volume. Edelman Gamblegrams inspired by traditional Gamblegrams but using the components of the Edelman equation, visually demonstrate how sodium, potassium, and water contribute to plasma sodium concentration under normal and pathological conditions. Scenarios that lead to hypotonic hyponatremia and hypernatremia in Edelman Gamblegrams are also discussed. Furthermore, examples of how these visual aids can enhance understanding of the pathogenesis of dysnatremias are also presented. Overall, the use of Edelman Gamblegrams has the potential to improve comprehension and retention of concepts related to water/plasma tonicity homeostasis.NEW & NOTEWORTHY This article introduces a new teaching tool called "Edelman Gamblegrams," modeled after the conventional Gamblegrams used in acid-base disorder analysis and using the independent physiological variables that determine the plasma sodium concentration (Edelman equation), that aims to help medical learners understand disorders related to water/plasma tonicity homeostasis.

Classifying Hypotonic Hyponatremia by Projected Treatment Effects - A Quantitative 3-Dimensional Framework

Introduction

The diagnostic algorithms currently used for hypotonic hyponatremia focus primarily on impaired urinary dilution and often neglect the influence of free water intake and solute excretion. We hypothesized that, in each case of hypotonic hyponatremia different pathophysiological mechanisms play a role simultaneously.

Methods

Using clinical data of the previous observational Co-Med study, we defined each case of hypotonic hyponatremia concurrently in 3 dimensions as follows: (i) high net free water intake (HNFWI), (ii) impaired dilution of the urine (IDU), and (iii) low nonelectrolyte solute excretion (LNESE). For each dimension, a "standard delta sodium" (sdna) was calculated reflecting the expected difference to the serum sodium concentration, that would result from changing a dimension to a specific and equivalent target level.

Results

Results from 279 patients were used for this analysis. With target levels of free water intake and urine osmolality at the fifth percentile, and nonelectrolyte solute excretion at the 95th percentile, median (interquartile range) sdna values were 7.1 (4.8-10.2) for HNFWI, 11.8 (7.0-18.6) for IDU and 2.6 (1.6-4.2) mmol/l per 24 hours for LNESE. Sdna results in individual patients were highest with IDU in 68.5%, HNFWI in 30.8% and 0.7% with LNESE. At an sdna-level of at least 4mmol/l per 24 hours, the prevalence of HNFWI was 78.9%, IDU 87.1%, and LNESE 26.5%. 77.5% of patients had 2 or all 3 mechanisms present. Hyponatremia was mostly multifactorial in subgroups according to classic categories of hyponatremia and typical comorbidities as well.

Conclusion

Hypotonic hyponatremia can be quantitatively defined by 3 dimensions. Most cases should be considered multifactorial.

Relationship between serum sodium level at dialysis initiation and all-cause mortality

BACKGROUND

Hyponatremia is a common electrolyte disorder in patients with chronic kidney disease. In addition, hyponatremia is associated with mortality in patients with chronic kidney disease, including those on dialysis. However, few studies have examined this relationship in patients with incident dialysis.

METHODS

We used a database of multicenter prospective cohort studies that included 1520 incident dialysis patients. The baseline was set at the time of dialysis initiation. The enrolled patients were classified into five groups according to their serum sodium levels (< 130 mEq/L, 130-134 mEq/L, 135-139 mEq/L, 140-144 mEq/L, and ≥ 145 mEq/L). Multivariate Cox proportional hazards analysis was conducted to determine factors associated with all-cause mortality.

RESULTS

A total of 392 all-cause deaths occurred during the follow-up period. The ultrafiltration volume per body weight during the first dialysis session was more significant in the groups with the lowest and highest sodium levels. The percentage of patients using loop diuretics and thiazide was higher in the group with lower sodium levels (< 130 mEq/L and 130-134 mEq/L). All-cause mortality was significantly different among the five groups (p = 0.025). Multivariate analysis indicated that all-cause mortality was significantly higher in the group with the lowest sodium level compared to the group with a serum sodium level of 135-139 mEq/L (hazard ratio: 1.61, 95% confidence interval: 1.04-2.49).

CONCLUSION

Hyponatremia of < 130 mEq/L at dialysis initiation was significantly associated with all-cause mortality. We considered the results relevant to underlying conditions, including cardiovascular disease and medications.

Consensus document on the management of hyponatraemia of the Acqua Group of the Spanish Society of Endocrinology and Nutrition

INTRODUCTION

Hyponatremia is the most prevalent electrolyte disorder in the outpatient and inpatient settings. Despite this frequency, hyponatremia, including severe hyponatremia, is frequently underestimated and inadequately treated, thus highlighting the need to produce consensus documents and clinical practice guidelines geared towards improving the diagnostic and therapeutic approach to it in a structured fashion.

MATERIAL AND METHODS

Members of the Acqua Group of the Spanish Society of Endocrinology and Nutrition (SEEN) met using a networking methodology over a period of 20 months (between October 2019 and August 2021) with the aim of discussing and developing an updated guideline for the management of hyponatraemia. A literature search of the available scientific evidence for each section presented in this document was performed.

RESULTS

A document with 8 sections was produced, which sets out to provide updated guidance on the most clinically relevant questions in the management of hyponatraemia. The management of severe hyponatraemia is based on the i.v. administration of a 3% hypertonic solution. For the management of chronic euvolemic hyponatraemia, algorithms for the initiation of treatment with the two pharmacological therapeutic options currently available in Spain are presented: urea and tolvaptan.

CONCLUSIONS

This document sets out to simplify the approach to and the treatment of hyponatraemia, making it easier to learn and thus improve the clinical approach to hyponatremia.

Hyponatremia Demystified: Integrating Physiology to Shape Clinical Practice

Hyponatremia is one of the most common problems encountered in clinical practice and one of the least-understood because accurate diagnosis and management require some familiarity with water homeostasis physiology, making the topic seemingly complex. The prevalence of hyponatremia depends on the nature of the population studied and the criteria used to define it. Hyponatremia is associated with poor outcomes including increased mortality and morbidity. The pathogenesis of hypotonic hyponatremia involves the accumulation of electrolyte-free water caused by either increased intake and/or decrease in kidney excretion. Plasma osmolality, urine osmolality, and urine sodium can help to differentiate among the different etiologies. Brain adaptation to plasma hypotonicity consisting of solute extrusion to mitigate further water influx into brain cells best explains the clinical manifestations of hyponatremia. Acute hyponatremia has an onset within 48 hours, commonly resulting in severe symptoms, while chronic hyponatremia develops over 48 hours and usually is pauci-symptomatic. However, the latter increases the risk of osmotic demyelination syndrome if hyponatremia is corrected rapidly; therefore, extreme caution must be exercised when correcting plasma sodium. Management strategies depend on the presence of symptoms and the cause of hyponatremia and are discussed in this review.

Diagnosis and management of hypernatraemia in children

Hypernatraemia is most commonly caused by excessive loss of solute-free water or decreased fluid intake; less often, the aetiology is salt intoxication. Especially infants, young children and individuals with a lack of access to water are at risk of developing hypernatraemia. Diagnosis is based on detailed history, physical examination and basic laboratory tests. Correction of hypernatraemia must be slow to prevent cerebral oedema and irreversible brain damage. This article reviews the aetiology, differential diagnosis and management of conditions associated with paediatric hypernatraemia. Distinguishing states with water deficiency from states with salt excess is important for proper management of hypernatraemic patients.

Electrolyte and Acid-Base Disorders associated with Cancer Immunotherapy

Novel immunotherapy drugs have changed the landscape of cancer medicine. Immune checkpoint inhibitors and chimeric antigen receptor T cells are being used and investigated in almost all solid cancers. Immune-related adverse events have been associated with immunotherapies. Acute kidney injury has been the most commonly associated kidney adverse event. In this review, we showcase the several associated electrolyte disorders seen with immunotherapy. Immune checkpoint inhibitors can lead to hyponatremia by several mechanisms, with the syndrome of inappropriate antidiuresis being the most common. Endocrine causes of hyponatremia are rare. Hypokalemia is not uncommon and is associated with both proximal and distal renal tubular acidosis. Hypercalcemia associated with immune checkpoint inhibitors has led to some interesting observations including immune checkpoint inhibitor-induced parathyroid hormone - related peptide production, sarcoid-like granulomas, and hyper-progression of the disease. Hypocalcemia and hyperphosphatemia may be seen with immune checkpoint inhibitor-induced tumor lysis syndrome. Chimeric antigen receptor T cell therapy-associated electrolyte disorders are also common. This is associated chiefly with hyponatremia, although other electrolyte abnormalities can occur. Early recognition and prompt diagnosis may help providers manage the mechanistically varied and novel electrolyte disorders associated with immunotherapy.

Clinical, Genetic and Functional Characterization of a Novel AVPR2 Missense Mutation in a Woman with X-Linked Recessive Nephrogenic Diabetes Insipidus

Nephrogenic diabetes insipidus (NDI) is a rare disorder characterized by renal unresponsiveness to the hormone vasopressin, leading to excretion of large volumes of diluted urine. Mutations in the arginine vasopressin receptor-2 (AVPR2) gene cause congenital NDI and have an X-linked recessive inheritance. The disorder affects almost exclusively male family members, but female carriers occasionally present partial phenotypes due to skewed inactivation of the X-chromosome. Here, we report a rare case of a woman affected with X-linked recessive NDI, presenting an average urinary output of 12 L/day. Clinical and biochemical studies showed incomplete responses to water deprivation and vasopressin stimulation tests. Genetic analyses revealed a novel heterozygous missense mutation (c.493G > C, p.Ala165Pro) in the AVPR2 gene. Using a combination of in-silico protein modeling with human cellular models and molecular phenotyping, we provide functional evidence for phenotypic effects. The mutation destabilizes the helical structure of the AVPR2 transmembrane domains and disrupts its plasma membrane localization and downstream intracellular signaling pathways upon activation with its agonist vasopressin. These defects lead to deficient aquaporin 2 (AQP2) membrane translocation, explaining the inability to concentrate urine in this patient.

Applying concepts of life course theory and life course epidemiology to the study of bladder health and lower urinary tract symptoms among girls and women

AIMS

Although lower urinary tract symptoms (LUTS) may occur at different periods during the life course of women, a little research on LUTS has adopted a life course perspective. The purpose of this conceptual paper is to demonstrate how life course theory and life course epidemiology can be applied to study bladder health and LUTS trajectories. We highlight conceptual work from the Prevention of Lower Urinary Tract Symptoms Research Consortium to enhance the understanding of life course concepts.

METHODS

Consortium members worked in transdisciplinary teams to generate examples of how life course concepts may be applied to research on bladder health and LUTS in eight prioritized areas: (a) biopsychosocial ecology of stress and brain health; (b) toileting environment, access, habits, and techniques; (c) pregnancy and childbirth; (d) physical health and medical conditions; (e) musculoskeletal health; (f) lifestyle behaviors; (g) infections and microbiome; and (h) hormonal status across the life span.

RESULTS

Life course concepts guided consortium members' conceptualization of how potential risk and protective factors may influence women's health. For example, intrapartum interventions across multiple pregnancies may influence trajectories of bladder health and LUTS, illustrating the principle of life span development. Consortium members also identified and summarized methodologic and practical considerations in designing life course research.

CONCLUSIONS

This paper may assist researchers from a variety of disciplines to design and implement research identifying key risk and protective factors for LUTS and bladder health across the life course of women. Results from life course research may inform health promotion programs, policies, and practices.