Body fluids and salt metabolism - part II

Relationship of severity of hyponatremia and adverse outcomes in children visiting the emergency department

Mild hyponatremia is often found in patients visiting pediatric emergency departments (PEDs), but there are few large-scale studies on its association with adverse outcomes, including mortality. We conducted this study to identify the association of mild hyponatremia with adverse outcome. This retrospective observational study included children under 18 years of age visiting the PED at a tertiary hospital. We used electronic medical record data from January 1, 2009 to December 31, 2020. Clinical outcomes, including ward admission, vasopressor administration, pediatric intensive care unit (PICU) admission, and mortality, were assessed for the total of 44,147 patients. Among these, 1,639 (3.7%) were in the hyponatremia group, with 1,521 (3.4%) exhibiting mild hyponatremia. Mild hyponatremia was more prevalent in younger patients, particularly in the 1-3 years age group, and less common in females. Patients with mild hyponatremia had a significantly prolonged median length of stay in the PED compared to normonatremic patients (5.8 h vs. 4.4 h, p < 0.001). Moreover, they showed significantly higher rates of ward admission (51.1% vs. 35.6%, p < 0.001), vasopressor administration (1.1% vs. 0.6%, p = 0.014), PICU admission (2.4% vs. 1.0%, p < 0.001), and mortality (1.5% vs. 0.3%, p < 0.001). Compared with the normonatremia group, the odds ratios (95% CI) for ward admission, vasopressor administration, PICU admission, and mortality in the mild hyponatremia group were 1.90 (1.71-2.10), 1.91 (1.17-3.13), 2.62 (1.86-3.68), and 5.56 (3.51-8.80), respectively. Furthermore, our findings demonstrate a notable upward trend in adverse outcomes, including vasopressor administration, PICU admission, and mortality, from mild hyponatremia to severe hyponatremia. In conclusion, we found that adverse outcomes increase with the severity of hyponatremia in children presenting to the PED, highlighting the importance of immediate intervention alongside the identification of the underlying cause.

Brain sodium sensing for regulation of thirst, salt appetite, and blood pressure

The brain possesses intricate mechanisms for monitoring sodium (Na) levels in body fluids. During prolonged dehydration, the brain detects variations in body fluids and produces sensations of thirst and aversions to salty tastes. At the core of these processes Nax , the brain's Na sensor, exists. Specialized neural nuclei, namely the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), which lack the blood-brain barrier, play pivotal roles. Within the glia enveloping the neurons in these regions, Nax collaborates with Na+ /K+ -ATPase and glycolytic enzymes to drive glycolysis in response to elevated Na levels. Lactate released from these glia cells activates nearby inhibitory neurons. The SFO hosts distinct types of angiotensin II-sensitive neurons encoding thirst and salt appetite, respectively. During dehydration, Nax -activated inhibitory neurons suppress salt-appetite neuron's activity, whereas salt deficiency reduces thirst neuron's activity through cholecystokinin. Prolonged dehydration increases the Na sensitivity of Nax via increased endothelin expression in the SFO. So far, patients with essential hypernatremia have been reported to lose thirst and antidiuretic hormone release due to Nax -targeting autoantibodies. Inflammation in the SFO underlies the symptoms. Furthermore, Nax activation in the OVLT, driven by Na retention, stimulates the sympathetic nervous system via acid-sensing ion channels, contributing to a blood pressure elevation.

Sodium Homeostasis, a Balance Necessary for Life

Body sodium (Na) levels must be maintained within a narrow range for the correct functioning of the organism (Na homeostasis). Na disorders include not only elevated levels of this solute (hypernatremia), as in diabetes insipidus, but also reduced levels (hyponatremia), as in cerebral salt wasting syndrome. The balance in body Na levels therefore requires a delicate equilibrium to be maintained between the ingestion and excretion of Na. Salt (NaCl) intake is processed by receptors in the tongue and digestive system, which transmit the information to the nucleus of the solitary tract via a neural pathway (chorda tympani/vagus nerves) and to circumventricular organs, including the subfornical organ and area postrema, via a humoral pathway (blood/cerebrospinal fluid). Circuits are formed that stimulate or inhibit homeostatic Na intake involving participation of the parabrachial nucleus, pre-locus coeruleus, medial tuberomammillary nuclei, median eminence, paraventricular and supraoptic nuclei, and other structures with reward properties such as the bed nucleus of the stria terminalis, central amygdala, and ventral tegmental area. Finally, the kidney uses neural signals (e.g., renal sympathetic nerves) and vascular (e.g., renal perfusion pressure) and humoral (e.g., renin-angiotensin-aldosterone system, cardiac natriuretic peptides, antidiuretic hormone, and oxytocin) factors to promote Na excretion or retention and thereby maintain extracellular fluid volume. All these intake and excretion processes are modulated by chemical messengers, many of which (e.g., aldosterone, angiotensin II, and oxytocin) have effects that are coordinated at peripheral and central level to ensure Na homeostasis.

Outdoor temperature and circulating sodium in children with acute gastroenteritis

BACKGROUND

Dysnatremias are frequent in acute gastroenteritis. High outdoor temperatures have been associated with hyponatremia in both adults and the elderly, but no data are available among children with gastroenteritis.

METHODS

Children <10 years of age admitted to the emergency department of the Policlinico Hospital, Milan (Italy) between 2009 and 2019 with acute moderate-severe gastroenteritis were enrolled. The association between hyponatremia (sodium < 135 mmol/L) and daily mean levels of temperature or apparent temperature from day of admission up to 14 days before was analyzed by multivariable logistic regression models.

RESULTS

In 202 included children (46% females), we observed an increased risk of hyponatremia per unit increase in outdoor temperature of the sixth, eighth and ninth day before admission [Odds Ratio = 1.24 (95% Confidence Interval: 1.04-1.47), 1.14 (1.01-1.28), and 1.14 (1.01-1.28), respectively]. Analyses considering average temperature levels of the ten days preceding admission returned similar findings as well as those on apparent temperature.

CONCLUSIONS

Our data suggest the existence of an association between outdoor temperature and circulating sodium levels in children with acute gastroenteritis. The role of meteorological conditions on electrolyte imbalance should be further explored in the context of climate change.

IMPACT

The role of meteorological variables in the development of dysnatremias has been demonstrated in children and adolescents with cystic fibrosis. This study shows for the first time that higher outdoor temperatures are associated with a higher risk of hyponatremia in children with gastroenteritis. In the context of climate change, the role of external climate conditions on the risk of electrolyte imbalance in children should be more and more considered and explored in future studies.

Sodium assessment in neonates, infants, and children: a systematic review

Hyponatremia is a common disorder in childhood. The indirect and the direct potentiometry are currently the most popular techniques employed for sodium assessment, although discrepancies between the two techniques may be > 10 mmol/L. It is known that < 20% of the recently published articles report information about the technique used for sodium analysis, but no data are available on pediatric studies. This study aimed at investigating the laboratory technique employed for sodium measurement in studies conducted in childhood. A systematic literature search in PubMed, Embase, and Web of Science was undertaken to identify articles containing the word "hyponatremia" in the title between 2013 and 2020. Papers with < 10 subjects were excluded. A total of 565 articles were included. Information on the laboratory technique used for sodium analysis was more commonly (p = 0.035) reported in pediatric (n = 15, 28%) than in non-pediatric (n = 81, 16%) reports. The frequency of reports with and without information on the technique for sodium assessment was not different with respect to the study characteristics, the quartile of the journal where the paper was published, the country income setting, and the inclusion of neonates among the 54 pediatric studies.   Conclusion: Most pediatric papers do not report any information on the technique used for sodium analysis. Although international authorities have recommended the implementation of direct potentiometry, a low awareness on this issue is still widespread in pediatric research. What is Known: • Direct potentiometry and indirect potentiometry are currently employed for sodium analysis in blood. • Direct potentiometry is more accurate. What is New: • Less than 30% of pediatric articles provide information on the technique employed for sodium analysis in blood. • Indirect potentiometry is more frequently employed than direct potentiometry in pediatric studies.

Central regulation of body fluid homeostasis

Extracellular fluids, including blood, lymphatic fluid, and cerebrospinal fluid, are collectively called body fluids. The Na⁺ concentration ([Na⁺]) in body fluids is maintained at 135-145 mM and is broadly conserved among terrestrial animals. Homeostatic osmoregulation by Na⁺ is vital for life because severe hyper- or hypotonicity elicits irreversible organ damage and lethal neurological trauma. To achieve "body fluid homeostasis" or "Na homeostasis", the brain continuously monitors [Na⁺] in body fluids and controls water/salt intake and water/salt excretion by the kidneys. These physiological functions are primarily regulated based on information on [Na⁺] and relevant circulating hormones, such as angiotensin II, aldosterone, and vasopressin. In this review, we discuss sensing mechanisms for [Na⁺] and hormones in the brain that control water/salt intake behaviors, together with the responsible sensors (receptors) and relevant neural pathways. We also describe mechanisms in the brain by which [Na⁺] increases in body fluids activate the sympathetic neural activity leading to hypertension.

Osmoregulation in children with cystic fibrosis

Hyponatremia is not rare in cystic fibrosis and might be due to several mechanisms. An endocrine and renal imbalance in water and salt homeostasis was suggested. To address this hypothesis, we assessed the urinary concentrating and diluting ability in 12 cystic fibrosis patients (6 females, 6 males) and in two control groups: 14 children with pneumonia (9 females, 5 males) and in 13 healthy children (9 females, 4 males). Renal concentrating ability was evaluated following overnight water deprivation. Urine osmolality was not significantly different between groups. Renal diluting ability was assessed by means of a water-load test. This provoked a decrease in urine osmolality, as well as an increase in diuresis and solute-free water excretion. These changes were comparable among groups.Conclusion: Children with cystic fibrosis show a preserved renal concentrating and diluting capacity. A generalized endocrine and renal imbalance in water and salt homeostasis therefore appears unlikely.What is Known:•Hyponatremia sometimes occurs in cystic fibrosis.What is New:•Osmoregulation is normal in cystic fibrosis.

In silico model of the dilutional effects of conventional component therapy versus whole blood in the management of massively bleeding adult trauma patients

BACKGROUND

There are multiple approaches to the blood product and fluid resuscitation of a bleeding trauma patient. An in silico model of different trauma resuscitation strategies was constructed to predict their effects on the volumes of the different body fluid compartments and on several important hemostatic factors.

STUDY DESIGN AND METHODS

This multicompartment dynamic deterministic model comprised four interconnected modules (hemostatic, resuscitation, body fluid compartment, and dilutional coagulopathy). The model was divided into five resuscitation phases with simulations using six different resuscitation strategies: whole blood (WB) only, conventional component therapy (CCT) only or 10 units of WB followed by CCT, with either 1 L of crystalloid or 1.5 units of WB or red blood cells in the prehospital phase.

RESULTS

At the end of the simulations using 1 L of crystalloid fluids in the prehospital resuscitation phase, the use of WB led to a 1.4 g/dL higher hemoglobin concentration, 32 mg/dL higher fibrinogen concentration, and 0.9 L lower total extracellular fluid volume compared to CCT. Prehospital blood product transfusion in place of crystalloid resulted in higher hemoglobin and fibrinogen concentrations and a lower international normalized ratio throughout the resuscitation regardless of the resuscitation strategy used. Throughout both the prehospital crystalloid and prehospital blood product transfusion simulations, the hemoglobin and fibrinogen concentrations and platelet counts were higher, and the international normalized ratio was lower, when WB was used compared to CCT.

CONCLUSIONS

This model predicted improved hemostatic factor levels and a smaller total extracellular fluid volume volume when WB was transfused instead of CCT to bleeding trauma patients.

Mechanism of Hyponatremia in Community-Acquired Pneumonia: Does B-type Natriuretic Peptide Play a Causative Role?

OBJECTIVE

Hyponatremia is a well-known sequela of community-acquired pneumonia (CAP). B-type natriuretic peptide (BNP) has a natriuretic effect and was found to be elevated in patients with CAP. We investigated whether BNP has a role in the pathophysiology of hyponatremia in pediatric CAP.

METHODS

Serum and urine electrolytes and osmolality, as well as NT-pro-BNP (N-BNP), were obtained in 49 hospitalized pediatric patients with CAP (29 with hyponatremia, 20 with normal sodium levels.

RESULTS

Urine sodium levels were lower in the hyponatremic group compared with the normonatremic group (24.3 meq/L vs 66.7 meq/L, P = 0.006). No difference in N-BNP levels was found between groups (median, 103.8 vs 100.1; P = 0.06; interquartile range, 63.7-263.3 pg/mL vs 47.4-146.4 pg/mL). N-BNP was not associated with serum or urinary sodium levels.

CONCLUSIONS

These results indicate that BNP is unlikely to play a causative role in the mechanism of hyponatremia in CAP.

One-Step Preparation of pH-Responsive Polymeric Nanogels as Intelligent Drug Delivery Systems for Tumor Therapy

In this work, pH-responsive polypeptide-based nanogels are reported as potential drug delivery systems. By the formation of pH-sensitive benzoic imine bonds, pH-responsive nanogels are constructed using hydrophilic methoxy poly(ethylene glycol)- b-poly[ N-[ N-(2-aminoethyl)-2-aminoethyl]-l-glutamate] (MPEG- b-PNLG) and hydrophobic terephthalaldehyde (TPA) as a cross-linker. At pH 7.4, MPEG- b-PNLG nanogels exhibit high stabilities with hydrophobic inner cores, which allow encapsulation of hydrophobic therapeutic agents. Under tumoral acidic environments (pH ∼6.4), the cleavage of benzoic imine bonds induces the destruction of MPEG- b-PNLG nanogels and leads to rapid release of their payloads. The formation and pH sensitivity of the nanogels are investigated by dynamic light scattering. These nanogels exhibit excellent stabilities in the presence of salt or against dilution. The globular morphologies of the nanogels are confirmed using transmission electron microscopy. Doxorubicin is used as a model drug to evaluate drug encapsulation and release. Finally, the anticancer activities of the drug-encapsulated nanogels are assessed in vitro.

D-lactic acidosis in humans: systematic literature review

BACKGROUND

D-lactic acidosis is an uncommon and challenging form of metabolic acidosis that may develop in short bowel syndrome. It has been documented exclusively in case reports and small case series.

METHODS

We performed a review of the literature in the National Library of Medicine and Excerpta Medica databases.

RESULTS

We identified 84 original reports published between 1977 and 2017. D-lactic acidosis was observed in 98 individuals ranging in age from 7 months to 86 years with short bowel syndrome. The clinical presentation included Kussmaul breathing, confusion, slurred speech, and gait disturbances. Furthermore, among 99 consecutive patients with short bowel syndrome, 21 reported having episodes with symptoms consistent with D-lactic acidosis. In addition, D-lactic acid might also contribute to acidosis in diabetes mellitus. Finally, abnormally high D-lactic acid was documented after administration or ingestion of large amounts of propylene glycol, as paraneoplastic phenomenon and perhaps also in a so far poorly characterized inherited inborn error of metabolism.

CONCLUSIONS

In humans with short bowel syndrome (or carbohydrate malabsorption), D-lactic acidosis is likely rather common and under-recognized. This condition should be included in the differential diagnosis of unexplained high-gap metabolic acidosis where the anion causing the acidosis is not known. Furthermore, diabetic acidosis might be caused by accumulation of both ketone bodies and D-lactic acid. Finally, there are endogenous sources of D-lactic acid in subjects with propylene glycol intoxication.

Management of Diarrhoeal Dehydration in Childhood: A Review for Clinicians in Developing Countries

The survival of a child with severe volume depletion at the emergency department depends on the competency of the first responder to recognize and promptly treat hypovolemic shock. Although the basic principles on fluid and electrolytes therapy have been investigated for decades, the topic remains a challenge, as consensus on clinical management protocol is difficult to reach, and more adverse events are reported from fluid administration than for any other drug. While the old principles proposed by Holliday and Segar, and Finberg have stood the test of time, recent systematic reviews and meta-analyses have highlighted the risk of hyponatraemia, and hyponatraemic encephalopathy in some children treated with hypotonic fluids. In the midst of conflicting literature on fluid and electrolytes therapy, it would appear that isotonic fluids are best suitable for the correction of hypotonic, isonatraemic, and hypernatraemic dehydration. Although oral rehydration therapy is adequate to correct mild to moderate isonatraemic dehydration, parenteral fluid therapy is safer for the child with severe dehydration and those with changes in serum sodium. The article reviews the pathophysiology of water and sodium metabolism and, it uses the clinical case examples to illustrate the bed-side approach to the management of three different types of dehydration using a pre-mixed isotonic fluid solution (with 20 or 40 mmol/L of potassium chloride added depending on the absence or presence of hypokalemia, respectively). When 3% sodium chloride is unavailable to treat hyponatraemic encephalopathy, 0.9% sodium chloride becomes inevitable, albeit, a closer monitoring of serum sodium is required. The importance of a keen and regular clinical and laboratory monitoring of a child being rehydrated is emphasized. The article would be valuable to clinicians in less-developed countries, who must use pre-mixed fluids, and who often cannot get some suitable rehydrating solutions.

Hyponatremia in infants with new onset moderate-severe bronchiolitis: A cross-sectional study

BACKGROUND

The reported cumulative prevalence of hyponatremia (sodium <135 mmol/L) in bronchiolitis is 28%. However, sodium level was never measured by direct potentiometry, the method recommended by the International Federation of Clinical Chemistry and Laboratory Medicine. Aim of this study was to assess the prevalence of hyponatremia, measured by direct potentiometry, in infants with moderate-severe bronchiolitis.

METHODS

A prospective cross-sectional study was conducted in infants ≥1month and ≤24months of age with bronchiolitis.

RESULTS

160 consecutive infants were enrolled. Hyponatremia was observed in 91 (57%) patients and occurred more commonly in infants ≤6 months than in older infant (P < 0.005).

CONCLUSION

The first study on sodium level measured by the direct potentiometry in infants with bronchiolitis points out that the prevalence of hyponatremia is two-fold higher than so far reported.

Medication Use as a Contributor to Fluid Overload in the PICU: A Prospective Observational Study

In this prospective observational study, we explored the association of daily fluid intake from medication use with fluid overload in 75 children beginning 24 hours after intubation. The mean percent daily fluid intake from medications was 29% in the overall cohort. Excess intake and inadequate output contributed significantly to fluid overload. In the 28 patients who became ≥10% fluid overloaded, the mean percent daily fluid intake from medications was 34%, but just 23% in the patients who did not. Awareness of volume contribution and maximized concentration of parenteral medications when able may lessen the burden of fluid overload.

Hyponatremia in children with acute respiratory infections: A reappraisal

Hyponatremia (<135 mmol/L), typically associated with an elevated anti-diuretic hormone level, is common among children admitted with bronchiolitis, pneumonia, or pulmonary exacerbation of cystic fibrosis. The main consequences of acute hyponatremia include cerebral edema and Ayus-Arieff pulmonary edema. A widespread belief is that, in children with pneumonia or bronchiolitis, hyponatremia results from inappropriate anti-diuresis. By contrast, the pathogenic role of extracellular fluid volume depletion or decreased effective circulating blood volume is underscored. Considering the prevalence of hyponatremia, sodium determination is advised on admission in children diagnosed with bronchiolitis, pneumonia, or pulmonary exacerbation of cystic fibrosis. There is no necessity to do anything beyond reassessing the appropriateness of fluid therapy in cases with mild (130-134 mmol/L) hyponatremia. In children with sodium <130 mmol/L, the underlying etiology is sometimes evident from history and physical findings. Given that clinical assessment of fluid volume status is difficult in hyponatremia, further laboratory evaluation is often required in these patients. An increase in sodium level ≤6 mmol/L per day is currently considered the therapeutic goal in all cases. Emergency correction with a 2 mL/kg body weight bolus of 3.0% saline over 10-15 min intravenously is advised in cases with severe symptoms due to hyponatremia and in cases with symptoms, even if mild, due to a rapid-onset (<48 h) of hyponatremia (two additional doses are administered if the patient's condition does not improve).

Na(+), K(+), Cl(-), acid-base or H2O homeostasis in children with urinary tract infections: a narrative review

Guidelines on the diagnosis and management of urinary tract infections in childhood do not address the issue of abnormalities in Na(+), K(+), Cl(-) and acid-base balance. We have conducted a narrative review of the literature with the aim to describe the underlying mechanisms of these abnormalities and to suggest therapeutic maneuvers. Abnormalities in Na(+), K(+), Cl(-) and acid-base balance are common in newborns and infants and uncommon in children of more than 3 years of age. Such abnormalities may result from factitious laboratory results, from signs and symptoms (such as excessive sweating, poor fluid intake, vomiting and passage of loose stools) of the infection itself, from a renal dysfunction, from improper parenteral fluid management or from the prescribed antimicrobials. In addition, two transient renal tubular dysfunctions may occur in infants with infectious renal parenchymal involvement: a reduced capacity to concentrate urine and pseudohypoaldosteronism secondary to renal tubular unresponsiveness to aldosterone that presents with hyponatremia, hyperkalemia and acidosis. In addition to antimicrobials, volume resuscitation with an isotonic solution is required in these children. In secondary pseudohypoaldosteronism, isotonic solutions (such as 0.9 % saline or lactated Ringer) correct not only the volume depletion but also the hyperkalemia and acidosis. In conclusion, our review suggests that in infants with infectious renal parenchymal involvement, non-renal and renal causes concur to cause fluid volume depletion and abnormalities in electrolyte and acid-base balance, most frequently hyponatremia.

Sodium sensing in the subfornical organ and body-fluid homeostasis

The brain monitors conditions of body fluids and levels of circulating neuroactive factors to maintain the systemic homeostasis. Unlike most regions in the brain, circumventricular organs (CVOs) lack the blood-brain barrier, and serve as the sensing center. Among the CVOs, the subfornical organ (SFO) is the sensing site of Na⁺ levels in body fluids to control water and salt intake. The SFO harbors neuronal cell bodies with a variety of hormone receptors and innervates many brain loci. In addition, the SFO harbors specialized glial cells (astrocytes and ependymal cells) expressing Na_x, a Na⁺-level-sensitive sodium channel. These glial cells wrap a specific population of neurons with their processes, and control the firing activities of the neurons by gliotransmitters, such as lactate and epoxyeicosatrienoic acids (EETs), relevant to water/salt-intake behaviors. Recent advances in the understanding of physiological functions of the SFO are reviewed herein with a focus on the Na⁺-sensing mechanism by Na_x.

Adipsic hypernatremia without hypothalamic lesions accompanied by autoantibodies to subfornical organ

Adipsic (or essential) hypernatremia is a rare hypernatremia caused by a deficiency in thirst regulation and vasopressin release. In 2010, we reported a case in which autoantibodies targeting the sensory circumventricular organs (sCVOs) caused adipsic hypernatremia without hypothalamic structural lesions demonstrable by magnetic resonance imaging (MRI); sCVOs include the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), which are centers for the monitoring of body-fluid conditions and the control of water and salt intakes, and harbor neurons innervating hypothalamic nuclei for vasopressin release. We herein report three newly identified patients (3- to 8-year-old girls on the first visit) with similar symptoms. The common features of the patients were extensive hypernatremia without any sensation of thirst and defects in vasopressin response to serum hypertonicity. Despite these features, we could not detect any hypothalamic structural lesions by MRI. Immunohistochemical analyses using the sera of the three patients revealed that antibodies specifically reactive to the mouse SFO were present in the sera of all cases; in one case, the antibodies also reacted with the mouse OVLT. The immunoglobulin (Ig) fraction of serum obtained from one patient was intravenously injected into wild-type mice to determine whether the mice developed similar symptoms. Mice injected with a patient's Ig showed abnormalities in water/salt intake, vasopressin release, and diuresis, which resultantly developed hypernatremia. Prominent cell death and infiltration of reactive microglia was observed in the SFO of these mice. Thus, autoimmune destruction of the SFO may be the cause of the adipsic hypernatremia. This study provides a possible explanation for the pathogenesis of adipsic hypernatremia without demonstrable hypothalamus-pituitary lesions.

The great fluid debate: saline or so-called "balanced" salt solutions?

Background

Intravenous fluids are commonly prescribed in childhood. 0.9 % saline is the most-used fluid in pediatrics as resuscitation or maintenance solution. Experimental studies and observations in adults suggest that 0.9 % saline is a poor candidate for fluid resuscitation. Although anesthesiologists, intensive care specialists, perioperative physicians and nephrologists have been the most active in this debate, this issue deserves some physiopathological considerations also among pediatricians.

Results

As compared with so-called “balanced” salt crystalloids such as lactated Ringer, administration of large volumes of 0.9 % saline has been associated with following deleterious effects: tendency to hyperchloremic metabolic acidosis (called dilution acidosis); acute kidney injury with reduced urine output and salt retention; damaged vascular permeability and stiffness, increase in proinflammatory mediators; detrimental effect on coagulation with tendency to blood loss; detrimental gastrointestinal perfusion and function; possible uneasiness at the bedside resulting in unnecessary administration of more fluids. Nevertheless, there is no firm evidence that these adverse effects are clinically relevant.

Conclusions

Intravenous fluid therapy is a medicine like insulin, chemotherapy or antibiotics. Prescribing fluids should fit the child’s history and condition, consider the right dose at the right rate as well as the electrolyte levels and other laboratory variables. It is unlikely that a single type of fluid will be suitable for all pediatric patients. “Balanced” salt crystalloids, although more expensive, should be preferred for volume resuscitation, maintenance and perioperatively. Lactated Ringer appears unsuitable for patients at risk for brain edema and for those with overt or latent chloride-deficiency. Finally, in pediatrics there is a need for new fluids to be developed on the basis of a better understanding of the physiology and to be tested in well-designed trials.

Sodium sensing in the brain

Sodium (Na) homeostasis is crucial for life, and the Na(+) level ([Na(+)]) of body fluids is strictly maintained at a range of 135-145 mM. However, the existence of a [Na(+)] sensor in the brain has long been controversial until Nax was identified as the molecular entity of the sensor. This review provides an overview of the [Na(+)]-sensing mechanism in the brain for the regulation of salt intake by summarizing a series of our studies on Nax. Nax is a Na channel expressed in the circumventricular organs (CVOs) in the brain. Among the CVOs, the subfornical organ (SFO) is the principal site for the control of salt intake behavior, where Nax populates the cellular processes of astrocytes and ependymal cells enveloping neurons. A local expression of endothelin-3 in the SFO modulates the [Na(+)] sensitivity for Nax activation, and thereby Nax is likely to be activated in the physiological [Na(+)] range. Nax stably interacts with Na(+)/K(+)-ATPase whereby Na(+) influx via Nax is coupled with activation of Na(+)/K(+)-ATPase associated with the consumption of ATP. The consequent activation of anaerobic glucose metabolism of Nax-positive glial cells upregulates the cellular release of lactate, and this lactate functions as a gliotransmitter to activate GABAergic neurons in the SFO. The GABAergic neurons presumably regulate hypothetic neurons involved in the control of salt intake behavior. Recently, a patient with essential hypernatremia caused by autoimmunity to Nax was found. In this case, the hypernatremia was considered to be induced by the complement-mediated cell death in the CVOs, where Nax specifically populates.

The Nax Channel

Na x, which is preferentially expressed in the glial cells of sensory circumventricular organs in the brain, is a sodium channel that is poorly homologous to voltage-gated sodium channels. We previously reported that Na x is a sodium concentration ([Na+])-sensitive, but not a voltage-sensitive channel that is critically involved in body-fluid homeostasis. Nax-knockout mice do not stop ingesting salt even when dehydrated and transiently develop hypernatremia. [Na+] in body fluids is strictly controlled at 135 to 145 mM in mammals. Although the set point must be within this range, Na x was shown to have a threshold value of ~150 mM for extracellular [Na+] ([Na+]o) for activation in vitro. Therefore, the [Na+]o dependency of Na x in vivo is presumably modified by an as yet unidentified mechanism. We recently demonstrated that the [Na+]o dependency of Na x in the subfornical organ was adjusted to the physiological range by endothelin-3. Pharmacological experiments revealed that endothelin receptor B signaling was involved in this modulation of Na x gating through protein kinase C and ERK1/2 activation. In addition, we identified a case of essential hypernatremia caused by autoimmunity to Na x. Occurrence of a ganglioneuroma composed of Schwann-like cells that robustly expressed Na x was likely to induce the autoimmune response in this patient. An intravenous injection of the immunoglobulin fraction of the patient’s serum, which contained anti-Na x antibodies, into mice reproduced the patient’s symptoms. This review provides an overview of the physiological functions of Na x by summarizing our recent studies.

Electrolyte abnormalities in cystic fibrosis: systematic review of the literature

BACKGROUND

Cystic fibrosis per se can sometimes lead to hyponatremia, hypokalemia, hypochloremia or hyperbicarbonatemia. This tendency was first documented 60 years ago and has subsequently been confirmed in single case reports or small case series, most of which were retrospective. However, this issue has not been addressed analytically. We have therefore systematically reviewed and analyzed the available literature on this subject.

METHODS

This was a systematic review of the literature.

RESULTS

The reports included in this review cover 172 subacute and 90 chronic cases of electrolyte imbalances in patients with cystic fibrosis. The male:female ratio was 1.57. Electrolyte abnormalities were mostly associated with clinically inapparent fluid volume depletion, mainly affected patients aged ≤2.5 years, frequently tended to recur and often were found before the diagnosis of cystic fibrosis was established. Subacute presentation often included an history of heat exposure, vomiting, excessive sweating and pulmonary infection. History of chronic presentation, in contrast, was often inconspicuous. The tendency to hypochloremia, hypokalemia and metabolic alkalosis was similar between subacute and chronic patients, with hyponatremia being more pronounced (P < 0.02) in subacute compared to chronic presentations. Subacute cases were treated parenterally; chronic ones were usually managed with oral salt supplementation. Retention of urea and creatinine was documented in 38 % of subacute cases.

CONCLUSIONS

The findings of our review suggest that physicians should be aware that electrolyte abnormalities can occur both as a presenting and a recurring feature of cystic fibrosis.

Low serum potassium concentration is a predictor of chronic kidney disease

AIMS

The aim of this study was to examine whether low serum potassium concentration could be a predictor of chronic kidney disease (CKD) in a community-based cohort.

MATERIALS AND METHODS

We enrolled 1001 subjects, median period of 5.7 years, and evaluated the risk factors for CKD, defined as estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m(2), and assessed whether low serum potassium concentration could predict CKD.

RESULTS

Compared with the subjects without development of CKD, age, body mass index, fasting plasma glucose, uric acid (UA), creatinine and serum sodium concentration were higher, and serum potassium concentration was lower in subjects with development of CKD. Univariate Cox regression analyses demonstrated that age, body mass index, fasting plasma glucose, UA, creatinine, serum sodium concentration and serum potassium concentration were associated with progression of CKD. Multiple Cox regression analysis revealed that age, gender, creatinine and serum potassium concentration were independent predictors of CKD after adjustment for covariates. When serum potassium concentration was below 4.0 mmol/l at baseline, hazard ratio (95% confidence interval) of developing CKD was 2.65 (2.04-3.44; p < 0.0001).

CONCLUSIONS

Serum potassium concentration could be a clinically relevant risk factor for the progression of CKD, defined as eGFR < 60 ml/min/1.73 m(2) , in healthy subjects.

Endothelin-3 expression in the subfornical organ enhances the sensitivity of Na(x), the brain sodium-level sensor, to suppress salt intake

Salt homeostasis is essential to survival, but brain mechanisms for salt-intake control have not been fully elucidated. Here, we found that the sensitivity of Na(x) channels to [Na(+)](o) is dose-dependently enhanced by endothelin-3 (ET-3). Na(x) channels began to open when [Na(+)](o) exceeded ~150 mM without ET-3, but opened fully at a physiological [Na(+)](o) (135–145 mM) with 1 nM ET-3. Importantly, ET-3 was expressed in the subfornical organ (SFO) along with Nax, and the level was robustly increased by dehydration. Pharmacological experiments revealed that endothelin receptor B (ET(B)R) signaling is involved in this modulation of Na(x) gating through protein kinase C and ERK1/2 activation. ET(B)R agonists increased the firing rate of GABAergic neurons via lactate in the SFO, and an ET(B)R antagonist attenuated salt aversion during dehydration. These results indicate that ET-3 expression in the SFO is tightly coupled with body-fluid homeostasis through modulation of the [Na(+)](o) sensitivity of Na(x).

CSWS Versus SIADH as the Probable Causes of Hyponatremia in Children With Acute CNS Disorders

OBJECTIVE

There is a major problem about the incidence, diagnosis, and differentiation of cerebral salt wasting syndrome (CSWS) and syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in patients with acute central nervous system (CNS) disorders. According to rare reports of these cases, this study was performed in children with acute CNS disorders for diagnosis of CSWS versus SIADH.

MATERIALS & METHODS

This prospective study was done on children with acute CNS disorders. The definition of CSWS was hyponatremia (serum sodium ≤130 mEq/L), urine volume output ≥3 ml/kg/hr, urine specific gravity ≥1020 and urinary sodium concentration ≥100 mEq/L. Also, patients with hyponatremia (serum sodium ≤130 mEq/L), urine output < 3 ml/kg/hr, urine specific gravity ≥1020, and urinary sodium concentration >20 mEq/L were considered to have SIADH.

RESULTS

Out of 102 patients with acute CNS disorders, 62 (60.8%) children were male with mean age of 60.47±42.39 months. Among nine children with hyponatremia (serum sodium ≥130 mEq/L), 4 children had CSWS and 3 patients had SIADH. In 2 cases, the cause of hyponatremia was not determined. The mean day of hyponatremia after admission was 5.11±3.31 days. It was 5.25±2.75 and 5.66±7.23 days in children with CSWS and SIADH, respectively. Also, the urine sodium (mEq/L) was 190.5±73.3 and 58.7±43.8 in patients with CSWS and SIADH, respectively.

CONCLUSION

According to the results of this study, the incidence of CSWS was more than SIADH in children with acute CNS disorders. So, more attention is needed to differentiate CSWS versus SIADH in order to their different management.

Renal salt-wasting syndrome in children with intracranial disorders

Hypotonic hyponatremia, a serious and recognized complication of any intracranial disorder, results from extra-cellular fluid volume depletion, inappropriate anti-diuresis or renal salt-wasting. The putative mechanisms by which intracranial disorders might lead to renal salt-wasting are either a disrupted neural input to the kidney or the elaboration of a circulating natriuretic factor. The key to diagnosis of renal salt-wasting lies in the assessment of extra-cellular volume status: the central venous pressure is currently considered the yardstick for measuring fluid volume status in subjects with intracranial disorders and hyponatremia. Approximately 110 cases have been reported so far in subjects ≤18 years of age (male: 63%; female: 37%): intracranial surgery, meningo-encephalitis (most frequently tuberculous) or head injury were the most common underlying disorders. Volume and sodium repletion are the goals of treatment, and this can be performed using some combination of isotonic saline, hypertonic saline, and mineralocorticoids (fludrocortisone). It is worthy of a mention, however, that some authorities contend that cerebral salt wasting syndrome does not exist, since this diagnosis requires evidence of a reduced arterial blood volume, a concept but not a measurable variable.