Clinical approach to disorders of salt and water balance. Emphasis on integrative physiology

Iatrogenic hyponatremia in hospitalized children: Can it be avoided?

Iatrogenic hyponatremia in hospitalized children is a common problem. It is usually caused by the administration of free water, either orally or through the prescription of hypotonic intravenous fluids. It can result in cerebral edema and death, and is most commonly reported in healthy children undergoing minor surgery. The current teachings and practical guidelines for maintenance fluid infusions are based on caloric expenditure data in healthy children that were derived and published more than 50 years ago. A re-evaluation of these data and more recent recognition that hospitalized children are vulnerable to hyponatremia, with its resulting morbidity and mortality rates, suggest that changes in paediatricians' approach to fluid administration are necessary. There is no single fluid therapy that is optimal for all hospitalized children. A thorough assessment of the type of fluid, volume of fluid and electrolyte requirements based on individual patient requirements, plus rigorous monitoring, is required in any child receiving intravenous fluids. The present article reviews how hyponatremia occurs and makes recommendations for minimizing the risk of iatrogenic hyponatremia.

The efficacy of hypotonic and near-isotonic saline for parenteral fluid therapy given at low maintenance rate in preventing significant change in plasma sodium in post-operative pediatric patients: protocol for a prospective randomized non-blinded study

BACKGROUND

Hyponatremia is the most frequent electrolyte abnormality observed in post-operative pediatric patients receiving intravenous maintenance fluid therapy. If plasma sodium concentration (p-Na+) declines to levels below 125 mmol/L in < 48 h, transient or permanent brain damage may occur. There is an intense debate as to whether the administered volume (full rate vs. restricted rate of infusion) and the composition of solutions used for parenteral maintenance fluid therapy (hypotonic vs. isotonic solutions) contribute to the development of hyponatremia. So far, there is no definitive pediatric data to support a particular choice of parenteral fluid for maintenance therapy in post-surgical patients.

METHODS/DESIGN

Our prospective randomized non-blinded study will be conducted in healthy children and adolescents aged 1 to 14 years who have been operated for acute appendicitis. Patients will be randomized either to intravenous hypotonic (0.23% or 0.40% sodium chloride in glucose, respectively) or near-isotonic (0.81% sodium chloride in glucose) solution given at approximately three-fourths of the average maintenance rate. The main outcome of interest from this study is to evaluate 24 h post-operatively whether differences in p-Na+ between treatment groups are large enough to be of clinical relevance. In addition, water and electrolyte balance as well as regulatory hormones will be measured.

DISCUSSION

This study will provide valuable information on the efficacy of hypotonic and near-isotonic fluid therapy in preventing a significant decrease in p-Na+. Finally, by means of careful electrolyte and water balance and by measuring regulatory hormones our results will also contribute to a better understanding of the physiopathology of post-operative changes in p-Na+ in a population at risk for hyponatremia.

TRIAL REGISTRATION

The protocol for this study is registered with the current controlled trials registry; registry number: ISRCTN43896775.

Hypernatremic Disorders in the Intensive Care Unit

Hypernatremia, defined as plasma sodium concentration >145 mEq/L, is frequently encountered in critically ill patients admitted to the intensive care unit (ICU). Hypernatremia indicates a decrease in total body water relative to sodium and is invariably associated with plasma hyperosmolality though total body sodium content may be normal, decreased, or increased. Hypernatremia usually occurs as a result of impaired thirst or access to water, with or without increased water losses from renal and extrarenal sources. Critically ill patients in ICU are at high risk of hypernatremia because of their inability to control free water intake as a result of sedation, intubation, change in mental status, and fluid restriction for various other reasons. In addition, excessive fluid losses from various renal or nonrenal sources and treatment with sodium containing fluids are commonly encountered in this population, predisposing them to hypernatremia. The consequences of hypernatremia result from osmotic movement of water across the cell membrane, leading to primarily intracellular and variable degree of extracellular volume depletion. The clinical features depend on severity and rapidity of hypernatremia development with abnormal cognitive and neuromuscular function in many cases and potential risk of hemorrhagic complications or death from vascular stretching and rupture in advanced cases. The management of hypernatremia focuses on judicious replacement of free water deficit to restore normal plasma osmolality as well as identification and correction of underlying causes of hypernatremia. Electrolyte-free water replacement is the preferred therapy though electrolyte (sodium) containing hypotonic fluids can also be used in some circumstances. Oral free water replacement guided by thirst is ideal though parenteral fluid replacement is usually necessary in critically ill ICU patients. Various calculations for estimating free water deficit are available and any can be used to guide initial fluid replacement therapy. Rate of correction depends on rapidity of hypernatremia development, though frequent monitoring of plasma sodium levels is essential to ensure appropriate response and to adjust the rate of fluid replacement to prevent the risk of cerebral edema from rapid correction of chronic hypernatremia. Free water requirements should be routinely assessed in ICU patients and judicious electrolyte and free water replacement prescribed for those at risk of hypernatremia.

Hyponatremia in neurosurgical patients: clinical guidelines development

OBJECTIVE

Neurosurgical patients have a high risk of hyponatremia and associated complications. We critically evaluated the existing literature to identify the determinants for the development of hyponatremia and which management strategies provided the best outcomes.

METHODS

A multidisciplinary panel in the areas of neurosurgery, nephrology, critical care medicine, endocrinology, pharmacy, and nursing summarized and classified hyponatremia literature scientific studies published in English from 1950 through 2008. The panel's recommendations were used to create an evaluation and treatment protocol for hyponatremia in neurosurgical patients at the University of Florida.

RESULTS

Hyponatremia should be further investigated and treated when the serum sodium level is less than 131 mmol/L (class II). Evaluation of hyponatremia should include a combination of physical examination findings, basic laboratory studies, and invasive monitoring when available (class III). Obtaining levels of hormones such as antidiuretic hormone and natriuretic peptides is not supported by the literature (class III). Treatment of hyponatremia should be based on severity of symptoms (class III). The serum sodium level should not be corrected by more than 10 mmol/L/d (class III). Cerebral salt wasting should be treated with replacement of serum sodium and intravenous fluids (class III). Fludrocortisone may be considered in the treatment of hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm (class I). Hydrocortisone may be used to prevent natriuresis in subarachnoid hemorrhage patients (class I). Hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm should not be treated with fluid restriction (class II). Syndrome of inappropriate antidiuretic hormone may be treated with urea, diuretics, lithium, demeclocycline, and/or fluid restriction (class III).

CONCLUSION

The summarized literature on the evaluation and treatment of hyponatremia was used to develop practice management recommendations for hyponatremia in the neurosurgical population. However, the practice management recommendations relied heavily on expert opinion because of a paucity of class I evidence literature on hyponatremia.

Increased urinary losses of carnitine and decreased intramitochondrial coenzyme A in gentamicin-induced acute renal failure in rats

BACKGROUND

This study examined whether carnitine deficiency is a risk factor and should be viewed as a mechanism during the development of gentamicin (GM)-induced ARF as well as exploring if carnitine supplementation could offer protection against this toxicity.

METHODS

Adult male Wistar albino rats were assigned to one of six treatment groups: group 1 (control) rats were given daily intraperitoneal (I.P.) injections of normal saline for 8 consecutive days; groups 2, 3 and 4 rats were given GM (80 mg/kg/day, I.P.), l-carnitine (200 mg/kg/day, I.P.) and d-carnitine (250 mg/kg/day, I.P.), respectively, for 8 consecutive days. Rats of group 5 (GM plus d-carnitine) received a daily I.P. injection of d-carnitine (250 mg/kg/day) 1 h before GM (80 mg/kg/day) for 8 consecutive days. Rats of group 6 (GM plus l-carnitine) received a daily I.P. injection of l-carnitine (200 mg/kg/day) 1 h before GM (80 mg/kg/day) for 8 consecutive days.

RESULTS

GM significantly increased serum creatinine, blood urea nitrogen (BUN), urinary carnitine excretion, intramitochondrial acetyl-CoA and total nitrate/nitrite (NOx) and thiobarbituric acid reactive substances (TBARS) in kidney tissues and significantly decreased total carnitine, intramitochondrial CoA-SH, ATP, ATP/ADP and reduced glutathione (GSH) in kidney tissues. In carnitine-depleted rats, GM caused a progressive increase in serum creatinine, BUN and urinary carnitine excretion and a progressive decrease in total carnitine, intamitochondrial CoA-SH and ATP. Interestingly, l-carnitine supplementation resulted in a complete reversal of the increase in serum creatinine, BUN, urinary carnitine excretion and the decrease in total carnitine, intramitochondrial CoA-SH and ATP, induced by GM, to the control values. Moreover, the histopathological examination of kidney tissues confirmed the biochemical data, where l-carnitine prevents and d-carnitine aggravates GM-induced ARF.

CONCLUSIONS

(i) GM-induced nephrotoxicity leads to increased urinary losses of carnitine; (ii) carnitine deficiency is a risk factor and should be viewed as a mechanism during the development of GM-induced ARF; and (iii) carnitine supplementation ameliorates the severity of GM-induced kidney dysfunction by increasing the intramitochondrial CoA-SH/acetyl-CoA ratio and ATP production.

Disorders of water and salt metabolism associated with pituitary disease

Disorders of water and sodium homeostasis are very common problems encountered in clinical medicine. Disorders of water metabolism are divided into hyperosmolar and hypoosmolar states, with hyperosmolar disorders characterized by a deficit of body water in relation to body solute and hypoosmolar disorders characterized by an excess of body water in relation to total body solute. This article briefly reviews the physiology of hyperosmolar and hypoosmolar syndromes, then focuses on a discussion of the pathophysiology, evaluation, and treatment of specific pre- and postoperative disorders of water metabolism in patients with pituitary lesions.

An improved method to compute the solute and water derangements of hyperglycaemia

Evaluation and treatment of hyperglycaemic hyponatremia, being quantitatively inaccurate, is open to new advancements. We herein describe the improvement of previous calculations of glucose appearance (G(A)), solute and solvent changes. From G(A) we derive the predicted plasma sodium concentration (PNa(G)), assuming no change in total body water (TBW), but only water shift from cells to the extracellular space (ECV). This assumption is validated by the respective solute ratios (PCl/PNa) unchanged from normal values, as well as the ratios between actual and normal solute concentrations (PNa(1)/PNa(0), PCl(1)/PCl(0)), identical for all solutes. When the assumption is met, G(A) can be exactly calculated. When the ratios are different from normal, they indicate the presence of a mixed abnormality due to a loss either of sodium, or sodium and water. These are estimated by computing the difference between PNa(G) and the actual PNa measured (PNa(1)). PNa(1) approximately equal PNa(G) if TBW and Na are unchanged, PNa(1) < PNa(G) in the presence of prevalent Na depletion, PNa(1) > PNa(G )when volume depletion prevails. In the first circumstance the ECV expansion is exactly established by appropriate mathematical formulas, in the latter conditions either Na or volume depletion are empirically estimated with algebric expressions. These equations were validated on computer-simulated models, and applied to 49 subjects with plasma glucose concentration >15 mM/L. G(A) and PNa(G) were computed, and, with the same formulas used in computer-simulated experiments, we calculated water and Na deficits. The PNa measured after correction of hyperglycaemia was correctly predicted (R(2) = 0.63, P < 0.0001). This method provides a firm ground to select the correct equation to accurately estimate the initial conditions of hyperosmolar hyperglycaemia, significantly improving its quantitative correction.

Diagnostic approach to a patient with hyponatraemia: traditional versus physiology-based options

The usual diagnostic approach to a patient with hyponatraemia is based on the clinical assessment of the extracellular fluid (ECF) volume, and laboratory parameters such as plasma osmolality, urine osmolality and/or urine sodium concentration. Several clinical diagnostic algorithms (CDA) applying these diagnostic parameters are available to the clinician. However, the accuracy and utility of these CDAs has never been tested. Therefore, we performed a survey in which 46 physicians were asked to apply all existing, unique CDAs for hyponatraemia to four selected cases of hyponatraemia. The results of this survey showed that, on average, the CDAs enabled only 10% of physicians to reach a correct diagnosis. Several weaknesses were identified in the CDAs, including a failure to consider acute hyponatraemia, the belief that a modest degree of ECF contraction can be detected by physical examination supported by routine laboratory data, and a tendency to diagnose the syndrome of inappropriate secretion of antidiuretic hormone prior to excluding other causes of hyponatraemia. We conclude that the typical architecture of CDAs for hyponatraemia represents a hierarchical order of isolated clinical and/or laboratory parameters, and that they do not take into account the pathophysiological context, the mechanism by which hyponatraemia developed and the clinical dangers of hyponatraemia. These restrictions are important for physicians confronted with hyponatraemic patients and may require them to choose different approaches. We therefore conclude this review with the presentation of a more physiology-based approach to hyponatraemia, which seeks to overcome some of the limitations of the existing CDAs.

Nephrolithiasis complicating treatment of diabetes insipidus

A decrease in urine volume is considered the therapeutic goal of the treatment of central diabetes insipidus (DI) with desmopressin (dDAVP). A low urine volume is a risk factor for kidney stone formation. This is the first report of nephrolithiasis in association with DI. It is likely that successful therapy with dDAVP and the patient's own purposeful decreased fluid intake contributed to calcium oxalate stone formation. Prevention of stone recurrence requires an increase in urine volume. The patient's compliance with this recommendation led to an episode of acute hyponatremia, a well-known complication of dDAVP therapy. The challenge of the management of stones in the setting of DI requires balancing the conflicting goals of both decreasing and increasing urine volume.

Rheumatoid Arthritis: Neuroendocrine Immune Integrated Physiopathogenetic Perspectives and Therapy

Current concepts of neuroendocrine immune (NEI) aspects of rheumatoid arthritis (RA) are reviewed and recent clinical trials of glucocorticoids and sex steroids are summarized. A novel physiopathogenetic perspective is presented. Data are provided of amplified NEI interactions and dysregulation, many years before symptomatic onset of RA. Chronic imbalances between the NEI, vascular endothelial, neural, and other vital counterregulatory intertwined networks are proposed to cause RA and influence its disease activity. Future research may reveal means of diminishing the onset risk as well as disease activity of RA by controlling these imbalances of NEI and other vital networks.