Clinical disorders of water metabolism

Stability of serum, plasma and urine osmolality in different storage conditions: Relevance of temperature and centrifugation

BACKGROUND

Osmolality reflects the concentration of all dissolved particles in a body fluid, and its measurement is routinely performed in clinical laboratories for the differential diagnosis of disorders related with the hydrolytic balance regulation, the renal function and in small-molecule poisonings. The aim of the study was to assess the stability of serum, plasma and urine osmolality through time and under different common storage conditions, including delayed centrifugation.

METHODS

Blood and urine samples were collected, and classified into different groups according to several preanalytical variables: serum or plasma lithium-heparin tubes; spun or unspun; stored at room temperature (RT), at 4°C or frozen at -21°C. Aliquots from each group were assayed over time, for up to 14days. Statistical differences were based on three different international performance criteria.

RESULTS

Whole blood stability was higher in the presence of anticoagulant. Serum osmolality was stable for 2days at RT and 8days at 4°C, while plasma was less stable when refrigerated. Urine stability was 5days at RT, 4days at 4°C and >14days when frozen.

DISCUSSION

Osmolality may be of great interest for the management of several conditions, such as in case of a delay in the clinical suspicion, or in case of problems in sample collection or processing. The ability to obtain reliable results for samples kept up to 14days also offers the possibility to retrospectively assess baseline values for patients which may require it.

Metabolic and Nutritional Aspects of Acute Renal Failure in Critically Ill Patients Requiring Continuous Renal Replacement Therapy

Acute renal failure (ARF) is rarely an isolated process but is often a complication of underlying conditions such as sepsis, trauma, and multiple-organ failure in critically ill patients. As such, concomitant clinical conditions significantly affect patient outcome. Poor nutritional status is a major factor in increasing patients' morbidity and mortality. Malnutrition in ARF patients is caused by hypercatabolism and hypermetabolism that parallel the severity of illness. When dialytic intervention is indicated, continuous renal replacement therapy (CRRT) is a commonly used alternative to intermittent hemodialysis because it is well tolerated by hemodynamically unstable patients. This paper reviews the metabolic and nutritional alterations associated with ARF and provides recommendations regarding the nutritional, fluid, electrolyte, micronutrient, and acid-base management of these patients. The basic principles of CRRT are addressed, along with their nutritional implications in critically ill patients. A patient case is presented to illustrate the clinical application of topics covered within the paper.

Neurologic manifestations of major electrolyte abnormalities

The brain operates in an extraordinarily intricate environment which demands precise regulation of electrolytes. Tight control over their concentrations and gradients across cellular compartments is essential and when these relationships are disturbed neurologic manifestations may develop. Perturbations of sodium are the electrolyte disturbances that most often lead to neurologic manifestations. Alterations in extracellular fluid sodium concentrations produce water shifts that lead to brain swelling or shrinkage. If marked or rapid they can result in profound changes in brain function which are proportional to the degree of cerebral edema or contraction. Adaptive mechanisms quickly respond to changes in cell size by either increasing or decreasing intracellular osmoles in order to restore size to normal. Unless cerebral edema has been severe or prolonged, correction of sodium disturbances usually restores function to normal. If the rate of correction is too rapid or overcorrection occurs, however, new neurologic manifestations may appear as a result of osmotic demyelination syndrome. Disturbances of magnesium, phosphate and calcium all may contribute to alterations in sensorium. Hypomagnesemia and hypocalcemia can lead to weakness, muscle spasms, and tetany; the weakness from hypophosphatemia and hypomagnesemia can impair respiratory function. Seizures can be seen in cases with very low concentrations of sodium, magnesium, calcium, and phosphate.

A novel way to monitor urine concentration: fluorescent concentration matrices

BACKGROUND

The amount of water found in urine is important diagnostic information; nevertheless it is not yet directly determined. Indirectly, the water content in urine is expressed by its density (specific gravity). However, without the diuresis value it is not possible to determine whether the increase in density of urine is due to a decrease in water secretion or an increase in the concentration of secreted substances. This problem can be solved by the use of fluorescent concentration 3D-matrices which characterise urine concentration through the pφ (or -logφ) value of the first fluorescence centre.

MATERIALS AND METHODS

The urine fluorescent concentration 3D-matrix was created by the alignment of the synchronous spectra of the dilution series of urine starting from undiluted (pφ = 0) to 1000-fold diluted urine (pφ = 3).

RESULTS

Using the fluorescence concentration 3D-matrix analysis of the urine samples from healthy individuals, a reference range was established for the value pφ, determining the normal, concentrated or diluted type of urine. The diagnostic potential of this approach was tested on urine samples from two patients with a chronic glomerulonephritis.

CONCLUSION

The pφ value of the urine fluorescence concentration 3D-matrix analysis determines whether the urine sample falls within the normal, concentrated or diluted type of urine. This parameter can be directly utilised in sportsmen's hydration state monitoring, as well as in the diagnosis and treatment of serious diseases. An important advantage of this novel diagnostic approach is that a 12/24 h urine collection is not required, which predetermines it for use especially within paediatrics.

The renal concentrating mechanism and the clinical consequences of its loss

The integrity of the renal concentrating mechanism is maintained by the anatomical and functional arrangements of the renal transport mechanisms for solute (sodium, potassium, urea, etc) and water and by the function of the regulatory hormone for renal concentration, vasopressin. The discovery of aquaporins (water channels) in the cell membranes of the renal tubular epithelial cells has elucidated the mechanisms of renal actions of vasopressin. Loss of the concentrating mechanism results in uncontrolled polyuria with low urine osmolality and, if the patient is unable to consume (appropriately) large volumes of water, hypernatremia with dire neurological consequences. Loss of concentrating mechanism can be the consequence of defective secretion of vasopressin from the posterior pituitary gland (congenital or acquired central diabetes insipidus) or poor response of the target organ to vasopressin (congenital or nephrogenic diabetes insipidus). The differentiation between the three major states producing polyuria with low urine osmolality (central diabetes insipidus, nephrogenic diabetes insipidus and primary polydipsia) is done by a standardized water deprivation test. Proper diagnosis is essential for the management, which differs between these three conditions.

Hyponatremia in hospitalized cancer patients and its impact on clinical outcomes

BACKGROUND

Hyponatremia is the most common electrolyte abnormality in clinical practice, yet little is known about its frequency in patients with cancer or its impact on their clinical outcomes.

STUDY DESIGN

Retrospective analysis of prospectively collected data.

SETTING & PARTICIPANTS

Patients with cancer admitted to the University of Texas M.D. Anderson Cancer Center in 2006 for 3 months.

PREDICTOR

Serum sodium levels categorized as eunatremia (serum sodium, 135-147 mEq/L) and mild (134-130 mEq/L), moderate (129-120 mEq/L), and severe (<120 mEq/L) hyponatremia.

OUTCOMES

(1) Length of hospital stay and (2) 90-day mortality.

RESULTS

In 4,702 admissions in 3,357 patients with cancer, hyponatremia (serum sodium <135 mEq/L) was noted in 47% of admissions. It was mild in 36%, moderate in 10%, and severe in 1%. Hyponatremia was acquired during the hospital stay in 24%. Using the first admission data, mean length of stay was 5.6 ± 5.0 days for patients with eunatremia and 9.9 ± 9.2, 13.0 ± 14.1, and 11.5 ± 12.6 days for those with mild, moderate, and severe hyponatremia, respectively. The respective HRs in the multivariate Cox model for longer hospital stay, using patients with eunatremia as reference, were 1.92 (95% CI, 1.75-2.13; P < 0.01), 2.94 (95% CI, 2.56-3.45; P < 0.01), and 2.32 (95% CI, 1.32-4.00; P = 0.01). 283 (8.4%) deaths occurred during 90 days, and in the multivariate model, the respective HRs for 90-day mortality for mild, moderate, and severe hyponatremia were 2.04 (95% CI, 1.42-2.91; P < 0.01); 4.74 (95% CI, 3.21-7.01; P < 0.01), and 3.46 (95% CI, 1.05-11.44; P = 0.04). These findings were consistent when analyses were repeated with sodium levels in tertiles.

LIMITATIONS

Observational study, retrospective, inability to adjust for all comorbid conditions.

CONCLUSION

Hyponatremia in patients with cancer is associated with longer hospital stay and higher mortality. Whether long-term correction of hyponatremia would improve these outcomes remains to be determined.

[Etiology, diagnostics and therapy of hyponatremias]

Etiopathogenesis, diagnostics and therapy of hyponatremias are summarized for clinicians. Hyponatremia is the most common electrolyte abnormality. Mild to moderate hyponatremia and severe hyponatremia are found in 15-30% and 1-4% of hospitalized patients, respectively. Pathophysiologically, hyponatremias are classified into two groups: hyponatremia due to non-osmotic hypersecretion of vasopressin (hypovolemic, hypervolemic, euvolemic) and hyponatremia of non-hypervasopressinemic origin (pseudohyponatremia, water intoxication, cerebral salt wasting syndrome). Patients with mild hyponatremia are almost always asymptomatic. Severe hyponatremia is usually associated with central nervous system symptoms and can be life-threatening. Diagnostic evaluation of patients with hyponatremia is directed toward identifying the extracellular fluid volume status, the neurological symptoms and signs, the severity and duration of hyponatremia, the rate at which hyponatremia developed. The first step to determine the probable cause of hyponatremia is the differentiation of the hypervasopressinemic and non-hypervasopressinemic hyponatremias with measurement of plasma osmolality, glucose, lipids and proteins. For further differential diagnosis of hyponatremia, the determination of urine osmolality, the clinical assessment of extracellular fluid volume status and the measurement of urine sodium concentration provide important information. The most important representative of euvolemic hyponatremias is SIADH. The diagnosis of SIADH is based on the exclusion of other hyponatremic conditions; low plasma osmolality (<275 mosmol/kg) and inappropriate urine concentration (urine osmolality >100 mosmol/kg) are of pathognomic value. Acute (<48 hrs) severe hyponatremia (<120 mmol/l) necessitates emergency care with rapid restoration of normal osmotic milieu (1 mmol/l/hr increase rate of serum sodium). Patients with chronic symptomatic hyponatremia have a high risk of osmotic demyelination syndrome in brain if rapid correction of the plasma sodium occurs (maximal rate of correction of serum sodium should be 0.5 mmol/l/hr or less). The conventional treatments for chronic asymptomatic hyponatremia (except hypovolemic patients) include water restriction and/or the use of demeclocycline or lithium or furosemide and salt supplementation. Vasopressin receptor antagonists have opened a new forthcoming therapeutic era. V2 receptor antagonists, such as lixivaptan, tolvaptan, satavaptan and the V2+V1A receptor antagonist conivaptan promote the electrolyte-sparing excretion of free water and lead to increased serum sodium.

Treatment of electrolyte disorders in adult patients in the intensive care unit

PURPOSE

The treatment of electrolyte disorders in adult patients in the intensive care unit (ICU), including guidelines for correcting specific electrolyte disorders, is reviewed.

SUMMARY

Electrolytes are involved in many metabolic and homeostatic functions. Electrolyte disorders are common in adult patients in the ICU and have been associated with increased morbidity and mortality, as has the improper treatment of electrolyte disorders. A limited number of prospective, randomized, controlled studies have been conducted evaluating the optimal treatment of electrolyte disorders. Recommendations for treatment of electrolyte disorders in adult patients in the ICU are provided based on these studies, as well as case reports, expert opinion, and clinical experience. The etiologies of and treatments for hyponatremia hypotonic and hypernatremia (hypovolemic, isovolemic, and hypervolemic), hypokalemia and hyperkalemia, hypophosphatemia and hyperphosphatemia, hypocalcemia and hypercalcemia, and hypomagnesemia and hypermagnesemia are discussed, and equations for determining the proper dosages for adult patients in the ICU are provided. Treatment is often empirical, based on published literature, expert recommendations, and the patient's response to the initial treatment. Actual electrolyte correction requires individual adjustment based on the patient's clinical condition and response to therapy. Clinicians should be knowledgeable about electrolyte homeostasis and the underlying pathophysiology of electrolyte disorders in order to provide the optimal therapy to patients.

CONCLUSION

Treatment of electrolyte disorders is often empirical, based on published literature, expert opinion and recommendations, and patient's response to the initial treatment. Clinicians should be knowledgeable about electrolyte homeostasis and the underlying pathophysiology of electrolyte disorders to provide optimal therapy for patients.

Increased plasma levels of substance P and disturbed water excretion in patients with liver cirrhosis

BACKGROUND

The pathogenesis of impaired water excretion in liver cirrhosis has not been fully elucidated.

METHODS

We induced an intravenous water overload of 20 ml/kg body weight in 10 cirrhotics without ascites (CLC), 11 cirrhotics with ascites (DLC), and 10 normal subjects (N) and investigated the relationship of plasma levels of substance P (SP), norepinephrine (NE), and antidiuretic hormone (ADH) to impaired water excretion.

RESULTS

Free water clearance (CH2O) was lower in DLC (mean, 2.7 ml/min) than in N (8.3 ml/min; P < 0.001) and CLC (6.9 ml/min; P < 0.001). In DLC the creatinine clearance (CCr), maximal urine flow rate/CCr, (CH2O + CNa)/CCr, and mean arterial pressure (MAP) were significantly lower than in N and CLC. There was a progressive increase in basal SP, from lowest in N to CLC, to highest in DLC. Basal NE increased in CLC and DLC. Basal ADH did not differ among N, CLC, and DLC. In cirrhotics CH2O was correlated positively with serum albumin and cholinesterase and negatively with the retention rate of indocyanine green at 15 min. Basal SP was negatively correlated with CH2O (r= -0.71: P < 0.001) and MAP (r= -0.56; P < 0.005). Basal NE was correlated positively with basal SP (r= 0.67, P < 0.01 ).

CONCLUSIONS

Decreased CH2O is closely related to the severity of the liver disturbance. Decreased CCr and reduced delivery of filtrate to the ascending limb of the loop of Henle secondary to an increased sodium reabsorption in the proximal tubule may play an important role in the impairment of water excretion. The increase in SP, which has a potent vasodilatory action, and the associated enhanced activity of the sympathetic nervous system may be responsible for the mild or moderate impairment of water excretion in the absence of nonosmotic hypersecretion of ADH in cirrhotics with ascites.

Hypercalcemia and electrolyte disturbances in malignancy

Hypercalcemia and electrolyte abnormalities are common problems in patients with malignancy. In this article we discuss the pathophysiology, clinical features, and management of hypercalcemia, which is the most common metabolic abnormality. We also analyze the electrolyte disturbances that occur in association with malignancy, including hyponatremia, hypokalemia, hypomagnesemia, hypophosphatemia, and hyperkalemia. Recognition and treatment of these disturbances are important parts of the management of patients with malignant disease.

Hyponatraemia in AIDS

Hyponatraemia is very common in AIDS patients. It is observed in about 40-50% of hospitalized patients. It may contribute to overall mortality in advanced disease. Vasopressin measurements in these patients basically present two distinct syndromes: hyponatraemia and 'normal' vasopressin levels (i.e. measurable vasopressin) and hyponatraemia with suppressed vasopressin. Hyponatraemia with suppressed vasopressin is very rare and has only been observed in AIDS patients with dementia and primary polydipsia. Hyponatraemia and measurable vasopressin can be also divided into two syndromes. In some patients vasopressin is 'appropriately' elevated, i.e. in those with body fluid losses (diarrhoea) or chronic hypovolaemia (adrenal failure); these patients also present with hyperuricaemia and other signs of low blood volume. In other patients vasopressin is 'inappropriately' elevated in those with no clinical evidence of hypovolaemia (typically characterized by low serum uric acid levels) such as in Pneumocystis carinii pneumonia and other opportunistic infections leading to SIADH. CSWS is a relatively frequent complication in some patients with cerebral infection or tumour. High-dose trimethoprim (for Pneumocystis carinii prevention) acts as an amiloride-like drug and induces a clinical state characterized by hyponatraemia and hyperkalaemia which is indistinguishable from hyporeninaemic hypoaldosteronism. The mechanism of the hyponatraemia caused by other drugs (miconazole, pentamidine, amphotericin, vidarabine) is not as yet known.

Indices of dehydration among frail nursing home patients: highly variable but stable over time

OBJECTIVE

To determine changes in standard laboratory measures of dehydration among residents of a nursing home care unit (NHCU) over a 6-month period.

DESIGN

A prospective cohort analytic study.

SETTING

A 130-bed NHCU in a Department of Veterans Affairs Hospital.

PATIENTS

Fifteen infirm but stable male residents (mean age 77 years; range (R) 62-93) on one ward of the NHCU.

MAIN OUTCOME MEASURES

We studied prospectively for 6 months the serum osmolality (osm), serum sodium (Na), blood urea nitrogen/creatinine (BUN/Cr) ratios and weight (wt) for 15 patients of the NHCU. None of the patients was acutely ill during the study period or exhibited clinical signs of dehydration.

RESULTS

Mean serum osm at baseline: 291.6 mOsm/kg (R 278 to 300); 3 months: 291.5 mOsm/kg (R 276 to 301); 6 months: 291.3 mOsm/kg (R 283-300) were all similar. Forty percent (6/15) of patients had at least one high normal/elevated reading (> or = 295 mOsm/kg) during the study. Three patients (20%) had readings of > or = 300 mOsm/kg, but none of these patients had either concurrent increased serum Na (> or = 146 mmole/L) or BUN/Cr ratios (> or = 25). Mean serum Na at baseline: 143.0 mmole/L (R 139-148); 3 months: 142.1 mmole/L (R 138-149); 6 months: 142.9 mmole/L (R 137-150) were all similar. Sixty percent (9/15) of the patients maintained normal (nl) serum Na levels throughout the study. The relationship between the change in serum Na and serum osm levels from baseline to 6 months was not significant (r = 0.242). BUN/Cr ratios ranged from 12-34 over the study period with 3 of 15 patients (20%) demonstrating elevated ratios consistently throughout the study without clinical evidence of dehydration. Only two patients had both high nl/elevated serum osm and elevated serum Na, although both had nl BUN/Cr ratios. Neither of these patients was thought by staff to be clinically dehydrated. Analysis of variance (ANOVA) indicated none of the laboratory measures changed significantly over time (serum osm: F(2,28) < 1; Na: F(2,28) < 1; BUN/Cr: F(2,28) < 1). There was no significant change in weight between the baseline and six month readings.

CONCLUSIONS

These data suggest that in the presence of clinical stability, long-term care residents may have a serum osm in the high normal/elevated range without overt clinical evidence of dehydration, an accompanying elevated Na, or BUN/Cr ratio. This may indicate a different central osm setting for these residents as the serum osm appeared to be stable for each resident over time. These data also suggest that measures of serum osm, Na, and BUN/Cr in the long-term care setting may accurately predict future laboratory values in an individual patient if baseline values are drawn when the patient is not acutely ill.

Hyper- and hyponatremia among geropsychiatric inpatients

We report our experience treating 14 elderly psychiatric patients with altered sodium states. Hypernatremia occurs more commonly among elderly psychiatric patients than among their younger counterparts, and elderly hypernatremic psychiatric patients suffer most commonly from dementia. Dilutional hyponatremia is less common and less severe among elderly schizophrenic patients compared with younger patients with schizophrenia. Central nervous system changes induced by altered sodium states among elderly psychiatric patients are sufficiently similar whether hyper- or hyponatremia is present; therefore, the clinician must not wait for specific features to develop, but must quickly measure serum sodium concentration in elderly psychiatric patients with altered mental states. Treatment of hypernatremia involves rehydration with normal saline or hypotonic solutions, and treatment of dilutional hyponatremia largely involves fluid restriction.

Hyponatremia in hospitalized patients with the acquired immunodeficiency syndrome (AIDS) and the AIDS-related complex

STUDY OBJECTIVE

To determine the frequency, etiology, and clinical association of hyponatremia in patients with the acquired immunodeficiency syndrome (AIDS) and AIDS-related complex (ARC).

PATIENTS AND METHODS

A prospective analysis of 167 patients with AIDS and 45 patients with ARC admitted on 259 occasions to a large metropolitan teaching hospital during a 3-month period.

RESULTS

Eighty-three patients (39%) with hyponatremia (serum sodium concentration less than 135 mmol/L) were observed during 99 hospitalizations, for a frequency of 38%. The mean (+/- standard error) of the lowest serum sodium concentration was 128 +/- 1 mmol/L in the hyponatremic patients and 138 +/- 1 mmol/L in the normonatremic patients. Hyponatremia was present on admission during 57 hospitalizations and was associated with gastrointestinal losses and hypovolemia in 43%. When hyponatremia developed during hospitalization, 68% of the patients were clinically euvolemic and had a syndrome consistent with inappropriate secretion of antidiuretic hormone (SIADH). Patients with hyponatremia were hospitalized longer than those with normal serum sodium concentrations (17 +/- 1 versus 9 +/- 1 days, p < 0.001). In addition, the mortality rate in the hyponatremic group was higher than that in the normonatremic group (36.5% versus 19.7%, p < 0.01).

CONCLUSION

Hyponatremia is a common electrolyte disorder in patients hospitalized with AIDS or ARC and is frequently associated with gastrointestinal losses or SIADH as well as increased morbidity and mortality.

Renal potassium bicarbonate release in humans exposed to an acute volume load

Cells of the renal medulla regulate their volume by transmembrane ion movements when exposed to large changes in osmolality. Since renal cells in culture release KHCO3 in response to hypotonic stress [11], we investigated the effect of an acute water load on urinary KHCO3 excretion in 5 healthy individuals. Water diuresis was induced by the ingestion of 1.5 l hypoosmolal fluid (22 mosm/kg H2O) over 15 min. The rate of urinary volume excretion increased from an initial value of 1.4 ml/min to 9.3 ml/min after 75 min. Urinary osmolality dropped from an initial value of 940 +/- 32 mosm/kg H2O to 74 +/- 4 mosm/kg H2O (n = 5). The decrease of osmolality was accompanied by the transient release of potassium and bicarbonate. Peak values of KHCO3 excretion were observed between 30 and 45 min after the onset of the experiment corresponding to the drop of urinary osmolality. The magnitude of renal potassium release correlated significantly (r = 0.93; P less than 0.05) with endogenous plasma aldosterone concentrations measured prior to the experiment in the 5 volunteers. We conclude that medullary epithelial cells release KHCO3 when exposed to hypotonic stress. The volume regulatory response is upregulated by aldosterone.

Disorders of water balance--hyponatraemia and hypernatraemia

Plasma sodium concentration depends on water balance, and is normally maintained in a narrow range by an integrated system involving the precise regulation of water intake via thirst mechanism and control of water output via vasopressin secretion. Anything that interferes with the full expression of either osmoregulatory function exposes the patient to the hazards of abnormal decreases or increases in plasma sodium level. Hyponatraemia is almost always due to a defect in water excretion. Increased intake may contribute to the problem but is rarely, if ever, a sufficient cause. Hypernatraemia is almost always due to deficient water intake; excessive water losses may contribute to the problem, but they are never a sufficient cause. The most dangerous and usually the most blatant clinical effects of the disturbed water balance are those involving the central nervous system. Complex adaptive mechanisms have been developed to mitigate the impact of both hypo- and hypernatraemia on brain cells. However, the same protective changes render the brain more susceptible to severe neuropathology that may arise from inappropriate treatment of these disorders.

Corticotropin deficiency: a rare cause of hyponatremia mimicking SIADH

We describe 2 patients presenting with severe chronic hyponatremia in whom clinical and biochemical features strongly suggested the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Both, however, were proven to have a primary pituitary deficiency of corticotropin. Their short synacthen tests were only mildly abnormal but associated with low basal ACTH levels. The diagnosis of ACTH deficiency was made more convincingly by their dramatic response to glucocorticoid replacement therapy. In patients in whom no cause for SIADH can be found, a trial of maintenance cortisol therapy is warranted to exclude this eminently treatable condition.

Survey of diurnal weight gain and urine volume in chronic schizophrenia

We found diurnal weight gain to be abnormal among 39 chronic schizophrenic patients. The patients were weighed and urine samples obtained weekly for three weeks at 7 a.m. and 4 p.m. We normalized the dirunal weight gain (NDWG) as a percentage by subtracting the 7 a.m. weight from the 4 p.m. weight, multiplying the difference by 100, and then dividing the result by the 7 a.m. weight. NDWG was 2.075 +/- 1.331% for the 38 study patients, .631 +/- .405% for 16 acutely psychotic controls and .511 +/- .351% for 29 normals. Seventy-seven percent of the study patients had abnormal NDWG values and 62% were polyuric. NDWG related to urine volume (n = 39, r = .356, p = .026) with the variability in urine excretion explaining 13% of the variability in NDWG. We discuss factors that may have contributed to our findings.

[Water intoxication in psychiatric patients. 13 cases of severe hyponatremia]

Water intoxication mostly occurs in psychiatric patients. We observed 13 episodes of severe hyponatremia (less than 120 mmol/l) following a period of increased water consumption in 10 psychiatric patients (5 men, 5 women, mean age 48.8 years) treated with neuroleptics and/or benzodiazepines. Other causes of hyponatremia were excluded. The initial clinical signs were associated with severe gastrointestinal and neurological disorders requiring intensive care. In every case a gradual return to normal of natremia was obtained by creating a negative water balance while compensating for the sodium loss. From a study of urine and plasma osmolality ratio (U/P osm) on admission, several physiopathological mechanisms could be envisaged. A U/P osm ratio lower than 1 (6 cases) suggested a water intake exceeding the maximum dilution capacity of the kidneys (20-25 1), or a lesser water intake with little or no osmolal intake, or again an intrarenal disorder of urine dilution. When the U/P osm ratio was higher than 1 (7 cases), reflecting inappropriate secretion of the antidiuretic hormone, the hyponatremia could be explained by the psychosis itself, the treatment taken by the patients, a disorder of thirst regulation and/or a non-osmotic stimulation of vasopressin. This population, therefore, was heterogeneous: the mechanisms which contribute to this pathology are not fully elucidated, and they probably involve several factors.

Hyponatremia

The serum sodium concentration reflects the osmolality of the extracellular fluid and provides no direct information about total body sodium content. Patients with hyponatremia may have decreased, normal, or increased total body sodium content. The first step in the approach to the patient with hyponatremia is measurement of plasma osmolality. Hyponatremia with normal plasma osmolality results from hyperlipemia or hyperproteinemia whereas hyponatremia with increased plasma osmolality results from hyperglycemia or mannitol infusion. Patients with hyponatremia and decreased plasma osmolality may be hypovolemic, hypervolemic, or normovolemic. The volume status of the patient is best determined by history, physical examination, and a few ancillary tests (e.g., total plasma protein concentration, hematocrit, blood pressure, central venous pressure). The clinical signs of hyponatremia are related more to the rapidity of onset than to the severity of the associated plasma hypoosmolality and reflect influx of water into the central nervous system. The main goals of treatment in hyponatremia are to manage the underlying disease and, if necessary, to increase serum sodium concentration and plasma osmolality.

Fetal plasma and renal responses to ruminal fluid

Amniotic fluid homeostasis is dependent on a balance of fetal fluid production and absorption. The fetal gastrointestinal tract is believed to resorb 500 to 1000 ml of amniotic fluid per day during 7 to 10 bouts of swallowing activity. However, the impact of ruminal fluid on fetal plasma composition and fluid homeostasis is largely unknown. Seven ovine fetuses (120 +/- 1 day) received intraruminal infusions of 0.9% or 3% saline solution on alternate days. In response to successive 40-minute intraruminal infusions of 0.9% saline solution (0.5 and 1.0 ml/kg/min), there was no change from basal levels of fetal plasma osmolality (295.7 +/- 2.9 mosm), plasma arginine vasopressin (1.45 +/- 0.29 pg/ml), urine osmolality (150 +/- 8 mosm), or urine volume (0.49 +/- 0.10 ml/min). In response to the 3% saline solution infusion, significant increases were noted in fetal plasma osmolality (295.4 +/- 3.1 to 302.6 +/- 2.6 mosm), plasma arginine vasopressin (1.77 +/- 0.31 to 4.84 +/- 0.79 pg/ml), and urine osmolality (157 +/- 13 to 342 +/- 25 mosm), whereas fetal urine volume significantly decreased (0.35 +/- 0.05 to 0.15 +/- 0.06 ml/min). These results indicate that hypertonic, but not isotonic, saline solution infusion into the fetal gastrointestinal tract may affect fetal plasma composition and urine production. Under conditions of significant plasma to luminal osmotic gradients, fetal gastrointestinal water and electrolyte transfer may be more rapid than can be compensated by either fetal renal function or placental equilibration.

Risk factors for dehydration among elderly nursing home residents

Dehydration is the most common fluid and electrolyte disorder among the elderly, yet risk factors are not known. This study identifies risk factors for dehydration in acutely ill nursing home residents. All 339 elderly resident of two nursing homes who developed an acute illness requiring hospitalization during 1984 were included in the study. The 173 patients having a serum Na less than 150 mg/dL and blood urea nitrogen to creatinine ratio (BUN:Cre) less than 20 were designated controls; 91 patients having a serum Na greater than 150 mg/dL or a serum BUN:Cre greater than 25 were designated cases. Odds ratios (OR) and confidence intervals were calculated for age, sex, chronic conditions, acute illnesses, medications, functional status measures, and season. Acutely ill dehydrated patients were female (OR, 3.3); over 85 years old (OR, 2.2); had more than four chronic conditions (OR, 4.0); took more than four medications (OR, 2.8); and were bedridden (OR, 2.9). Among the most severely dehydrated (serum Na greater than 150 mg/dL and BUN:Cre greater than 25), the odds ratios for the above factors were strengthened and other factors, such as inability to feed oneself and type of acute diagnosis, emerged as risk factors. Among the variables unrelated to functional status, laxatives (OR, 3.2) and chronic infections (OR, 1.8) were risk factors. We conclude that a group at high risk for dehydration can be defined and that they are better characterized by the number of chronic diseases and debilitated functional status than by acute disease processes.

Rapid correction of acute salt poisoning by peritoneal dialysis

A 12-month-old girl with end-stage renal disease secondary to primary oxalosis was erroneously given an overdose of sodium chloride (400 mEq NaCl over 12 h) to treat hyponatremia. She became lethargic and hypotonic with signs of intracellular dehydration, and laboratory values revealed severe hypernatremia and hyperchloremia. Since hypernatremia was acute and development of intracellular idiogenic osmoles was presumably minimal, serum sodium was lowered rapidly over 14 h by hourly peritoneal dialysis using a commercial dialysate. This method of treatment proved to be safe and the patient survived without any short or long-term neurological sequelae.

Pathogenesis of clinical hyponatremia: observations of vasopressin and fluid intake in 100 hyponatremic medical patients

The pathogenesis of hyponatremia remains debated; therefore, we determined the roles of plasma vasopressin, fluid intake and renal free water excretion in hyponatremic medical patients. We evaluated 100 consecutive hypo-osmolar hyponatremic patients (PNa = 127 +/- 0.7 mM l-1) in a prospective manner. We observed: hyponatremia was often found in association with advanced congestive cardiac failure (twenty-five of 100 patients), liver cirrhosis (16%) and primary volume contraction (29%). There was a 17% in-hospital mortality of hyponatremic patients. This was primarily related to the severity of underlying illnesses rather than to hyponatremia per se. The most consistently observed laboratory finding of hyponatremia was non-osmotic vasopressin stimulation; mean observed PADH was 4.7 +/- 0.7 pg ml-1 and vasopressin was detectable by radioimmunoassay (RIA) in 91% of all patients. In addition to vasopressin stimulation we also found evidence of advanced 'circulatory underfilling' in most hyponatremic patients. Mean urinary osmolality was hypertonic to plasma (441 +/- 17.4 m0sm kg H2O-1). This applied to patients with hyponatremic cardiac failure, liver cirrhosis and volume contraction. Almost all of these patients received high ceiling diuretics. (v) Spontaneous mean daily fluid intake was 2.4 +/- 0.2 l. In summary, our findings suggest that disturbances of vasopressin, fluid intake and renal free water excretion co-operate in the pathogenesis of hyponatremia. In clinical states of advanced circulatory underfilling the occurrence of hyponatremia indicates a poor prognosis of the patient.

Hyponatremia: cerebral symptoms and role in central pontine myelinolysis

Central nervous system symptoms due to hyponatremia is highly dependent on its acuteness and cause. Severe acute hyponatremia (serum sodium less than 125 mEq/l) often causes confusion, lethargy, seizures or frank coma due to brain oedema. If therapy is delayed, hyponatremia carries a high mortality rate, and risk of irreversible brain damage. Hyponatremia should probably be corrected to 125-130 mEq/l at a rate of 1.5-2.0 mEq/l/h. Malnourished alcoholic patients with hyponatremia may represent a special case with possible dangers of central pontine myelinolysis if a very low serum sodium is corrected acutely to normonatremic or hypernatremic levels. Mortality in this subgroup is high whatever the therapy.

Posttransurethral prostatic resection hyponatremic syndrome: case report and review of the literature

Hyponatremia is a potentially life-threatening complication of transurethral prostatic (TURP) resection. The post-TURP syndrome, although well-recognized by urologists, is not discussed in recent clinical reviews on hyponatremia. We present a case report and review of the literature of this striking clinical syndrome.

Electrolyte disorders in the elderly

Normal human ageing impairs homeostatic mechanisms in such a way as to exaggerate and prolong the effects of stress. Thus, an event--pathological or traumatic--which produces a trivial change in plasma electrolytes of young people may produce major oscillations of plasma levels in the elderly, which take much longer to return to 'normal levels'. This is especially apparent with perturbations in the plasma levels of sodium and potassium, mainly due to changes in renal function and neurohumeral mechanisms which occur with increasing age. Paradoxically this does not mean that the clinician should be over-enthusiastic in attempting to correct electrolyte imbalance because, for the same reasons, the danger of over-treatment producing the opposite and equally dangerous electrolyte imbalance is ever-present. Indeed, in clinical practice most electrolyte disturbances in old age are iatrogenic in origin. Cautious patience and vigilance should be the clinical approach with elderly patients. A high index of suspicion should lead to a careful appraisal of the drug (diuretic, intravenous fluid) and environmental (dehydration) aetiology of most electrolyte disturbances in old age.

Hyponatremia and natriuresis following subarachnoid hemorrhage in a monkey model

A monkey model of subarachnoid hemorrhage (SAH) was used to study both the incidence of hyponatremia and natriuresis and the associated changes in antidiuretic hormone (ADH) secretion and salt and water balance. Following SAH, seven of nine monkeys became natriuretic and hyponatremic. The natriuretic period lasted an average of 4.4 +/- 0.4 days. The mean nadir of serum sodium content was 125.7 +/- 1.6 mEq/liter, and occurred on the average on the 5th day following SAH. The sodium balance after SAH was negative as compared to the preoperative positive sodium balance (p less than 0.001). The plasma vasopressin level was usually elevated for a day following surgery, but there was no significant difference in the levels during the preoperative period and during the period of natriuresis following SAH. The daily urine output and aldosterone levels were not significantly different, and the plasma volume was slightly, but not significantly, decreased after SAH. Four of the animals that had a hyponatremic and natriuretic response following SAH showed a normal regulation of vasopressin in response to both a water challenge and hypertonic saline challenge. The three monkeys that underwent sham procedures did not become hyponatremic and natriuretic postoperatively. The sham-operated monkeys did not show significant differences in their plasma vasopressin levels, urine volume, plasma volume, and aldosterone levels following surgery. These observations are more consistent with primary natriuresis as the cause of hyponatremia rather than the syndrome of inappropriate secretion of ADH. The cause of the renal loss of sodium is not known, but the possibility of a brain natriuretic factor or an alteration in the neural control of the kidney should be considered.

Current concepts. Serum osmolality. Uses and limitations

The serum osmolality measurement has a clearly circumscribed use in clinical medicine. Comparison of the measured osmolality with the osmolality calculated from the concentrations of the major solutes in serum gives information about large deviations in the serum water content. In addition, comparison of the measured and calculated values of osmolality provides rapid screening information about the presence of foreign low-molecular-weight solutes in the blood. Taken at face value, the test cannot be used to determine whether abnormalities in tonicity homeostasis are present. A simple and direct way to assess whether tonicity is normal is to calculate the effective osmolality from the concentrations of sodium and glucose in serum. With rare exceptions, this calculation provides the information needed to make decisions about therapy.

Investigation of hypothalamic-pituitary disease

It can be readily appreciated from the preceding discussion that many endocrine and non-endocrine tests are available for the evaluation of patients with suspected hypothalamic-pituitary disease. The endocrine evaluation of these subjects should be tailored according to the type and extent of pathology suspected (see Tables 2 and 3). For patients with pituitary adenomas and clinical features of hyperpituitarism, such as hyperprolactinaemia, Cushing's disease or acromegaly, the initial tests should be directed at the hormone whose excess is suspected. For example, a glucose suppression test for acromegaly or dexamethasone suppression test for Cushing's disease should be performed early in the evaluation. The possibility of deficiencies of the other pituitary hormones should then be addressed in patients with secretory tumours, but initially in those with apparent non-functioning adenomas. In patients with large macroadenomas pituitary hormone deficiencies are almost invariable with GH and FSH/LH being the most commonly affected, followed by TSH and ACTH in that order (Snyder et al, 1979a; Valenta et al, 1982). Basal thyroid function tests, serum oestradiol or testosterone, and basal gonodotrophins should be routinely obtained in patients with macroadenomas. Additionally, the integrity of the pituitary-adrenal axis should be determined and an overnight water deprivation test for assessment of neurohypophyseal function is also recommended. GH stimulation testing is valuable as a test of pituitary function in patients with suspected pituitary tumours since GH reserve is lost very early in the development of hypopituitarism. Evaluation of the pituitary-thyroid axis with TRH or the pituitary gonadal axis with LHRH generally provides limited additional information of diagnostic value in individual patients with macroadenomas. However, the 'paradoxical' responses to TRH and LHRH may be useful as a biological marker following therapy in patients with GH- or ACTH-secreting tumours. In patients with microadenomas, pituitary hormone deficiencies are uncommon (Valenta et al, 1982). Despite this observation, it may be beneficial to determine basal thyroid levels, gonadotrophin levels, serum testosterone or oestradiol levels, and the response to an overnight metyrapone test in such patients to provide a baseline for future care.(ABSTRACT TRUNCATED AT 400 WORDS)

Ion transport in hypertension

A wide range of abnormalities of membrane sodium and potassium transport can be demonstrated in patients with essential hypertension, and in rats with genetic hypertension and with some forms of experimental hypertension. In the human red cell increased permeability to sodium and potassium, increased ouabain-sensitive sodium pumping, lithium-sodium counter-transport, and frusemide-sensitive co-transport have been described; by contrast, in the human leucocyte sodium pumping is reduced. In the spontaneously hypertensive rat and the rat with mineralocorticoid-induced hypertension, increased permeability to sodium and potassium, with increased ouabain-sensitive pumping, is shared by the red cell and the arterial smooth muscle. This abnormality is associated with decreased cell-membrane affinity for calcium and increased cell-membrane viscosity. It is proposed that in essential hypertension the decreased membrane affinity for calcium is a primary pathogenetic change giving rise to secondary changes in sodium and potassium transport.

Diagnostic strategies in disorders of fluid, electrolyte and acid-base homeostasis

Our understanding of the physiology and biochemistry of acid-base and fluid-electrolyte regulations has greatly expanded in recent years. Key physiologic principles have emerged that now permit rational diagnosis and therapy of clinical disorders of serum electrolyte concentration. This paper describes diagnostic strategies based upon these principles. The etiology of the myriad factors in hyponatremia is best derived by first measuring serum tonicity and then assessing extracellular fluid volume. The hyper-, iso- and hypotonic hyponatremia are defined, and the hypotonic group is subclassified into hypo-, iso- and hyper volemic forms. The hypernatremias are best categorized by their state of volume expansion. Classification into the hypo-, hyper- and isovolemic hypernatremias simplifies their diagnosis. Metabolic acidoses are classified in terms of the anion gap. Clinical and chemical aspects of increased and normal anion gap acidoses are described. Metabolic alkaloses require a source of new bicarbonate and its retention by the kidney. The means by which new alkali is synthesized and urinary loss prevented serve to effectively classify the alkaloses. Hypokalemic syndromes are defined in terms of associated changes in body potassium. The potassium-depleted states are further subclassified by whether normotension or hypertension is associated. Hyperkalemia is produced by redistribution of cellular and extracellular potassium or by increased body potassium. Defects in the renin-angiotensin-aldosterone-distal renal tubule effector arm usually underlie hyperkalemic states, which are than classified in terms of this regulatory hormonal cascade. Classifications for disordered serum concentrations of calcium, magnesium, phosphorus and uric acid are presented. Hormonal, metabolic and renal regulatory factors form the basis for an organized approach to these disorders.