Sodium

Hyponatremia, arginine vasopressin dysregulation, and vasopressin receptor antagonism

Hyponatremia is often associated with arginine vasopressin (AVP) dysregulation that is regulated by the hypothalamo-neurohypophyseal tract in response to changes in plasma osmolality, commonly in patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Potentially lethal complications of hyponatremia most frequently involve the central nervous system and include anorexia, fatigue, lethargy, delirium, seizures, hypothermia and coma, and require prompt treatment. Chronic hyponatremia also complicates patient care and is associated with increased morbidity and mortality, particularly among patients with congestive heart failure. Conventional treatments for hyponatremia (e.g. fluid restriction, diuretic treatment, and sodium replacement) may not be effective in all patients and can lead to significant adverse events. Preclinical and clinical trial results have shown that AVP receptor antagonism is a promising approach to the treatment of hyponatremia that directly addresses the effects of increased AVP and consequent decreased aquaresis, the electrolyte-sparing excretion of free water. Agents that antagonize V(2) receptors promote aquaresis and can lead to increased serum sodium. Dual-receptor antagonism, in which both V(2) and V(1A) receptors are blocked, may provide additional benefits in patients with hyponatremia.

Nephrogenic syndrome of inappropriate antidiuresis in adults: high phenotypic variability in men and women from a large pedigree

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a recently described genetic cause of hyponatremia in male infants. Whether this X-linked condition could be detected in the adult or also could affect women is unknown. A large five-generation family was identified in which the recently described arginine-vasopressin receptor type 2 (AVPR2) mutation that is responsible for NSIAD was segregated. The proband was a 74-yr-old patient who had a syndrome of inappropriate antidiuresis and whose hyponatremia resisted administration of two AVPR2 antagonists. The phenotype of family members who carry the mutation was investigated. Patients with normal serum sodium were subjected to a water-load test. The previously reported activating missense R137C mutation in the AVPR2 gene in three hemizygous male and four heterozygous female individuals was identified. Except in one woman, spontaneous episodes of hyponatremia or abnormal water-load test were identified in all patients with the mutation, whether male or female. Skewed X inactivation was evidenced in the blood of the asymptomatic woman, which is compatible with preferential inactivation of her mutated allele. NSIAD is not limited to male infants. The diagnosis also should be considered in both male and female adults.

Role of Na+and K+in Enzyme Function

Metal complexation is a key mediator or modifier of enzyme structure and function. In addition to divalent and polyvalent metals, group IA metals Na+and K+play important and specific roles that assist function of biological macromolecules. We examine the diversity of monovalent cation (M+)-activated enzymes by first comparing coordination in small molecules followed by a discussion of theoretical and practical aspects. Select examples of enzymes that utilize M+as a cofactor (type I) or allosteric effector (type II) illustrate the structural basis of activation by Na+and K+, along with unexpected connections with ion transporters. Kinetic expressions are derived for the analysis of type I and type II activation. In conclusion, we address evolutionary implications of Na+binding in the trypsin-like proteases of vertebrate blood coagulation. From this analysis, M+complexation has the potential to be an efficient regulator of enzyme catalysis and stability and offers novel strategies for protein engineering to improve enzyme function.

Is asymptomatic hyponatremia really asymptomatic?

Consequences of hyponatremia are generally mild and remain unnoticed by both physician and patient. When water restriction, usually prescribed to avoid water intoxication, fails to normalize serum sodium values, clinicians will tolerate mild stable hyponatremia (especially when serum sodium is >125 mEq/L [1 mEq/L = 1 mmol/L]). In a recent study, we observed that mild chronic hyponatremia contributes to an increased rate of falls, probably due to impairment of attention, posture, and gait mechanisms. Eight attention tests were used to assess 16 patients with asymptomatic hyponatremia (mean serum sodium, 128 +/- 3 mEq/L) due to syndrome of inappropriate antidiuretic hormone secretion. On attention tests for visual and auditory stimuli, there was an increase in mean response latency of 58 msec (P <0.001) and an increase in total error number of 20% (P <0.001). The results of 3 stereotyped steps on a platform "in tandem" with eyes open, expressed as total traveled way of center of pressure, was also different in patients with hyponatremia (mean serum sodium, 128 +/- 3 mEq/L) when compared with normonatremic patients (1.3 vs 1 m; P <0.003). Noteworthy, in volunteers of similar age, after mild alcohol intake (0.55 g/kg body weight), attention and gait tests were less affected. In another series of 122 consecutive patients hospitalized from the emergency room with mild hyponatremia, approximately 21% were admitted for falls. After controlling for age, sex, and other known risk factors for falls, the adjusted odds ratio for falls in patients with hyponatremia was 67, compared with a control group. These data show that the concept of asymptomatic hyponatremia does not withstand a detailed epidemiologic analysis of falls or of sensitive posture, gait, and attention tests.

Hypernatremia in the neurologic intensive care unit: how high is too high?

Hypernatremia is associated with increased mortality in hospitalized patients and in medical/surgical intensive care units. This relationship has not been studied in neurologic/neurosurgical intensive care units (NNICUs), where hypernatremia is often a component of treatment of cerebral edema. We performed a retrospective analysis of prospectively collected data in patients admitted to the NNICU over a 6.5-year period. Hypernatremia (serum sodium >150 mEq/L) was seen in 339 patients (7.9%) and was more common (24.3%) in patients who were treated with mannitol. Hypernatremic patients had a lower median admission Glasgow Coma Scale score (8 vs 14, P < .001), higher initial Acute Physiology and Chronic Health Evaluation II probability of death (34.9% vs 19.1%, P < .001), higher incidence of mechanical ventilation (80.5% vs 41.1.5%, P < .001), higher mortality (30.1% vs 10.2%, P < .001), and higher incidence of renal failure (10.3% vs 0.9%, P < .001). Mortality increased with increasing hypernatremia; however, only severe hypernatremia (serum sodium >160 mEq/L) was independently associated with increased mortality. Other factors independently associated with mortality were age, mechanical ventilation, initial Acute Physiology and Chronic Health Evaluation II probability of death or low admission Glasgow Coma Scale score, and a diagnosis of cerebrovascular disease. In conclusion, hypernatremia is common in the NNICU, more so in patients treated with mannitol. In this population, severe (but not mild or moderate) hypernatremia is independently associated with increased mortality.

Oxcarbazepine add-on in the treatment of refractory bipolar disorder

OBJECTIVE

To assess the effectiveness and safety of oxcarbazepine (OXC) in bipolar disorder (BD) and related conditions.

METHODS

We reviewed medical records of patients given OXC treatment between March 2003 and March 2005 at the University of British Columbia Hospital. Response to treatment was assessed retrospectively using the Clinical Global Impression of Severity (CGI-S), and the Clinical Global Impression of Improvement (CGI-I) scales.

RESULTS

OXC was prescribed to 15 patients with bipolar I (n = 12), bipolar II (n = 2) and schizoaffective (n = 1) disorder who presented with depression (n = 9), mania (n = 3), hypomania (n = 1), or mixed state (n = 2). Six patients had Axis II diagnoses and 10 patients had a family history of mood disorders. Psychiatric co-morbidity was found in four patients. The mean daily dose of OXC was 775 +/- 556.11 mg/day and the mean duration of follow-up was 31.60 +/- 41.51 weeks. The OXC add-on led to a significant reduction in symptoms as indicated by reduction in CGI-S scores at 1 and 2 months. Nine of 12 patients at 1 month and seven of 14 at 1 or 2 months were much or very much improved on CGI-I scale. One patient (7%) developed hyponatremia. Six patients (40%) experienced no side effects and three patients (20%) stopped the medication because of side effects.

CONCLUSION

OXC was effective and well-tolerated in refractory BD and schizoaffective disorder. These preliminary data are promising but controlled studies are needed to confirm its efficacy in refractory BD.

Isotonic is better than hypotonic saline for intravenous rehydration of children with gastroenteritis: a prospective randomised study

AIMS

To determine whether the risk of hyponatraemia in children with gastroenteritis receiving intravenous (IV) fluids is decreased by the use of 0.9% saline.

METHODS

A prospective randomised study was carried out in a tertiary paediatric hospital. A total of 102 children with gastroenteritis were randomised to receive either 0.9% saline + 2.5% dextrose (NS) or 0.45% saline + 2.5% dextrose (N/2) at a rate determined by their treating physician according to hospital guidelines and clinical judgement. Plasma electrolytes, osmolality, and plasma glucose were measured before (T(0)) and 4 hours after (T(4)) starting IV fluids, and subsequently if clinically indicated. Electrolytes and osmolality were measured in urine samples. Results were analysed according to whether children were hyponatraemic (plasma sodium <135 mmol/l) or normonatraemic at T(0).

RESULTS

At T(0), mean (SD) plasma sodium was 135 (3.3) mmol/l (range 124-142), with 37/102 (36%) hyponatraemic. At T(4), mean plasma sodium in children receiving N/2 remained unchanged in those initially hyponatraemic (n = 16), but fell 2.3 (2.2) mmol/l in the normonatraemic group. In contrast, among children receiving NS, mean plasma sodium was 2.4 (2.0) mmol/l higher in those hyponatraemic at baseline (n = 21) and unchanged in the initially normonatraemic children. In 16 children who were still receiving IV fluids at 24 hours, 3/8 receiving N/2 were hyponatraemic compared with 0/8 receiving NS. No child became hypernatraemic.

CONCLUSIONS

In gastroenteritis treated with intravenous fluids, normal saline is preferable to hypotonic saline because it protects against hyponatraemia without causing hypernatraemia.

Mild chronic hyponatremia is associated with falls, unsteadiness, and attention deficits

OBJECTIVE

The study objective was to determine the eventual consequences (falls, unsteadiness, and cognitive impairment) of mild chronic hyponatremia, which is generally considered as asymptomatic.

METHODS

In a case-control study, we focused on the incidence of falls among 122 patients (mean age 72+/-13 years) with asymptomatic chronic hyponatremia (mean serum sodium concentration [SNa] 126+/-5 mEq/L), who were admitted to the medical emergency department, compared with 244 matched controls. To explore the mechanisms of the excess of falls, we prospectively asked 16 comparable patients (mean age 63+/-15 years; SNa+/-2 mEq/L) to perform 8 attention tests and a gait test consisting of 3 steps "in tandem," in which we measured the "total traveled way" by the center of pressure or total traveled way. Thereafter, the patients were treated and tested again (50% of the patients were tested first with normal SNa to avoid learning biases).

RESULTS

Epidemiology of falls: Twenty-six patients (21.3%) of 122 were admitted for falls, compared with only 5.3% of the control patients (adjusted odds ratio: 67; 95% confidence: 7.5-607; P <.001). The frequency of falls was the same regardless of the level of hyponatremia. Gait: The total traveled way by the center of pressure significantly increased in hyponatremia (1336+/-320 mm vs 1047+/-172 mm with normal SNa; P=.003). Attention tests: The mean response time was 673+/-182 milliseconds in hyponatremia and 615+/-184 milliseconds in patients with normal SNa (difference: 58 milliseconds, P <.001). The total error number in hyponatremia increased 1.2-fold (P=.001). These modifications were comparable to those observed after alcohol intake in 10 volunteers.

CONCLUSIONS

Mild chronic hyponatremia induces a high incidence of falls possibly as the result of marked gait and attention impairments. Treating these patients might prevent a considerable number of hospitalizations.

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.

High antidiuretic hormone levels and hyponatremia in children with gastroenteritis

OBJECTIVES

Nonosmotic antidiuretic hormone (ADH) activity can cause severe hyponatremia during involuntary fluid administration. We looked for evidence of this before and during intravenous (IV) fluid administration in children treated for gastroenteritis.

METHODOLOGY

In this prospective observational study, plasma ADH, electrolytes, osmolality, and glucose were measured in 52 subjects before (T0) and 4 hours after (T4) starting 0.45% saline + 2.5% dextrose and subsequently when indicated. Hormonal markers of stress were measured at T0. Urine samples were collected to measure electrolytes and osmolality.

RESULTS

The nonosmotic stimuli of ADH secretion that we identified were vomiting (50 of 52), dehydration (median: 5%; range: 3-8%), hypoglycemia (2 of 52), and raised hormonal markers of stress (mean +/- SD: cortisol, 1094 +/- 589 nmol/L; reverse triiodothyronine, 792 +/- 293 pmol/L). At T0, half the children were hyponatremic (plasma sodium concentration of < 135 mmol/L; n = 27). The median plasma ADH concentration at T0 was significantly elevated (median: 7.4 pg/mL; range: < 1.9-85.6 pg/mL). ADH was high in both hyponatremic and normonatremic children and remained high at T4 in 33 of the 52 children, 22 of whom were concurrently hyponatremic. At T4, mean plasma sodium concentration was unchanged in the hyponatremic children but was 2.6 mmol/L (+/-2.0) lower in those who were initially normonatremic. Urine tonicity was high compared with 0.45% saline in 16 of 19 children at baseline and in 20 of 37 children after 3 to 12 hours of IV fluids.

CONCLUSIONS

Nonosmotic stimuli of ADH secretion are frequent in children with gastroenteritis. Their persistence during IV-fluid administration predisposes to dilutional hyponatremia. The use of hypotonic saline for deficit replacement needs to be reassessed.

A prospective study of agitation in a medical-surgical ICU: incidence, risk factors, and outcomes

STUDY OBJECTIVES

Although agitation is thought to be common in the ICU, it has been poorly studied. We evaluated the incidence, risks factors, and outcomes of agitation in ICU.

DESIGN

Prospective observational study.

INTERVENTIONS

None.

METHOD

All consecutive ICU admissions over an 8-month period were analyzed.

MEASUREMENTS AND RESULTS

Two hundred eleven patients were admitted a total of 216 times during the period of the study. Twenty-nine patients were excluded from the study because their pathology findings did not allow an evaluation of their level of consciousness; 182 patients were actually enrolled. Agitation developed in 95 of 182 patients (52%). Agitation began 4.4 +/- 5.6 days (+/- SD) after admission to the ICU and lasted 3.9 +/- 4.1 days. Patients with agitation had a higher Simplified Acute Physiology Score II on ICU admission than those who did not have agitation (40 +/- 16 vs 33 +/- 13, p < 0.01). By stepwise logistic regression, the independent risks factors for development of agitation included psychoactive drug use at the time of ICU admission (odds ratio, 5.63; 95% confidence interval [CI], 1.32 to 23.70), history of alcohol abuse (odds ratio, 3.32; 95% CI, 1.12 to 10.00), dysnatremia (odds ratio, 4.95; 95% CI, 1.95 to 12.54), fever (odds ratio, 4.52; 95% CI, 1.80 to 11.49), use of sedatives in the ICU (odds ratio, 4.03; 95% CI, 1.62 to 10.40), and sepsis (odds ratio, 2.61; 95% CI, 1.03 to 6.58). Agitation was associated with a prolonged ICU stay (16 +/- 19 days vs 6 +/- 6 days, p = 0.0001), nosocomial infections (34% vs 7%, p < 0.0001), unplanned extubations (17% vs 2%, p = 0.003), and unplanned central venous catheter removal (16% vs 1%, p = 0.001), but not with mortality (12% in the agitation group vs 8% in patients without agitation).

CONCLUSIONS

Agitation is a common event in a mixed medical-surgical ICU. It is associated with adverse outcomes including prolonged stay, nosocomial infections, and unplanned extubations. A better knowledge of incidence and risk factors should facilitate identification of patients at risk and decrease the incidence of agitation.

Disorders of water imbalance

Disorders of water imbalance manifest as hyponatremia and hypernatremia. To diagnose these disorders, emergency physicians must maintain a high index of suspicion, especially in the high-risk patient, because clinical presentations may be nonspecific. With severe water imbalance, inappropriate fluid resuscitation in the emergency department may have devastating neurological consequences. The rate of serum sodium concentration correction should be monitored closely to avoid osmotic demyelination syndrome in hyponatremic patients and cerebral edema in hypernatremic patients.

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.

Exercise-Associated Hyponatraemia

In 1958, Edelman and colleagues empirically showed plasma sodium concentration ([Na+]p) to be primarily a function of the sum of exchangeable sodium and potassium (E) divided by total body water (TBW). Based on Edelman's equation, Nguyen and Kurtz derived an equation to show how [Na+]p changes as a function of TBW, change in TBW (DeltaTBW), and change in the sum of exchangeable sodium and potassium (DeltaE). Using the Nguyen-Kurtz equation, the present study examines the sensitivity of [Na+]p to these parameters: [Na+]p is very sensitive to DeltaTBW and moderately sensitive to DeltaE, and is modulated by TBW. For example, for a person with 50 L TBW, a net increase of 1L water lowers [Na+]p by 3.2 mEq/L, but for a person with 25 L TBW it lowers [Na+]p by 6.3 mEq/L (assuming initial [Na+]p is 140 mEq/L). In each case, a loss of 159 mEq of sodium plus potassium (roughly equivalent to 1.5 teaspoons of table salt) would be required to produce the same effect as the net increase of 1 L water. The present review demonstrates why fluid overload predominates over electrolyte loss in the aetiology of exercise-associated hyponatraemia (EAH), and why the excretion of electrolyte-dilute urine is highly effective in correcting EAH (nonetheless, loss of sodium and potassium is significant in long events in warm weather). Sports drinks will, if overconsumed, result in hyponatraemia. Administration of a sports drink to an athlete with fluid overload hyponatraemia further lowers [Na+]p and increases fluid overload. Administration of either a sports drink or normal (0.9%) saline increases fluid overload.

Kidney dysfunction in the postoperative period

The development of perioperative acute renal failure is associated with a high incidence of morbidity and mortality. Although this incidence varies with different surgical procedures and with the definition used for renal failure, we now understand better the aetiology of the underlying problem. However, successful strategies to provide renal protection or strategies for 'rescue therapy' are either lacking, unsubstantiated by randomized clinical trials, or show no significant efficacy. The present review considers the physiology and pharmacology of the kidney; the characterization of tests of renal function; the cause of postoperative renal dysfunction; what is presently available for its prevention and treatment; and the effect of postoperative renal impairment on patient outcome.

Prognostic importance of hyponatremia in acute ST-elevation myocardial infarction

PURPOSE

To determine the prevalence and prognostic implications of hyponatremia in the setting of acute ST-elevation myocardial infarction.

METHODS

The study sample consisted of 1047 consecutive patients presenting with acute ST-elevation myocardial infarction. Plasma sodium concentrations were obtained on admission and at 24, 48, and 72 hours thereafter. Infarct size was determined by echocardiographic examination that was performed on day 2 or 3 of hospitalization.

RESULTS

Hyponatremia, defined as a plasma sodium level <135 mmol/L (<135 mEq/L), was present on admission in 131 patients (12.5%) and developed during the first 72 hours of hospitalization in 208 patients (19.9%). Plasma sodium levels decreased to < or = 130 mmol/L in 45 patients (4.3%). In a multivariate logistic regression analysis, hyponatremia was independently associated with 30-day mortality. The risk of 30-day mortality associated with hyponatremia on admission (odds ratio [OR] = 2.0; 95% confidence interval [CI]: 1.0 to 3.9; P = 0.04) was similar to that of hyponatremia developing after admission (OR = 2.4; 95% CI: 1.5 to 4.2; P = 0.002). The risk of 30-day mortality increased with the severity of hyponatremia, with an odds ratio of 2.1 in patients with sodium levels between 130 and 134 mmol/L (95% CI: 1.2 to 3.5; P = 0.007) and 3.4 in those with levels <130 mmol/L (95% CI: 1.5 to 7.8; P = 0.002).

CONCLUSION

Hyponatremia on admission or early development of hyponatremia in patients with acute ST-elevation myocardial infarction is an independent predictor of 30-day mortality, and prognosis worsens with the severity of hyponatremia. Further studies are required to determine if plasma sodium levels may serve as a simple marker to identify patients at high risk.

A woman with postoperative hyponatremia related to desmopressin acetate

A patient was referred to the intensive care unit with sudden delirium and a serum sodium level of 111 mEq/L (mmol/L). A computerized tomographic scan revealed marked cerebral edema. Laboratory values were highly consistent with the action of the antidiuretic hormone. She had received desmopressin acetate (DDAVP) for 4 days preoperatively and postoperatively for putative van Willebrand's disease. Hyponatremia as a sequel to DDAVP treatment is an unusual complication and the medication is generally safe. However, our patient nevertheless teaches that vigilance equals avoidance.

Drugs used to promote diuresis: a treatment for fluid balance charts?

Renal failure is a complex process characterized by the retention of nitrogenous waste products, electrolyte disturbances and decreased urine production. Diuretics are often prescribed as a treatment for decreased renal functioning. Diuretics induce urine production by different mechanisms of action. Diuretic therapy has not been found to decrease mortality nor decrease the need for further intervention. The current development of national framework standards will provide guidelines for the treatment of all patients suffering acute renal failure.

Critical issues in endocrinology

Endocrine emergencies are commonly encountered in the ICU. This article focuses on several important endocrine emergencies, including diabetic hyperglycemic states, adrenal insufficiency, myxedema coma, thyroid storm, and pituitary apoplexy. Other endocrine issues that are related to intensive care, such as intensive insulin therapy, relative adrenal insufficiency, and thyroid function test abnormalities are also covered in detail.

Diagnosis and management of electrolyte emergencies

Electrolyte and fluid imbalances are disorders frequently observed in critical care patients. In many instances patients are asymptomatic, but they may also present with neurological alterations, severe muscle weakness, nausea and vomiting or cardiovascular emergencies. Therefore, a pathophysiological understanding of these disorders is necessary for initiating an appropriate therapy. After a precise history-including drug prescriptions-has been obtained from the patient or his/her relatives, determination of the hydration status of the patient and measurement of acid-base status, plasma and urine osmolality and electrolytes are the first steps in the assessment of the disease. Once a diagnosis has been established, great attention has to be paid to the rate at which the disorder is corrected because this-if inappropriate-may cause more severe damage to the patient than the disease itself. This chapter addresses the initial diagnostic and therapeutic steps of the most common electrolyte emergencies.

Causes of hyponatremia in the Departments of Internal Medicine and Neurosurgery

BACKGROUND: Hyponatremia is a common electrolyte disorder in hospitalised patients. The distribution of the various causes of hyponatremia has been studied in hospitalised patients in general, but little is known about the distribution in specific departments. We performed a prevalence study on the aetiology of hyponatremia in two departments in our hospital, namely, the Department of Internal Medicine and the Department of Neurosurgery. METHODS: Consecutive adult patients with hyponatremia (serum sodium concentration</=130 mmol/l) who had been admitted to the Departments of Internal Medicine and Neurosurgery were included in the study. The cause of hyponatremia was determined on the basis of information obtained from medical records, estimation of extracellular fluid volume status, water balance and biochemical parameters in blood serum and urine. RESULTS: Out of 41 hyponatremic patients, 12 had hyponatremia due to normovolemic disorders, 10 due to hypervolemic disorders, 11 due to hypovolemic disorders with extrarenal sodium loss and eight due to hypovolemic disorders with renal sodium loss. The most frequent causes of hyponatremia were extrarenal sodium loss due to vomiting or diarrhoea, hepatic cirrhosis, drug-induced hyponatremia and the syndrome of inappropriate ADH secretion. CONCLUSIONS: In the Departments of Internal Medicine and Neurosurgery, certain causes of hyponatremia are more prevalent than others. The use of clinical data, in combination with a few simple laboratory tests, can lead to a correct diagnosis of the principal cause of hyponatremia.

Validity of hospital discharge International Classification of Diseases (ICD) codes for identifying patients with hyponatremia

Medical diagnosis can be studied using various sources of information, such as medical and hospital discharge records and laboratory measurements. These sources do not always concur. The objective of the present study was to assess the sensitivity, specificity, and positive and negative predictive values of hospital discharge diagnosis compared with clinical laboratory data for the identification of hyponatremia. Patients with hyponatremia were selected from a hospital information system determined by the International Classification of Diseases, 9th edition (ICD-9). The validity parameters for hyponatremia (ICD code 276.1) were estimated by comparison with accurate serum sodium (Na+) levels. A total of 2632 cases of hyponatremia were identified using laboratory measurements (Na+ < or =135 mmol/L). The sensitivity of ICD coding for hyponatremia was maximally about 30% for patients with very severe hyponatremia (Na+ < or =115 mmol/L). Corresponding specificities were high (>99%). In 87% of the cases with severe hyponatremia (Na+ < or =125 mmol/L), other discharge ICD codes reflecting severe morbidity were found. This study suggests that ICD codes for hyponatremia represent only one third of the patients admitted to the hospital and experiencing hyponatremia. About two thirds of the patients with hyponatremia were classified as hospitalized for other reasons. To assess the validity of case finding of patients with hyponatremia, the use of analytical techniques, such as certain laboratory measurements, is advisable.

Post-operative hyponatraemia in orthopaedic injury

Post-operative hyponatraemia can be dangerous and can go unrecognised as the presenting signs and symptoms are often confused with post-operative or post-anaesthesia sequelae. Infusion of dextrose containing fluids in the peri-operative period is a well-documented cause of this electrolyte imbalance. We conducted a retrospective study to identify the incidence of hyponatraemia following surgery for orthopaedic injury. Medical notes and fluid charts of the patients were scrutinised. We detected 32 cases of post-operative hyponatraemia over a period of 1 year. Eleven hundred and thirty-one patients underwent orthopaedic surgery during this period. Calculated incidence of hyponatraemia was 2.8%. In the hyponatraemic group, the mean pre-operative sodium was 134 mmol/l and mean post-operative sodium was 126 mmol/l. There was a statistically significant difference between mean pre-operative and mean post-operative serum sodium concentration (P<0.0001, two sample t-test). The mean volume of dextrose containing fluids received by each patient was 3.26 l. There is a significant risk of hyponatraemia following orthopaedic surgery, especially in the elderly. Orthopaedic units need to be aware of this easily avoidable condition. Fluid infusion regimes should be carefully formulated with exclusion of dextrose containing fluids to prevent the danger of hyponatraemia.

Effect of the vasopressin receptor antagonist conivaptan in rats with heart failure following myocardial infarction

Myocardial infarction often induces congestive heart failure accompanied by a significant increase in plasma vasopressin concentration. To delineate the role of vasopressin in the pathogenesis of congestive heart failure, the acute hemodynamic and aquaretic effects of conivaptan (YM087, 4'-(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phenylbenzanilide monohydrochloride), a combined vasopressin V(1A) and V(2) receptor antagonist, were assessed in rats with heart failure induced by myocardial infarction. Left coronary artery ligation resulted in decreased left ventricular systolic pressure and first derivatives of left ventricular developed pressure, as well as increased left ventricular end-diastolic pressure, lung and right ventricular weight. Single oral administration of conivaptan (0.3 to 3.0 mg/kg) dose-dependently increased urine volume and decreased urine osmolality in heart failure rats. Furthermore, conivaptan (3.0 mg/kg) attenuated the changes in left ventricular end-diastolic pressure, lung and right ventricular weight induced by heart failure while reducing blood pressure. These results show that vasopressin plays a significant role in elevating vascular tone through vasopressin V(1A) receptors and plays a major role in retaining free water through vasopressin V(2) receptors in this model of congestive heart failure. Additionally, conivaptan, with its dual vasopressin V(1A) and V(2) receptor-inhibiting properties, could exert a beneficial effect on cardiac function in the congestive heart failure rat model.

Osmolar gap hyponatremia in critically ill patients: evidence for the sick cell syndrome?

OBJECTIVE

Accumulation of nondiffusible solutes in plasma leads to redistribution hyponatremia with an increased osmolar gap (i.e., the difference between measured and calculated osmolality). In critically ill patients, intracellular solutes may leak out of the cell because of an increased membrane permeability and may lead to redistribution hyponatremia with increased osmolar gap, a concept called the "sick cell syndrome." The aims of this prospective study were to determine whether an increased osmolar gap related to endogenous solutes accumulation was present in intensive care patients with true hyponatremia and to identify the solutes accounting for this increased osmolar gap.

SETTING

A 14-bed medical intensive care unit in an 821-bed university hospital.

DESIGN

A 20-wk prospective observational study.

PATIENTS

Fifty-five consecutive patients with a measured plasma sodium concentration <or=130 mmol/L (mean +/- sd, 126 +/- 6 mmol/L) were automatically identified by the Biochemistry Department. Patients were excluded in the case of reduced plasma water content resulting from hyperlipidemia or hyperproteinemia, in the case of hyperglycemia, or if exogenous compounds known to increase the osmolar gap were present.

INTERVENTIONS

Plasma osmolar gap was calculated.

MEASUREMENTS AND MAIN RESULTS

Plasma osmolar gap was considered significant if >10 mosm/kg. Total plasma amino acid concentration also was measured. Organ dysfunctions were assessed with the Sequential Organ Failure Assessment. Thirty of the 55 patients (54%) had an osmolar gap >10 mosm/kg (17.2 +/- 7.1 mosm/kg). Sequential Organ Failure Assessment score was significantly higher in the osmolar gap patients (6.4 +/- 3.2 vs. 4.5 +/- 2.0; p =.015). No difference of amino acids concentration was observed between osmolar gap and non-osmolar gap patients, and no correlation was observed between osmolar gap and amino acid concentration. Accumulation of ketone bodies and lactic acid was also unlikely. During correction of hyponatremia in osmolar gap patients, a significant decrease of plasma osmolar gap was observed and a statistically significant inverse relationship was demonstrated between osmolar gap decrease and plasma sodium concentration increase.

CONCLUSION

Hyponatremia with increased osmolar gap related to endogenous solutes accumulation is observed frequently in hyponatremic intensive care patients, especially in patients with the most severe organ dysfunctions. The nature of the endogenous solutes accounting for the increased osmolar gap remains to be determined. Simultaneous correction of sodium and osmolar gap suggests a causal link between increased osmolar gap and hyponatremia and may support the concept of sick cell syndrome.

Effects of oxcarbazepine on sodium concentration and water handling

Oxcarbazepine, a keto-analogue of carbamazepine, was recently approved in the United States for the treatment of seizures of partial onset. Some patients treated with oxcarbazepine showed the development of hyponatremia, which in most instances was asymptomatic. Understanding the mechanisms by which oxcarbazepine can lead to a reduction of serum sodium levels could have therapeutic implications for the few patients in whom symptomatic hyponatremia develops. In this study, we evaluated sodium and water handling in patients with epilepsy and in healthy subjects titrated over 3 weeks to a maximum daily oxcarbazepine dose of 2,400mg. All subjects were evaluated in a hospital setting after an overnight fast and after an acute water-load test performed before oxcarbazepine exposure and after maintenance on the medication for 3 weeks. Before oxcarbazepine exposure, the percentage of water load excreted was normal as both groups excreted more than 80% of the administered water load. After the intake of oxcarbazepine, the water load resulted in a reduction of the serum sodium and free water clearance without a concomitant increase in the arginine vasopressin serum levels. Most subjects in both groups failed to excrete 80% or more of the water load, suggesting that the effect of oxcarbazepine is physiological. We found that, after the water load, serum sodium and free water clearance were diminished in both groups without a concomitant increase in the arginine vasopressin serum levels. These findings indicate that oxcarbazepine-induced hyponatremia is not attributable to the syndrome of inappropriate secretion of antidiuretic hormone. Possible mechanisms include a direct effect of oxcarbazepine on the renal collecting tubules or an enhancement of their responsiveness to circulating antidiuretic hormone.

Association between antidepressant drug use and hyponatraemia: a case-control study

AIMS

To estimate the risk of, and risk factors for, hyponatraemia associated with the use of selective serotonin reuptake inhibitors (SSRIs) compared with the use of other antidepressant drugs.

METHODS

A case-control study of psychiatric in- and out-patients on antidepressant drugs performed in the mid-southern part of The Netherlands over a 2 year period. Cases (n=29) were all using antidepressant drugs with a serum sodium concentration of < or = 130 mmol l(-1) while controls (n=78) were patients on antidepressants with a normal sodium concentration (136-144 mmol l(-1)). Information on blood sodium concentrations was obtained from clinical chemistry data while information on drug use was obtained from community and hospital pharmacy databases. Medical records were used to ascertain possible risk and confounding factors. Unconditional multivariate logistic regression was used to estimate odds ratios for hyponatraemia in patients on SSRIs compared with patients on other antidepressant drugs.

RESULTS

SSRIs were associated with an increased risk of hyponatraemia (OR 3.3; 95% CI 1.3, 8.6) compared with other classes of antidepressant drugs. Stratified and interaction analyses revealed that elderly patients using diuretics concomitantly with SSRIs were at the highest risk of experiencing hyponatraemia (OR 13.5; 95% CI 1.8, 101).

CONCLUSIONS

SSRIs are more frequently associated with hyponatraemia than other classes of antidepressant drugs. This adverse drug reaction was more common in older patients (> or = 65 years) and in those using diuretics.

Malnutrition and childhood epilepsy in developing countries

A high prevalence of epilepsy in children is frequently found in developing countries. Though high rates of acquired brain injury may contribute, the possibility that malnutrition may lower seizure threshold has rarely been examined. This review suggests potential biochemical mechanisms that could adversely affect seizure threshold, particularly the effect of malnutrition on inhibitory neurotransmitters and electrolytes. Supporting evidence from animal research and epidemiological findings in children are discussed.

Sustained hyposmotic stress induces cell death: apoptosis by defeat

We describe sustained hyposmotic stress as a novel type of environmental condition enforcing apoptosis. In a dose- and time-dependent fashion, hyposmotic stress leads to a delayed type of apoptosis with considerable variations in constitutive sensitivity among different cell types. For example, after 48 h at 84 mosmol/l, the death rate ranged from 10.8 +/- 0.7% in AsPc1 human pancreatic carcinoma cells to 72.0 +/- 1.6% in HK-2 human kidney tubule cells. Caspase inhibitors rendered cells more resistant to hyposmolar stress; the caspase 3 inhibitor Ac-Asp-Glu-Val-aspartic acid aldehyde was the most efficient. After 24 h of stress, HT-29 colon carcinoma and HK-2 cells had increased their mitochondrial mass. This went along with an increase in mitochondrial membrane potential in HT-29 cells but with a decrease in HK-2 cells. Starting at 2 h of stress, we detected transient CD95L transcription followed by surface expression of CD95L in HT-29 but not in HK-2 cells. Inhibitory CD95L antibody partially inhibited specific death in HT-29 but not in HK-2 cells. Thus, as in other types of stress-induced apoptosis, the CD95/CD95L system is one of the different routes to suicide optionally used by hyposmotically stressed cells. Our findings may have clinical implications for the prevention and treatment of tissue damage caused by severe hyposmolar states.

Fluid and electrolyte abnormalities

Patients with cancer are at risk for developing a variety of fluid and electrolyte disturbances caused by the disease process or by complications from therapy. An understanding of the pathophysiology of these potential abnormalities allows the clinician to manage patients expectantly and to avoid severe metabolic disarray by correcting imbalances promptly.

Subacute hyponatraemia after transurethral resection of the prostate

We present a case of subacute hyponatraemia which developed 3 days after a transurethral resection of the prostate. Symptoms consisted of nausea, vomiting and headache. Release of vasopressin due to excessive surgical bleeding, combined with liberal oral and intravenous administration of sodium-free fluids, was considered to be the cause.

Basic Bibliographies

In order to help readers monitor the most important developments in specialized areas of pharmacy practice in organized health systems, Hospital Pharmacy commissions Basic Bibliographies by guest editors, who have expertise in their respective fields. These guest editors survey the relevant literature and rank approximately 15 to 20 references that represent the most significant research and practice contributions in their areas. The more fundamental are listed first so that persons with limited time can select reading appropriate to their needs. Readers are urged to forward reactions or challenges to: Joyce A. Generali, Contributing Editor, Drug Information Center, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160 or jgeneral@kumc.edu .

Physiologic acid-base and electrolyte changes in acute and chronic renal failure patients

Patients with acute and chronic renal failure are vulnerable to a wide variety of acid-base and electrolyte disturbances. The variety is related not only to predictable disturbances that arise as a consequence of impaired urinary excretion, but also to associated factors, such as intercurrent disease processes, chronic medications, and renal replacement therapy. This article emphasizes the pathogenesis, diagnosis, and treatment of common problems, including metabolic acidosis, hyponatremia, hypernatremia, hyperkalemia, hyperphosphatemia, and hypocalcemia.

Abnormalities in fluids, electrolytes, and metabolism of organ donors

Abnormal serum concentrations of electrolytes, hormones, and glucose are common throughout donor care. The organ procurement coordinator must properly interpret and plan treatment for these changes to prevent intracellular dysfunction in donor organs. This article describes abnormalities in magnesium, phosphorous, calcium, sodium, potassium, and glucose levels; polyuria; and thyroid and pituitary changes. Their potential consequences are discussed, and recommendations for treatment options are presented.

Hyponatremia in acute-phase response syndrome patients in general surgical wards

BACKGROUND

In surgical patients, hypoalbuminemia may occur as a component of acute-phase response (APR) syndrome, which we hypothesized could decrease serum sodium levels.

AIM

To compare the frequency of hyponatremia in adult surgical inpatients with or without APR syndrome.

METHODS

All the simultaneous plasma sodium and albumin results (n = 168), obtained from adults in surgical wards and corresponding to a 6-month period, were searched in the hospital mainframe. Other relevant laboratory and clinical data were also registered. APR was ascertained by the presence of major physical trauma, surgery or infection, plus hypoalbuminemia (serum albumin <3.5 g/dl) and neutrophil left shift (>/=7% of band count) associated with peripheral leukopenia (white blood cells <4, 000/mm(3)) or leukocytosis (WBC >9,000/mm(3)). Hyponatremia was defined by serum sodium concentration <135 mEq/l.

RESULTS

APR-positive patients (n = 113) had lower blood hemoglobin (10.92 +/- 2.18 vs. 13.53 +/- 2.30 g/dl), and serum albumin levels (median, range: 2.8, 1.9-3.4 vs. 3.7, 3.5-4.2 g/dl) than APR-negative (n = 55) ones, the same occurring in relation to antibiotics (54.8 vs. 10. 9%) and intravenous 5% dextrose in water (55.7 vs. 20.0%) or isotonic saline (46.0 vs. 9.1%) infusion. The hyponatremia frequency was higher among APR-positive patients (31.0 vs. 10.9%).

CONCLUSION

The higher percentage of hyponatremia among APR-positive patients could be attributed to decreased serum albumin levels associated with APR.