H yponatremia, defined as a decrease in serum sodium below 136 mmol/L, is a common occurrence in both inpatients and outpatients and can be found in up to 15% of the general hospital populations.1,2 Acute hyponatremia (duration < 48 h) and its management can be a cause of major morbidity and mortality among patients in hospital.3 Chronic hyponatremia (duration > 48 h), which is typically seen among older (≥ 65 yr) outpatients, also contributes to morbidity because it is often unrecognized.3,4 Typically, correction of serum sodium concentration in patients with acute hyponatremia should occur at a more rapid rate than in patients with chronic hyponatremia because the symptoms are usually more severe when serum sodium rapidly decreases over a short period. 1It is essential to determine the underlying cause of hyponatremia because the type of hyponatremia dictates the approach to therapy. Once the type is determined, clinicians need to weigh the evidence to determine what treatment will be the most effective. This can prove confusing and challenging for both primary care physicians and specialists because there are a myriad of treatment-related reviews and publications with no clear guide as to what the best evidence suggests for the treatment of hyponatremia in each setting.In this review, we discuss the evidence for the management of hyponatremia. A variety of management approaches (both pharmacologic and nonpharmacologic) exist in clinical practice. We set out to review the evidence from randomized controlled trials (RCTs) for strategies to treat hyponatremia. Not surprisingly, most RCT-level evidence comes from industry-sponsored trials of newer pharmacologic agents. 5,6 Our review was performed systematically; our methods are described in Box 1. After completing the review, it became clear that to provide the reader with a clinical ap proach that could be applied in practice, we also needed to review and discuss management strategies that are well established in practice but are not supported by RCT-level evidence. The clinical application of our results is shown in Box 2. How does the type of hyponatremia affect treatment?Although there are many approaches to the management of hyponatremia, one of the most common approaches used by nonexpert clinicians begins with an assessment of extracellular fluid (ECF) volume status. Because diabetes mellitus is becoming more prevalent in the adult population, clinicians should be mindful of ruling out hyperosmolar hyponatremia caused by hyperglycemia as a potential cause of hyponatremia. The clinical history and physical examination provide important diagnostic clues that help to classify the cause of hyponatremia as hypovolemic, euvolemic or hypervolemic. Hypovolemic hyponatremiaHypovolemic hyponatremia occurs in cases of volume contraction, such as is seen with vomiting and diarrhea, excessive sweating and use of diuretics.1 A patient may present with frank hypotension or with postural hypotension or tachycardia. In this setting, release of both antidiuretic hormone (...

Both anemia and sleep disordered breathing are common in patients with dialysis-dependent stage 5 chronic kidney disease. Erythrocytosis resulting from obstructive sleep apnea (OSA) is rare in the general population and has never been described in the hemodialysis population. We present a case of asymptomatic isolated erythrocytosis and elevated serum erythropoietin level in an otherwise well and previously erythropoietin-dependent chronic hemodialysis patient with chronic kidney disease secondary to ischemic nephropathy. There was no history or symptoms of cardio-pulmonary or hepatic diseases nor any relevant family history. Screening work-up for malignancies was negative. The clinical history was highly suggestive of OSA and severe OSA (respiratory disturbance index of 59) was confirmed by polysomnographic studies. Successful treatment of the OSA with continuous positive airway pressure resulted in permanent stabilization of the hemoglobin to levels below 13 g/dL without the need for repeated phlebotomies and in dramatic lowering of serum erythropoietin levels. To our knowledge, this is the first case of OSA mediated erythrocytosis in a dialysis patient documented in the literature.

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