Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 21-03: Hypernatremia + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Serum sodium > 145 mEq/L (> 145 mmol/L) Increased thirst and water intake are the main defense against hypernatremia Urine osmolality helps differentiate renal from nonrenal water loss +++ General Considerations ++ Develops when there is a relative loss of water (compared to sodium) that is inadequately compensated for by water ingestion The primary responses to hypernatremia are stimulation of thirst (to increase water intake) and increased secretion of ADH (to minimize water loss in the urine) Nearly impossible to develop hypernatremia in the context of an intact thirst mechanism with appropriate access to water Cells in the hypothalamus sense minimal changes in serum osmolarity, triggering the thirst mechanism, and subsequent intake of water All patients with hypernatremia have hyperosmolality, unlike hyponatremic patients who can have a low, normal, or high serum osmolality Rarely, excess sodium intake contributes to hypernatremia when it is associated with an increase in extracellular volume + Clinical Findings Download Section PDF Listen +++ ++ With dehydration, orthostatic hypotension and oliguria are typical findings Because water shifts from the cells to the intravascular space to protect volume status, symptoms may be delayed Lethargy, irritability, and weakness are early signs In severe hypernatremia (sodium > 160 mEq/L), symptoms include Hyperthermia Delirium Seizures Coma Symptoms in older adults may not be specific + Diagnosis Download Section PDF Listen +++ +++ Laboratory Tests ++ Urine volume, osmolarity and the osmole excretion rate Determine whether the patient with hypernatremia is oliguric (urine flow < 0.5 mL/min) or nonoliguric (urine flow > 0.5 mL/min) Elevated levels of copeptin suggest presence of vasopressin and therefore excludes a diagnosis of central diabetes insipidus + Treatment Download Section PDF Listen +++ ++ In general, treatment involves inducing a positive water balance by the administration of hypotonic fluids Can be accomplished either through the GI tract with oral intake or boluses via a feeding tube or intravenously (or a combination of both) Because it can be difficult to correct large water deficits via the GI tract alone, the most common strategy is infusion of 5% dextrose in water (distilled water is contraindicated due to the development of hemolysis) For chronic hypernatremia, fluid replacement should include correcting the free water deficit based on total body water (TBW) (Table 21–1) in the formula below and adding maintenance fluid from ongoing water loss via urinary output and insensible losses (estimated at 500–1000 mL daily but they can vary significantly) Although there appears to be little risk in the rapid correction of hypernatremia, caution should be exercised when infusing large amount of 5% dextrose in water due to the theoretical risk of cerebral edema because of the osmotic brain adaptation that occurs with chronic hypernatremia In patients who are concurrently volume depleted, priority should be to restore euvolemia via the administration of isotonic fluids ++Table Graphic Jump LocationTable 21–1.Total body water (as percentage of body weight) in relation to age and sex.View Table||Download (.pdf) Table 21–1. Total body water (as percentage of body weight) in relation to age and sex. Age Male Female 18–40 60% 50% 41–60 60–50% 50–40% Over 60 50% 40% + Outcome Download Section PDF Listen +++ +++ When to Refer ++ Patients with refractory or unexplained hypernatremia should be referred to a nephrologist for consultation +++ When to Admit ++ Patients with symptomatic hypernatremia require hospitalization for evaluation and treatment Significant comorbidities or concomitant acute illnesses, especially if contributing to hypernatremia, may necessitate hospitalization + References Download Section PDF Listen +++ + +Chauhan K et al. Rate of correction of hypernatremia and health outcomes in critically ill patients. Clin J Am Soc Nephrol. 2019 May 7;14(5):656–63. [PubMed: 30948456] + +Fenske W et al. A copeptin-based approach in the diagnosis of diabetes insipidus. N Engl J Med. 2018 Aug 2;379(5):428–39. [PubMed: 30067922] + +Seay NW et al. Diagnosis and management of disorders of body tonicity-hyponatremia and hypernatremia: Core Curriculum 2020. Am J Kidney Dis. 2020 Feb;75(2):272–86. [PubMed: 31606238]