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SOURCE

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Source: Chessman KH, Haney J. Disorders of sodium and water homeostasis. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146061710. Accessed April 18, 2017.

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DEFINITION

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  • Serum sodium >145 mEq/L (>145 mmol/L)

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ETIOLOGY

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  • Results from deficit of water relative to extracellular fluid (ECF) sodium content.

  • Most commonly seen in patients with impaired thirst response or without access to water.

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PATHOPHYSIOLOGY

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  • Homeostasis: Physiologic processes that maintain relatively stable equilibrium between interdependent elements.

    • Mechanisms for regulating blood volume and plasma osmolality involve control of sodium and water balance.

      • Homeostatic mechanisms for controlling blood volume focused on controlling sodium balance.

      • Plasma osmolality largely determined by serum sodium concentration and controlled by water balance.

      • 60% of total body water distributed intracellularly; 40% contained in extracellular space.

        • Sodium, chloride, and bicarbonate comprise >90% of total osmolality of ECF.

        • Intracellular osmolality depends primarily on concentration of potassium.

  • Insensible water loss in patients deprived of water (eg, mechanical ventilation) may result in hypernatremia.

  • Diabetes insipidus (DI) causes excretion of large volumes of dilute urine/day.

    • Classified as central [decreased arginine vasopressin (AVP) secretion] or nephrogenic (decreased renal response to AVP).

  • Iatrogenic administration of hypertonic sodium chloride results in hypernatremia and expanded ECF volume.

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EPIDEMIOLOGY

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  • Incidence in general medical-surgical hospital patients: 1% to ~8%.

    • Majority of cases are hospital acquired.

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PREVENTION

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  • Awareness of potential for hypernatremia in mechanically ventilated patients.

  • Intact thirst mechanism.

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RISK FACTORS

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  • Age.

    • Infants.

    • Elderly or disabled patients with impaired sensorium or functional status.

  • Diuretic therapy.

  • Use of mechanical ventilators.

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CLINICAL PRESENTATION

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SIGNS AND SYMPTOMS
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  • Symptoms related to decrease in neuronal cell volume:

    • Weakness.

    • Lethargy.

    • Restlessness.

    • Irritability.

    • Confusion.

  • Symptoms related to more severe [serum sodium >160 mEq/L (>160 mmol/L)] or rapid development:

    • Twitching.

    • Seizures.

    • Coma.

    • Death.

  • Signs:

    • Postural hypotension.

    • Tachycardia.

    • Dry oral mucosa.

    • Diminished skin turgor.

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DIAGNOSIS

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MEANS OF CONFIRMATION AND DIAGNOSIS
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  • Serum sodium value >145 mEq/L (>145 mmol/L)

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LABORATORY TESTS
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  • Metabolic panel.

  • Plasma osmolality.

  • Urine osmolality: to differentiate renal from nonrenal water loss.

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DIFFERENTIAL DIAGNOSIS
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DESIRED OUTCOMES

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  • Resolve underlying cause.

  • Normalize ECF volume.

  • Safely correct hypernatremia.

    • Rapid correction can result in movement of excessive water into brain cells, resulting in:

      • Cerebral edema.

      • Seizures.

      • Neurologic damage.

      • Death.

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TREATMENT: NONPHARMACOLOGIC AND PHARMACOLOGIC THERAPY

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  • Hypovolemia hypernatremia.

    • Restore hemodynamic stability with normal saline infusion.

      • Rate of infusion depends on how rapidly hypernatremia developed.

        • Over ...

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