Hypernatremia

SOURCE

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.

DEFINITION

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

ETIOLOGY

• 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.

PATHOPHYSIOLOGY

• 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.

EPIDEMIOLOGY

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

  • Majority of cases are hospital acquired.

PREVENTION

• Awareness of potential for hypernatremia in mechanically ventilated patients.

• Intact thirst mechanism.

RISK FACTORS

• Age.

  • Infants.

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

• Diuretic therapy.

• Use of mechanical ventilators.

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

• 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.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

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

LABORATORY TESTS

• Metabolic panel.

• Plasma osmolality.

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

DIFFERENTIAL DIAGNOSIS

• Cirrhosis.

• Type 1 diabetes mellitus.

• Hypocalcemia

• Hyponatremia

DESIRED OUTCOMES

• 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.

TREATMENT: NONPHARMACOLOGIC AND PHARMACOLOGIC THERAPY

• Hypovolemia hypernatremia.

  • Restore hemodynamic ...