Source: Coyle JD, Matzke GR. Disorders
of Sodium and Water Homeostasis. In: DiPiro, JT, Talbert RL, Yee
GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic
Approach. 8th ed. http://www.accesspharmacy.com/content.aspx?aid=7983523.
Accessed August 18, 2012.
- Serum sodium >145 mEq/L (>145 mmol/L)
- 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.
- 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
mechanisms for controlling blood volume focused on controlling sodium
- 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.
chloride, and bicarbonate comprise >90% of total osmolality
- Intracellular osmolality depends primarily on concentration
- Insensible water loss in patients deprived of water (e.g.,
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.
- Incidence in general medical-surgical hospital patients:
1% to ~8%.
- Majority of cases are hospital acquired.
- Awareness of potential for hypernatremia in mechanically
- Intact thirst mechanism
- Elderly or disabled patients with impaired sensorium or functional
- Diuretic therapy
- Use of mechanical ventilators
- Symptoms related to decrease in neuronal cell volume:
- Symptoms related to more severe (serum sodium >160 mEq/L [>160
mmol/L]) or rapid development:
- Postural hypotension
- Dry oral mucosa
- Diminished skin turgor
Means of Confirmation
- Serum sodium value >145 mEq/L (>145 mmol/L)
- Metabolic panel
- Plasma osmolality
- Urine osmolality: to differentiate renal from nonrenal water
- 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
- Neurologic damage
- Hypovolemia hypernatremia
- Restore hemodynamic stability with normal saline infusion.
- Rate of infusion depends on how rapidly hypernatremia developed.
- Over a few hours: ~1 mEq/L (1 mmol/L) per hour
- Slower onset: 0.5 mEq/L (0.5 mmol/L) per hour
- Do not exceed 10 mEq/L (10 mmol/L) per day.
- Hyperglycemia-induced: correct hyperglycemia with insulin and administer normal saline.
- Central DI (Table 1)
- Treat with intranasal desmopressin, beginning with 10 mcg/day and titrating as needed, usually to 10 mcg twice daily
- Nephrogenic DI
- Decrease ECF volume with thiazide diuretic.
- Restrict dietary sodium (2000 mg/day)
- Treatment with drugs with antidiuretic properties (Table 1).
- Sodium overload
- Treat with loop diuretics
(furosemide 20–40 mg IV every 6 hours) ...