0071643192.pdf

■ Euvolemic hypo-osmolar hyponatremia
■ Urine sodium is usually high (>20 mEq/L)
■ Etiology is either endocrine or nonendocrine caused:
■ Endocrine: Hypothyroidism, SIADH, and glucocorticoid deficiency
■ Nonendocrine: Drugs or psychogenic polydipsia
■ SIADH is a diagnosis of exclusion but typical lab findings are:
■ High urine Na+(>20 mEq/L)
■ High urine osmolality (>150)
■ Low BUN
■ Hypovolemic hypo-osmolar hyponatremia (dehydrated)
■ Caused by dehydrated states where the kidney is actively trying to reab-
sorb water
■ Signs of dehydration including poor skin turgor and tachycardia.
■ If urine sodium is low (<10 mEq/L), the etiology is likely extrarenal sodium
loss such as vomiting diarrhea, fistula, sweating, or traumatized muscle.
■ If urine sodium is high (>20 mEq/L), the etiology is likely renal sodium
loss such as from diuretics, hyperglycemia, nephropathy, or mineralo-
corticoid deficiency.

TREATMENT

■ Treatment focuses on identification and correction of the underlying cause.
■ Emergent hyponatremia requiring hypertonic 3% saline is reserved for pa-
tients with an altered level of consciousness or seizures with Na+<115.
■ Patients who are dehydrated and hyponatremic need to be volume resusci-
tated as well, hence should be resuscitated with 0.9 NS.

ENDOCRINE, METABOLIC, FLUID, AND

ELECTROLYTE DISORDERS

A high urine sodium (> 20

mEq/L) in a patient with

hyponatremia suggests a

renal-related etiology (SIADH,

nephropathy, diuretics,

hyperglycemia, or

mineralcorticoid deficiency).

Na+ < 135 mEq/L.

Check measured and

calculated

osmolality.

Normal to high

measured osmolality =

pseudohyponatremia.

Low measured and

serum osmolality =

true hyponatremia.

Check volume status

and urine sodium.

High calculated

osmolality = ↑ sugar,

mannitol, or contrast;

Tx: saline ± insulin

Hypervolemic Euvolemic

Hypothyroid,

glucocorticoid deficiency,

SIADH, drugs,

psychogenic

Hypovolemic

↓ UNa+ =

nephrotic,

cirrhosis,

CHF

Tx: H 2 O

restriction

↑ UNa+ = renal

diuretics, Na+

wasting,

mineralocorticoid

deficiency,

osmotic Tx: NS

↓ UNa+ =

extrarenal

V/D, sweating

Tx: NS

Low calculated

osmolality = MM or

↑ lipids

↑ UNa+ = renal

failure

Tx: dialysis

FIGURE 7.1. Evaluation of hyponatremia.