0071643192.pdf

Hyponatremia (Na+<135 mEq/L)

SYMPTOMS

■ Headache

■ Confusion

■ Seizures

■ Many patients are asymptomatic.

EXAM

■ Besides often presenting with altered mental status, patients may have find-

ings consistent with the underlying cause of their hyponatremia, including:

■ CHF

■ Cirrhosis

■ Vomiting

■ Diarrhea

■ Excessive thirst or water intake

DIFFERENTIAL

■ A wide differential of altered mental status should include vital sign abnor-

malities (hypoxia, hypotension), head injury, toxic/metabolic abnormality,

infection, or psychiatric illness.

DIAGNOSIS ANDCAUSES

■ Na+<120 mEq/L is considered severe hyponatremia. Most patients will be

symptomatic.

■ If etiology of hyponatremia is not clearly evident on history, checking

serum and calculated osmolality will help differentiate pseudohypona-

tremia from true hyponatremia.

■ Figure 7.1 charts the basic algorithm for evaluation of hyponatremia.

■ Pseudohyponatremia (falsely elevated)

■ Normal to high measured osmolality

■ If low calculated osmolality state:

■ Low water state with high amounts of unmeasured solute found in

multiple myeloma and hyperlipidemia

■ If high calculated osmolality state:

■ Water moves from intracellular into higher solute extracellular

space in conditions like hyperglycemia and radio contrast or manni-

tol administration.

■ Hyperglycemia is by far the most common cause of hyperosmolar

hyponatremia. The correction factor is an expected decrease in

sodium by 1.6 mEq/L for every 100 mg/dL rise in glucose for glu-

cose levels above 100 mg/dL. For glucose levels >400 mg/dL, some

authors advocate a correction factor of 2.4 mEq/L.

■ True hypo-osmolar hyponatremia (elevated TBW)

■ Measured and calculated osmolality are low and similar.

■ Checking volume status and urine sodium will help differentiate the

type of disorder.

■ Hypervolemic hypo-osmolar hyponatremia

■ Signs of fluid overload

■ Etiology is usually from a perceived low intravascular volume by the

kidneys and active water reabsorbtion in excess to sodium retention.

■ If urine sodium is low (<10 mEq/L) =loop diuretic, cirrhosis, CHF,

or nephrotic syndrome.

■ If urine sodium is high (>20 mEq/L) =acute or chronic renal failure.

ENDOCRINE, METABOLIC, FLUID, AND

ELECTROLYTE DISORDERS

Differential for

altered mental

status—

AEIOU TIPS

Acidosis/Alcohol

Epilepsy

Infection

Overdose

Uremia

Trauma to head

Insulin

Psychosis

Stroke

Hypervolemic hyponatremia

may be caused by liver

failure, heartfailure, or renal

failure.