Hyponatremia

Adalyn Almora

Questions 3 and 4

3. Compute for the plasma osmolality and the effective

plasma osmolality. What is the importance of

computing for such?

Computation for plasma osmolality

= 2[Na+ ] + [Glucose]/18 + [ BUN ]/2.8

= 2[123 mEq/L] + [98 mg/dL]/18 + [ 22 mg/dL ]/2.8

=246 + 5.44 + 7.86

= 259.3 mOsm/Kg

• NV = 275-295 mOsm/Kg

Computation for effective plasma osmolality

= 2 [Na] + [Glucose]/18

= 2 [123] + [98]/18

= 246 + 5.44

= 251.44 mOsm/Kg

NV = 270-285 mOsm/Kg

Importance

• Osmolality of blood increases with dehydration

• decreases with overhydration.

• increased osmolality in the blood will stimulate secretion of antidiuretic hormone (ADH). This will result in increased water reabsorption, more concentrated urine, and less concentrated blood plasma.

Importance

• A low serum osmolality will suppress the release of ADH, resulting in decreased water reabsorption and more concentrated plasma.

• changes in ECF osmolality have a great affect on ICF osmolality - changes that can cause problems with normal cell functioning and volume.

4. What are the significance of urine osmolality and urine

sodium ?

Urine osmolality Significance

• Urine osmolality is a measure of urine concentrationin

• large values indicate concentrated urine and small values indicate diluted urine.

• important test for the concentrating ability of the kidney.

• For determining the differential diagnosis of hyper- or hyponatraemia.

• For identifying SIADH (urine osmolality > 200 mmol/kg, urine sodium > 20 mmol/L, low serum sodium, patient not dehydrated and no renal, adrenal, thyroid, cardiac or liver disease or interfering drugs)

• For identifying and diagnosing diabetes insipidus (low urine osmolality not responding to water restriction).

• For differentiating pre-renal from renal kidney failure (high urine osmolality is consistent with pre-renal impairment, in renal damage the urine osmolality is similar to plasma osmolality).

Urine Sodium Significance

• The sodium urine test measures the amount of salt (sodium) in a urine sample.

• Normal values are generally 15 to 250 milliequivalents per liter per day (mEq/L/day), depending on how much fluid and salt you consume.

• Greater than normal urine sodium levels may be caused by too much salt in the diet.

• Lower than normal urine sodium levels may indicate:

• Aldosteronism• Congestive heart failure • Diarrhea and fluid loss • Kidney failure