Adalyn Almora Questions 3 and 4 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 The stimulus for AVP secretion is an activation of hypothalamic osmoreceptors, which occurs when the plasma osmolality reaches a certain threshold (approximately 280 mOsm/kg). At plasma osmolalities below this threshold level, AVP secretion is suppressed to low or undetectable levels.

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 thirst is mediated by an increase in effective plasma osmolality of only 2-3%. Thirst is thought to be mediated by osmoreceptors located in the anteroventral hypothalamus. The osmotic thirst threshold averages approximately 288-295 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