Heart failure and liver cirrhosis are important causes. ġ.4.2 Hypervolemic hyponatremia (Hyponatremia associated with an increase in ECF volume): Patients in this category have signs of hypervolemia such as peripheral edema and ascites. Some patients with chronic kidney disease especially chronic interstitial nephritis have salt wasting nephropathy which is characterized by hypovolemia, hyponatremia and high urine Na > 40 mEq/l. If serum sodium is found to be low (100-300 mOsm/kg H 2O, urine Na > 40 mEq/l. In case of sodium the value is the same in mEq/l or mmol/l. Serum osmolality (mmol/kg) = 2 x Na (mmol/l) + glucose (mmol/l) + BUN (mmol/l) If SI units are used the equation becomes: Serum osmolality (mOsm/kg H 2O) = 2 x Na (mEq/l) + glucose/18 (mg/dl) + BUN/2.8 (mg/dl) Serum osmolality is estimated based on the following equation : Normal urine osmolality is 50-1200 mOsm/kg H 2O. Significant hypoosmolality is 310 mOsm/kg H 2O. The normal range in adults is280-295 mOsm/kgH 2Oor280-295 mmol/kg (in SI units). Serum osmolality is a measurement of different solutes that exist in the serum. For example, giving 1 mEq/kg of IV potassium chloride to correct hypokalemia will raise serum sodium by 2 mEq/l assuming that TBW is 50% of body weight. Once potassium is replaced, sodium exits the cells, resulting in a rise in serum sodium. In hypokalemia sodium shifts from the extracellular space intracellularly to maintain cellular volume and osmolality. This issue becomes relevant in case of hyponatremia and severe hypokalemia, because potassium replacement will lead to a rise in serum sodium in a similar fashion to sodium replacement. It is important to know that both Na e + and K e + contribute to serum sodium, but the contribution of Na e + is significantly larger because of its higher concentration. An example of osmotically inactive sodium is the bound sodium in bone, cartilage and skin. Not all sodium and potassium in the body is osmotically active. Exchangeable sodium and potassium are osmotically active. Based on Edelman’s equation serum sodium is approximately the sum of exchangeable sodium Na e + and potassium K e + divided by total body water (TBW). Sodium is the main cation in the extracellular fluid and the main contributor (with its accompanying anion: chloride or bicarbonate)to serum osmolality. Water is increased in the extracellular compartment relative to sodium, and the body’s ability to excrete excess water is impaired. Obstructive jaundice due to high level of lipoprotein X (LpX)įor the purpose of this discussion, hyponatremia refers to hyponatremia with hypoosmolality (hypotonic hyponatremia). It is seen in certain clinical scenarios such as:Ĭ. Pseudohyponatremia: is rare and is avoided by measuring sodium by direct ion-selective electrode. No shift of water from the intracellular space occurs.Ĥ. Isotonic hyponatremia (plasma osmolality is normal 280-295 mOsm/kg H 2O): is encountered after some urological and gynecological surgeries due to absorption of sodium-free irrigation solutions such as mannitol, sorbitol or glycine which expand extracellular fluid space. Water shifts from the intracellular to the extracellular compartment.ģ. Hypotonic hyponatremia (plasma osmolality 295 mOsm/kg H 2O): serum osmolality is high, and serum sodium is low as in hyperglycemia and administration of intravenous immune globulin (IVIG suspended in disaccharide such as sucrose). Hyponatremia can be hypotonic, hypertonic or isotonic. Hyponatremia, Hypernatremia, Water balance, Electrolyte disorder The review will conclude with clinical cases that apply the discussed principles in diagnosis and treatment. Complex tables, flow charts and algorithms will be avoided. The following review will cover the most salient aspects of hyponatremia and hypernatremia and provide the clinician with a practical guide to the diagnosis and treatment. Hypernatremia is associated with high mortality due to associated co-morbid conditions even after successful correction. Quick and uncontrolled correction of chronic hyponatremia may lead to severe clinical consequences. Even mild hyponatremia is associated with many non-specific symptoms and may quickly evolve into severe hyponatremia. Most of hyponatremia and hypernatremia cases are mild but they are clinically significant. Hyponatremia is defined as serum sodium 145 mEq/l (mmol/l). Hyponatremia and hypernatremia are disorders of water balance and are very common especially in hospitalized patients.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |