Definition Serum sodium concentration less than 132 mmol/l The sodium con.. Is a reflection of water balance rather than total body sodium.
Type of hyponatremia Hypovolemic hyponatremia Euvolemic hyponatremia Hypervolemic hyponatremia Redistributive hyponatremia Pseudohyponatremia
Hypovolemic hyponatremia A decrease in total body water (TBW) and a greater decrease in total body sodium (Na + ) occur. The extracellular fluid (ECF) volume is decreased.
Euvolemic hyponatremia An increase in TBW with normal total sodium occurs. The ECF volume is increased minimally to moderately, but edema is not present.
Hypervolemic hyponatremia An increase in total body sodium and a greater increase in TBW occur. The ECF is increased markedly, and edema is present.
Redistributive hyponatremia A shift of water from the intracellular to the extracellular compartment occurs with a resultant dilution of sodium. The TBW and total body sodium are unchanged. This condition occurs with hyperglycemia.
Pseudohyponatremia A dilution of the aqueous phase by excessive proteins or lipids occurs. The TBW and total body sodium are unchanged. This condition is seen with hypertriglyceridemia and multiple myeloma.
Low ( BP, HR) poor skin turgor Elevated (edema) Normal Hypovolemic Hypotonic hyponatremia hypervolemic Hypotonic hyponatremia Isovolemic Hypotonic hyponatremia Total body Na deficit GI, skin,lung kidney Adrenal insufficiency Total body Na excess CHF, Liver damage Nephrosis Total body Na normal H2O intoxication SIADH, Renal Failure K loss Reset Osmstat Diagnostic approach to hyponatremia cont’d
Interpreting Lab. Data Urinary Sodium help to distinguish between renal and nonrenal losses. urine sodium < 20 mEq/L. e.g cirrhosis, nephrosis, congestive heart failure SIADH will have urine sodium levels in excess of 20 mEq/L.
Calculate adult Na deficit in hyponatremia Na mEq.= (140 mEq/L - patient's serum Na) x (0.5X body weight). An increase in serum sodium of 4-6 mEq/L is generally sufficient 0.5 mEq/L/hr or 12 mEq/L/day or 18 mEq/L/2 day’s.
Definition Serum sodium concentration More than 145 mmol/l The sodium con.. Is a reflection of water balance rather than total body sodium.
Etiology and Pathophysiology Hypernatremia in adults has a mortality of 40 to 60%. The elderly are particularly susceptible, especially in warm weather, due to a reduced thirst response and underlying diseases.
Principal Causes of Hypernatremia Extrarenal losses GI: Vomiting, diarrhea Skin: Burns, excessive sweating Renal losses Intrinsic renal disease Loop diuretics Osmotic diuresis (glucose, urea, mannitol) Hypernatremia with hypovolemia (decreased TBW and Na; relatively greater decrease in TBW)
Principal Causes of Hypernatremia cont’d Extrarenal losses Respiratory: Tachypnea Skin: Fever, excessive sweating Renal losses Central diabetes insipidus Nephrogenic diabetes insipidus Other Inability to access water Primary hypodipsia Reset osmostat Hypernatremia with euvolemia (decreased TBW; near-normal total body Na)
Principal Causes of Hypernatremia cont’d Hypertonic fluid administration (hypertonic saline, NaHCO3, total parenteral nutrition) Mineralocorticoid excess Adrenal tumors secreting deoxycorticosterone Congenital adrenal hyperplasia (caused by 11- hydroxylase defect) Hypernatremia with hypervolemia rare
Symptoms and Signs The major signs of hypernatremia result from CNS dysfunction due to brain cell shrinkage. Confusion, neuromuscular excitability, seizures, or coma may result; cerebrovascular damage with subcortical or subarachnoid hemorrhage and venous thromboses are frequent in patients dying from severe hypernatremia.
Treatment Free water deficit = TBW × [(plasma Na/140) − 1] TBW × [(plasma Na/140) − 1] TBW = body wt x 0.6 = liters if hypernatremia is chronic or of unknown duration, it should be corrected over 48 h, and the plasma osmolality should be lowered at a rate of no more than 2 mOsm/L/h to avoid cerebral edema caused by excess brain solute. Loop diuretics
Treatment cont’d In patients with hypernatremia and depletion of total body Na content (ie, who have volume depletion), the free water deficit is greater than that estimated by the formula. In patients with hypernatremia and ECF volume overload (excess total body Na content), the free water deficit can be replaced with 5% D/W, which can be supplemented with a loop diuretic.
Treatment cont’d In patients with hypernatremia and euvolemia, free water can be replaced using either 5% D/W or 0.45% saline.