Diabetes Insipidus.pdf

DIABETES INSIPIDUS  Osmosis Passage of fluid through permeable membrane Fluid flow: From region of ↑ water concentration to ↓water concentration = equalized concentrations  Osmosis Definitions Solute: The dissolved substance in a solution (usually a salt) Solvent...

DIABETES INSIPIDUS  Osmosis Passage of fluid through permeable membrane Fluid flow: From region of ↑ water concentration to ↓water concentration = equalized concentrations  Osmosis Definitions Solute: The dissolved substance in a solution (usually a salt) Solvent: The liquid in which a solute is dissolved (usually water) Osmolality: Measurement of the amount of solute mixed per volume of solvent Tonicity: Measurement of the osmotic pressure between two solutions  Types of IV Fluid Does not promote osmosis Isotonic - 0.9% Increase extracellular volume only NaCl in H2O Increases circulating volume without changing concentration (dehydration) Low Na+ (solute) & high fluid (solvent) Hypotonic - Promotes osmosis of the extracellular fluid into cells 0.45%NS (1/2 NS) Used to correct cellular dehydration (chronic hypernatremia, DKA) High Na+ (solute) & low fluid (solvent) Hypertonic - 3% Promotes osmosis of fluid out of cells & to the extracellular space NS Used to correct sodium & circulating water deficits (severe hyponatremia, hypovolemia)  Antidiuretic Hormone ADH or antidiuretic hormone is “anti” diuresis ADH promotes water retention AKA Vasopressin = vasoconstriction ADH promotes increased blood pressure ADH is synthesized by the paraventricular & supraoptic nuclei of the hypothalamus ADH released in response to hyperosmolality &/or hypovolemia→ released from the posterior pituitary enters the bloodstream & travels to the renal tubule Effects of ADH (Vasopressin)  Diabetes Insipidus Disorder of salt & water metabolism Pathophysiology: Inability to concentrate urine in kidneys Causes excessive water loss = ↑plasma Na+ conc. (hypernatremia) ↑ Na+ = hyperosmotic state Can cause neuronal shrinkage (from cellular dehydration) & permanent damage Hypernatremia = Na+ >145 mEq/L ↑water loss = ↓intravascular volume (excessive = hypovolemia) Can cause circulation problems  Diabetes Insipidus Two Types of Diabetes Insipidus Central: Disease due to ADH insufficiency Nephrogenic: Condition in which the renal tubules fail to respond to normal levels of ADH  Central Diabetes Insipidus Disease due to insufficiency of ADH (Arginine Vasopressin) Etiology: About 50% of the cases are idiopathic Injury to the hypothalamic pituitary area which may result from: Trauma Tumor Neurologic procedures Less common causes: Sarcoidosis, syphilis, encephalitis, infiltrative diseases (such as Langerhans cell histiocytosis), Hand-Schuller-Christian Disease  Nephrogenic Diabetes Insipidus Renal tubules fail to respond to NORMAL circulating levels of ADH Renal insensitivity to ADH Can occur in infancy & can be primary or occur secondarily Due to conditions like chronic renal disease, sickle cell anemia, amyloidosis, in association with hypokalemia & hypercalcemia, use of certain drugs like lithium, demeclocycline, cidofovir, foscarnet, orlistat, amphotericin B  Diabetes Insipidus Presentation Polyuria: In the absence of ADH Inability to reabsorb free water Loss of the ability to concentrate urine (DILUTE URINE) Large volumes of dilute urine (3-5 liters per day) Nocturia Polydipsia: Thirst results, leading to increased fluid intake Altered mental status Visual field defects  Diabetes Insipidus Diagnostic Testing Labs to order: CMP - Na, Ca, K, BUN, glucose Urine Dipstick - specific gravity & glucose 24 hr Urine for volume & osmolality Imaging: Pituitary MRI (CT)  Diabetes Insipidus Laboratory Findings 24-h urine volume > 40 mL/kg body weight Dilute urine Urine Osmolality