Fluid and Electrolyte Disorders PDF

FLUID AND ELECTROLYTE DISORDERS Composition of the fluid compartments & Total Body Water Most of the body consists of fluid and the percentage varies according to age and gender. on average 55% - 60% of the body consists of fluid Normal TBW: ◆ Men: 60% of body weight ◆ Women: 55% of body weig...

FLUID AND ELECTROLYTE DISORDERS Composition of the fluid compartments & Total Body Water Most of the body consists of fluid and the percentage varies according to age and gender. on average 55% - 60% of the body consists of fluid Normal TBW: ◆ Men: 60% of body weight ◆ Women: 55% of body weight ◆ Pediatrics: 70% of body weight ◆ Geriatrics: 50% of body weight Distribution of Water The major Cation in the intracellular fluid (ICF) is potassium (K), The major Cation in the extracellular fluid (ECF) it is sodium (Na). The major force maintaining the difference in cation concentration between the ICF and ECF is the sodium–potassium pump.  Hypothalamus is the main control of the TBW content and the management of Na+ The stimulation of the osmoreceptors causes the secretion of ADH from the posterior pituitary gland. the vasopressin (ADH) will go to the cortical collecting ducts where it will activate the vasopressin type 2 (V2) receptors in the medullary and papillary collecting ducts, upregulating AQP2 channel production and insertion into the apical membrane, leading to increased water reabsorption from the tubular lumen (water channels) so the water will move from the side of tubules to the body The osmolality of the blood through the hypothalamus will control the ADH which will control the absorption or excretion of the water in the urine Adding water channels back in to the collecting duct would allow some of that water to get reabsorbed, and that’s what ADH does Plasma OsmolaLity Definition: the number of osmoles per kiLo of water (mOsm/kg water). Normal osmolality of body fluids: 285-295 (mOsm/kg water). Here glucose is measured in (mmol/l ) If you use glucose in (mg/dl) you need to divide it by 18 Introduction Whether we look at hypernatremia or hyponatremia as we all know it’s a ratio. Plasma sodium concentration = ratio between the amounts of sodium and water (concentration). How does hyponatremia and hypernatremia happen? To get hyponatremia you can have too little sodium or too much water. the majority of the hyponatremia cases are related to water (water excess) To get hypernatremia you can have too much sodium or too little water. the majority of the hypernatremia cases are related to water (water deficit) Dysvolemia = Sodium Disorder Dysnatremia = Water Disorder/Tonicity Disorder Hypovolemia = Sodium Deficit (too little sodium) (Dehydration) Hyponatremia = relative water Excess (too much water) (low volume = Low sodium content) (Low sodium conc. = high water) Hypervolemia = Sodium Excess (too little sodium) (Dehydration) Hypernatremia = relative water Deficit (too less water) (High volume = Highsodium content) (High sodium conc. = Low water) Introduction Hyponatremia: reduced serum sodium concentration (< 135 mEq/L) Hyponatremia is common findings in the elderly: Inpatient (15-20%, Outpatient (7-11%) settings. Cognitive impairment and decline Falls Fractures and osteoporosis Gait instability Mortality Calcium-forming kidney stones The most common electrolyte disorder encountered in clinical practice When we manage hyponatremia Two kinds of problems can happen: Complications due to hyponatremia itself Complications due to overly rapid correction of hyponatremia by physicians Classification Based on biochemical severity Mild hyponatremia Moderate hyponatremia Sever hyponatremia Serum sodium concentration Serum sodium concentration Serum sodium concentration between 130 and 135 mmol/l between 125 and 129 mmol/l 24 hours 2. Overcorrection of hyponatremia 3. large amplitude of correction (> 15-25 mEq/day) 4. Rapid correction (>12 mEq/day) 5. Alcoholism 6. Malnutrition 7. Liver disease 8. Malignancy 9. K depletion 10.Female gender SIADH Causes Hypoosmolar Hyponatremia (Plasma osmolality 100 mOsm/Kg Essential Criteria Urinary sodium > 30 mmol/L with normal dietary salt and water intake Absence of pituitary, thyroid, adrenal or renal insufficiency No diuretic use Low Serum uric acid Low normal Serum urea serum creatinine Fractional sodium excretion >1%, Fractional urea excretion >55% Supplemental Criteria Failure to correct hyponatraemia after 0.9% saline infusion Correction of hyponatremia through fluid restriction Abnormal water loading test (excretion 7 mM can occur without obvious EKG changes).  Exclude Pseudo-hyperkalemia  This refers to an artificially elevated plasma K+ concentration due to K+ movement out of cells immediately before or after venipuncture.  Contributing factors include a. Prolonged use of a tourniquet with or without repeated fist clenching. This can cause acidosis and subsequent K+ loss from cells (Repeat the test to confirm this.) b. Additionally, if the sample is not processed quickly, some red blood cells will hemolyze and cause spillage of K+ leading to a falsely elevated result. The test should be repeated in this case.  Other contributing factors include leukocytosis and thrombocytosis.  Evaluate renal function and medication lists Estimate glomerular filtration rate using MDRD equation, Cockroft-Gault equation, and/or 24-hour creatinine clearance.